Keithley 228 Service manual

Model 228 Voltage/Current Source Instruction Manual

Contains Operating and Servicing Information

Publication Date: April 1986 Document Number: 228-901-01 Rev C

WARRANTY

Keithley Instruments, Inc. warrants this product to be free from defects in material and workmanship for a period of 1 year from date of shipment. During the warranty period, we will, at our option, either repair or replace any product that proves to be defective.

To exercise this warranty, write or call your local Keithley representative, or contact Keithley headquarters in Cleveland, Ohio. You will be given prompt assistance and return instructions. Send the instrument, transportation prepaid, to the indicated service facility. Repairs will be made and the instrument returned, transportation prepaid. Repaired

products are warranted for the balance of the original warranty period,

or at least 90 days.

LIMITATION OF WARRANTY

This warranty does not apply to defects resulting from unauthorized

modification or misuse of any product or part. This warranty also does not apply to fuses, batteries, or damage from battery leakage.

This warranty is in lieu of all other warranties, expressed or implied, including any implied warranty of merchantability or fitness for a par-

ticular use. Keithley Instruments, Inc. shall not be liable for any indirect, special or consequential damages.

STATEMENT OF CALIBRATION

This instrument has been inspected and tested in accordance with

specifications published by Keithley Instruments, Inc. The accuracy and calibration of this instrument are traceable to the

National Bureau of Standards through equipment which is calibrated at

planned intervals by comparison to certified standards maintained in the Laboratories of Keithley Instruments, Inc.

KEITHLEY INSTRUMENTS, INC.

INSTRUMENT DIVISION I 28775 Aurora Road I Cleveland. Ohio 44139 / U.S.A. I 12161 248-0400 / Telex: 98-5469 WEST GERMANY: Keithley Instruments GmbH I Heiglhofstr. 5 I 8000 Mtinchen 70 / IO891 710020 / Telex: 52-12160 GREAT BRITAIN: Keithley Instruments. Ltd. / 1, Eoulton Road I Reading, Berkshire RG 2 ONL / (07341 86.12.87/88 /Telex: 84-7047 FRANCE: Keithley Instruments SARL / 2, 8is Rue Leon Blum ! 8.P. 60 / 91121 Palaiseau Cadex / (6) 011-51-55 /Telex: 600-933 NETHERLANDS: Keithley Instruments BV ! Arkelsedijk 4 I Postbus 559 / 4200 AN Gorinchem / 10) 1830-25577 /Telex: 24-684 SWITZERLAND: Keithley Instruments SA / Kriesbachstr. 4 / 8600 Dibendorf / 01/821-94-44 / Telex: 57-536 AUSTRIA: Keithlev Instruments Ges.m.b.H. / Doblinger Haupstr. 32 / 1190 Wien / 314 289 I Telex: 13-4500

Model 228

Voltage/Current Source

Instruction Manual

01986, Keithley Instruments, Inc.

Cleveland, Ohio, U.S.A.

Publication Date: April 1986

Document Number: 228-901-01 Rev. C

SPECIFICATIONS

AS A CONSTANT VOLTAGE SOURCE RANGE OVTPVT

ACCVRACY

MAXI- RESO.

MUM LUTION

loo” *,o,.o” lmm” *(o.l%+o.l “I *1.010 A ImA *K.l%+ ImA)

10” *,0.1Lw lam” *(o.l%+ lonw f10.10 A lomA *(o.s%+ 4cmA)

,1 YEAR1

W-WC Muhl LIJTION

I” *,.o,o” lnw *,0.1%+1.otr”~ *10.10.4 *on-A *w.s%+ 4omN

TEMPERAT”RE COEFF,CIENT (0”.1S”C a 28”.SO”0 f(0.1 Xapplic-

able acc”raw suwificationll”C.

NOISE:

1ov 2.OmV p-p

OUTPUT RESISTANCE (max.): lOOV Range: 1Omfl. 1OV Range: 1W pfl.

1v Range: ml pfl.

OUTPUT INDUCTANCE: l&$H typical.

SENSING: Rear panel witch selectable REMOTE and LOCAL sensing.

REMOTE SENSING: Corrects for up to 0.5V drop per ““t

im,,,,, s” per fence lead for rated accuracy. Maximum 0.5

for rated output resistance.

0.1.3oOHz 0.1~300kHz

5.omv p-p

0.7mV p-p

COMPLIANCE ,souru or Shk,

MAXI- RESO (1 YEAR)

*o.loloA k-m p.4 *,O.l%+4co #A) *l.oloA 1mA *ml%+ ImAl

*o.loloA m&A *KLl%+4m#A)

f1.010 A ,mA *,o.l%+ 4mA) *0.1010A ,MpA *:(0.l%+mpAl

15mV p-p 15nlv p-p 15mV p-p

AccmAcY

16’.WC

0.1.20MHz

mv P-P ‘YP. 25m” p-p typ.

25mV P-P w

“t lead. Max-

per sense lead

AS A CONSTANT CURRENT SOURCE

1 A *,.010A 1mA *~O.l%+l.cmA~ **o,.ov mmv *K.l%+mlrvl

0.1.4 *0.,0,0,4 ,MpA *(O.l%+O.,d~ *,o,.ov mlm” *~o.l%+mv~

‘Abave 0.4% of range.

TEMPERATURE COEFFICIENT (0”~ls”C dr 26”-50°C): f(O.l Xapplic-

able accuracy specificationl/“C.

NOISE:

OUTPUT RESISTANCE wn.1: IOA RanBe:

Range: lo*“. OUTPUT CAPACITANCE: 0.2rrF typical. OUTPUT LOAD: M”st be non-inductive.

“f,““A”

1 A O.lA 0.5mA D-D 3mA D-D Ml

0.1~300Hz

25 mA p-p

5 mA p-p

~,O.,O” lmn” *Ku%+ 4omVl *1.01ov

mm;;; mmv *ml%+ 4omVl

0.1~3OOkHz 0.1~MMHz 2smA p-p

Inl” *K%l%+ 4m”,

,mv *,O.*%+ h”,

;$ ;I:

lo4

iA Range: i&fl:b.lA

25* P-P typ. ‘OmA P-P tyP.

CURRENT MONITOR OUTPUT

SCALE FACTOR: 1” - 10% of range. ACCURACY: Same as constant currat mode. BANDWIDTH: 5kHz typical. OUTPUT RESISTANCE: lokIlo.

EXTERNAL MODULATION

INPUT RESISTANCE: 6.8M. SENSITIVITY: -lOV incraws magnitude of programmed output by

lW% of full scale; + 1OV decreaws magnitude of programmed output by

x0% of full scale. ACCURACY: 2% typical, dc to 6OHz. MAXIMUM MODULATION: Modulation and programmed settin should

not cause operation exceeding the range of zero to 101% of ful f scale.

MODULATION FREQUENCY: 6OOHz bandwidth.

IEEE-488 BUS IMPLEMENTATION (IEEE-4881978)

M~&IW&COMMANDSi DCL, LLO. SDC. GET, GTL. UNT. UNL. UNILINE COMMANDS: IFC, REN, EOI, SRQ, ATN.

INTERFACE FUNCTIONS: SHI. AHl, T6, TEO, L4, LEO, SRI. RLI. PPO.

DCl, DTl, CO, El.

PROGRAMMABLE PARAMETERS: Output (operate or standby), Range,

Voltage, Current. Trigger Mode. Sink. Modulation (Voltage or Current).

Dis lay Mode, Output Prefix (data format an readback), SRQ Mask,

EO , Terminator Characters, Status, Self Test, Memory Location (100 P

point memoryl, Dwell Time.

GENERAL

DISPLAY: Dual 3’/r-digit LED (0.5 in.) indicate programmed values in

Standby and output value8 in Operate. READBACK ACCURACY: Same as o”tp”t accuracy FRONT PANEL PROGRAMS: COPY, SINK, IEEE address, MOD V,

MOD 1. TEST, RESET.

LOAD TRANSIENT RECOVERY TIME: With a resistive load the o”tp”t

will recover 90% of any load changer within Ims after end of changen,

Provided the changes do not cause transfer to another control mode.

STANDBY: Programs output to OV. OA without changing rangff or polarity LINE REGULATION: Less than 0.01% output change for ac power line

changer within specified limits.

PROGRAM MEMORY (battery backed up): Stores up to 100 output set-

tings. Ra.nge of Dwell Time: 20mr to lw(k. Accuracy of Dwell Times:

* (0.05%+ 2msL

BATTERY BACKUP: Rechargeable 3.6V nickel-cadmium. 1 month reten-

tion of data with “nit turned off. TRIGGER: IN and OUT ITL-compatible. RESPONSE TIME: 30,“s max. to 99% of programmed change. MAXIMUM COMMON MODE VOLTAGE ,o”tp”t “I o”tp”t common t”

chassis): IWV dc.

OUTPUT CONNECTIONS: Quick disconnect card with screw terminals

for output, modulation, current monitor. and external sense. BNC (chassis isolated) connectors for TRIGGER IN/OUT.

SELF TEST: Analog acd digital circ”its tested at power-on. Power sup-

plies. temperatures. and output continuously monitored.

WARMUP: 10 min”teS to rated accuracy.

POWER: 105.125 or 210.250 V ac (internally switch selectable), 50 or

6OHz. 500 VA maximum. COOLING: Internal fan for forced air coaling. ENVIRONMENTz Opratlng: O” to 50°C. less than 80% non-condensing

RH below 35°C. Storage: -25’ to 70°C.

DIMENSIONS, WEIGHT: 133mm high X 43Smm wide X 448mm deep

(5%

in. X 17Y. in. x 17% in.). Net weight 10.9kg (24 Ibs.).

ACCESSORIES AVAILABLE:

Model 2288: Fixed Rack Mounting Kit Model 2289: Slide Rack Mounting Kit Model 7008-3: IEEE-488 Cable (3 ft.) Model 7&X-6: IEEE-488 Cable (6 ft.)

TABLE OF CONTENTS

SECTION l-GENERAL INFORMATION

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

Introduction........................,...,.,,,..,.....,,............,,.,,.,,,,.,,,..,,......... 1-l

Features . . . . . . . . . . . . . . . . . . . . . ..~

Using the Instruction Manual Warranty Information

ManualAddenda...................,,...,..,,,,...,,.,.,...,......,.,..,.,,,,.,,,..,.....,.... l-2

SafetySymbolsandTerms........................................................,.......,..... 1-2

Specifications. l-2 Unpacking and Inspection Accessories, 1-3

SECTION 2-SAFETY AND GENERAL OPERATION

2.1

2.2

2.3

SafetyPr~autions............................................................................. 2-I

GeneralOperatingProcedure..................................................,.......,......... 2-l

StandbyModeNotes........................................................................... 2-3

SECTION 3-FRONT PANEL OPERATION

3.1

3.2

3.2.1

3.2.2

3.3

3.4

3.5

3.6

3.7

3.8

3.9

3.10

3.11

3.11.1

3.11.2

3.11.3

3.11.4

3.11.5

3.11.6

3.11.7

3.12

3.12.1

3.12.2

3.12.3

3.12.4

3.12.5

3.12.6

3.13

3.13.1

3.13.2

Introduction PreparationFor Use

Line Voltage Selection ........

FuseChecks

PowerUp

Wan,,Up

Environmental Conditions

OperatingInstructions

Front PanelDescription ........................................................................

RearPanelDescription

QuickDisconnect Board .......................................................................

RemoteandLocalSensing .....................................................................

FrontPanelPrograms .........................................................................

Program1Copy

Program2Sink ............................................................................

Program3lEEE.. ..........................................................................

Program 4 MOD V (Modulate Output Voltage) Program 5 MOD I (Modulate Output Current) Program 6 Test (Diagnostic Self Test)

Program9Reset ............................................................................

Loads ......................................................................................

Load Line Description, ResistiveLoads ReactiveLoads InductiveLoads

CapacitanceLoads ..........................................................................

LoadRegulation

Operating Examples ..........................................................................

Example 1: lO.OOV, lO.OOAOutput

Example2:100V,1AOutput .................................................................

.................................................................................. 3-1

............................................................................

........................................ ........................

................................................................................ 3-l

....................................................................................

.................................................................................... 3-2

......................................................................

......................................................................... 3-2

........................................................................ 3-14

........................................................................

.................................................. 3-20

..........................................................

............................................. ........................

............................................................................. 3-24

.............................................................................

............................................................................ 3-24

............................................................................

............................................................ 3-27

1-I l-2 1-2

l-2

3-1

3-l 3-2 3-7

3-16 3-18 3-18

3.18 3-19

3-19

3-21 3-21 3-21

3-22

3-24 3-26

3-26

3-27 3-28

3.13.3

3.13.4

3.13.5

3.13.6

3.13.7 Example 7: Using the External Trigger (Input and Output)

3.13.8 Example 8: Floating Operation (Extended Compliance)

3.14 Applications......................................................

3.14.1

3.14.2

3.14.3 External Modulation

3.14.4

3.14.5

Example 3: 1V. 10A. lsec: lOV, 10A Zsec; and lCOV, lA, 3sec Output

in the Continuous Memory Control Mode Example 4: Model 228 as an Active Load (Current Sink) Example 5: Operation as Source and Sink. Example 6: Fabricating Output Waveforms

Low Resistance Measurements BatteryTests

Ramp Generation Power Semiconductor Testing

SECTION 4-IEEE BUS OPERATION

4.1

4.1.1

4.1.2

4.1.3

4.1.4

4.2

4.2.1

4.2.2

4.2.3

4.3

4.4

4.4.1

4.4.2

4.4.3

4.5

4.5.1

4.5.2

4.5.3

4.5.4

4.5.5

4.5.6

4.5.7

4.5.8

4.5.9

4.5.10

4.5.11

4.5.12

4.5.13

4.5.14

4.6

4.6.1

4.6.2

4.6.3

Introduction. ............ .........

Software Considerations, ...........

Interface BASIC Programming Statements

Interface Function Codes ....................

Model 228 Interface Commands. ..............

IEEE-488 Bus Lines. ...........................

Bus Management Lines ......................

HandshakeLines.. .........................

Data Lines

System Set Up Procedure ......................

BusCommands.. ........ ...................

Uniline Commands .........................

Universal Commands .......................

Addressed Commands ......................

Device-Dependent Commands. .................

Display Mode (D) ..........................

Memory Control (I’) .......... .............

Prefix(G) .................................

SRQ Request Mode (M) .....................

TriggerModes .............................

Programmable Terminator(Y). ...............

Inputs(I,V,WandB). ......................

Function(F) .......... .........

Range(R)

External Modulation (A, C) ..................

Sink Mode (S) ... ........................

Status Word(U). ...........................

Self Test(J). ...................

EOI and Bus Hold-Off Modes (K) ..........

Front Panel Error Messages. ....................

IDDCError ...............................

IDDCO Error. .............................

No Remote Error ...........................

................................

..............................

..... ...

.........

........

......

SECTION S-PERFORMANCE VERIFICATION

5.1

5.2

Introduction ...................................................................

Environmental Conditions .......................................................

5-l 5-l

5.3

5.4

5.5

5.5.1

5.5.2

RecommendedTestEquipment ....................................................

Initial Conditions.

....... ..

Performance Verification Procedure

..............

..... ...... ............... .... .............

Voltage Mode Verification (IV, 1OV and 1OOV) Output Current Verification, ...

..... ........ ..

SECTION B-THEORY OF OPERATION

.........

..................

..........................

.................

........

.....

..........

5-l 5-l 5-1 5-l 5-2

6.1

6.2

6.2.1

6.2.2

6.3

6.4

6.5

Introduction. Power Supply

Linear Power Supply

Switching Power Supply

Analog Control

Digital Board

Display Board

SECTION ‘I-MAINTENANCE

7.1

7.2

7.3

7.4

7.4.1

7.4.2

7.4.3

7.4.4

7.5

7.5.1

7.5.2

7.5.3

7.6

7.6.1

7.6.2

7.6.3

7.6.4

7.6.5

7.6.6

7.6.7

7.6.8

7.7

Introduction. FuseReplacement Line Voltage Selection Disassembly

Removing the Top and Bottom Covers RemovetheRearPanel Digital Board, Mother Board and Power Supply Board Access. Heat Sink Assembly and Fan Access

Troubleshooting .............................................................................

RecommendedTestEquipment ...............................................................

DigitalSelfTest

Troubleshooting

Calibration

RecommendedTest Equipment ...............................................................

EnvironmentalConditions ...................................................................

warnlup .................................................................................

TopCoverRemoval ........................................................................

+15VSupplyAdjustment ...................................................................

TestSetup

+lV Reference Adjustment

Current Calibration

Special Handling of Static Sensitive Devices

................................ ............................ ..................

..............................

...............

.................................................................................

............................................................................

...........................................................................

..................................................................................

.................................................................................

.........................................................................

.............................................

.........................................................

......................................................................

.....................................

...........................................................

..................................................................

.......................................................

6-l 6-l 6-l 6-2 6-2 6-6 6-6

7-1

7-l 7-l 7-2 7-2 7-3 7-3

7-3 7-10 7-10 7-10 7-10 7-13

7.13

7-13 7-13 7-13

7-14

7-14 7-14

7-14

7-15

SECTION 6-REPLACEABLE PARTS

8.1

8.2

8.3 a.4

8.5

Introduction ReplaceableParts Ordering Information Factory Service Schematic Diagram and Component Location Drawings

.....................................................

...............................

.............................................

.................................

.........

.......

.............

.............................................

8-l 8-l 8-l

8-l 8-l

iii

LIST OF ILLUSTRATIONS

3-1 3-2 3-3

3-4 3-5 3-6

3-7 3-8

3-9 3-10 3-11 3-12 3-13 3-14 3-15

3-16 3-17 3-18 3-19 3-20 3-21 3-22 3-23 3-24 3-25 3-26 3-27 3-28 3-29 3-30

GraphofOperation

Model228FrontPanel

......................................................

...................................................

Model228RearPanel ............. ...................

QuickDisconnectBoard Quick Disconnect Board Installatmn Graph of Operation for External Modulation Load Line (Positive Line Shown) Resistive Load Connections Limiting Inductive Reaction Voltage InductiveLoadConnections Capacitive Load Connections Model 228 Recommended Operating Limits Model228AsAnActiveLoad.. Output Waveform External Trigger Connections Connections for Floating Operation Low Resistive Measurements

..................................................

........................................

.................................

...........................................

...............................................

.......................................

...............................................

.............................................

..................................

...........................................

.......................................................

..............................................

........................................

..............................................

Battery LifeTest .........................................................

Data Logging Configuration. Power Supply Protection Circuit

Connections for External Modulation

Typical Modulated Output.

RampGeneration

.......................................................

Ramp Characteristics Power Transistor Test Set Up. Power Transistor IC/VCE Curves

Automated Test Set Up.

.....................

...........................................

.......................................

...............................................

....................................................

........................

..........................................

..................................................

FETTestSetUp .........................................................

FET Curves. ............................................................

Automated Test Set Up for FETs

...........................................

..................

........................

.........

..........

3-2

,. 3-5

3-5 3-77 3-17 3-20 3-23 3-24 3-25 3-26 3-26 3-26 3-26 3-36

., 3-37

3-37 3-38 3-39 3-39 3-39 3-40 3-40 3-40 3-41 3-41 3-42 3-42 3-42 3-42

...,. 3-43

4-l 4-2 4-3 4-4 4-5 4-6 4-7 4-E 4-9

5-l 5-2

6-1 6-2 6-3 6-4 6-5 6-6 6-7

Bus Structure ...........................................................

Handshakesequence

Contact Assignments

Typical Bus Connector

General Format of SRQ Byte and Mask Format of SRQByte ErrorStatusWord

Status WordFormat IEEEDispIayErrorMessage..

Output Voltage Configuration Output Current Configuration.

Model 228 Block Diagram

.....................................................

....................................................

...................................................

......................................

.....................................................

.......................................................

.....................................................

.............................................

............................................

....

..................................

Analog Control .............

Voltage Sensing .............

...............................

Current Sensing .............

Output Amplifier.

...........

A/D Converter .............

Display and Keyboard

.......

..................................

....... ..................

.....

4-4 4-5 4-6

4-6 4-19 4-19 4-27 4-28 4-29

s-2

5-2

6-I

b-3

6-4

6-5

7-l 7-2A 7-2B 7-3 7-4 7-5 7-6

TopandBottomCoverRemovaI .................................................................

RearPanelRemoval WiringInput

...........................................................................

.................................................................................

Model228ExplodedView ......................................................................

DetailofConnectors ...........................................................................

Heat Sink Assembly (Exploded View) CalibrationSetup

............................................................................

............................................................

7-4 7-5

7-6 ‘,:;

7-11 7-17

8-l 8-2 8-3 8-4

8-5 8-6 8-7 8-8

Mother Board, Component Location Drawing, Dwg. No. 228-100 Mother Board, Schematic Diagram, Dwg. No. 228-106

..............................................

Display Board, Component Location Drawing, Dwg. No. 228-110 Display Board, Schematic Diagram, Dwg. No. 228-116

.............................................

.....................................

....................................

Power Supply Board, Component Location Drawing, Dwg. No. 228-150. Power Supply Board, Schematic Drawing, Dwg. No. 228-156 Digital Board, Component Location Drawing, Dwg. No. 228-140

Digital Board, Component Location Drawing, Dwg. No. 228-146

........................................

.....................................

..............................

8-6

8-7 8-15 8-17 8-22 8-23 8-27

8-29

LIST OF TABLES

3-l 3-2 3-3 3-4 3-5 3-6 3-7 3-8 3-9

4-1 4-2 4-3 4-4 4-5 4-6 4-7 4-8 4-9 4-10 4-11 4-12

5-l 5-2 5-3

Line Voltage Setting .... ......... ......

Front Panel Controls ....................

Rear Panel Description .............

....

Front Panel Messages .. .................

Front Panel Messages and Prompts ........

Error Messages (Either Display)* ..........

Power Up Default Conditions. ............

Summary of Front Panel Programs

Maximum Inductive Reaction Voltage, HP-85 and IBM BASIC Statements

........

.....

.............................

Model 228 Interface Function Codes ............................

IEEE Command Groups. ......................................

IEEE Contact Designations ......

DCL and SDC Default Conditions

......... ................

........... ..................

Device-Dependent Commands .................................

Device-Dependent Commands Not Available to the Front Panel.

Hierarchy of Command Execution ..............................

SRQMaskCommands .......................................

Input CommandSummary ....................................

RangeCommands ...........................................

HoldOFFTimes .............................................

Recommended Test Equipment. ........

Output Voltage Verification ...........

Output Current Verification ...........

....

3-1 3-3 3-4 3-a 3-a

3-8 3-10 3-18 3-26

4-2

4-3 4-3 4-6 4-8

4-11 4-13 4-14 4-19 4-22 4-24 4-29

5-l

5-2

7-l 7-2 7-3 7-4 7-5 7-6 7-7 7-a 7-9 7-10

8-l

8-2 8-3

8-4 8-5

Fuse Replacement ....................

Low Voltage Operation, Part Changes

Line Voltage Selection ................

Recommended Test Equipment. ........

Power Supply Checks ................

Analog Circuitry Checks. .............

Digital Circuitry Checks ..............

Display Board Checks ................

Recommended Calibration Equipment

Model 228 Static Sensitive Devices. .....

Mother Board Parts List. ..............

Display Board Parts List ..............

Power Supply Parts List. ..............

Digital Board Parts List ...............

Mechanical Parts List .................

7-1

7-2

7-10 7-11 7-11 7-12 7-13 7-13 7-15

8-2

8-13 8-19 8-25 8-31

SECTION 1

GENERAL INFORMATION

1.1 INTRODUCTION

The Model 228 Voltage/Current Source is both a constant

voltage and constant current source with front panel and

IEEE operation. The Model 228 can be used as a constant

voltage source or a constant current source. It has four

quadrant operation. This means that the voltage or current sources can operate as a source or a sink in either positive or negative polarities. Full power capability of 1OOW may be ob-

tained in any quadrant.

Parameter entry is done in one of two ways. Either using the data keypad to enter the desired value into the display or using the display modify function. The display modify function allows the user to modify either display by selecting a digit of the display and incrementing or decrementing that digit with the appropriate keys. With the carry, borrow and autorepeat capability, front panel operation is flexible and easy to program. The user selects the range with the decimal point.

The Model 228 has a 100 point data memory that allows the

user to store up to 100 unique values of current, voltage and dwell time for future use. Once a particular level is stored in the data memory, the user need not reprogram that level.

The output terminals are located on a quick disconnect board

that inserts into the rear panel of the mainframe. The output

is disconnected from the quick disconnect board when it is removed from the mainframe.

1.2 FEATURES

The Model 228 includes the following features:

l Six ranges that allow a wide variety of voltage/current

values.

l Seven front panel programs. The programs include:

Program 1 Copy for duplicating memory location informa-

tion. Program 2 Sink for sink only operation. Program 3 IEEE for changing IEEE primary address. Program 4 MOD V for modulating output voltage. Pronram 5 MOD 1 for modulatinn output current. Pro&m 6 Test for Model 228 self tes;,

Program 9 Reset for resetting the Model 228 to factory set values. See paragraph 3.13.7

l Dual displays for easy reference of the instrument’s status.

The left display has two display modes (voltage and mem-

ory step). The right display also has two display modes

amps and seconds).

l Two methods of modifying the source or sink value: Data

entry from the data keypad, and increment or decrement of

displayed valued using the decade keys.

l 100 point data memory to store up to 100 unique values of

voltage, current and dwell time. Each location also includes:

sink mode status and voltage current modulation status.

All information stored in a memory location is battery backed up. This means that if the instrument is powered down, the stored information (voltage, current and dwell

time parameters) remains in a particular location until

changed by the user.

l OPERATE/STANDBY switch that places the output in

either the operate mode (displayed value is present at output) or in the standby mode (output is programmed to approximately zero).

l Compliance status is easy to read on the front panel com-

pliance graph. The graph shows the user at a glance how the Model 228 is operating (source or sink polarity and voltage

or current compliance).

l IEEE-488 bus operation is standard. This enables the Model

228 to be incorporated into a system

that

uses programmed

control over the IEEE-488 bus.

l Single step, single cycle and continuous memory modes

control the sequence between data points in the 100 point data memory. The program mode may be controlled in one of three ways; using the front panel START/STOP key, the

external trigger pulse or by commands over the IEEE-488

bus.

l Output terminals are located on the quick disconnect board

for optimum safety. The output terminals, the sense ter-

minals, current monitor terminals and

the

external modula-

tion terminals are also located on the quick disconnect

board. Several quick disconnect boards may be wired with their own unique wiring configuration. When one configur-

ation is required, simply insert into the mainframe. In this

way, cumbersome rewiring of one board is avoided.

l Remote and Local Sensing. This allows the user to sense at

the output terminals or at the load or source. Remote sens-

ing compensates for the effects of the I*R lead drop by

maintaining regulation at the load instead of at the output

terminals of the Model 228.

l Four Quadrant Operation. This means that the voltage or

current outputs can operate as a source or a load in either positive or negative polarities. The front panel compliance

graph shows the user where the Model 228 is operating (source or sink).

1-1

. Output Modulation. This feature allows the output signal

to be modulated from an external AC signal source. Voltage

or current may be modulated.

l Bipolar Output. This means that the polarity of the output

may be reversed by using front panel controls instead of

reversing the wires.

l Most of the front panel keys autorepeat if held in.

1.5 MANUAL ADDENDA

Information concerning improvements or changes to the instrument which occur after the printing of this manual may be found on an addendum sheet included with this manual. Be sure to review these changes before attempting to operate the instrument.

1.3 USING THE INSTRUCTION MANUAL

This manual contains information necessary for operating,

programming and servicing the Model 228 Voltage/Current Source and is divided into the following sections:

Section 2 contains safety instructions and a general

1. operating procedure.

Section 3 contains front and rear panel descriptions, a

2. general operating procedure and specific operating examples showing how to use the Model 228.

Section 4 contains information pertaining to the IEEE-488

including primary address selection, device-

bus, dependent command programming, bus connection and several sample programs.

Section 5 includes a procedure to verify the performance

4. of the Model 228.

Section 6 contains theory of operation with detailed

5. schematics and block diagrams. This section facilitates understanding of the individual circuits of the Model 228.

Section 7 contains servicing information for the Model

228. Calibration, troubleshooting, line voltage selection,

fuse replacement and static sensitive device information is

contained in this section.

Section 8 gives replaceable parts information.

If an additional manual is required, order the manual package (Keithley Part Number 228-901-00). The manual package includes an instruction manual and all pertinent addenda.

1.6 SAFETY SYMBOLS AND TERMS

The following safety symbols and terms are used in this manual or found on the Model 228:

The symbol

should refer to the operating instructions in this manual.

The symbol /L* on the mstrument indicates that a lethal

potential may be present at the output terminals. Standard safety practices should be observed when such potentials are encountered.

The WARNING heading used in this manual explains dangers

that could result in personal injury or death.

The CAUTION heading used in this manual explains hazards

that could damage the instrument.

on the instrument indicates that the user

1.7 SPECIFICATIONS

1.4 WARRANTY INFORMATION

Warranty information may be found inside the front cover of

this manual. Should it become necessary to exercise the warranty, contact your nearest Keithley representative or the factory to determine the course of action. Keithley Instruments maintains service facilities in the United States, United Kingdom and throughout Europe. Addresses of these facilities may be found inside the front cover of this manual. Information concerning the application, operation or service of your instrument may be directed to the application engineer at any of these locations.

1-2

Detailed Model 228 specifications may be found immediately preceding this section of the manual.

1.6 UNPACKING AND INSPECTION

The Model 7.28 Voltage/Current Source was carefully inspected, both electrically and mechanically before shipment. Upon receiving the Model 228, carefully unpack all items from the shipping containers and check for any obvious signs for physical damage that may have occurred during ship-

mat. Report any damage to the shipping agent immediately. Retain the original packing materials in case reshipment becomes necessary. The following items are included with every Model 228 order:

Model 228 Voltage/Current Source Model 228 Instruction Manual, Reference and Program In-

structions and the Instruction Label. Quick Disconnect Board Additional accessories as ordered.

rewiring for each configuration, several quick disconnect boards could be wired for each unique configuration. The

Keithley part number of the quick disconnect board is 228-160. One quick disconnect board is supplied with each Model 228.

Model 2288 Fixed Rack Mount-The Model 2286 is a fixed or

stationary rack mounting kit that mounts the Model 228 in a standard 19 inch rack.

1.9 ACCESSORIES

Quick Disconnect Board-The quick disconnect board con-

tains output, sense, external modulation and current monitor

terminals. The quick disconnect board inserts into the rear panel of the Model 228 mainframe. When the board is in place, the terminals are connected to the actual potentials (if in the operate mode). Removing the board from the mainframe disconnects the terminals from the output. This is a safety feature designed so the user should not have to come into contact with a dangerous potential.

With all of the terminals on the board, many configurations

could be wired. To avoid cumbersome and time consuming

Model 2289 Slide Rack Mount-The Model 2269 is a sliding

rack mount kit. It enables one Model 228 to be rack mounted with the added feature of sliding the instrument for fast access.

Model 700&j-The Model 7008-3 is a 1 meter (3 feet)

IEEE-488 cable. The cable has 24 stranded wire conductors and is terminated on each end with standard IEEE-488 connectors.

Model 700%6-The Model 7008-6 is a 2 meter (6 feet)

IEEE-466 cable. The cable has 24 stranded wire conductors and is terminated on each end with standard IEEE-488 connectors.

SECTION 2

SAFETY

AND GENERAL OPERATION

2.1 SAFETY PRECAUTIONS

Safety information such as warnings and cautions are located

throughout this manual. The information is placed in the appropriate places in the manual where a hazard may exist. The warnings refer to a potentially dangerous situation where personal injury or even death may occur. The cautions refer to a potentially hazardous situation where the instrument may be damaged. Take the time to read and most of all understand these warnings and cautions.

The following safety information is provided as a general safety practice before, during and after operation of the Model 228.

1. Do not operate the instrument with the top cover and/or bottom cover removed. Lethal potentials are present throughout the mainframe. The covers must also be in place to allow proper air flow through the instrument. Proper air flow is required to cool the instrument during operation. If proper cooling is impeded the instrument may overheat.

2. Never assume the output is at a safe potential while the AC line is connected.

3. The Model 228 is capable of producing several times its current rating for short periods of time (“WC). Keep this

in mind when choosing a load. Brief bursts of high current are still enough to damage other instrumentation and cause serious injury.

4. Using the Model 228 to sink power from an external source requires some precautions that are outlined as follows:

A. A temporary loss of line voltage resets the Model 228

output to a high impedance state. Therefore, a user supplied voltage limiting circuit may be required to control the external source. A zener diode placed across the output is recommended.

B. When the voltage polarity of an external source op-

poses the programmed polarity of the Model 228,

voltage has priority. where: Vs = Source Voltage (V~O~RCE) 1s = source Current (Iso”& RL = Load Resistance when:

vs + vzzs

is greater than the current setting of the

Model 228.

The standby mode programs the Model 228 for approximately O.OV, O.OA.

is + vz,, =

Therefore, 1s = VS/RL up to the limits of the output

fuse. The output fuse is factory rated at 20A. In some circuit applications it may be necessary to limit the current with a resistor or select a lower rated output fuse. The output fuse must have a minimum voltage rating of 250V.

C. When the voltage polarity of an external source mat-

ches the programmed polarity of the Model 228, current has priority.

when: Vs--lsR~ is greater than the voltage setting of

Before operation, ground the instrument through a pro-

oerlv earth mounded recentacle. Failure to mound the in-

‘, Y

strument may result in severe injury or even death in the event of a short circuit or malfunction.

After extensive use of the Model 228, set the instrument to standby and allow it to cool down for a few minutes before turning off the power to the instrument.

Never come into contact with the output connections

while the instrument is turned on. Observe proper polarity when operating in the sink

mode. A reversed polarity may allow the instrument to operate at a current limit of the output fuse.

Use cables for the output that have appropriate current

and insulation rating. For example, if 1OV at 1OA is to be produced or dissipated then the cables must be rated for that amount. Also, use insulated lugs for connections on the quick disconnect board.

Do not leave the instrument unattended when it is in the

operate made. Always place the instrument in standby after the measurement or test is completed.

Always set up the test circuit while the power is turned

off. Do not come into contact with any part of the test circuit while power is on.

vs + 0

Model 228.

is greater than zero,

2.2 GENERAL OPERATING PROCEDURE

This is a general operating procedure to familiarize the user with front panel operation of the Model 228. There are

several operating parameters involved with Model 228 operation. These parameters are taken into account in this procedure. Of course, every detail of Model 228 operation is not

2-1

covered in the general procedure. Section 3 includes several specific examples of Model 228 operation.

NOTE Most of the front panel keys autorepeat if held in. Refer to the operation notes at the end of this procedure.

1. Turn on the Model 228 and allow 10 minutes for warm up. NOTE

To achieve rated accuracy, run Program 6 immediately after the lo-minute warm-up period.

2. Select the desired memory location. There are two methods for selecting memory locations, This procedure covers both methods.

NOTE

The unit powers up to memory location 1. This need not be changed if memory control is not be-

ing used.

Method 1: Select Memory Location A. Press the VOLTS/MEMORY STEP key if not in the

memory step display. The present memory location is displayed on the left display.

B. Press the SELECT key to select the display to be

modified (left or right). The selected display is indicated by the flashing bright digit.

C. Press the left or right key (indicated by the left and

right arrows) to select the digit that is to be modified. The selected digit is indicated by the flashing bright digit. digit.

D. Press the increment or decrement keys (indicated by the D. Press the increment or decrement keys (indicated by the

up and down arrows) to modify the selected digit for up and down arrows) to modify the selected digit for

the desired memory location, the desired memory location,

Method 2: Select Memory Location A. Press the VOLTS/MEMORY key to select MEMORY

STEP. The present memory location is displayed on the left display.

B. Press the SELECT key to select the left display. The

selected display is indicated by the flashing bright digit.

C. Enter the desired memory location number using the

DATA keys.

D. Press ENTER.

3. Program the desired source, There are two methods for programming the source. The source may be voltage or current.

Method 1: Program the Source A. Press either the VOLTS/MEMORY STEP key to

display the source voltage on the left display, or the

AMPS/DWELL TIME key to display the source current on the right display.

8. Press the SELECT key to select the display to be

modified. The left display is for voltage and the right

display is for current. The selected display is indicated by the flashing bright digit.

C. Press the left OF right key to select which digit is to be

modified, The selected digit is indicated by the flashing bright digit.

D. Press the increment or decrement key to modify the

selected digit and source value. The output value is up-

dated continuously along with the display when using the increment or decrement keys.

Method 2: Proeram the Source

Press the VOLTS/MEMORY STEP key to display the source voltage, or the AMPS/DWELL TIME key to display the source current.

Dress the SELECT key to select the left display: the left display for voltage or the right display for current. The selected display is indicated by the flashing bright digit.

Enter the desired source value on the display using the DATA key.

D. Press ENTER.

4. Program the desired dwell time. This may be done by one of two methods.

Method 1: Program Dwell Time A. Press the AMPS/DWELL TIME key if dwell time is not

displayed. The present dwell time is displayed on the right display.

Press the SELECT key to select the left display. The selected display is indicated by the flashing bright digit.

Press the left or right key to select the digit to be

modified. The selected digit is indicated by the flashing bright digit.

D. Press the increment or decrement key (indicated by the

up and down arrows) to modify the selected digit and dwell time. The value is undated continuouslv alone with the display when using the increment or decrement keys.

Method 2: Program Dwell Time A. Press the AMPS/DWELL TIME key if not in the dwell

time mode. The present dwell time is displayed on the right display.

8. Press the SELECT key to select the left display. The selected digit is indicated by the flashing bright digit.

C. Enter the d+d dwell time using the DATA keys. D. Press ENTER.

5. Select the desired memory control mode (single step, single cycle or continuous).

6. Connect appropriate load.

7. Select remote or local sensing (rear panel switch).

8. Program the instrument to the operate mode by pressing

the OPERATE/STANDBY key.

9. If applicable, press the START/STOP key to start the

selected memory control mode.

2-2

Notes

1. Using the increment or decrement keys to either exceed the maximum value for that range or change sign, briefly

displays an error message and the last key pressed is ignored. Refer to Tables 3-4, 3-5 and 3-6 for front panel messages.

2. Using the increment and decrement keys to adjust the most significant digit does not change the range. The range error message is displayed for about one second and the instrument remains at the previous setting.

3. During the edit mode, if no activity has happened on the front panel for approximately 20 seconds or if the ENTER key is pressed, the edit mode is cancelled and the display returns to normal intensity.

4. For the current function the output load must be, in general, non-inductive. A small amount of inductance in the load can be tolerated if the inductive reactive voltage L $ is limited to the maximum compliance voltage of the

range. Table 3-9 lists the maximum inductive reaction voltage for each current range. Refer to paragraph 3.12.3

5. Operation of the Model 228 as a power sink produces heat. The Model 228 employs a fan for forced air cooling. Do not block the airflow of the fan. The instrument may overheat and go into the thermal shut down mode.

6. When using the DATA keypad to modify the displayed data, the actual value is not entered until the ENTER button is pressed.

7. In the operate mode (OPERATE LED on), the actual

voltage and current are monitored and displayed. For ex-. ample, if 5V. 5A are programmed and the load is drawing

2.3A, then 5V. 2.3A is displayed.

8. All of the front panel keys (except PROGRAM, CANCEL, OPERATE and LOCAL) autorepeat if held in.

9. In the immediate mode (which uses DECADE keys and

output is updated along with the display), the ENTER key need not be pressed. After approximately 20 seconds the Model 228 cancels the edit mode and returns to the previous operating mode. The new data remains.

10. The STANDBY LED is of amber color to distinguish it from the OPERATE LED which is red.

11. If the internal operating temperature reaches over 100°C,

the Model 228 displays an error message as shown in

Tables 3-4,3-5 and 3-6. At this point the instrument locks up and displays the error message. The Model 228 must be turned off and allowed to cool down before continuing operation.

12. The Model 228 when first txned on, goes through a

power up sequence that is described in Section 3.

13. The Model 228 has a bipolar output. This means that the polarity of the output may be reversed without having to reverse the output leads.

14. All of the information programmed into the memory locations is battery backed up. This means that if the instrument is powered down, the information programmed in the memory locations is not lost. The information remains in the memory location until changed by the user.

15. Tables 3-4, 3-5 and 3-6 contain a complete list of front panel messages and their definition. Included are error and instrument status messages.

16. The user selects the range with the absolute location of the decimal point. l.OCOV selects the 1V range, 1V output. l.COV selects the 1OV range, 1V output. 0Ol.V selects the 1WV range, 1V output.

17. Increment and decrement keys do not change the range or polarity. These functions increase/decrease the magnitude of both positive and negative limits.

ls. After power on, the current range select relays remain

o P en until the operate key is pressed the first time. This e fectively open-circuits the output and may cause hansients on the output during auto cal and the first time operate is selected.

CAUTION

The MONITOR and MODULATION terminals re-

main connected to the Model 228’s internal clr-

cultry; therefore, lerge voltages or currents may exist between OUT+ and these tsrmlnels durIng callbretlon.

19. While in the standby mode, the output remains programmed the same as when first programmed to standby. Therefore range changes, source/sink status, (etc.) take affect when operate is selected.

20. The front panel compliance graph may show multiple LEDs. As an example; when current is zero, +O and -0 are approximately the same magnitude so two LEDs will show.

21. If the measured output current exceeds 200% of range, the output is disconnected and the Model 228 is placed in the standby mode. Normal operation returns bipressing the OPERATE key.

2.3 GENERAL OPERATION NOTES

1. Using the increment or decrement keys to either exceed the maximum value for that range or change sign, causes the Model 228 to briefly display an error message. The last key pressed is ignored. Refer to Tables 3-4, 3-5 and 3-6 for front panel messages.

2. Using the increment or decrement key to adjust the most significant digit does not change the range. The range error message is displayed for about one second; and the instrument remains at the maximum display for that range or zero, whichever is programmed.

3. During the edit mode, if no activity has happened on the front panel for approximately 20 seconds, or if the ENTER key is pressed, the edit mode is cancelled. The display returns to normal intensity.

4. For the current function, the output load must be, in general non-inductive. A small amount of inductance in

the load can be tolerated if the inductive reactive voltage,

2-3

L 2, is limited to the maximum compliance voltage of the range. Table 3-4 lists the maximum inductive reaction voltage for each current range.

6. When using the DATA keypad to modify the displayed data, the actual value is not entered until the ENTER button is pressed.

7. In the operate mode (OPERATE LED on), the actual voltage and current are monitored and can be displayed. For example, if SV, 5A are programmed and the load is drawing 2.3A. then SV, 2.3A is displayed.

8. All of the front panel keys (except PROGRAM, CAN-

CEL, OPERATE and LOCAL) autorepeat if held in.

9. In the immediate mode (using DECADE keys and the output is updated along with the display) the ENTER key need not be pressed. After approximately 20 seconds, the

Model 228 cancels the edit mode and returns to the

previous operating mode. The new data remains.

10. The STANDBY LED is of amber color to distinguish it from the OPERATE LED which is red.

11. If the internal operating temperature reaches over 100°C. the Model 228 displays an error message as shown in

Table 3-4. At this point, the instrument locks up with the

error message displayed. The Model 228 must be turned off and allowed to cool down before continuing operation.

12. The Model 228 goes through an autocalibration cycle when the instrument is powered on. Refer to the maintenance section for complete details.

13. The Model 228 has a bipolar output. This means that the polarity of the output may be reversed without having to reverse the output leads.

15. Tables 3-5, 3-6 and 3-7, contain a complete list of front panel messages and their definition. The messages include: error messages and instrument status messages.

2.4 STANDBY MODE NOTES

The following situations depict when the Model 228 output is

electrically disconnected (via internal relays) from the instrument.

1. Power is off.

2. During the auto calibration cycle. Upon power up, until the end of the calibration cycle and during a portion of

front panel Program 6.

3. Within a few line cycles for low or missing line voltage. If the microprocessor is reset, the normal power up sequence occurs. If the microprocessor is not reset, the next time the A/D is triggered (approximately six times a second) or when the output is changed.

In the standby mode the Model 228 output is still active. The standby mode has the same effect as programming the output for the following conditions:

1. OV +four counts (on the same voltage range and same

polarity).

2. OA ffour counts (on the same current range and same

polarity).

3. MOD V off.

4. MOD I off. The output is NOT disconnected. Programming the output

for the new values, ranges polarity, sink mode or modulation does NOT change the output until the Model 228 is placed in the operate mode.

Notes

1. Since the output is still active, the quick disconnect card should be removed from the mainframe BEFORE any wiring changes are to be made.

2. The Model 228 looks like a short or an open circuit to an external source. This depends on whether the voltage polarities oppose or match before the Model 228 is placed in standby. Polarity changes do not affect the output until the Model 228 is placed in the operate mode.

3. Large reactive loads are not immediately discharged by

placing the Model 228 in the standby mode. This is because the OV setting does not change the current through

an inductor and the OA setting does not change the voltage

across a capacitor. In reality, capacitors and inductors discharge at approximately 0.4% of range when the Model 228 is in the standby mode.

2-4

SECTION 3

FRONT PANEL OPERATION

3.1 INTRODUCTION

Information in this section concerns front panel operation of

the Model 228 and is divided into four categories: operating instructions, operating examples, front panel programs and applications. Operating instructions include using the Model

228 to source or sink, voltage or current, in the positive or negative direction. Operating examples cover many aspects of Model 228 operation. The front panel programs section describes each program and gives a few examples of Model

226 uses.

3.2 PREPARATION FOR USE

The following steps must be performed to prepare the Model 228 for operation. These steps can be performed quickly and will ensure proper line voltage and fuse selection,

3.2.1 Line Voltage Selection

The Model 228 may be operated from either 105V-125V or 21OV-25OV. 50Hz or 6OHz power source. The instrument was shipped from the factory set for an operating voltage that is marked on the rear panel. The operating voltage of the instrw ment is internally selectable. Refer to Section 7 Maintenance,

for information on setting the line voltage.

CAUTION

Do not on a supply voltage outside the indicated range. Damage to the instrument may occur.

attempt

to operate the instrument

3.2.2 Fuse Checks

It is important to check each of the three fuses for proper rating before applying power to the Model 228. If the line voltage was recently changed, the linear supply fuse (LINE FUSE 1) and the switching supply fuse (LINE FUSE 2) must also be changed to accomodate the new line voltage. The output fuse (OUTPUT FUSE) should also be checked for proper rating. Refer to Section 7 Maintenance, for information on proper fuse rating.

CAUTION Check all three fuses for appropriate rating. The fuse ratings are listed in Tables 7-1 and 7-2. and they are also shown on the rear panel. Incorrect rating may cause damage to the instrument in case of short circuit or malfunction.

3.3 POWER UP

Plug the Model 228 into the proper power source. (see Table 3-l.) For fuse replacement of line switch (S102) setting, refer

to Section 7 Maintenance.

WARNING

Ground the instrument through a properly

earth grounded receptacle before operat-

ing. Failure to ground the instrument may result in severe injury or death in the event

of e short circuit or malfunction.

Table

Input Voltage (SW302l/ Fuse 1

sov-11ov* 115v 6.3A. 250v 1A. 250V

105V-125V 115V 5A. 250V 3/4A. 250V

IEOV-22OV” 230V 3.ljA. 250V 0.5A,‘250V

21OV-250V 230V 2.5A. 250V 3/8A, 250V

*Operation at these input voltages requires power supply

modifications. Refer to the maintenance section of this manual for more information

Turn the instrument on. The Model 228 runs through a power up sequence that is described as follows:

1. Immediately after turning on the Model 228 via the front panel POWER switch, both displays indicate the following for several seconds:

A. This is a display test. The operator can note inoperative

display segments by comparing the Model 228’s display

with the above figure.

8. In addition, all LEDs are turned on for the same oeriod

of time. The LEDs include: VOLTS, MEM STEP, AMPS, SECONDS, STANDBY, OPERATE, STOP,

3-l. Line Voltage Setting

1 Switch 1

Setting I

Fuss 2

3-1

START, SINGLE MODULATE I, MODULATE V and SINK ONLY. All of these LEDs light simultaneously if operating properly.

C. While the display test is running, the Model 228 is per-

forming a digital self test on the RAh4 circuitry and cyclic redundancy check (CRC) on the ROM circuitry. If there is a problem, the Model 228 displays an error message. For further information, refer to Section 7 Maintenance.

If the Model 228 did not pass the RAh4 test the following is displayed.

If the Model 228 did not pass the ROM test the following is displayed.

2. The Model 228 displays the software revision level. The following is an example of software revision Al.

3.5 ENVIRONMENTAL CONDITIONS

Operate the Model 228 in an environment with an ambient

temperature within the range of 0°C to 5O”C, up to 35°C at

80% non-condensing relative humidity. Environmental con-

ditions for storage are from -25°C to 70°C.

3.6 OPERATING INSTRUCTIONS

The following instructions show how to operate the Model 228 using the front panel controls. In order to operate the Model 228, the user must understand the front and rear panel controls. It is important to read and follow the safety precautions and warnings before operating the instrument. A brief description of the front panel controls is provided in Table 3-2. A more detailed description of the front panel controls is contained in paragraph 3.7. A brief description of the rear panel terminals and controls is provided in Table 3-3. A more detailed description of the rear panel controls is contained in paragraph 3.8. Figure 3-2 shows the front panel of the Model

228. Figure 3-3 shows the rear panel of the Model 228. A graph of operation is contained in Figure 1.

3. Next, the Model 228 displays the present primary address. The following is an example of primary address set to 11.

3.4 WARM UP

In order to achieve rated accuracy, the Model 228 requires ten minutes for warm up.

NOTE

To achieve rated accuracy, run Program 6 immedi-

ately after the lOminute warm-up period.

-I

L j

--- -_ B

---

I I

-V

--IG

3-2

Figure 3-I-Graph of Operation

Table 3-2. Front Panel Controls

Control POWER ON/OFF

OPERATE/STANDBY

VOLTS/MEMORY STEP AMPS/DWELL TIME

DISPLAY MODIFY GROUP

SELECT

DECADE

ENTER DATA

MEMORY CONTROL GROUP

Description

Turns the unit on or off.

Places the output in either standby or operate. Standby programs the output

terminals for OV, DA. Operate places the programmed value fvoltage or cur-

rent) on the output terminals. Places the left display (viewed from the front panel) in either the volts display

mode or the memory step mode. Places the left display (viewed from the front panel1 in either the amps display

mode or the dwell time display mode.

Determines which display (left or right) to modify.

The DECADE keys (left, right, up and down) modify the selected display. The

left and right keys (indicated by the left and right arrows1 select which digit is

to be modified. The increment and decrement keys (indicated by the up and

down arrows) increment or decrement the value of the selected (bright) digit and therefore the displayed value by one unit each

time

the key is pressed.

The output tracks the increment or decrement of the displayed value. The ENTER key places the displayed data into the present memory location.

The DATA keys enter the desired value on the display. ENTER must be pressed to update the value to the output. The DATA keys also activate the desired front panel program. Refer to paragraph 3.11 for front panel programs.

START/STOP SINGLE STEP

SINGLE CYCLE

CONTINUOUS

PROGRAM CONTROL GROUF PROGRAM

CANCEL

LOCAL

The START/STOP key enables or disables the memory control functions. Selects the SINGLE STEP memory control function which allows the user to

step through the programmed memory locations one at a time. Each successive key pressed advances the unit to the next memory location. The memory control mode must be activated in order for single step to operate.

Selects the single cycle memory control function which allows the user to run

through one complete cycle of the programmed memory location. The

memory control mode must be activated in order for Single Cycle to operate. Selects the CONTINUOUS memory function which allows the user to run

through the programmed memory locations continuously. The memory con-

trol mode must be activated in order for CONTINUOUS to operate.

The PROGRAM key is used as the first step in activating the front panel programs.

The CANCEL key has two functions. In the program mode, the CANCEL key takes the instrument out of the program mode. During entry of new data, the

CANCEL key terminates editing. The instrument is then returned to the previous operating mode.

The LOCAL key enables front panel operation. In the remote mode (over

IEEE-488 bus), pressing the LOCAL key enables front panel operation and

takes the Model 228 out of the remote mode.

3-3

Table 3-3. Rear Panel Description

Connectlon8/Controls

OUTPUTCONNECTOR

SENSE

CURRENT MONITOR TRIGGER IN TRIGGER OUT EXTERNAL MODULATION SENSING FUSE 1

FUSE 2 FUSE 3

IEEE-488 Connector LINE RECEPTACLE

Description

The outout connections are located on a card that is inserted into the Model 228 mainframe. When the connector is removed from the mainframe the output connections are disengaged from the actual output potentials.

The sense connectors are located on a card that is inserted into the Model 228 mainframe. The sense lines ara used to sense the output at the output connector (Local) or sense the output at the load (Remote).

This connection supplies a voltage proportional to the output current for use with oscilloscopes or DMMs.

The TRIGGER IN connector accepts a TTL level negative going pulse of greater than lO@ec to initiate the selected memory mode.

The TRIGGER OUT connector outputs a TTL level negative going pulse of greater than lO@ec at the end of each programmed dwell time.

This connector allows the output (voltage or current) to be externally modulated.

The REMOTE/LOCAL SENSING switch selects sensing from the sense terminals or the output terminals.

This is the line power fuse for the linear power supply on the analog board. The fuse is rated as shown in Tables 7-1 and 7-2. If this fuse is blown the

Model 228 will not power up.

This is the switching supply fuse. It is rated as shown in Tables 7-1 and 7-2. If this fuse is blown there is no output present.

This is the output fuse. The fuse is rated at 20A. This connector is used to connect the instrument to the IEEE-488 bus. The

IEEE interface functions are marked above the connector.

The line receptacle connects to a three wire line cord which provides con-

nections to the line voltage.

3-4

3 !

lrlllllllll I

II II II II II

3.7 FRONT PANEL DESCRIPTION

OPERATION GROUP

POWER ON/OFF-The ON/OFF switch operates on the push-push principle. Depressing this switch turns the instrument on. Once the instrument is on, pressing (releasing) this switch turns the instrument off. When the Model 228 is turned on, the output is programmed to about OV, OA and the programmed settings are displayed. Note that the Model 228 does not change range polarity or sink status while in the

standby modes, and external modulation is disabled.

VOLTS/MEMORY STEP-The VOLTS/MEMORY STEP key is an alternate action control which places the left display in either the volts display mode or the memory step mode. In the volts display mode, the voltage for the present memory location (step) is displayed on the left display. In the memory

step mode, the present memory location is displayed on the left display. This key allows the user to view either the present memory location or the voltage at the present memory location. There are 100 memory locations (steps). Each memory location contains five parameters (Voltage, Current, Dwell Time, Modulation on or off and Sink Mode on or off).

These parameters are defined (programmed) by the user. This

means that each memory location may have its own unique

VdWS.

OPERATE/STANDBY-The OPERATE/STANDBY key is an alternate action control (toggle) which places the Model 228 in either the operate mode or the standby mode. In the operate mode, the OPERATE LED is turned on and the programmed source value is present on the output terminals. In the standby mode, the STANDBY LED is turned on the output is programmed to approximately zero and the displayed value remains the same.

In the standby mode the Model 228 is still active, The standby mode has the same effect as programming the output for the following conditions:

1. OV +four counts (on the same voltage range and polarity),

2. OA +four counts (on the same current range and same polarity).

3. MOD V off.

4. MOD I off.

The output is NOT disconnected. Programming the output for a new value, range polarity, sink mode or modulation, does not change the output until the Model 228 is placed in the operate mode.

AMPS/DWELL TIME-The AMPS/DWELL TIME key is an alternate action control which places the right display in either the amps display mode or the dwell time display mode. In the amps display mode, the current for the present memory location is displayed on the right display. In the dwell time display mode, the dwell time for the present memory location is displayed on the right display. This key allows the user to view either the dwell time for the present memory location or the current for the present memory location. The dwell time ranges from 20msec to 1000s~.

DISPLAY MODIFY GROUP (EDIT)

DECADE

III)

Notes

1. Since the output is still active the quick disconnect board

should be removed from the mainframe before any wiring changes are to be made.

3. Large reactive loads are not discharged immediately after placing the Model 228 in the standby mode. This is because the OV setting does not change the current through an in-

ductor and the OA setting does not change the voltage across a capacitor. In general, capacitors and inductors discharge at approximately 0.4% of range when the Model 228 is in the standby mode.

SELECT-The SELECT key determines which display (left or right) can be configured. Pressing the SELECT key once selects the previously selected display for modification. Subsequent key presses toggle the edit mode between displays. Use the SELECT key before modifying the volts, memory step, amps or dwell time functions.

DECADE-The DECADE keys (right, left, up and down) modify the selected display. The left and right keys (indicated

3-7

by left and right arrows) select which digit on the display is to be modified. These keys wrap the cursor around to the opposite end (most significant) digit if attempting to go beyond the left most or right most (least significant) digit. The modify

digit is indicated by the “Lvight flashing” digit on the display.

The left and right keys autorepeat if held in. That is, the left

key when pressed and held in keeps advancing to the next digit to the left. The same is true for the right key except, of course, it advances to the right.

The increment and decrement keys (indicated by the up and

down arrows) increment and decrement the modify (bright) digit and therefore the displayed value. The modify digit is modified by one unit each time the increment or decrement

Table 3-4. Front Panel Messages

key is pressed. The increment/decrement keys are autorepeating. That is, pressing and holding in the increment key increments the display continually until the range limit is reached or the key is released. The same is true for the decrement key.

The incremenl key has the mathematical carry capability. This means that if the modify digit is a 9, pressing the increment key once sets the modify digit to 0 and the next significant digit is increased by one. If the display is at the maximum (IOIO), pressing the increment key causes an error message Lo be displayed for approximately one second. Refer

to Tables J-4,3-5 and 3-6 for front panel messages and Table 3-7 for the power up default conditions. The display then

returns to the previous condition.

Mssaage

Left Display

buF

-5

+15

-15

+115

-115

- 500 + 900

+ 1000

CAL

CAL CAL CAL

IEEE

buF

“0

Massage

ight Dlsplar

Err

Err Err Err Err Err Err Err Err

Err Err1 Err2 Err3 Err4

AdFb

Err

Pro

Err

End

IddC

IddCo

Comments Bad data was copied from the memory buffers.

+ 5V analog supply is outside of a f 50% range.

-5V analog supply is outside of a ~50% range. + 15V analog supply is outside of a f50% range.

- 15V analog supply is outside of a f50% range. + 115V analog supply is outside of a f 50% range.

- 115V analog supply is outside of a f50% range. Temperature sensor is not operating properly. Heat sink temperature has increased past 90°C. Turn sink mode on.

Temperature exceeds 100°C. The Model 228 turns off the switching supply and locks up the front panel. Turn off power and let it cool down.

Calibration error. Autocalibration cannot be performed. Voltage DAC (Digital to Analog Converter) gain is out of cal range.

Calibration error. Auto calibration cannot be performed. Voltage DAC (Digital to Analog Converter) offset is out of cal range.

Calibration error. Auto calibration cannot be performed. Current DAC (Digital to Analog Converters) gain is out of cal range.

Calibration error. Auto calibration cannot be performed. Current DAC (Digital to Analog Converter) offset is out of cal range.

No data transmits across the opt@isolators.

AID error. The AID does not read the 1V reference and ground properly.

No program exists. Illegal program number attempted. IEEE address error. An attempt to enter an illegal IEEE address was made.

The range of IEEE addresses is O-31.

Buffer end. The end of memory locations is reached. Maximum of 100 locations.

Illegal Device-Dependent Command

Illegal Device-Dependent Command Option No remote. The instrument wss not in remote when programmed.

3-9

Table 3-6. Front Panel Messages and Prompts

Message

.eft Display Right Display Comments

IEEE

Message

IEEE address, Address 11 shown. Front panel Program 3 activated or power

up sequence. rEU Pro 7

CAL

Software revision level. Revision A shown.

Prompt to enter the number of the desired front panel program.

Calibration, The Model 228 is going through the autocalibration sequence.

The Model 229 counts down from 20 to 0 during this sequence. This se-

quence may be bypassed by pressing the CANCEL key. However, the

previous cal will be valid.

U U

I Sill Sln

COP

Off

on OFF 002 Copy program enabled. Contents of memory location 1 duplicated into

External modulate V program is on. External modulate V program is off. External modulate I program is on. External modulate I program is off. Sink program on. Sink program off.

memory location 2.

Table 3-6. Error Messages (Either Display)*

Message Comments

oFL

Overflow. Attempt to output beyond the present range. Reading exceeds 1999 on any range.

Range. Attempt to program beyond the present range. Illegal range combination.

Err

Error. Exceeded 1010 limit or attempt to program below zero.

‘NOTE: These messages appear on the display where the error occurred.

3-g

Table 3-7. Power Up Default Conditions

Mode Value Status Display

DO Left Display=Volts, Right Display= Amps. Left Display ready for edit. Function FO Standby (output programmed to +4 counts on present range) Data Format

GO Prefix of buffer location contents. EOI KO Send EOI. SRQ

MO Disabled Program Mode PO Single Step Mode. Range Trigger Terminator

RO Autorange

T6 Stop on X

CR LF Carriage Return Line Feed

Buffer Location BOO1 Location #I

Voltage V

Current I Dwell Time w Sink Mode S External Modulation A

Program 1

Copy Disabled

Program 2

Dependent on previously programmed values of memory location I. Dependent on previously programmed values of memory location I. Dependent on previously programmed values of memon/ location 1, Dependent on previously programmed values of memory location I. Dependent on previously programmed values of memory locetion I. Dependent on previously programmed values of memory location I.

Sink Dependent on previously programmed values of memory location 1,

Program 3 IEEE Not affected

Program 4 Program 5 Porgram 6

Mod V Dependent on previously programmed values of memory location 1.

Mod I Dependent on previously programmed values of memory location 1.

Test Jl if passed; in status byte

J2 if failed; in status byte

Program 9 Reset Disabled

The decrement key has the mathematical borrow capability. This means that if the modify digit is 0, pressing the decrement key sets the modify digit to 9 and the next significant digit is decreased by one unit. If the display is 0000, pressing the decrement key causes an error message to be displayed for approximately one second. The display then returns to the previous condition.

Using the increment and decrement keys to change the sign of the displayed value causes and error message to be displayed for approximately one second. The display then returns to the previous condition.

The DECADE keys operate in the immediate mode. In the immediate mode, the output value is updated as the display is

3-10

updated. For example: If 95.OV is displayed and present on

the output, selecting the 5 digit and pressing the increment key increases the display to 96.OV. At the same time, the output is also changed to 96.OV.

ENTER-The ENTER key loads the displayed data into the present memory location. Pressing the ENTER key after modifying the displayed data, loads the new data into the present memory location. The display then reverts to normal intensity and the display modifying operation (edit) is terminated. The DATA keys do not affect the output until the ENTER key is pressed.

DATA GROUP

START/STOP-The START/STOP key serves three functions that are described as follows:

1. When the START/STOP key is pressed,

the selected

memory control mode (Single Step, Single Cycle or Con-

tinuous) is started.

2. Pressing the START/STOP key while the memory control mode is running stops

present memory location.

the memory control mode at the

3. In the single step memory control mode, pressing the

START/STOP key advances the instrument to the next programmed memory location.

The START/STOP LED is turned on while the single cycle

and continuous cle.

In the

memory control mode is going through its cy-

single step memory control mode, the START/ STOP LED is turned off for the duration of the programmed dwell time of the memory location.

DATA-The DATA keys have dual functions. In the enter

mode, these keys enter the desired number on the display. In the program mode, the keys activate the desired program. The front panel programs are described

paragraph 3.11. Entering data on the display using the DATA keys always start with the left most (most significant) digit on the display.,

MEMORY CONTROL GROUP

MEMORY CONTROL

STOP

[

STARl

When the Model 228 is in

the

standby mode (OPERATE LED is turned off) and either the single cycle or continuous memory control mode, the START/STOP key continues to control the buffer with no output present on output terminals, For example: The continuous mode keeps going on its cycle even though the Model 228 is in the standby

(STANDBY LED

on).

mode

SINGLE STEP-In the single step mode (SINGLE STEP LED is on), the memory

location

is advanced by one step each time the START/STOP key is pressed or the proper external trigger pulse is received. The voltage , current and dwell time may

different for each memory location. That is, the user

defines these parameters for each memory location.

At the completion of the programmed dwell time a pulse is sent out via the external trigger output connector. The START/STOP LED is turned off at this time. The pulse is a negative going TTL level pulse with a duration of greater than 10psec. The pulse could be used to trigger another instrument into its special function (e.g. chart recorder, DMM, etc).

Pressing the SINGLE STEP key when in the last programmed memory location and the single step mode causes the Model

228 to revert to memory location 1.

SINGLE STEP

f, SINGLE CYCLI

0 CONTINUOUS

A zero dwell time for any memory location causes the Model

228 to jump to memory location 1.

3-11

SINGLE CYCLE-In the single cycle mode (SINGLE CYCLE LED is on), and upon actuation of the START/STOP key or

upon receiving a proper external trigger pulse, the Model 228

advances to the next memory location. After the duration of

the dwell time for the memory location the Model 228 ad-

vances to

turned on. This cycle continues advancing through the pro-

grammed memory location until

tion is reached or stops at last memory location before zero dwell time. Pressing the START/STOP key jumps the Model 228 to memory location 1.

The voltage, current and dwell time parameters may be different for each memory location. That is, the user defines

these three parameters.

the

next memory location. START/STOP LED is

the last

programmed loca-

PROGRAM GROUP

PROGRAM CONTROL

PROGRAM

CANCEL

At the completion of each programmed dwell time, the Model 228 outputs a negative going TTL level pulse of greater than 10~s~ in duration. The pulse appears at the external trigger output connector on the rear panel. This pulse could be used to trigger another instrument into operation (e.g. DMM, con-

troller, etc.)

CONTINUOUS-In the continuous mode (CONTINUOUS LED is on) and upon actuation of the START/STOP key or after the proper external trigger pulse is received, the Model 228 advances to the next programmed memory location. After the duration of the present memory location the Model 228 advances to the next programmed memory location and remains there for its programmed dwell time. This cycle con-

tinues until the last programmed memory location is reached or a memory location with a zero dwell time is reached. At this point the Model 228 jumps to memory location 1. The cycle then repeats and continues repeating until it is stopped.

The voltage, current and dwell time parameters may be dif-

ferent for each memory location. That is, the user defines these three parameters. Just like the single step and single cy-

cle modes, in the continuous mode a negative going TTL level

pulse of greater than 10fisec appears at the external trigger output connector upon completion of each programmed dwell time. This pulse could be used to trigger another instru-

ment into its function in the system (e.g. start measurement cycle on DMM, inform a controller that the dwell time is ended, etc.). A zero dwell time for any memory location reverts

the Model 228 to memory location 1.

PROGRAM-The PROGRAM key is used as the first step in activating the front panel address.

CANCEL-The CANCEL key has two levels of operation and they are described as follows:

1. Pressing the CANCEL key when a front panel program is running terminates the program mode and reverts the Model 228 to the previous mode of operation.

2. Pressing the CANCEL key during the entry of data in any of the programs, reverts the new data to the previous data, terminates the program and then terminates the program mode. The instrument is then reverted to the previous

mode of operation.

COMPLIANCE Graph-The COMPLIANCE graph indicates

the

state of the output. Refer to the front panel and/or following Figure. By noting the front panel COMPLIANCE graph four parameters concerning the output are known.

1. The polarity of the voltage.

2. The polarity of the current.

3. The controlling function (Voltage or Current)

4. Operation as a sink or source.

For example: If the LED just above the +I ( +Imd symbol is turned on, then four parameters are known.

1. The polarity of the voltage positive.

2. The polarity of the current is positive,

3. The controlling function is current.

4. The instrument is operating as a source.

3-12

The reason that the current is the controlling function is that

the line for that LED goes through the +I axis the current is

constant and the voltage is the parameter that varies. For line

intersecting the voltage axis it is the voltage that is the controlling function and the current is the parameter that varies.

LOCAL-In the remote mode (IEEE-488 bus operation) of

operation all front panel controls except LOCAL and

POWER ON/OFF are disabled. Pressing the LOCAL key

takes the Model 228 out of the remote mode and enables all of the front panel controls.

As another example consider that the LED just to the right of the -V(-VS~NK) symbol is turned on. As in the previous example, four parameters are known by noting the COMPLIANCE graph.

1. The polarity of the voltage is negative

2. The polarity of the current is positive.

3. Voltage is the controlling function.

4. The instrument is operating as an active load (current

-”

REMOTE LED-When the REMOTE LED is on, the Model 228 is in the remote mode of operation (IEEE-488 bus operation). When the REMOTE LED is off, the Model 228 is in the local mode of operation. Refer to Section 4 for more information concerning IEEE-486 bus operation.

TALK LED-When the TALK LED is on, the Model 228 is in the talk mode. Refer to Section 4 for more information concerning IEEE-bus operation.

LISTEN LED-When the LISTEN LED is on, the Model 228 is in the listen mode, Refer to Section 4 for more information concerning IEEE-488 bus operation.

MODULATE I-When the MODULATE I LED is on, external current modulation is enabled. An external AC signal can be superimposed on the ouput current through the external modulation connector on the rear panel. This assumes that current is the controlling function. Current is the controlling function when the Model 228 voltage (V) setting is greater than the product of the Model 228 current (I) setting and the user load.

MODULATE V-When the MODULATE V LED is on, the Model 228 is in the voltage modulation mode. An external AC signal up to the specified limits may be superimposed on

the output voltage through the quick disconnect board on the rear panel. This assumes that voltage is the controlling func-

tion. Voltage is the controlling function when the Model 228 voltage (V) setting is less than the product of the Model 228 current (I) setting and the user load.

STATUS GROUP

ILOCAL 0 REMOTE 1

------I

STATVS

0 TALK

0 MODULATE I

0 MODULATE V 0 SINK ONLY

q LlSTEN

SINK ONLY-When the SINK ONLY LED is on, the Model 228 is in the sink mode of operation. Take note of the front panel COMPLIANCE graph. The COMPLIANCE graph in-

dicates which quadrant of sink mode the Model 228 is

operating.

3.13

DISPLAYS

is an IR lead drop between the load and the Model 228. In some situations the IR lead drop is negligible and not need be taken into consideration. This is where local sensing may be used. In other situations the IR lead drop may cause an error in the actual voltage delivered. In this case the Model 228 could be configured for remote sensing.

LEFT DISPLAY

RlGHT DISPLAY

VOLTS/MEMORY STEP Display-The left display (viewed

from the front panel) is used exclusively for the volts and the memory step modes. The display is a 3% digit f1999 count LED display. The VOLTS LED and the MEMORY STEP LED are located next to the display. These LEDs indicate which mode is activated (volts or memory step).

AMPS/DWELL TIME Display-The right display (viewed

from the front panel) is used exclusively for the amps and the dwell time modes. The display is a 3% digit +1999 count LED display. The AMPS LED and the DWELL TIME LED are located next to the display. These LEDs indicate which mode

is activated (amps or dwell time).

3.8 REAR PANEL DESCRIPTION

Remote sensing compensates for the IR lead drop by main-

taining regulation at the load instead of at the output terminals of the Model 228.

When using remote sensing, the output sense + (S + ) terminal

must be connected to OUT+ and the output sense -(S -) terminal must be connected to OUT- at the load.

CAUTION Take cere to connect the sense terminals to the load with the proper polarity. Improper

polarity may result in damge to the instrument and the load.

Current Monitor Terminals-The Model 228 monitors the

output current internally and provides a voltage proportional to the output current for the user.

TRIGGER GROUP

TRIGGER

OUTPUT CONNECTOR GROUP

Output Connector-The output connector (OUT+ and OUT- terminals) are located on the quick disconnect board. This board fits into the Model 228 mainframe. The output is disconnected when the quick disconnect board is removed from the mainframe. The output terminals are screw type terminals that accept up to #16 AWG wire. Only insulated lugs should be used to connect to the output terminals on the quick disconnect board. An example of an insulated lug is Keithley part number LU-99-2.

CAUTION Care should be taken to avoid shorting the terminals on the quick disconnect board.

Instrument damage may occur.

Sense Terminals-The sense terminals are located on the quick disconnect board. The sense terminals are used in the volts mode. When a load is connected to the Model 228. there

3-14

@ @

TRIGGER IN-The TRIGGER IN connector is a female BNC connector that accepts a TTL level negative going pulse of greater than 10pzc that when received starts the selected memory control mode (Single Step, Single Cycle or Continuous). In the single step mode, one pulse is required for each memory location. In the single cycle mode, one pulse required for each cycle of the programmed memory locations. In the continuous mode, one pulse is required to start the cy-

cle.

TRIGGER OUT-The TRIGGER OUT connector is a female

BNC connector that outputs a TTL level negative going pulse of greater than 10~s~~ at the end of the programmed dwell time. This pulse appears at the end of the dwell time for each

programmed memory location.

TTL HIGH

NEGATIVE

GOING

PULSE

SENSING

LOCAL

TTL LOW -

CAUTION: DO NOT EXCEED STANDARD TTL LEVELS

lOpSEC+

MINIMUM

External Modulation Terminals-The external modulation terminals consists of two screw terminals that are located on the quick disconnect board. External modulation allows the user to modulate the output voltage or current. With an AC signal (up to specified limits). The limits are given in the instrument specifications that precede Section 1 and Figure 3-6. Modulation input is a voltage across a 6.8k impedance. The front panel MODULATE I and MODULATE V LEDs indicate whether the output current or output voltage is being modulated.

When using the external modulation, use shielded cables. Connect the shield to output LO. This action shields any extraneous noise from being introduced into the signal.

REMOTE/LOCAL SENSING Switch-The REMOTE/ LOCAL SENSING switch selects remote or local sensing. Refer to the explanation of the sense connector for more information.

AC LINE-The AC LINE connector mates with a three wire line cord which provides connections to line voltage. For COTrect line voltage setting refer to paragraph 7.3.

WARNING

Ground the instrument through a properly earth grounded receptacle before operation. Failure to ground the instrument may result in severe injury or death in the event of B short circuit or malfunction.

AC LINE

3-15

Fuses-There are three fuses that are located on the rear panel Each fuse protects a different circuit of the Model 228.

Fl-Fuse 1 is the linear power supply fuse. The fuse is a SLO-

BLO fuse and is rated at 3/4A for 9OV-125V operation and 3/8A for 18OV-250V operation.

FZ-Fuse 2 is the line power fuse for the switching power supply on the analog board. The fuse is a normal blow fuse rated at 5A for WV-125V operation and 2.5A for 19OV-250V

operation. This fuse protects the line and the Model 228 linear power supply.

F3-Fuse 3 is the output fuse. The fuse is rated at 20A, 25OV. normal blow. If this fuse is blown the is no output present on the output connectors except through the sense connection.

CAUTION

Do not install s fuss with B higher rating

than speclfled. Instrument damage may oc-

ClN.

3.9 QUICK DISCONNECT BOARD

Instead of the more common terminals used on other sources for output connections, the Model 228 output connector, along with the sense, modulation and current monitor terminals, are located on the quick disconnect board. This board fits through the rear panel into the Model 228 mainframe. The output, sense, current monitor and external modulation

cables are connected to the terminals on the board of the

Model 228. The card is plugged into the appropriate slot in

the rear panel. When the card is removed from the mainframe, the output, sense, current monitor and external modulation terminals are disconnected from the mainframe connections. As a result, the user should never have to come in contact with a live output. Figure 3-4 shows the quick disconnect board and the location of each terminal.

Several quick disconnect boards could be used, each with a unique configuration. In that way, when a particular configuration is required, it is simply plugged into the Model 228. Thus, redundant rewiring of just one quick disconnect board is avoided. Figure 3-5 shows how to install the quick disconnect board into the Model 228 mainframe. The Keithley part number of the quick disconnect board is 228-160. One quick disconnect board is supplied with each Model 228.

3-16

ASSEMBLY 500-X

Figure 3-4. Quick Disconnect Board

EXTERNAL TRIGG

CONNECTORS

Figure 3-5. Quick Disconnect Board Installation

3-17

3.10 REMOTE/LOCAL SENSING

The sense (S+ and S-) terminals are located on the quick disconnect board. The sense terminals are used in the volts mode. When a load is connected to the Model 228, there is an IR lead drop between the load and the Model 228. In some situations the IR lead drop is negligible and does not need to be taken into consideration. This is where local sensing may be used. In more sensitive applications, the IR lead drop may cause an intolerable error in the actual voltage delivered to

the load. In this case, the Model 228 could be configured for

remote sensing. Remote sensing compensates for the IR lead drop by maintaining regulation at the load instead of at the output terminals of the Model 228. When using remote sensing, the output sense (S -) terminal must be connected to the OUT - line and the output sense (S + ) terminal must be connected to the OUT+ line. This should be done at the load.

CAUTION

Take care to connect the sense terminals

(S+ and S-l to the load with the proper polarity. Connect S+ to the positive twmine1 and S- to the negative terminal. Improper polarity may result in damage to the instrument.

entered. The Model 228 completes the constant with trail-

ing zeroes where necessary.

5. Invalid key presses are ignored. If an invalid key is pressed, the flashing digit (cursor) remains at the present digit.

6. If an incorrect digit is entered, the complete constant must be re-entered. The new value may be entered by cycling the cursor around to the most significant digit. To do this,

repeatedly press any one of the number keys.

7. If too many digits are entered Err is displayed and the program is terminated.

8. Once all the digits of the desired constant are shown on the display, the constant is entered into the program by pressing the ENTER key. This applies only to Programs 1 and 3.

Table 3-S. Summary of Front Panel Programs

Program Operation

G 4 Mod V (Voltage Modulation)

: 9

COPY Sink

IEEE (Set IEEE primary address) Mod I (Currant Modulation)

Teat (Diagnostic Self Test) Reset (Factory Conditional

3.11 FRONT PANEL PROGRAMS

This section contains instructions necessary for operating the seven front panel programs of the Model 228. The programs are activated by pressing the PROGRAM key along with the DATA key that represents the desired program. The programs do a number of various tasks which are summarized in

Table 3-8.

Program Notes:

1. Each program is entered by pressing the PROGRAM key followed by the desired program number.

2. After the PROGRAM key is pressed the Model 228

displays the following on the right display.

PRO7

As you have noticed, the question mark is flashing. This is a prompt for the user to enter the desired program number

(refer to Table 3-7). After entering the program number, the Model 228 goes into the program selected.

3. Data is entered on the right display by pressing the desired number key. As each digit is entered, the cursor moves one place to the right until the last digit (least significant) is reached. Then it is wrapped around to the first digit on the left (most significant) of the display.

4. Only as many significant digits as necessary need to be

3.11.1 Program 1 Copy

Program 1 is used to duplicate the voltage, current, dwell time data, sink only mode and modulation status of one memory location into the next memory location. This program is useful in an application when one to four of the five parameters required are constant. The variable parameter(s)

is (are) the only one that needs to be changed for each

memory location. For example: Plotting the IV characteristics

of a diode is an example where the current could be set at a certain level and the dwell time be constant. The voltage could be programmed to increase O.lV in each successive memory location. Program 1 could duplicate the current and dwell time data in each programmed memory location. Only

the voltage would have to be changed for each programmed memory location.

NOTE For this example the sink mode and modulation status are off.

In this case the voltage, current and dwell time parameters are programmed in the first memory location and Program 1 is

activated. All the data is duplicated into the next memory location. The next step is to change the voltage of the programmed memory locations to the desired level. The memory

3-18

control mode is selected and the START/STOP key is pressed. The Model 228 outputs the parameters in each memory location at the programmed rate (dwell time).

indicated by the flashing SINK ONLY LED. In this mode the sourcing capability is reduced. Return to normal operation by pressing PRO, 2.

Using Program 1 saves many programming steps. Use the following procedure to duplicate the current and dwell time of memory location 1 to memory locations 2 through 10.

Required Parameters: 5OOmA Current Limit One Second Dwell Time O.lV to 1V in OJV steps

1. Turn on the Model 228 and allow ten minutes for warm up.

2. Select memory location 1.

3. Program OJV

4. Program 5OOmA for memory location 1.

5. Program a one second dwell time for memory location 1.

6. Press PROGRAM.1. Duplicates data from one location into the next location.

7. Repeat step 6 for every location up to location 10.

8. Reprogram the voltage for each memory location. (0.2V in location 2, 0.3V in location 3, etc.)

9. Press AMPS/SECONDS. Selects the current for display.

10. Press OPERATE/STANDBY.

Il. Select SINGLE CYCLE. Press START/STOP.

After the START/STOP key is pressed the Model 228 outputs the programmed parameters in one second intervals. All

of the memory locations are covered and the cycle stops after memory location 10. By noting the left display (for each memory location), the current level is known. The voltage level is also known. The IV graph could be plotted with this information. Program 1 saves the user from programming all

three parameters for each memory location.

for

memory location 1.

For example: Consider charging and discharging a battery. While charging, the Model 228 sources power. When discharging, the Model 228 sinks power. In the sink mode the Model 228 is an accurate and stable load. When operating the Model 228 as an active load ensure that the recommended

operating limits of Figure 3-12 are not exceeded,

Press the following keys to enable the sink only program: PROGRAM, 2.

The sink program allows the instrument to decrease its high power supply and still operate as an active load. With the supply reduced, the Model can dissipate full power con-

tinuously at 50°C ambient temperature with no derating.

3.11.3 Program 3 IEEE

Program 3 is used to set the primary address of the Model 228

for IEEE-488 bus operation. The primary address of the Model 228 is set to 11 at the factory, but it may be set to any value between 0 and 31 (as long as address conflicts are avoided) via front panel Program 3. This is a convenient feature that eliminates the cumbersome rear panel switches

that are generally used in other instruments to set primary address. Note that the primary address of the instrument must agree with the address specified in the controller’s programming language. Program 3 is the only way to change the Model 228’s primary address. The programmed primary address is briefy displayed as part of the power up cycle, the selft test sequence and Program 9 sequence.

3.11.2 Program 2 Sink

Use Program 2 when the Model 228 is to be used as a high power load above 5OW. By noting the front panel, the state of the output is known. The front panel COMPLIANCE graph shows when the Model 228 is operating in the sink mode (active load). In the sink mode the Model 228 acts as a load and dissipates power instead of sourcing. The connected external

source and 228 setting indicates that the Model 228 is in the

sink mode.

If the Model 228 is operating near the maximum dissipation limit (1oOW). and this is causing the internal temperature to

exceed 90°C. the sink only program (Program 2) activates as

NOTE NOTE If other instrumentation is connected to the bus, If other instrumentation is connected to the bus, be sure that each device has a different primary be sure that each device has a different primary address. If this precaution is not observed, er- address. If this precaution is not observed, er-

ratic bus operation may result. ratic bus operation may result.

To initiate Program 3 and change the primary address to 22, press the following keys:

1. Press PROGRAM (Selects program mode and displays Pro7).

2. Press 3 (selects Program 3 and displays the following).

IEEE 11

3-19

Where:

IEEE = IEEE indicator 11 = Primary Address

3. Press 2,2,ENTER. This step loads the number 22 onto the display. Pressing the ENTER key programs the primary address 22 and reverts the Model 228 to the previous operating mode.

4. Press PROGRAM.3. This step shows

the

user that the

primary address has indeed changed to 22.

5. Now that you know how, change

the

primary address

back to 11. A. Press PROGRAM.3. B. Press l,l.ENTER.

3.11.4 Program 4 MOD V (Modulate Output Voltage)

AREAS S and C INCREASE THE MAGNITUDE OF THE OUTPUT SE’ITING AREASAand D DECREASETHEMAGNlTUDEOFTHEOUTPUTSEi7NG

This program is used to allow an AC signal to be superimposed on

the

rear panel external modulation terminals on the quick

disconnect board. Program 4 is activated

the

output. The modulation signal is applied to

and then the

front

panel MODULATE V LED turns on. Figure 3-6 shows a graph of operation for the external modulation feature. When Program 4 is activated Program 5 is disabled.

Use the following procedure to activate Program

1. Connect

the external

signal source to the

external

modula-

tion connector on the quick disconnect board.

2. Press Program, 4. This step activates Program 4 and turns

on the front panel MODULATE V LED.

3. Program the Model 228 for the desired output.

4. Set the Model 228 to the operate mode.

5. The modulate &put is now present on the output connec-

tors.

NOTE NOTE

Use shielded cables when

tion.

The shield should be connected to output

tion.

The shield should be connected to output

using external modula-

LO. Shielded cables help in reducing extraneous LO. Shielded cables help in reducing extraneous noise

Figure 3-6. Graph of Operation for External

Modulation

3.11.5 Program 5 MOD I (Modulate Output Current)

Program 5 is used to allow an AC signal to be superimposed on the output. The modulation signal is applied to nal modulation terminals on the quick disconnect board. Program 5 is activated and then the front panel MODULATE I LED turns on. Figure 3-6

external

modulation feature. ;When Program 5 is activated,

shows

a graph of operation for the

Program 4 is disabled.

Use the following procedure to activate Program 5

1. Connect the external signal source to the external modula-

tion terminals.

2. Press PROGRAM, 5. This step activates Program 5 and

turns on

the

front panel MODULATE I LED.

3. Program the Model 228 for the desired output.

4. Set the Model 228 to

the operate mode.

5. The modulation signal is now present on the output signal.

the exte~-

3-20

NOTE Use shielded cables when externally modulating the output of the Model 228. The shield should be connected to output LO. Shielded cables help in reducing extraneous noise.

After the CAL cycle message, the Model 228 reverts to the

previously shown display. For example, if the Model 228 was displaying +1.234V then that is the display it reverts to after

the CAL 00 message.

3.11.6 Program 6 Test (Diagnostic Self Teat)

Program 6 is used to run a test on the ROM, RAM circuitry, perform auto cal sequence and tests the front panel LEDs. This test is also performed in the power up sequence. If it is

desired to run the self test without using the IEEE-488 bus,

Program 6 can be used. Use the following procedure to ac-

tivate Program 6.

1. Press PROGRAM. Selects the program mode.

2. Press 6. Initiates the Program 6 test sequence.

Once step 2 is completed the Model 228 performs the following sequence:

The Model 228 turns on all the segments in the display and also turns on the rest of the front panel LEDs (e.g. LOCAL, REMOTE, SINGLE CYCLE, VOLTS, etc). The display segments are shown as follows:

This is a display test, the operator can note inoperative display segments by comparing the display with the above figure. All the LEDs should turn on if operating correctly. While the LEDs are on, the Model 228 is performing a cyclic

‘redundancy check (CRC) of the ROM circuitry. A digital self

test of the RAM circuitry is also being performed at this time. If the digital self test reveals a problem with the RAM circuitry the Model 228 displays the following.

3.11.7 Program 9 Reset

Program

tions. These conditions are the same as the device clear (DCL) command with one exception. The exception is that all of the programmed memory locations are cleared of all previous data. To activate Program 9 use the following procedure:

The sequence for Program 9 is the same sequence as upon power up.

1. Press PROGRAM, 9. Selects Program 9.

2. All digits and LEDs are turned for a few seconds.

3. The Model 228 displays the software revision level.

4. The Model 228 displays the primary address.

5. The Model 228 reverts to the VOLTS and AMPS display

Once the VOLTS and AMPS display show zero, the Model 228 is reset to the factory on conditions.

9 is used to reset the Model 228 to the factory condi-

and memory location I.

3.12 LOADS

The Model 228 is capable of delivering power to a load or sinking (dissipating) power. Either mode depends on the programming of the instrument. If the actual voltage and current have the same polarity (both positive or both negative), the Model 228 is operating in the source mode. The front panel COMPLIANCE graph displays the state of the Model 228 (source or sink).

If the CRC reveals a problem with the ROM circuitry the Model 228 displays the following.

If all tests pass, the Model 228 displays the following:

In the source mode, the Model 228 must have a device in which to deliver the programmed power. This device is generally known as the “load.” The load stores or dissipates the Model 228 output power. The load must be rated to handle the programmed output power of the Model 228. If the load is not properly rated, damage may result. There are three categories of loads: resistive, capacitive and inductive. These different loads all have their own unique parameters. Each type of load contains in some small amount each of these parameters. In general, however, loads are considered to be mostly one parameter, either resistive, capacitive or inductive. Each type of load is described in the following paragraphs.

3-21

The Model 228 is a constant voltage/constant current source. The load determines which parameter is constant, either voltage or current. For example, if the load is of high im-

pedance, the voltage is controlled with the impedance determining the amount of current. If the load is of low impedance, the current is controlled with the impedance determining the voltage. For example: If the Model 228 is programmed to 1OV and 1OA. a load of

than la controls

the current, and a load of less than 10 controls the voltage.

“SEnING

ISETTING

then, the Model 228 operates as a current

source.

Where:

V = The voltage setting on the Model 228. I = The current setting on the Model 228.

R = User load.

I = lOV/252 = 5.OOA (2Q load, current limits to 5A) V=lOAX0.50=5.OOA (0.5Cl load, voltage limit of 5V)

R >

VSETTINC

___-..

ISETTING

then, the Model 228 operates as a voltage

source.

3.12.1 Load Line Description

The information contained in Figure 3-7 is a general descrip-

tion only. Refer to other sections of this information.

manual

for detailed

3-22

SUADRANT 1 l’his quadrant is used for normal operation. The Model 228

Nil1 source positive voltage and current. The Model 228 is sourcing power to a load. Since V= I X R, the combination of load R and the Model 228

settings will determine if the Model 228 is operating as a consant current or constant voltage source.

The Model 228 will maintain a constant voltage output as

o”g =s kElTlNC >VSETTING/RLOAD.

The Model 228 will maintain a constant current output as

o”t3 as kElTlNG qVSETTINGIRLOAD.

Standby mode is a setting of 0 volts and 0 amps.

ZUADRANT 2: rhis quadrant is used for general constant voltage load or

:onstant current load applications. The Model 228 is dissipating (sinking) power from an external

&vice. The Model 228 will maintain a constant voltage across its ter-

ninals as long as the external device’s current into the Model 128 is less than the Model 228’s current setting.

The Model 228 will operate as a constant current load as long 1s the external device’s voltage is greater than the Model 228 {oltage setting.

In standby mode, the Model 228 will appear to be an open circuit.

NOTE: For operating in this quadrant the polarity qf the Model 228’s voltage setting and the polarity of the external

device’s voltage must be the same.

QUADRANT 3: This quadrant is not on the positive load line shown above. If

the Model 228 were set to -V and -I the Model 226’s load line would then cross this quadrant.

QUADRANT 4: This quadrant is used for a constant voltage load on a current

source. The Model 228 is dissipating (sinking) power from an external

device. The Model 288 will maintain a constant voltage across its ter-

minals as long as the external device’s current is greater than or equal to the Model 228’s current setting.

In standby mode, the Model 228 will appear to be a short cir-

cuit. NOTE: For operation in this quadrant the polarity of the

Model 228’s voltage setting and the polarity of the external

device’s voltage must be opposite.

Figure 3-7. Load Line IPositive Line Shown)

3-23

3.12.2 Resistive Loads

capacitance and inductive loads. Reactive loads require certain considerations that are listed as follows:

Using a resistive load, the Model 228 is capable of delivering a constant voltage or constant current up to the programmed compliance. With a resistive load as shown in Figure 3-8, the

voltage developed across the load resistance is defined as VL

= IL X RL.

Where:

VL = The voltage developed across the load.

IL = The current through the load. RL = The load resistance.

If the voltage is programmed to less than the voltage VL, then the Model 228 is voltage controlled. If the current is programmed to less than the current IL, then the Model 228 is current limited.

The power delivered to the resistive load must not exceed the

power rating of the load. If excessive power is delivered to the load, damage may result. For example, if the load is a resistor and is rated at lOW, then the power must not exceed 1OW. This means that if the Model 228 voltage is programmed for 10”. then the current must not be programmed for more than 1A (10” X 1A = 1OW) or 10A and 1V (10A X 1V = low). In any case, the voltage/current combination must not exceed the limits of the load. Otherwise, the load may be damaged.

1. The user must supply the necessary circuitry to limit the voltage across inductors. Voltage above 101% of the selected voltage range may damage the instrument. During power on, calibration, low or missing line power, the Model 228 disconnects the output with relays. This could

cause uncontrolled arcing along the inductive circuit. Refer to Figure 3-9 for suggested clamp circuit.

2. Capacitors and inductors require proper discharging before touching any output wiring. This is because in the

standby mode or when power failures occur, the reactive circuit could be left with a full charge.

3. Settling times are longer for large reactive loads, as a result overshoot and ringing may occur. Damping resistors could be used to improve the response. Refer to Figure 3-9 for damping resistor circuits.

3.q2.4 Inductive Loads

In general, in the constant current mode the output load should be resistive. However, a small amount of inductance in the load can be tolerated, but only if the inductive reaction voltage, L 2 , is limited to less than the maximum compliance voltage for each range. Figure 3-9 shows a suggested method of limiting the inductive reaction voltage. The zener diodes must be rated for each current range as listed in Table 3-9. An inductive load may not be obvious. Loads that contain wirewound resistors or relay coils, (etc.) are inductive and could produce damaging voltage spikes. Figure 3-10 shows induc-

tive load connections.

LOAD

IRESISTIVE

“L = IL RL

Figure 3-g. Resistive Load Connections

3.12.3 Reactive Loads

The Model 228 is stable for an exceptionally wide range of

3-24

CAUTION In the current function, if the output load connected to the Modal 228 is inductive, limit the inductive reaction voltage to less

than the maximum compliance voltage for that range. Otherwise. instrument damage

may occur.

Some examples of inductive loads include:

1. Relay Coils

2. Electric Motors

3. Wirewound Resistors

4. Transformers

5. Solenoids

MODEL 228 MODEL 228

LOAD

MODEL 228

LOAD

VMAX = IMAX ‘R

MODEL 228

DAMPING

RESSTOR

LOAD

Figure 3-9. Limiting Inductive Reaction Voltage

LOAD

WVJ

r_ LOAD

3-25

QUICK

LOAD RESISTANCE

LOAD

INDUCTANCE ,L

Figure 3-10. Inductive Load Connection

Some examples of capacitive loads include:

1. Capacitor

2. Power Supplies

‘3

LOAD

CAPACITANCE

Table 3-9. Maximum Inductive Reaction Voltage

3.12.6 Capacitance Loads

When a capacitive load is connected to the Model 228 output,

the Model 228 delivers a constant current until the voltage developed reaches the programmed compliance voltage, instrument voltage compliance limit or the working voltage of the load. The voltage charges to a maximum Vc with the following equiation:

Vo = $ \ I $ up to Vc (maximum) Figure 3-11 shows the Model 228 connected to a capacitive load. If the Model 228 compliance voltage is changed to a

smaller value than is charged on the capacitor, the capacitor starts discharging into the Model 228. For this period, the Model 228 is in the sink mode. Notice the front panel COMPLIANCE graph; it indicates the Model 228 is in the sink mode. When the capacitor charge voltage reaches the lower compliance voltage, the Model 228 returns to the source mode.

Figure 3-11. Capacitive Load Connections

3.12.6 Load Regulation

Load regulation is an important parameter that is to be considered when using the Model 228 as a current source or a

voltage source. Load regulation may be computed by the following two methods:

1. As a Current Source:

Load Regulation (Current Mode) = Ram X 100%

3-26

As a Voltage Source:

‘OUT

*“L

Load Regulation (Voltage Mode) = [AIouT;RouTI X 100%

As an example; consider the 1A range and 1OOV compliance. The ROD specification is 105n.

Load Regulation= RoUT X100%= 1OKl X lOO%=O.l%

[1oovJ

The Model 228 is a constant voltage/constant current

K-V/CC) source. This means that the voltage and current are programmed into the instrument. The output of voltage or current depends on the load. If the load is of high impedance,

the voltage is controlled with the impedance determining the amount of current drawn from the source. If the load is of low impedance, the current is controlled with the impedance determining the voltage. The maximum value of voltage or current (up to rated specifications) is defined by the user. The

user defines these parameters when programming the voltage and current values. In this example:

If the load is less than 10, the source controls current. The

LED just above the + ( +IsouncE) on the front panel COM-

PLIANCE graph is on.

If the load is greater than la, the source controls voltage. The

LED just to the right of the +V (+Vsou& on the front

panel COMPLIANCE graph is on.

3.13 OPERATING EXAMPLES

The following examples give specific instructions on how to use the Model 228 in various configurations. These examples are written with the first time user in mind. However, refer to

the front and rear panel control descriptions in Tables 3-2 and 3-3 before proceeding with these examples. Note all of the warning and cautions associated with these examples. Take

the time to read them and, most of all, to understand them.

3.13.1 Example 1: lO.OOV, lO.OOA Output

In this example, the Model 228 will be programmed for

+!.O.OOV and +lO.OOA. These values were chosen to keep the numbers simple (lOV/lOA = In). With these values, the user can concentrate on the front panel instead of a cumbersome number calculation. The 1OV range has a maximum compliance current of 10A; conversely, the 10A range has a maximum compliance voltage of 1OV. Refer to the specifications that precede Section 1. In this example, voltage and current are limited to lO.OOV and lO.OOA by the user; and in this case, the instrument limits these values. This information is stored in memory location 1.

This example does not step the user through the selection of a memory location, Memory location 1 is selected upon power up and that is sufficient for this example. Since there is just one memory location used in this example, programming the dwell time is not covered. Later examples explain the use of memory locations.

For example: A 2Il load results in a current of SA (voltage is controlled by the Model 228).

I = = = 5.00A.

A 0.512 load results in a voltage of 2.5V (current is controlled by the Model 228).

V = 0.5R x 10A = 5.OOV. If

VSETTINC

‘SEEK source.

VSE7TING

lsErrlNC source.

Where: V = The voltage setting of the Model 228. I = The current setting of the Model 228. R = User Load

Also, in the operate mode, the display shows the actual parameter value. For example, if 1OV and 10A are programmed and the load is drawing 7.5A, then 7.50A is

displayed on the right display (right display must be in amps display mode).

To program the Model 228 for lO.OOV, lO.OOA, use the following procedure:

then, the Model 228 operates as a voltage

then, the Model 228 operates as a current

3-27

CAUTION

This example outputs IOOW. Make sure that

the connected load is rated to at least IOOW. Otherwise, damage to the load may

OCCW.

1. Turn on the Model 228 and allow ten minutes for warm UP.

WARNING Do not operate the instrument with the top cover and/or the bottom cover removed. Lethal potentials exist throughout the Model 228 mainframe. The covers must also be in place to allow proper airflow

through the instrument. If proper airflow is impeded, the instrument may overheat.

NOTE

Upon power up, memory location 1 is selected.

2. Program the desired voltage value. There are two methods to do this and both are given as follows:

Method 1: Program Desired Voltage Value

A. Press the VOLTS/MEMORY STEP key to display volts

(VOLTS LED on).

B. Press the SELECT key until the left display is selected.

The selected display is depicted by the flashing bright

digit.

NOTE During the edit mode, if nothing happens on the front panel for approximately 20 seconds, the Model 228 cancels the edit mode and returns the display to the previous conditions.

Press 1, 0, 0, 0.

D. Press ENTER.

3. Program the desired current value. Like the voltage value, this can be done in one of two methods. Both methods are

given as follows:

Method 1: Program Desired Current Value A. Press the AMPS/DWELL TIME key to display current

(AMPS LED on).

8. Press the SELECT key until the display on the right is

selected. The selected display is depicted by the flashing bright digit.

C. Press the left or right keys (these keys are indicated by

the arrcws on the front panel) to select the modify digit.

The modify digit is depicted by the flashing bright digit.

D. Press the increment/decrement keys to modify the cur-

rent value. The output tracks the display when using the increment/decrement keys.

Method 2: Proaram Desired Current Value

A. Press the AMPS/DWELL TIME key to display current

(AMPS LED on).

8. Press the SELECT key until the right display is selected.

The selected display is depicted by the flashing bright

digit.

c. Press 1, 0, ., 0, 0.

D. Press ENTER.

4. Connect the appropriate load. For this example, the load must be rated at least 10oW.

5. Press OPERATE/STANDBY to place the instrument in the operate mode. In the operate mode, the scurce value is present on the output terminals.

After step 5 is completed, the Model 228 outputs the voltage and current to the connected load. This simple example is designed to set the Model 228 to output a source v&e. The,, next example sets the Model 228 to ,output lOOV, 1A.

C. Press the left or right key to select the modify digit. The

left and right keys are indicated by the arrows on the front panel. The modify digit is depicted by the flashing bright digit.

D. Press the increment or decrement key to modify the

voltage value. The output tracks the display when using the increment or decrement keys. The increment/decrement keys are indicated by the up/down arrows on the front panel.

Method 2: Program Desired Voltage Value A. Press the VOLTS/MEMORY STEP key to display volts

(VOLTS LED on).

B. Press the SELECT key until the left display is selected.

The selected display is depicted by the flashing bright digit. As an example, assume a battery is rated at 1.5V and

3-28

3.13.2 Example 2: IOOV, 1A Output

This example will program the Model 228 to output a value of lOOV, 1A. The maximum current compliance of a 1oOV range is 1A; conversely, the 1A range has a maximum voltage compliance of 1COV. Refer to the specifications that precede Section 1. Like Example 1, this example does not explain the use of memory locations which.will be discussed later.

Again, the output value depends on the load. If the load is of high impedance, the value is voltage controlled. If the load is of low impedance, the value is current controlled. A comparison between the Model 228 and a battery is a simplified way of understanding the load of a voltage/current source.

lA/hour. If the battety has a load of 1kiI. the battery outputs

1.511~4 at 1.5V. Therefore, the current output is limited by

the load.

The same is true for the Model 228. If the load is of high impedance, the load determines the current. If the load is of low impedance, the load determines the voltage.

NOTE When voltage is controlled by the Model 228, the load determines the current by Ohm’s law I = V/R. When current is controlled by the Model 228, the load determines the voltage by Ohm’s law, V=I*R.

This example is designed to allow the user to become familiar with the front panel operation of the Model 228. It illustrates some basic operating methods of the Model 228.

WARNING This procedure outputs a dangerous potential of 1OOV up to 1A. Take care not to come

into contact with the live output, as per-

sonal injury or death may occur.

CAUTION This example outputs 1OOW. Make sure the load is rated for at least 1OOW. Otherwise, damage to the load may occur.

2. Program the desired source. There are two methods to do this. Both are given.

Method 1: Program Desired Source A. Press the VOLTS/MEMORY STEP key to display volts

(VOLTS LED on).

B. Press the SELECT key until the left display key is

selected. The selected display is depicted by the flashing bright digit.

C. Press the left or right key to select the modify digit. The

left and right keys are indicated by the arrows on the front

panel.

The modify digit is depicted by the flashing

bright digit.

D. Press the increment or decrement key to modify the cur-

rent source value. The output tracks the display when

using the increment/decrement keys to modify the display. The increment/decrement keys are indicated by the up and down arrows on the front panel.

Method 2: Program Desired Source A. Press the VOLTS/MEMORY STEP key to display volts

(VOLTS LED on).

B. Press the SELECT key until the right display is selected.

The selected display is depicted by

the

flashing bright

digit.

C. Press 1, 0, 0, ., 0. D. Press ENTER. Program the desired current value. This may be done by

one of two methods. Both methods are given.

In the operate mode, the display shows the actual parameter value. For example, if 1COV and 1A are programmed and the load is drawing 75Om.4, then .75OA is displayed on the right display. The right display must be in the amps display mode in order to display the current.

The Model 228 operates as a voltage source when the following condition occurs: Vc I X R.

The Model 228 operates as a current source when the follow-

ing condition occurs: V> 1 X R.

Where: V = The voltage setting of the Model 228. I = The current setting of the Model 228. R = User Load.

1. Turn on the Model 228 and allow ten minutes for warm UP.

NOTE

Upon power up, memory location 1 is selected.

Method 1: Program Desired Current Value

A. Press the AMPS/DWELL TIME key to display the cur-

rent

(AMPS LED on).

B. Press the SELECT key until the right display is selected.

The selected display is depicted by the flashing bright

digit.

C. Press the left or right key to select the modify digit. The

left and right keys are indicated by arrows on the front panel. The modify digit is depicted by the flashing bright digit.

D. Press the increment or decrement key to modify the

current value. The output tracks

the

display when using

the increment/decrement keys.

Method 2: Program Desired Current Value

A. Press the AMPS/DWELL TIME key to display current

(AMPS LED on).

B. Press the SELECT key until the right display is selected.

The selected display is depicted by the flashing bright

digit. C. Press 1, ,, 0, 0, 0. D. Press ENTER. Connect the appropriate load. The load must be rated for

. _ ^ ^. .

3-29

NOTE

The output load must be non-inductive. A small

amount of inductance in the load can be tolerated if

the

inductive reaction voltage, L $, is limited to less than the compliance voltage of that range. Refer to paragraph 3.92.

moving to the next location. After the dwell time is entered,

the modulation mode must be entered. The modulation shows the user that Model 228 is in either current or voltage modulation. Then the last parameter (source or sink) must be entered. The order of programming these five parameters does not matter, as long as all five are programmed into the memory location.

5. Press

the

OPERATE/STANDBY key. This step places the

l.OOA source current on the output terminals.

WARNING

The completion of step 5 outputs a dangerous potential. Make sure the load is

properly rated. Do not come into contact

with the live output as personal injury or

death may occur.

After step 5 is completed, 1OOV at 1A is delivered to the out-

put connector and therefore, is available to the load. The actual voltage drop and current output depends upon

the value

of the load, This simple example is designed to set the Model

228 to 1OOV at 1A to a predetermined load. In the next exam-

ple, the user will set the Model 228 to output three separate source values in succession.

3.13.3 Example 3: IV, IOA, Isec; IOV, IOA 2s~; and IOOV, IA, 3sec Output in the

Continuous Memory Control Mode

This example will set the Model 228 to output three separate

source v&es in succession. This could be used to test certain parameters of a resistor. The higher voltage could be used to test the voltage coefficient of the resistor. The higher current could be used to test the power rating of the resistor. The accuracy could also be verified by using curate voltage source. The parameters may vary for this type

of application, The parameter values chosen represent several ranges of the Model 228.

In order to obtain the three source values, program the desired values into

the

memory locations, Each memory loca-

tion contains five distinct parameters

memory location: Voltage, Current, Dwell Time, Modula-

tion (V or 1) and Source or Sink mode. Each parameter must

be programmed into each memory location.

the

Model 228 as an ac-

that make

up the

This example may be used as a model for storing several (up

to 100) source values. Up to 100 unique values may be stored

in the Model 228. All of the information storei

in the mem-

ory locations (Voltage, Current and Dwell Time, Source/ Sink and Modulate V or I) is battery backed up. This means that if

the

instrument is powered down,

the

information is still valid. The stored parameters remain as is until they are changed by the user. Before beginning

the example, read the

following outline. The outline gives a short description of the example. The main parts of the example are sectioned off to show the complete exaniple in a simplified form. The actual example follows this short outline.

1. Turn the instrument on.

2. Select memory location 1.

3. Program the desired voltage of memory location 1.

4. Program the desired current of memory location 1.

5. Program the desired dwell time of memory location 1.

6. Program either source or sink for memory location 1.

7. Program modulate V or I for memory location 1.

8. Select memory location 2. 9 Program the desired voltage of memory location 2.

10. Program the desired current of memory location 2.

11. Program the desired dwell time of memory location 2.

12. Program either source or sink for memory location 2.

13. Program modulate V or I.

14. Select memory location 3.

15. Program the desired voltage for memory location 3.

16. Program the desired current for memory location 3.

17. Program the desired dwell time of memory location 3.

18. Program either source or sink for memory location 3.

19. Program modulate V or 1 for memory location 3.

20. Select memory location 4.

21. Program the dwell time of memory location 4 to zero.

22. Select memory location 1.

23. Select the continuous memory control mode.

24. Connect appropriate load.

25. Select the operate mode.

26. Press the START/STOP key.

After the source values are entered into the memory loca-

tions the user must select

the

desired dwell time. The dwell

time ‘is the time spent on a specific memory location before

3-30

WARNING

Memory location 3 contains a lethal poten-

tial of IOOV and a current of up to IA. Take

care not to come Into contact with a I/w circuit that may cause personal injury or death.

NOTE There are two methods of programming values into the Model 228. Examples 1 and 2 explain in detail each method. In th& example, data keys method is used.

1. Turn on the Model 228 and allow ten minutes for warm up.

NOTE

Upon power up, memory location 1 is selected.

2. Select memory location 1. A. Press the VOLTS/MEMORY STEP key to display the

present memory location (MEM STEP LED on).

8. Press the SELECT key until the left display is selected. The selected display is depicted by the flashing bright digit.

C. Press 1, ENTER.

3. Program the desired voltage value. A. Press the VOLTS/MEMORY STEP key to display

volts (VOLTS LED on).

B. Press the SELECT key until the left display is selected.

The selected display is depicted by the flashing bright

digit.

C. Press 1, ., 0, 0, 0, ENTER.

4. Program the desired current value. A. Press the AMPS/DWELL TIME key to display current

(AMPS LED on).

B. Press the SELECT key until the right display is

selected. The selected display is depicted by the flashing bright digit.

C. Press 1, 0, ., 0, 0, ENTER.

5. Program the desired dwell time value. A. Press the AMPS/DWELL TIME key to display the

dwell time (SECONDS LED on).

B. Press the SELECT key until the right display is

selected. The selected display is depicted by the flashing bright digit.

C. Press 1, ., 0, 0, 0, ENTER.

6. Program Modulation (V or I). Press Program 4 to modulate V or press Program 3 to modulate I.

Notice that the approprate LED turns on.

7. Program source or sink. A. Press Program 2 to enable the sink mode. Notice that

the appropriate SINK LED turns on.

B. If source mode is desired, turn off the sink program.

8. Select memory location 2. A. Press the VOLTS/MEMORY STEP key to display the

memory location (MEM STEP LED on).

B. Press the SELECT key until the left display is selected.

The selected display is depicted by the flashing bright

digit.

C. Press 2, ENTER.

9. Program the desired voltane value for memory location 2. A. Press the VOLTS/MEMORY STEP key to display

volts (VOLTS LED on).

B. Press the SELECT key until the left display is selected.

The selected display is depicted by the flashing bright digit.

C. Press 1, 0, ., 0, 0. ENTER.

10. Program the desired current value for memory location 2. A. Press the AMPS/DWELL TIME key to display the

dwell time (AMPS LED on).

B. Press the SELECT key until the right display is

selected. The selected display is depicted by the flashing bright digit.

C. Press 1, 0, ., 0, 0, ENTER.

11. Program the desired dwell time for memory location 2. A. Press the AMPS/DWELL TIME key to display the

dwell time (SECONDS LED on).

B. Press the SELECT key until the right display is

selected. The selected display is depicted by the flashing bright digit.

C. Press 2, ., 0, 0, 0, ENTER.

12. Program modulate V or I. Press Program 4 to modulate V or press Program 5 to modulate I. Notice that the appropriate LED turns on.

13. Program source or sink.

A. Press Program 2 for sink mode. Notice that the SINK

LED turns on.

8. If source mode is desired, turn off sink mode.

14. Select memory location 3.

A. Press the VOLTS/MEM STEP key to display the

memory location (MEM STEP LED on).

B. Press the SELECT key until the left display is selected.

The selected display is depicted by the flashing bright digit.

C. Press 3, ENTER.

15. Program the desired voltage value for memory location 3.

A. Press the VOLTS/MEMORY STEP key to display

volts (VOLTS LED on).

8. Press the SELECT key until the right display is selected. The selected display is depicted by the flashing bright digit.

C. Press 1, 0, 0, ., 0, ENTER.

16. Program the desired current value of memory location 3. A. Press the AMPS/DWELL TIME key to display the

dwell time (AMPS LED on).

8. Press the SELECT key until the right display is

3-31

selected. The selected display is depicted by the flashing bright digit.

c. Press 1, ., 0, 0, 0, ENTER.

17. Program the desired dwell time for memory location 3. A. Press the AMPS/DWELL TIME key to display the

dwell time (SECONDS LED on).

B. Press the SELECT key until the right display is

selected. The selected display is depicted by the flashing bright digit.

C. Press 3, ., 0, 0, 0, ENTER.

18. Program modulate V or I. Press Program 4 to modulate V or press Program 5 to modulate I. Notice that the appropriate LED turns on.

19. Program source or sink.

A. Press Program 2 for sink mode. Notice that the SINK

LED turns on.

B. If source mode is desired, turn off sink mode.

20. Select memory location 4.

A. Press the VOLTS/MEM STEP key to display the

memory location (MEM STEP LED on).

B. Press the SELECT key to select the left display for

modification.

C. Press 4, ENTER.

21. Program the dwell time to zero.

A. Press the AMPS/DWELL TIME key to display the

dwell time on the right display (SECONDS LED on).

B. Press the SELECT key until the right display is

selected. The selected display is depicted by the

flashing bright digit.

C. Press 0, 0, 0, 0, ENTER.

22. Select memory location 1.

23. Press the CONTINUOUS key. This step places the Model 228 in the continuous memory control mode.

24. Connect the appropriate load. The load must be rated at

least 1oow.

25. Press OPERATE/STANDBY to place the source value at

the output terminals.

NOTE Before placing the instrument in the operate mode, take the time to read and understand the safety precautions described in Section 2. These precautions are presented for user safety,

After step 26, the Model 228 continuously cycles through the programmed memory locations. Since the OPERATE LED is on, the source values are present at the output terminals.

The single step memory control mode allows the user to step

through the programmed memory locations one at a time. Each time it is desired to advance to the next programmed memory location, the user need only press the START/STOP button. The START/STOP LED turns on for the duration of the programmed dwell time and then turns off. When the last programmed memory location is selected (memory location 3, in this example), pressing the START/STOP key reverts the instrument to memory location 1. This is true for the last programmed location as long as the next location has a zero dwell time.

The single cycle memory control mode allows the user to cy-

cle through all the programmed memory locations one time.

To start the single cycle mode, press the START/STOP key.

Once the single cycle mode is activated, the Model 228 starts from the next programmed memory location and advances to each programmed memory location. The instrument remains at each memory location for the programmed dwell time and

then advances to the next location. After the dwell time of the

last programmed memory location, the START/STOP LED

turns off and the single cycle mode is ended.

The continuous memory control mode allows the user to cycle through all of the programmed memory locations con-

tinuously. To start the continuous memory control mode, press the START/STOP key. To stop the continuous memory control mode, press the START/STOP key a second

time. When the START/STOP key is pressed the second

time, the continuous mode stopped at the present memory

locatio?. Once the continuous memory control mode is ac-

tivated, the Model 2213 advances to the next memory loca-

tion. The instrument remains at this location for the program-

med dwell time (dwell time can vary for each location) and

then advances to the next memory location. The cycle con-

tinues up to and including the last programmed memory loca-

tion (or memory location with a zero dwell time) and then

reverts to memory location 1. At this point, the cycle starts

over again and keeps repeating until the START/STOP key is

pressed and the instrument is turned off or another memory

control mode is activated.

26. Press the STOP/START key to start the memory control mode.

WARNING

Memory location 3 contains a lethal potential. Do not come into contact with the live output. Personal injury or death may occur.

3-32

Memory Control Mode Notes

1. The START/STOP key has three functions: A. Start ‘the memory control mode. B. Stop the memory control mode. C. Advance to the next memory location in the single

step mode.

2. The single step mode allows the user to step through the programmed memory locations one at a time.

3. The single cycle mode allows the user to cycle through the

programmed memory locations one at a time.

4. The continuous mode allows the user to cycle through the

programmed memory locations continuously.

5. Dwell time is the time spent on one memory location.

An entry of zero for the dwell time for any memory location reverts the instrument to memory location 1.

(20msec

to 1COOsec in lmsec steps. (lsec steps in 1000sec

range).

7. Each memory location contains five distinct parameters: A. Voltage

B. Current C. Dwell Time D. Modulate V or I E. Source or Sink

13. There is a total of 100 memory locations.

9. The memory control mode may be started by one of three

methods. A. Pressing the START/STOP key. B. Applying proper external trigger. C. Sending the proper command over the IEEE-468 bus.

This means that the PROGRAM command (PO, Pl or Pz) is selected and the appropriate trigger command is implemented. For example, if the TO (Start on TALK) mode is selected, and the instrument is addressed to

talk, the selected memory control mode is initiated.

10. When the continuous or single cycle memory control modes are running, stopping the sequence halts the instrument at the present memory location. Continuing the sequence starts at the next memory location.

As can be seen by the graph and/or Figure 3-12, when voltage and current both have the same sign (positive or negtive), the Model 228 is in the source mode.

If the voltage or current have different polarity, then the Model 228 is in the sink mode. In the sink mode, the Model 228 accepts power (dissipates) instead of providing the power. Operating the Model 228 as an active load dissipates power up to the limits shown in Figure 3-12. Of course, the limits shown in Figure 3-12 must not be exceeded.

CAUTION When the Model 228 is used in the sink mode, that is, power is delivered to the

Model 228 by an external power source. Care should be taken to limit the power delivered to the Model 228 as shown in Figure 3-10. If power dissipated within the

Model 228 exceeds these limitations, overheating and damage to the instrument

may occur. For example, if the external power source is capable of delivering greater than 1A. then the voltage across the

Model 228 output terminals must be less than 1OOV IlOOV x 1A = 1OOW).

WARNING During the sink mode of operation. the Model 228 and the external source must have the same voltage polarity in order for

the current limiting to operate. Otherwise, the output fuse l20Al is the current limit.

Examples 1, 2 and 3 all deal with

the

Model 228 programmed as a source. This means that the Model 228 outputs voltage and current. Observe the front panel COMPLIANCE graph and notice that the Model 228 is operating in the source mode (+V and +I LEDS are turned on one at a time). The source mode is depicted by the voltage and current having the same polarity. The polarity could be either positive or negative it does not matter as long as the polarity is the same for the voltage and the current, the instrument is operating in the source mode.

3.13.4 Example 4: Model 228 as an Active Load

(Current Sink)

This next example deals with the Model 228 operating in the

sink mode. In the sink mode of operation, power is delivered to the Model 228 by an external source.

The COMPLIANCE graph on the front panel provides the user with the location of where the Model 228 is operating. By noting the front panel COMPLIANCE LEDs, four parameters concerning the output are known:

I. The polarity of the voltage.

2. The polarity of the current. 3, The controlling function (voltage or current).

4. The operating mode (sink or source). For example: If the LED just above the +I (+I-& sym-

bol is turned on, then:

1. The polarity of the voltage is positive because it is in the +V half.

2. The polarity of the current is positive because it is in the +I half.

3. The controlling function is current because the line for that LED goes through the +I axis, the current is constant and the voltage is the parameter that varies. For lines intenec-

ting the voltage axis, the voltage is constant and the cur-

rent is the parameter that varies.

3-33

4. The instrument is operating as a source because the voltage and the current both have the same polarity (positive). (The LED is in a “source” quadrant.)

+”

+V LIMIT OF RANGE

RECOMMENDED

ENABLING SINK

PROGRAM

-I LIMIT

OF AANGE

+ I LIMIT

RECOMMENDED ENABLING SINK

-” LIMIT OF RANGE

OF RANGE

Figure 3-12. Model 228 Recommended Operating

Limits

In this example, the Model 228 accepts (dissipates) power from the battery voltage. In the sink mode, the Model 228 is

active load that is both constant and accurate. The con-

figuration is shown in Figure 3-13. Make sure the polarity of

the connections are correct before placing the Model 228 in the operate mode. Normally, this only occurs at high ambient temperatures and high power sink operation.

L__, L__,

-’ ,E -’ ,E

Figure 3-13. Model 228 as an Active Load

NOTE

The external source connected to the Model 228

output determines whether the Model 228 operates as an active load. In other words, the

Model 228 operates as an active load whenever

its output is connected to a voltage source that exceeds the programmed output voltage of the instrument.

The following procedure programs the Model 228 to sink

25V. lOOmA = (2.5W).

1. Turn on the Model 228 and allow ten minutes for warm UP.

NOTE

Upon power up, memory location 1 is selected.

Using the SINK program (front panel Program 2) reduces the

internal power dissipation within the Model 228. The sink only mode activates automatically if the internal temperature of the instrument reaches 90°C.

NOTE

The sink only mode is only useful on the 1OA

ranee. between 5V and 1OV. The sink onlv mo-

gram iimits sourcing capability to approximately

1.5A and also limits sink capability when voltages are less than three volts:

3-34

2. Program the desired voltage value. In this example, the voltage must be positive.

A. Press the VOLTS/MEMORY key. This step displays

the present voltage value on the left display.

B. Press the SELECT key. This step selects the left display

for modification.

C. Press 2, 5, ,, 0, 0, ENTER.

3. Program the desired current value. In this example, the current is programmed as positive. The external source determines whether the Model 228 acts as a source or an active load. Refer to Figure 3-12 and/or the front panel COMPLIANCE graph.

A. Press the AMPS/DWELL TIME key. This step displays

the present current value on the right display,

3.13.6 Example 5: Operation as Source and Sink

To help illustrate the Model 228 source and sink characteristics, this example shows how the Model 228 can source a current to charge a capacitor and then when the capacitor is fully charged, the Model 228 will be programmed as an active load to accept the charge.

The voltage values of this example were chosen on the same range (100V. 100mA). The current values were chosen so that

the capacitor would charge and discharge at a somewhat slow rate. In this way, the user could watch the display and see what was going on in the circuit. The dwell time was chosen

so the Model 228 would remain at the memory locations long

enough to see the capacitor charge and discharge.

Even though modulation is a parameter of memory location,

it was not used in this example. Memory location 2 turned on

the sink mode. This is not required for less than 50W dissipa-

tion. Also, note that while Program 2 is active, sourcing

capabilities is reduced.

1, Connect a 10,OOO~F. 50V capacitor on the output terminals

of the Model 228. Observe proper polarity when connecting the capacitor.

z Charging the Capacitor (Operating as a Source). Program

memory location 1 for the following parameters: A. 50V B. 25mA C. 60 second Dwell Time D. Turn off modulation.

E. Turn off sink mode.

3 Discharging the Capacitor (Operating as an Active Load).

Program memory location 2 for the following parameters: A. 20V B. 25mA

C. 60 second Dwell Time D. Turn off modulation. E. Turn on sink mode.

4 Program the dwell time of memory location 3 to zero.

5. Set the Model 228 to the continuous program mode.

6. Set the Model 228 to the operate mode.

7. Press the START/STOP key.

8. Watch the front panel displays.

+I is on). The capacitor is charging at the rate programmed. When the capacitor is charged to SOV, the amps display shows approximately zero current flowing (capacitor charged). The LED to the right and left of the +V symbol are on indicating that the capacitor is at the voltage level programmed.

When the Model 228 is in memory location 2, the capacitor is discharging. Note the voltage on the left display. It decreases as the capacitor discharges. As the capacitor discharges, the compliance graph shows the Model 228 in current limit (LED above the -1 is on). When the capacitor is discharged to the 20V programmed level, the LED to the right and left of the

+V symbol are on indicating that the capacitor is at the level programmed.

This simple example illustrates several operating modes of the Model 228. The following features and functions of the Model 228 are used in this example.

1. Prbgramming a voltage value.

2. Programming a current value.

3. Programming memory control mode (continuous).

4. Programming the five parameters of a memory location: Voltage, Current, Dwell Time, Modulation, Source or

Sink.

5. Operation as a source (memory location 1).

6. Operation as an active load (memory location 2).

3.13.6 Example 6: Fabricating Output

Waveforms

The Model 228 is capable of fabricating output waveforms.

With the 100 available memory locations, the Model 228 can fabricate waveforms with up to 100 individual steps. 100 steps of a waveform may not be necessary. A less complicated waveform could consist of just two memory locations. A square wave is an example of a two memory location waveform. The following is an example of programming the Model 228 to output a squarewave of +5V to OV at 20Hz. To keep the example simple the current parameter for each of the

two memory locations will be set to 1COmA.

NOTE To avoid confusion in this example, set all the parameters of memory location 3 to zero.

When the Model 228 is in memory location 1, the capacitor is charging. Note the voltage on the left display. It increases as

the charge on the capacitor charges. The compliance graph

shows the Model 228 is in current limit (LED just above the

1. Turn on the Model 228 and allow ten minutes for warm UP.

2. Press VOLTS/MEMORY STEP, SELECT. (Selects volts display and sets the left display for modification).

3-35

3. Press 5, ., 0, 0, ENTER. (Programs voltage for 5V).

4. Press AMPS/DWELL TIME, SELECT. (Selects amps display and sets the right display for modification).

5. Press ,, 1, 0, 0, ENTER. (Programs memory location 1 current for lOOmA).

6. Press AMPS/DWELL TIME, SELECT. (Selects dwell time display and sets the display for modification).

7. Press ., 0, 2, 5, ENTER. (Programs memory location 1 for 25msec dwell time).

8. Dress VOLTS/MEMORY STEP, SELECT. (Selects memory step display and sets the display for modificadon).

9. Press 2, ENTER. (Selects memory location 2).

10. Press VOLTS/MEMORY STEP, SELECT. (Selects volts display and sets the display for modification).

11. Press 0, ., 0, 0, ENTER. (Programs memory location 2 for O.OV)

12. Press AMPS/DWELL TIME, SELECT. (Selects amps display and sets the display for modification).

13. Press ., 1, 0, 0, ENTER. current for lOOmA).

14. Press AMPS/DWELL TIME, SELECT. (Selects the dwell time display and sets the display for modification).

15. Press ,, 0, 2, 5, ENTER. (Program memory location 2 dwell time to 25msec).

16. Connect load.

17. Press CONTINUOUS, OPERATE, START/STOP. (Selects the continuous memory control mode, enables the output and starts the continuous mode).

Upon completion of step 17, the Model 228 outputs a 5V to OV, 2OHz square wave. Refer to Figure 3-14.

+w ,

‘\

\ /

(Programs

L ,1

memory

memory location 2

25msec

location 1

3.13.7 Example 7: Using the External Trigger (Input and Output)

A TTL level negative going pulse of greater than 1O~sec applied at the rear panel external TRIGGER connector initiates the selected or Continuous). The pulse starts the memory control mode in the same manner as the front panel START/STOP key. To output any programmed values, the memory control mode must be selected, the OPERATE key enabled and the proper external trigger pulse must be applied to the rear panel external TRIGGER input connector.

The external trigger output is a TTL level negative going greater than 10~sec pulse that signifies the completion of a programmed dwell time. The pulse appears at the rear panel

external trigger output connector at the end of the progammed dwell time in all three memory control modes (Single Step, Single Cycle and Continuous). For the single cycle and continuous memory control mode, there is an output pulse at

the end of every programmed dwell time. For the single step mode, there is an output pulse at the end of the programmed dwell time for the one memory location. To go on to the next step, another external trigger input pulse is required. Refer to paragraph 3.7 Memory Control Group.

As an example of using external input and output triggering, assume the Model 228 is to be used in conjuction with the Model 195A System DMM. The Model 228 can be programmed to output up to 100 voltage/current levels for given periods of time. As each output voltage/current is applied, the Model 228 triggers the Model 195A to take a reading. When the Model 195A completes its reading, it triggers the Model 228 to output the next programmed +oltage/current value. The sequence repeats itself until all readings have been taken.

To use the Model 195A with the Model 228 perform the following steps:

1. Connect the Model 228 and the Model 195A as shown in Figure 3-15. Use suitable shielded cables with BNC connec-

tors. The Model 195A voltmeter complete output should be connected to the Model 27.8 external trigger input. The Model 195A external trigger input should be connected to the Model 228 external trigger output.

(memory

memory

control mode (Single Step, Single Cycle

location); and therefore output another pulse,

3-36

Figure 3-14. Output Waveform

2. Place the Model 195A in the external trigger mode.

3. Connect both the Model 228 and the Model 195A to the

circuit under test.

4. Program the Model 228 with the desired output voltage,

current and dwell time values (refer to paragraph 3.10, Examples 1, 2 and 3). Set the Model 195A to the ap-

propriate function and range. If desired, enable the Model 195A data buffer for reading storage.

5. Select the Model 228 memory control mode. To illustrate this example, select the single step mode.

6. Place the Model 228 in the operate mode.

7. Press the START/STOP key on the Model 228 to output the first voltage/current value.

8. Press the Model 195A front panel trigger button. This starts the measurement cycle on the Model 195A.

9. After the Model 195A completes the reading, it triggers the Model 228 into the next memory location; and

therefore, output the next voltage/current value.

10. Each instrument will trigger the other until the trigger cycle is stopped.

CAUTION

Do not exceed 30V between the external

trigger connectors (outer ring) and chassis

ground or instrument damage may occur.

EXTERNAL TRIGGER IN C,--

EXTERNALTRIGGER OUT 0--

MODEL 228

REAR PANEL

MODEL 195

REAR PANEL

VOLTMETER

0 COMPLETE

Figure 3-15. External Trigger Connections

3.13.8 Example 8: Floating Operation (Extended Compliance)

1OOV MAX

‘IF THE EXTERNAL VOLTAGE SOURCE IS NOT A MODEL 228, THE

DIODES SHOWN ID, Et D2l SHOULD SE USED TO PROTECT THE EX-

TERNAL SOURCE FROM SUCH ERRORS AS:

1. INCORRECT MODEL 228 PROGRAMMED POLARIP/.

2. IMPROPER POWER ON SEDUENCE.

3. EXCESSIVE MODEL 228 PROGRAMMEO VOLTAGE.

I< ,.O,AMP,O”MAXTD1.01< I<lO.1,

Figure 3-16. Connection for Floating Operation

CAUTION When sn external voltage sc~rcs is ccnnetted in series with the Model 228 output

(as shown in Figure 3-161, csre should be

taken to observe the power limits specified

in Figure 3-12. Also, the current MONITOR and MODULATION connectors are held within a few volts of the OUT- terminal by the Model 228.

3.14 APPLICATIONS

The following applications allow the Model 2.28 tc be used in several situations including: scurce current and an active load

(current sink).

The Model 228 may be floated up tc 1OlV off of chassis ground (earth ground). Floating the Model 228 off of earth ground increases the compliance voltage by that level. The maximum float voltage is 1OlV and the maximum compliance voltage is IOOV. This increases the compliance level to 201V.

This does not mean that the Model 228 will deliver 201V of

compliance. 1oOV is from the Model 228 and 1OlV from the external supply. A second Model 228 is a good choice to use for the external supply. Before floating the Model 228 above earth ground with an external supply, always check for the

proper circuit connections. Figure 3-16 shows the proper ccn-

nections when floating the Model 228 above earth ground.

3.14.1 Low Resistance Measurements

Connectors, switch and relay contacts, printed circuit boards and other devices with $l resistances can be measured with current, scurce and sensitive voltmeters, For example: Using

10A and 1mV range gives 1CO~n resolution (lmV/lOA) = lOOwn This resolution is obtainable without using an additional digital multimeter.

3-37

NOTE

For this example remote sensing should be used.

3.14.2 Battery Tests

The four terminal measurement eliminates the effects of test lead resistances. The Model 228 could be used to supply a current (I) through the device under test (DUT). This developes a voltage (IRDuT) which could be read by the sen-

sitive voltmeter. Using a lOOmA current, the 1OnV resolution of the Keithley Model 181 Nanovoltmeter corresponds to

O.lpQ, Thermal EMFs, electrochemical and other effects add

an extraneous DC voltage (VOFFSET) to the voltage devloped by the current source. This offset may be eliminated by ap plying first a positive and then a negaitve current, both of the same magnitude (I).

For positive current: Vx+ = IRD~ + VOFFSET

For negative current: Vx- = -IRDUT + VOFFSET

The difference of these voltages is a follows:

(VX+-VX-)=(IRDUT+VOFFSET)-(-IRDUT~VOFFSET)= ZIRDUT or

wxc -vx-)

Rour =

The DUT can be installed in the Model 8003 Low Resistance Test Box, which employs Kelvin sensing and includes all interconnecting cables to Models 181 and 228.

The same measurement techniques can be applied to materials testing, where a metal under stress eventually microfractures, causing an increase in resistance. Small laboratory samples or even large airplane wings can be tested in ttiis manner. Refer to Figure 3-17 for an example configura-

tion.

The Model

228

is capable of acting as a source or as a ac-

curate and stable load. Testing the life of a battery requires

such a load. The Model 228 could be set to dissipate power

from the battery. The load conditions could be programmed over the IEEE-488 bus or from the front panel.

Figure 3-18 shows the configuration of the Model 228 sinking

power from the battery. The battery in the figure is rated at 1OV therefore the Model 228 should be programmed for a voltage less than 1OV in order to operate in the sink mode. When the voltage of

the Model

228 is less than the voltage of

the battery, current is drawn from the battery into the Model

228.

The COMPLIANCE graph shows that the instrument is operating in the sink mode. The voltage is positive but current is being drawn from the battery which shows up on the COMPLIANCE graph as negative current.

The battery could be discharged in this manner. A data logger

would be useful to log the decline in battery voltage over a long period of time. The Keithley Model 197 DMM has a

built-in 100 point data logger that would be ideal for this ap-

plication. The data logger of the Model 197 has six selectable rates at which the data may be logged automatically. It also has a numerical trigger for manual data logging. The automatic rates range from three readings per second to one reading per hour. The Model 197 and the Model 228 would work in conjunction with each other to accomplish the bat-

tery test. Figure 3-19 shows the configuration of the Model 228, Model 197 and the battery for the test.

When using the Model 228 to test power supplies; most power supplies would be damaged if external voltages or cur-

rents are forced upon the, Figure 3-20 is a suggested protection circuit. The two diodes in Figure 3-20 protect most sup-

plies in the event of the following errors.

228

CURRENT

SOURCE

Figure 3-17. Low Resistance Measurements

3-38

1. Incorrect Model 228 polarity.

2. Improper power on sequence.

3. The Model 228 is programmed for excessive voltage.

181

NANOVOLT

METER

MODEL228 ;

r -OUT; & L -?FA

OUICK

) DISCONNECT

BOARD

3.14.3 External Modulation

The output of the Model 228 may be externally modulated. This means the user supplies a low frequency (DC to 6COHz) low voltage (rtlOV) signal that is superimposed on the output signal of the Model 228. This external AC signal is applied to

the external modulation terminals on the quick disconnect

board and therefore the output signal. The polarity of the

modulation is determined by the programmed polarity of the output signal. The input resistance to the external modulate terminal is 6.8kQ. The maximum modulation with the output programmed to zero is +O.OV to -lOV. The modulation

with

the output programmed to full scale is

+1ov to -o.ov.

maximum

Figure

MODEL 228

3-18. Battery Life Teat

QUICK

DISCONNECT

MODEL 197 OMM

LO a

Figure 3-19. Data Logging Configuration

r----:

MODEL 228

I I L----

I I

The front panel MODULATE I and MODULATE V LEDs indicate which function is selected.

The external modulation feature could be used to add low frequency signals to the Model 228 output. An example could be performing power supply rejection tests without the burden of large transformer or additional power amplifiers. Figure

3-21

shows the configuration for using the external modula-

tion feature. Figure 3-22

shows

a typical modulated output.

where:

PSRR = loglo -

NOTE

Use shielded cables the outout of the Model be co&ected to output LO. Shield cables help in reducing extraneous noise.

when

externally modulating

228.

The shield should

USER SUPPLY

PROTECTION FOR USER’S SUPPLY

Figure 3-20. Power Supply Protection Circuit

3-39

QUICK

DlSCONNECT

BOARD

POWER

SUPPLY AC DIGITAL

c- UNDER

TEST

0”T

VOLTMETER ,V,)

SIGNAL GENERATOR

EITHER VOLTAGE OR CURRENT MAY BE MODULATED.

AC MODULATION SUPERIMPOSED

ON PROGRAMMED LEVEL

‘ROGRAMMED

LEVEL --.

CAUTION

DO NOT EXCEED RATED SPECIFICATIONS FOR

MODULATION VOLTAGE OR MODULATlON CURRENT,

INSTRUMENT DAMAGE MAY OCCUR,

CAUTION: MOD IS NOT ISOLATED FROM OUTPUT,

Figure 3-21. Connections for External Modulation

MODEL 228

T--L

PSRR = 20 log,lJ k

-- “c

LOAD CAPACITOF

Figure 3-22. Typical Modulated Output

3.14.4 Ramp Generation

A very accurate ramp may be generated by charging a capacitor with the Model 228. The Model 228 charges the capacitor with a constant current up to the compliance limit of the Model 228 or the working voltage of the capacitor. Figure 3-23 shows the Model 228 connected to a capacitor. Figure 3-24 shows the ramp that is generated by the constant

current being applied to the capacitor.

3-40

Figure 3-23. Ramp Generation

228 has a built-in IEEE-486 interface that allows the test cir-

cuit to be incorporated into the measurement system. Figure

3-27 shows the configuration with the Model 228s connected

to the computer over the bus.

With the system configuration, the computer may be pro-

grammed to control the testing automatically. The Model 228

responds to IEEE-468 protocol concerning commands and data. With the Keithley Model 8573 IEEE-488 interface the Model 228 may be controlled with the IBM PC or XT. The

Model 8573 IEEE-468 is supplied with its own software boot

disk and instruction manual. The instruction manual provides clear instructions for operating the Model 8573 with the IBM PC or XT.

Figure 3-24. Ramp Characteristics

The ramp is generated as the capacitor charges. When the compliance limit of the Model 228 is reached or the capacitor

is fully charged, the ramp levels out to the voltage level on the capacitor. The ramp could be used with a data logger (e.g. Keithley Model 197 DMM in data logger mode). The data

logger could be used to store up to 100 data points of the

ramp to verify the accuracy of the ramp.

3.14.5 Power Semiconductor Testing

The Model 228 is suitable for testing power semiconductors such as VMOS FETs, diodes, power Bipolar transistors, etc. Typical curves for the transistors may be obtained using one or two Model 228s. The Model 228 supplies up to 1COW for

these applications. Obtaining the curves for bipolar tran-

sistors involves two Model 228s. One Model 228 is connected

between the base and emitter and another Model 228 is connected between the collector and the emitter. Figure 3-25

shows the configuration for obtaining the family of curves for

a power transistor. The curves shown are the collector-

emitter voltage versus collector current (VCE, 1~ curves).

Other transistor tests may be performed using the Model 228

and the configuration shown in Figure 3-25. Examples of these tests include:

1. DC Current Gain-The graph of DC current gain shows collector current UC) versus hfe.

2. “ON” Voltages-The graph of “ON” voltages shows the collector current UC) versus the “ON” voltage of the transistor.

3. Collector Saturation Region-The collector saturation region graph shows base current (1~) versus collector emit-

ter voltage (VCE).

Most VQ/IC curves illustrated in data manuals show the maximum safe forward bias area. This area is self explanatory and should not be exceeded. Figure J-Z.6 shows

typical a structure of Vc& curves. Also shown in Figure

3-26

is the maximum safe forward bias area.

For incoming inspection testing, manual testing may not be cost efficient. The configuration shown in Figure

3-25

may be

connected to the IEEE-488 bus and a computer. The Model

Figure 3-25. Power Transistor Test Set Up

3-41

COLLECTOR

CURRENT

IICI

COLLECTOR-EMITTER VOLTAGE P&I

MAXIMUM

SAFE FORWARD

BIAS AREA

IS BASE CURRENT

bipolar transistor. Figure 3-28 shows the configuration using a FET instead of a bipolar transistor. Figure 3-29 shows the family of curves for a FET instead of a bipolar transistor.

Figure 3-30 shows the automated test set up with a FET instead of a bipolar transistor.

G '

pl, Q

VGS

MODEL 228

Figure 3-26. Power Transistor Ic/vcE

CU~SS

Figure 3-28. FET Test Set Up

NOTE

Using the bipolar capability of the Model 228, both polarity transistors can be tested without rewiring.

DRAIN

CURRENT

IIDI

MAXIMUM

SAFE FObWARD

BIAS AREA

Figure 3-27. Automated Test Set Up

The test set up is shown in Figure 3-25, the curves shown in Figure 3-26 and the automated set up shown in Figure 3-m could all apply to FETs as well as bipolar transistors. In Figure 3-25 the set up would be slightly different for a FET than for a

3-42

DRAIN-SOURCE VOLTAGE (VDSI

Figure 3-29. FET Curves

To check the circuit’s noise sensitivity, try the following: COMMON MODE-Connect a sine wave generator be-

tween the “earth” ground and circuit ground. Monitor any changes in the circuit’s performance as frequency is swept to determine its noise sensitivity.

NORMAL MODE-Connect a sine wave generator in series with “safe” level (<3OV)

signal lines.

Be careful not to violate grounding through the function generator (since many function generators connect one output terminal to

“earth” ground). Isolate the function generator from high level ( > 30V) signals with a transformer. Check circuit performance as in common mode testing to determine noise sensitivity.

MODEL 228

Figure 330. Automated Test Set Up for FETs

3.14.6 Compensation

for

Noise

OUTPUT NOISE For most applications, electrical noise coming from the

Model 228 is negligible. However, some Model 228 users may have some output noise questions when operating thii instrument in extremely sensitive applications. The follow-

ing information will help you determine possible sources

of the noise, which noise frequency range your test application is sensitive to, and what you can do to isolate or reduce the noise.

Before you can isolate or reduce electrical noise effects in

your application, you must determine what frequencies

your test is most sensitive to.

A good source of information is the specification sheet from the device under test.

Add a “known” controlled noise source (such as a function generator) to the circuit and measure the circuit’s sensitivity to it.

Set up a “noise free” environment, then add one noise source at a time to determine which noise sources affect

the test,

NOISE SOURCES There are many possible sources of electrical noise both

from the Model 228 and from external sources. The following characterizes noise sources within the Model 228:

The Mode1 228’s microprocessor is isolated from the output circuitry by opto-isolators. However, some microprocessor hash in the 25-1OOMHz range may appear on the output due to capacitive coupling within the Model 228. When viewed with a wideband oscilloscope, the noise may look much greater than low frequency noise. However, this is usually not a problem in ex-

periments since it is mostly common mode and not seen

across the load. The low common mode rejection ratio of most scopes at these frequencies impairs their ability to make accurate normal mode (across the load) noise

measurements.

There may be low level noise at the Model 228 power line

frequency.

There may also be some noise generated at 50kHz and

harmonics of 50kHz due to the switching power supply.

Some noise sources in typical laboratory environments include:

Equipment with Microprocessors and/or Digital Circuitry:

This includes personal computers, peripherals, and test

equipment. Noise from these sources is coupled through

cables. Frequency components of this type of noise in-

clude multiples and subharmonics of internal clocks and

hash from signal edges.

Computer Terminals: Terminals may generate noise at l5kHz and harmonics of 15kHz. In addition, some lMHz-1OOMHz microprocessor hash may be‘generated.

3-43

Fluorescent Lighting: Noise can be generated at the harmonics of the power line frequency.

DC motors: All frequencies can produce some amount of noise (white noise source).

Broadcast Stations and Commercial Transmitters: Again, a continuous spectrum of noise is generated, most usually around lMHz and above 5OMHz.

Bypass the p wer supply at the circuit under test. Use

polystyrene, ylar or ceramic capacitors.

Shield the circ it. : (A ground plane connected at only one point will do.

All wires eve’ 6” long (including power supply line) should be shi ‘lded or of the “twisted-pair” type. Note-large diamete wire is usually less inductive than small diameter wire of the same length.

CHECKING FOR NOISE SOURCES

When characterizing electrical noise, a spectrum analyzer or an oscilloscope would be very helpful.

A spectrum analyzer is very useful when used with an antenna and “sniffer” probe. The analyzer provides relative amplitude and frequency information. Multiply the relative

amplitude information with the circuit sensitivity at particular frequencies to determine the most significant problems.

If your oscilloscope has an adjustable bandwidth control, it may be used like a spectrum analyzer. Unfortunately, many oscilloscopes have a greater sensitivity-bandwidth product than most circuits. Note that spikes have less energy than a continuous waveform of the same peak amplitude.

NOISE REDUCTION TECHNIQUES

The following suggestions are “rules of thumb which

may

solve many commonly encountered problems.

Low Frequency Noise Reduction Techniques (to 3OOHz)

of equipment may not be at the

otential even if they are plugged into the

High Frequent 20MHz)

Noise Reduction Techniques (300kHz-

To reduce high f requency noise, try the following:

Put the circuit under test in a conductive box (for full

shielding 1 effec s).

Make sure the cads on bypass capacitors are t/4” or less

in length. This ‘equires bringing conductors to capacitors,

not vice versa.,

Use mica, gl ss, low-loss ceramic or polystyrene

capacitors.

Bypass all wire : going in to or out of the circuit under test.

-Ferrite beads are most useful when the DC and peak AC current oes not exceed about lOmA.

-Wire wrappe around a 100 or lOOR carbon composition resistor and soldered to its leads makes a good low

Q inductor capable of handling higher currents.

-Capacitors that short noise to protective shields should have leads as short as possible (t/p”). Feedthrough type capacitors are preferred.

Low frequency noise is often the result of less than optimal shielding, grounding or circuit layout. Try these solutions:

Run power lines and grounds for control circuitry

separately from noise-selection circuitry.

If you must ground one of the Model 228’s leads, do it at the circuit under test. Only one “earth” connection is

allowed for a system to avoid ground loops.

Employ the “remote sense” capability of the Model 228.

Use twisted-pair wire for the Model 228’s output and

sense leads.

Medium Frequency Noise Reduction Techniques (300Hz300kHz)

Lead inductance and capacitor equivalent series resistance become significant at medium frequencies. Try the following:

3-44

Use bulkhead connectors bolted to the shield for coaxial cables if possible.

Line filters (electromagnetic interference suppressors) in a metal case work well at higher frequencies if bolted to the circuit shield. Be sure to use the proper current rating.

Use twisted-pair wire for proper supply and sense lines. Noise coupled into the Model 228 through sense lines will appear on the output and degrade specified performance.

Avoid using a large value capacitor in parallel with a small value capacitor since this can form a parallel resonant circuit? Otherwise, isolate the two capacitors with a damcrt~~;esistor (100 carbon composition is a good starting

* Large value capacitors appear inductive at high frequen-

cies while the small value capacitor may still appear capacitive. The parallel combination will then have a higher impedance at some frequencies than either capacitor by itself.

SECTION 4

IEEE BUS OPERATION

4.1 INTRODUCTION

This section contains information necessary to operate the Model 228 over the IEEE-488 bus. The Model 228 has a standard IEEE interface that allows the user to give commands and read data via an external device. Front panel Programs 2,4, 5 and 6 may be activated over the bus.

A typical set up for controlled operation is shown in Figure 4-l. Generally, a system will contain one controller and a number of other instruments to which the commands are given. Device operation is categorized into three operators: controller, talker and listener. The controller does what its

name implies; it controls the instruments on the bus. The talker sends data while a listener receives data. Depending on the type of instrument, any particular device can be a talker only, a listener only or both a talker and a listener.

Any given system can have only one active controller, but

any number of talkers or listeners may be present up to the hardware limitations of the bus. Generally, the bus is limited

‘to 15 devices, but this number may be reduced if higher than

normal transfer rates are required or if longer than normal cables are used.

4.1.1 Software Considerations

The most sophisticated computer in the world would be

useless without the necessary software. This basic require-

ment is also true of the IEEE-488 bus, which requires the use

of handler routines as described in this section.

Before a controller can be used with the IEEE-488 interface, the user must make certain that the appropriate handler software is present within the controller. With the HP-85 com-

puter, for example, the HP-85 interface card must be used

with an additional l/O ROM, which contains the necessary handler software. As another example, the IBM PC (use the Keithley Model 8573 IEEE-488 interface) also requires handler software. This handler software is on the disk that is provided with the Keithley Model 8573.

Other small computers that can be used as controllers have limited IEEE capability. The PET/CBM computer, for example, is incapable of sending multiline commands from BASIC, although these commands language routines. The capabilities of other small computers depends on the particular interface being used. Often, little software “tricks” are required to achieve the desired results.

can

be sent through machine

Only one device on the bus may be a talker at any given time while several devices can be commanded to listen. Before a device can be commanded to talk or listen it must be appropriately addressed. Devices are selected by their primary address. Usually, each device on the bus has its own primary address so that each device may be addressed individually. The primary address of the Model 228 is set at the factory to

11. The primary address may be changed by front panel Program 3. For more information concerning front panel programs refer to paragraph 3-11.

Once a device is addressed to talk or listen, the appropriate bus transactions take place. For example: if the Model 228 is

addressed to talk, it places its data string on the bus one byte at a time. The controller reads the information and the appropriate software can be used to direct the information to

the desired location.

From the preceding discussion, the message is clear, make sure the proper software is being used with the interface. Often, the user may incorrectly suspect that a hardware problem is causing fault when it

the problem all along.

was

the software that was causing

4.i.2 Interface BASIC Programming Statements

Many of the programming instructions covered in this section use examples written in Hewlett-Packard Model 85 BASIC and Keithley Model 8573 interface statements. These computers and interfaces were chosen for these examples because

of their versatility in controlling the IEEE-488 bus. This section covers those HP-85 and Model 8573 statements that are essential to Model 228 operation.

4-1

A complete list of HP-85 BASIC and Model 6573 interface statements is shown in Table 4-1. HP-85 statements have

one or three digit argument that must be specified as part of the statement. The first digit is the interface select code, which is set to 7 at the factory. The last two digits of those statements with a 3-digit argument specify primary address.

Those statements with a 3-digit argument listed in the table

show a primary address of 11 (the default primary address of the Model 228). For a different address the last two digits need to be changed to the required value. For example, to send a GTL command to a device using a primary address of 11 the following statement would be used:

LOCAL 711.

Some of the statements have two forms; the exact configura-

tion depends on the command to be sent over the bus. For example, CLEAR 7 sends a DCL command, while CLEAR 711 sends the DC command to device with a primary address of

11.

figuration file called CONFIG.SYS must be present on the DOS boot disk (see the Model 6573 Instruction Manual).

1. Boot up the system in the usual manner and enter BASICA.

2. Place the Model 6573 software disk into the default drive and load the program called “DECL.BAS”. Modify the program by changing the XXXXX values in lines 1 and 2 to

16000.

3. Add the following lines to the declaration file: 7 NA$=“GI’IBO”:CALL IBFIND(NA$,BRDO%) 8 NA$=“DEVO”:CALL IBFIND(NA$,M228%) 9 V%=ll:CALL IBPAD(M228%,V%)

4. Now save the modified declaration file for future use. Remember that you must load and run this short program before using the Model 6573 programming examples throughout this section. Also, do not use the BASIC CLEAR or NEW commands after running this program.

4.1.3 Interface Function Codes

The Model 8573 statements, which are also listed in Table 4-1, are different than the HP-85 statements. Each of these statements use the IBM BASIC CALL statement, with a different variable passed as shown in the table. The command words, such as IBCLR (Interface Bus Clear) and IBSRE (Interface Bus Send Remote Enable), are BASIC variables. These variables must be initialized at the start of each BASIC program. These keywords should not be used for any other purpose in your BASIC program.

Before using the Model 8573 examples, the software must be configured with the following procedure. Note that the binary handler file called GPIB.COM and the system con-

Table 4-l. HP-85 and IBM BASIC Statements

Action

Transmit string to device 11.

Obtain string from device Il. Sand GTL to device 11. Sand SDC to device 11. Sand DCL to all devices.

Sand remote enable. Serial poll device 11. Sand local lockout.

Sand GTL to device 11.

HP-55 Statement Model 8573 Statement

OUTPUT 7ll;AS (CALL IBWRT(M22896,CMDS~

ENTER 711;AS CALL IBRD (M228%,CMDS) CALL LOCAL 711 CALL IBLOC(M22896) CLEAR 11 CALL IBCLR(M228%) CLEAR 7

REMOTE 7 V% = l:CALL IBSRE(BRDO%,V%) SPOLL(711) CALL IESRP(M228%,SB%~

LOCAL LOCKOUT 7 CMDS=CHR$(&Hll):CALL IBCMD

TRIGGER 711 CALL IBTRG(M228%) ABORT10 7 CALL IBSIC(BRDO%)

The interface codes are part of the IEEE-488-1978

standards. These codes define an instrument’s ability to sup-

port various functions and should not be confused with pro-

gramming commands found elsewhere in this section.

Table 4-2 lists the codes for the Model 228. These codes are also listed on the rear panel of the Model 2213. The codes are

located near the IEEE connector. The numeric value following each one or two letter codes defines the Model 228 capabilities as follows:

SH (Source Handshake Function)-The ability for the Model

228 to initiate the transfer of message/data on the data bus is

CMD$=CHRSl&H14):CALL IBCMD

lBRDO%,CMDS)

(BRDO%,CMD$)

4-2

provided by the SH function.

AH (Acceptor Handshake Function)-The ability for the

Model 228 to guarantee proper reception of message data on the data bus is provided by the AH function.

T (Talker Function)-The ability for the Model 228 to send device-dependent data over the bus (to other devices) is provided by the T function. Model 228 talker capabilities exist only after it has been addressed to talk.

L (Listener Function)-The ability for the Model 226 to

receive device-dependent data over the bus (from another

device) is provided by the L functions. Listener function capabilities exist only after the Model 228 has been addressed to listen.

SR (Service Request Function)-The ability for the Model 228

to request service from the controller is provided by the SR

functi0.n.

Table 4-2. Model 228 Interface Function Codes

Code] interface Function SHl (Source Handshake Capability

AH1 Acceptor Handshake Capability

Talker (Basic Talker, Serial Poll, Unaddressed

To Talk On LAG)

Listener (Basic Listener, Unaddressed To

Listen On TAG) SRI Service Request Capability RLl Remote/Local Capabilitv PPO No Parallel Poll Capabili&

DC1 Device Clear Capability DTI Device Trigger Capability

No Controller Capabilitv

Open Collector Bus Drivers

TEO No Extended Talker Capabilities

LEO No Extended Listener Capabilities

RL (Remote-Local Function)-The ability for the Model 228

to be placed in the remote or local mode is provided by the RL function.

I’P (Parallel Poll Function)-The Model 228 does not have parallel polling capabilities.

DC (Device Clear Function)-The ability for the Model 228

to be cleared (initialized) is provided by the DC function.

DT (Device Trigger Function)-The ability for the Model 228

to have its basic operation is provided by the DT function. C (Controller Function)-The Model 228 does not have con-

troller capabilities. TE (Extended Talker Capabilities)-The Model 228 does not

have extended talker capabilities.

LE (Extended Listener Capabilities)-The Model 228 does not have extended listener capabilities.

4.1.4 Model 228 Interface Commands

Interface commands controlling Model 228 operation are listed in Table 4-3. Not included in the table are devicedependent commands, which are covered in detail in paragraph 4-5.

Table 4-3. IEEE Command Groups

HANDSHAKE COMMAND GROUP

DAC = DATA ACCEPTED RFD = READY FOR DATA DAV = DATA VALID

UNIVERSAL COMMAND GROUP

ATN = ATTENTION

DCL = DEVICE CLEAR IFC = INTERFACE CLEAR REN = REMOTE ENABLE SPD = SERIAL POLL DISABLE

SPE = SERIAL POLL ENABLE ADDRESS COMMAND GROUP LISTEN: LAG = LISTEN ADDRESS GROUP

MLA = MY LISTEN ADDRESS

UNL = UNLISTEN TALK:

ADDRESSED COtitiAN~D~ GROUP

STATUS COMMAND GROUP

TAG = TALK ADDRESS GROUP

MTA = MY TALK ADDRESS

UNT = UNTALK

OTA = OTHER TALK ADDRESS

ACG = ADDRESSED COMMAND GROUP

GET = GROUP EXECUTE TRIGGER

GTL = GO TO LOCAL

SDC = SELECTIVE DEVICE CLEAR RQS = REQUEST SERVICE

SRQ = SERIAL POLL REOUEST ST6 = STATUS BYTE

EOI = END

4-3

4.2 IEEE-488 BUS LINES

As shown in Figure 4-1, the signal lines on the IEEE-488 bus

are divided into three groups; management, handshake and data lines. The management and handshake lines ensure that proper data transfer and bus operation take place while the

data lines handle bus information. Each of the bus lines are low true with approximately zero volts as a logic 3

ATN (Attention)-The state of the ATN line determines whether information placed in the data bus by the controller is to be considered data or a command.

REN (Remote Enable)-Setting the REN line low (true) sends

the REN command and sets up the instrument on the bus for

remote operation. If REN is followed by the primary address

of the Model 228, then it will be the only instrument to be

placed in the remote mode.

TO OTHER DEVICES

DATA BYTE

TRANSFER

CONTROL

,TA IS LINES1

HP-88 Programming

(true) by the HP-85 when the following line is entered into the

HP-85.

REMOTE 711 (END LINE)

When the END LINE key is pressed, the Model 228 is placed in the remote mode and the front panel REMOTE LED turns

on.

Model 8573 Programming

low (true) by the IBM PC through the Model 8573 interface when the following is entered into the IBM PC.

V% =l:CALL IBSRE(BRDO%,V%) (return)

CMD$=“X”:CALL IBWRT(M228%,CMD$) (return)

When the return key is pressed the second time, the Model 228 is placed in the remote mode and front panel REMOTE LED turns on.

IFC (Interface Clear)-The IFC command is sent by the con-

troller to set the Model 228 to the talk and listen idle states. The instrument responds, to the IFC command by turning off the front panel TALK or LISTEN LEDs if the instrument was previously in one of those modes. To send the IFC command, the controller only has to set the IFC line true.

Example-The REN line is set low

Example-The REN line is set

Figure 4-1. Bus Structure

4.2.1 Bus Management Lines

The bus management group consist of five signal lines that send certain single line bus commands and ensure an orderly

transfer of data. The five signal lines are:

4-4

HP-85 Programming

IFC command, turn on the front panel REMOTE and TALK LEDs by entering the following statement into the HP-85:

ENTER 711;A$ (END LINE)

The front panel TALK and REMOTE LEDs should now be

on. The IFC command may now be sent by entering the

following statements into the HP-85:

Example-Before demonstrating the

REMOTE 711 (END LINE)

ABORT10 7 (END LINE)

CLEAR 7 (END LINE)

After the END LINE key is pressed the second time, the TALK LED turns off, indicating the Model 228 is in the talk idle state. Note that the remote mode is not cancelled.

have accepted the data. Each device releases the NDAC line at its own rate, but the NDAC line will not go high until the slowest device on the bus has accepted the data.

Modal 8673 Programming strating the IFC command, turn in the front panel REMOTE and TALK LEDs by entering the following statements into the IBM PC.

V%=l:CALL IBSRE(BRDO%,V%) (return)

CMD$=CHR$(&HA):CALL IBCMD(BRDO%,CMD$)

The front panel TALK and REMOTE LEDs should now be

on. The IFC command may now be sent by entering the following statement into the IBM PC:

CALL IBSIC(BRDO%) (return)

After the return key is pressed, the TALK LED turns off, in-

dicating the Model 228 is in the talk idle state. Note that the remote mode is not cancelled.

EOI (End Or Identify)-The EOI is used to identify the last byte of multibyte transfer sequence.

SRQ (Service Request)-The SRQ line is set low (true) by a device when it requires service. SRQ may be identified by reading the status word.

Example-Before

(return)

demon-

After the NDAC line goes high, the source sets the DAV line high indicating that the data is no longer valid. At this point, the NDAC line goes low. The NRFD line is released by each device on the bus, but does not go high until the slowest device on the bus has released the line. The bus is now set to repeat the sequence with the next data byte.

The sequence just described is used to transfer both data and multiline commands. The state of the ATN line determines whether the data bus contains data or commands.

DA”’ SOURCE

--1 I------

4.2.2 Handshake Lines

The handshake group consists of three handshake lines which operate in an interlocked sequence. The interlocked sequence ensures reliable data transfer regardless of the transfer sequence. The rate of transfer is usually determined by the slowest device on the bus. The three handshake lines are:

1. DAV (Data Valid)

2. NRFD (Not Ready For Data)

3. NDAC (Not Data Accepted)

The DAV line is controlled by the source. The NRFD and NDAC lines are controlled by the accepting devices. The

complete sequence is shown in Figure 4-2. This sequence handles information one byte at a time.

Once the data is on the bus. the source checks to see that NRFD is high, At the same time NDAC should be low from

the previous transfer. Once the NRFD and NDAC lines are properly set, the source sets the DAV line low. The NRFD

line goes low; the NDAC line goes high once all the devices

Figure 4-2. Handshake Sequence

4.2.3 Data Lines

The IEEE-468 bus uses eight data lines that transfer data one

byte at a time. DlOl through DIOB (Data Input/Output) are the eight data lines used transmit both data and multiline commands and arc bidirectional. The data lines operate with low true logic.

4.3 SYSTEM SET UP PROCEDURE

There are two primary set up steps that prepare the system for operation. The two steps are as follows:

4-6

1. Bus Connections-The Model 228 is connected to the bus via the rear panel connector. It is a standard IEEE bus connector. Maximum cable length for any device on the bus is 20 meters. The Keithley Models 7008-3 and 7008-6 are

ideal for connecting instruments to the bus. Figures 4-3 and

4-4 show the connector pin assignments and the IEEE bus connector. The connector contact designations are listed in Table 4-4.

CONTACT 12

CONTACT 1

4.4 BUS COMMANDS

The Model 228 may be given a number of special bus commands through the IEEE-486 interface. This section briefly describes the purpose of the bus commands which are grouped into the following three categories:

Uniline Commands-Sent by setting the associated bus line low.

Multiline Commands-General commands that are sent with the ATN line low.

Device-Dependent Commands-Special commands that depend on device configuration; sent with ATN high,

CONTkT 24 CON?ACT 13

Figure 4-3. Contact Assignments

2. Primary Address Selection-The primary address of the Model 228 must be set to the appropriate value when using

the Model 228 in the addressable mode. The primary ad-

dress is selected by using front panel Program 3. For more

information concerning the front panel programs refer to

paragraph 3.11.

Table 4-4. IEEE Contact Designations

contact

Number

2 3 4

: 7 8 9

12 13 14

16” 17

20 21 22 23 24

IEEE-488 Designation

DlOl Dl02 I

Dl03 Dl04 I

EOI (24)* I

DAV I

NRFD

I NDAC

IFC

SRQ 4TN

SHIELD** I Dl05 I Dl06 I

Dl07 Dl08

REN (24)* Gnd, (6)” Gnd, (71” Gnd, W Gnd, (9)” Gnd, (IO)* Gnd, (Ill* Gnd, LOGIC

Type

Data

Data Data Dafa Management Handshake Handshake Handshake Management Management Management Ground Data Data Data Deta Management Ground

Ground Ground Ground Ground Ground Ground

Figure 4-4. Typical Bus Connector

*Number in parentheses refer to signal ground return of

referenced contact number. EOI and REN signal lines return on oontact 24.

**The cable shield is normally connected to contact 12. This

shield should be connected to ground only at the controller end to avoid ground loop problems.

4.4.1 Uniline Commands

As stated previously, uniline commands are sent by setting

the associated bus line low (true). The five uniline (single line) commands are:

ATN (Attention)-The ATN are sent when the information

on the data bus is a” universal or addressed command. Universal and addressed commands are described in paragraphs 4.4.2 and 4.4.3. When the ATN line is high, the byte on the bus is considered to be data. The Model 228 responds to the appropriate universal and addressed commands when the ATN line is low and to the device-dependent commands when the ATN line is high, assuming it is properly addressed.

When the END LINE key is pressed after the CLEAR 7 statement, the Model 228 reverts to the power up default conditions which are listed in Table 4-5. This means that all the parameters of memory location 1 were set to the default conditions listed in Table 4-5. All the parameters

each memory location are battery backed up. Therefore, the programmed parameters are unchanged.

Model 8673 Programming Example-Using

front panel

controls, program a voltage of s.cOv, a current of lOO.O”lA

and a dwell time of 3.00 seconds into memory location one.

Now enter the following statement into the IBM PC:

CMD$==CHR$(&HA):CALL IBCMD(BRDO%,CMD$)

(return)

REN (Remote Enable)-The controller sends the command to all devices on the bus when remote operation is desired. The Model 2213 responds by setting itself up for remote operation as indicated by the front panel REMOTE LED.

EOI (End Or Identify)-EOI is sent during the last byte of a multiline transfer by setting the EOI line low. In this way, the last byte is identified allowing variable length data words to be transmitted. The Model 228 implements this command when in the appropriate bus response mode as stated in paragraph 4.5.5.

IFC (Interface Clear)-The IFC command sets the bus to a known state by setting the IFC line low (true).

SRQ (Service Request)-The SRQ line is pulled low (true) by a” external device thereby informing the controller the device requires service. The Model 228 implements this command in the appropriate bus response mode as stated in paragraph

4.5.5.

4.4.2 Universal Commands

The universal commands are sent when the ATN line is low

(true). There are six universal commands and their effect on

Model 228 operation is described as follows:

When the return key is pressed, the Model 228 reverts to the power up default conditions listed

Table 4-5. All the parameters in each memeory location are battery backed up, Therefore, the programmed parameters are unchanged.

SPE (Serial Poll Enable)-The serial poll enable sequence is used to obtain the Model 228 status byte. Usually, the serial polling

sequence

is used to determine which of several devices has requested service over the SRQ line. The serial polling sequence is conducted as follows:

1. The controller sets the ATN line true.

2. The SPE command is placed on the bus by the controller.

The Model

228

is addressed to talk.

4. The controller sets the ATN line false.

5. The instrument then places its status byte on the bus to be

read by the controller.

6. The controller then sets the ATN line low and places SPD

on the bus to end the serial polling sequence.

HP-85 Programming Example-The HP-85 SPOLL state-

ment automatically performs the serial polling sequence. To

demonstrate serial polling, turn the instrument off then on

and then enter the following statements into the HP-85:

DCL (Device Clear)-The DCL command is used to clear the Model 228, thereby setting it to a known state. Program memory is cleared of all previously stored data when a DCL

or SDC command is received, The buffer is set to location

one.

HP-85 Programming

Example-Using front panel controls, program a voltage of 5.OOV, current of lOO.OmA and a dwell time is 3.00 seconds into memory location 1. Now enter

the following statements into the HP-85:

REMOTE

711

(END LINE)

CLEAR 7 (END LINE)

REMOTE 711 (END LINE)

S=SPOLL (711) (END ELINE)

DISP S (END LINE)

When the END LINE key is pressed after the S = SPOLL statement, the controller performs the serial polling sequence. When the END LINE key is pressed after the DISP S statement the status byte value is shown on the CRT. The status byte has a value of zero (0) with this example because all the bits are set to zero (0).

4-7

Table 4-5. DCL and SDC Default Conditions

.-.--- _-.I- -.I._”

Display Function

Data Format EOI

SRO

Program Mode Range

External Modulation Trigger Terminator Sink Mode Memory Location B

Voltage

Current I Dwell Time Program 1 Program 2 Program 3 Program 4 Mod V Dependent on previously programmed values of present memory location. Program 5 Mod I Dependent on previously programmed values of present memory location. Program 6 Program 9 Reset Disabled

DO Left display =Volts, Right display = Amps, Left display ready for edit. FO

Standby. Output set to f 4 counts on present range. Refer to paragraph

2.3.

Pr=‘r;~;;,buffer location contents,

MO SRQ Disabled

Single Step Mode

I30 Autorange

A & C Dependent on previously programmed values of present memory location.

T6 Stop on X

CR LF Carriage Return Line Feed

Dependent on previously programmed values of present memory location. Present memory location.

V Dependent on previously programmed values of present memory location.

Dependent on previously programmed values of present memory location,

Copy Disabled

Sink Dependent on previously programmed values of present memory location. IEEE Not affected

Test Disabled

Model 8573 Programming Example-The IBM PC conducts a serial poll when the following statements are entered.

- . lo demonstrate serial polling, turn the instrument ott then on

and then enter the following statements into the IBM PC.

V% -1:CALL IBSRE(BRDO%,V%) (return)

CALL IBSRl’(M228%,SB%) (return)

When the return key is pressed after the CALL IBSRP (M228%,SB%) statement, the controller performs the serial polling sequence. When the return key is pressed after the PRINT statement the status byte value is shown on the CRT. The status byte has a value of zero (0) with this example because all the bits are set to zero (0).

SPD (Serial Poll Disable)-The controller automatically sends the SPD command on the bus to end the serial polling sequence in SPE.

UNT (Untalk)-The controller sends the UNT command to

clear the bus of any talkers. IJNL (Unlistenl-The controller sends the IJNL command to

clear the bus of any talkers.

. . . .

PRINT SB% (return)

. .

4.4.3 Addressed Commands

Each of the addressed commands are sent to a specific device on the bus. Bach device is selected on the basis of its primary address. The Model 225 responds to these commands only if the primary address of the command is the same as the primary address of the Model 228. All of the following commands are implemented by addressing the Model 228 to listen.

SDC (Selective Device Clear)-The SDC command performs the same function as the DCL command except that only the addressed device responds. The instrument returns to the set

conditions listed in Table 4-5 when responding to an SDC

command. The program memory of the addressed Model 225

is cleared of all previously stored data when an SDC com-

mand is received. In addition, the buffer and the display

pointers are set to memory location 1.

HP-85 Programming Example-Using the front panel con-

trols program a voltage of 7V, a current of 1.5A and a dwell time of 250msec for memory location 1. Now enter the following statements into the HP-85:

REMOTE 711 (END LINE)

CLEAR 716 (END LINE)

Notice that when the END LINE key is pressed after the CLEAR 711 statement that the Model 228 did not respond to the SDC because the command was sent with the wrong primary address (16). Now enter the following statement into the HP-85:

CLEAR 711 (END LINE)

Where I’1 is the command to set the instrument into the con-

tinuous mode and T2 is the command to set the instrument to the start on GET mode. Now the instrument may be triggered to start with the following statement:

TRIGGER 711 (END LINE)

After this statement is entered, the front panel START/STOP LED turns on indicating the instrument has been triggered. To stop the continuous mode, enter the following statements into

the HP-85.

When the END LINE key is pressed after the CLEAR 711 statement, notice that the instrument returns to the power up default conditions listed in Table 4-5. Note that the program memory is cleared of previously stored data.

Model 8573 Programming Example-Using front panel controls program a voltage of 7V, a current of 1.5A and a dwell time of 250msec for memory location 1. Now enter the

following statements into the IBM PC:

CALL IBCLR(M228%) (return)

When the return key is pressed, notice that the instrument

returns to the power up default conditions listed in Table 4-5.

Note also that the program memory is cleared of previously

stored data.

GET (Group Execute Trigger)-The GET command is used to

trigger devices to perform a specific action that depends on

device configuration. Although GET is considered to be an

addressed command, many devices respond to GET without

being addressed. Using the GET command is only one of

several methods that can be used to start or stop the Model

228 program operation.

HP-85 Programming Example-To help illustrate this ex-

ample, first set the Model 228 to a known state, such as the

default conditions. As in the previous example, to do this use

the SDC command as follows:

OUTPUT 711;“T3X” (END LINE)

TRIGGER 711 (END LINE)

Where T3 is the command to set the instrument into the stop

on GET mode. When the END LINE key is pressed after the OUTPUT 711;“T3X” statement, the continuous mode is stopped. When the END LINE key is pressed after the TRIGGER 711 statement the START/STOP LED turns off indicating the instrument has received the trigger.

The Model 228 also responds to the GET command without addressing. This command is sent with the following HP-65 statement:

TRIGGER 7

Model 8573 Programming Example-To help illustrate this example, first enter the following statements into the IBM PC.

V%=l:CALL IBSRE(BRDO%,V%) (return)

CMD$=“TZPZX”:CALL IBWRT(MZZB%,CMD$) (return)

When the return kev is Dressed the first time the Model 228 reverts to the conditions listed in Table 4-5. When the return key is pressed the second time the Model 228 is placed in the start on get trigger mode and the continuous mode.

REMOTE 711 (END LINE)

CLEAR 711 (END LINE)

When the END LINE key is pressed after the CLEAR 711

statement, the Model 228 reverts to the default conditions listed in Table 4-5. Now enter the following statement into the HP-85 to place the instrument in the continuous memory control mode (Pl) and start on GET trigger mode.

OUTPUT 711;“PlTZX” (END LINE)

P2 is the command to set the instrument into the continuous mode and T2 is the command to set the instrument into the start on GET mode. Now the instrument may be triggered with the following statement:

CALL IBTRG(M228 % ) (return)

After this statement is entered, the front panel START/STOP

LED turns on indicating the instrument has been triggered. To stop the continuous mode enter the following statement into the IBM PC:

CMD$=“T3X”:CALL IBWRT(M228%,CMD$) (return)

4-9

T3 is the command to set the instrument into the stop on GET mode. The next line provides the trigger required to stop the continuous mode. After the trigger has been received the front panel START/STOP LED turns off.

CALL IBTRG(M228%) (return)

GTL (Go To Local)-The GTL command is used to remove the instrument from the remote mode. The REN line MUST BE SET HI (FALSE) in order for the GTL command to restore operation of the locked out Model 228 front panel controls.

HP-85 Programming Example-To illustrate this example

the Model 228 must first be placed in the remote and lockout modes. To place the instrument in these modes enter the following statements into the HP-85:

REMOTE 711 (END LINE)

LOCAL LOCKOUT 7 (END LINE)

When the END LINE key is pressed after the LOCAL LOCKOUT statement, the Model 228 is in the remote mode

(REMOTE LED on) and the front panel controls are locked out (except ON/OFF and LOCAL). The GTL command se-

quence is automatically sent by the HP-65 with the following statement:

LOCAL 711 (END LINE)

Note that the REMOTE LED on the front panel control is restored. Setting the REN line false with the LOCAL 7 statement also takes instrument out of the remote mode.

Model 8573 Programming Example-To illustrate this example the Model 228 must, first be placed in the remote and local lockout modes. To place the instrument in these modes enter the following statements into the IBM PC:

V% =l:CALL IBSRE(BRDO%,V%) (return)

CMD$=“X”:CALL IBWRT(M228%,CMD$) (return)

NOTE The Model 228 may be placed in the local mode by pressing the LOCAL button on the front panel.

4.5 DEVICE-DEPENDENT COMMANDS

The device-dependent commands allow the user to send commands to the Model 228 that perform the same operations as the front panel controls (except for POWER ON/OFF). There are a number of commands that control parameters which are not available from the front panel and they are listed in Table 4-6. Each command is entered as an ASCII character followed by a specific parameter that is sent over the bus by the controller. The bus treats these commands as data in that the ATN line is high (false) when the commands are transmitted.

Several commands may be grouped together. Before a command or command string is executed, the ASCII character X must be sent. Commands sent without an X (execute) are retained within the command buffer until the execute character is received.

The condition of the status word with the Model 228 is af-

fected by the device-dependent commands. The status word may be obtained from the unit by using commands covered in this section. Refer to paragraph 4.5.13 for status word information. Illegal commands do not change the mode of the

Model 228, but the status byte condition changes as described

in paragraph 4.5.5. Normal Model 228 commands are covered in the following paragraphs. All the devicedependent commands for the Model 228 are listed in Table 4-6. Table 4-7 lists the device- dependent commands that are not available to the front panel.

The Model 228 executes the programmed commands in the order listed in Table 4-8. This means that if a statement is entered into the HP-85 as follows:

OUTPUT 711:“PlW3.5DlX” (END LINE)

The Model 228 executes the commands in the following order

When the return key is pressed after the CALL IBLOC(BD%)

statement, the Model 228 is in the remote mode (REMOTE LED on). The GTL command sequence is automatically sent by the IBM PC with the following statement: 2. Selects the continuous mode (Pl).

CALL IBLOC(M228%) (return)

After return key is pressed, the RMT indicator turns off and the instrument is returned to local operation.

according to Table 4-8.

1. Displays memory step (Dl).

3. Programs the dwell time to 3.5 seconds (W3.5).

With the Model 6573, the instrument executes the commands in the same order as did the HP-85.

4-10

There are two types of commands that make up the device-

dependent commands listed in Table 4-8. They are as follows: Independent Commands-Commands that do not interact

Table 4-6. Device-Dependent Commands

with each other. Timer Commands-Commands that control the time and

date.

lisplay

+ogram

‘refix

530

Trigger

Left Display DO Dl D2 D3 D4

Pl P2

GO Gl G2 G3

:z MO

Ml M2

TO Start on TALK Tl Stop on TALK T2 Start on GET T3 Stop on GET T4 T5 Stop on X T6 T7 Stop on External Trigger

VOLTS

MEM STEP

VOLTS

MEM STEP

Display Message Mode

Single Step Mode

Single Cycle Mods

Continuous Mode

Buffer location contents with prefix. Buffer location contents without prefix. Full buffer contents with prefix.

Full buffer contents without prefix. Volts, amps readings with prefix. Volts, amps readings without prefix.

Disabled

Error (IDDC, IDDCO or No Remote)

Ready

End of Buffer

End of Dwell Time

Start on X Start on External Trigger

Right Display AMPS AMPS

DWELL TIME

Terminator

Inputs

Function

YfASCII) Any ASCII except capitals, numbers, + - / or e

Ym One Terminator

Y mn

YfDELI

V Voltage

B FO Fl

Two Terminator

None

Current

Dwell Time Memory Location

Standby (output set to +4 counts on present range). Refer to paragraph 2.3 for details concerning the standby mode. Operate (output is present on terminals).

4-11

Table 4-6. Device-Dependent Commands (Cont.)

Mode

qange

External Mod

sink

;tatus

jelf Test

:ommenc

R2 Fl:

A0 Al co Cl

SO Sl

uo Ul

Notes

Autorange

lV, IOOmA lV, 1A lV, 1OA 1OV. lOOmA IOV, 1A 1OV. 10A lOOV, lOOmA lOOV, 1A

Turn off Voltage Modulation Turn on Voltage Modulation

Turn off Current Modulation Turn on Current Modulation

Turn off sink mode. Turn on sink mode.

Send Status Word Send Error Status word

Inactive 0; in statys byte. Passed 2; in status byte. Failed 1; in states byte.

iO1

&execute

KO z

Send EOI, hold off bus until commands processed on X. Send no EOI, hold off bus until commands processed on X. Send EOI, do not hold off on X. Send no EOI, do not hold off on X. Execute other device-dependent commands.

4-12

Table 4-7. Device-Dependent Commands Not Available to the Front Panel

lode

isplay refix

iR0

‘rigger

C ommand

D4 GO

Gl G2 G3

G4 G5

K3 MO

Ml M2 M4 MB

Uotes

Iisplay Message Mode suffer location contents with prefix.

3uffer location contents without prefix. %rlI buffer contents with prefix. %I buffer contents without prefix. Jolts, amps readings with prefix. Jolts, amps readings without prefix.

Send EOI, hold off bus until commands processed on X. Send no EOI, hold off bus until commands processed on X. 3and EOI, do not hold off on X. Send no EOI, do not hold off on X.

Disabled Error (IDDC, IDDCO or No Remote) Ready End of Buffer End of Dwell Time

Start on TALK Stop on TALK Start on GET Stop on GET Start on X Stop on X Start on External Trigger Stop in External Trigger

‘erminata

itatus

ixecute

tanga

YIASCII)

Ymn

YIDEL)

uo Ul

RO Rl R2

ri: R5 R6 R7 RB

Any ASCII except capitals, numbers, + - / or a One terminator Two terminator

None Sand status word

Send error word

Execute other device-dependent commands.

Autorange

1V. lOOmA lV, 1A lV, 1ov IOV, lOOmA lOV, 1A lOV, 10A lOOV, lOOmA

lOOV, 1A

4-13

Table 4-8. Hierarchy of Command Execution

“Function ‘Prefix

EOl *SRI3 ‘Program ‘External Modulation / *Trigger ‘Terminator *status

*Execute ‘Self Test

*“Range

***Inputs

‘Executed first

**Executed second

***Executed last

Command

DO, Dl, D2, D3 and D4 FO and Fl GO, Gl, G2, G3, G4 and G5 KO ,Kl, K2 and K3 MO, Ml, M2, M4 and M6

PO, Pl and P2 AO, Al, CO and Cl TO, Tl, T2, T3, T4, T5, T6 and n Y(ASCII), Y(m), Y(mnl and Y(DELI UO and Ul

JO RO. Rl, R2, R3, R4, R5, R6, R7 and R8

V, I, Wand B

4.5.1 Display Mode (D)

The following five commands set the display for the volts, memory step, amps, dwell time or display message mode.

DO=The DO command sets the Model 226 for the volts display and amps display mode. Volts is shown on the left display. Amps is shown on the right display. Refer to paragraph 3.7.

Dl=The Dl command sets the Model 226 for the memory

step and amps mode. The memory step is shown on the left

display. Amps is shown on the right display. Refer to

paragraph 3.7. DZ=The DZ command sets the Model 226 for the dwell time

and volts display mode. Dwell time is shown on the right display. Volts is shown on the left display. Refer to paragraph

3.7. D3=The D3 command sets the Model 228 for the dwell time

display mode. The dwell time is shown on the right display. Refer to paragraph 3.7.

D4=The D4 command sets the Model 228 for the display message mode. The display message mode allows the user to display a customized message on the Model 228 front panel

display.

HP-65 Programming Example-To display and transmit the present memory location with a prefix and display the data on the HP-65 CRT, enter the following statement into the HP-85:

PROGRAM COMMENTS

5 DIM A!$[501 Dimension A$.

10 REMOTE 711

(END LINE) remote mode. 20 CLEAR 7 (END LINE) 30 OUTPUT 711;“GODlX” Disolav mesent memorv loca-

(END LINE)

40 ENTER 711;A$

(END LINE) 50 DISP A$ 60 END

After typing in the program, press the RUN key on the HP-65

to run the program. After the RUN key is pressed the present

memory location with the prefix is displayed on the HP-85

CRT as follows:

NDCV+l.OOOE-2, ODCI+O.OOOE+O, W+3.500E+O,

Set the Model 226 to the Clear the Model 228.

. . .

tion on the Model 228 display and send memory location with prefix. Obtain data string.

Display data string

B+l.OOOE+O

DCV = O.OlV Amps = .OOOOA Memory Step = 1 Dwell Time = 3.5 seconds

N = function in control 0 = function not in control

This program can be used for any of the prefix (G) com-

mands.

Model 8673 Programming Example-To display and transmit the present memory location with a prefix and display the data on the IBM PC CRT, enter the following statements into the IBM PC.

V% =l:CALL IBSRE(BRDO%,V%) (return)

CMD$=“GODiX”:CALL IBWRT(M228%,CMD$) (return)

RD$=SPACE$(25):CALL IBRD(M228%,RD$) (return)

PRINT RD$ (return)

12 3 4

Notes

1. The first character on both displays must be a plus (+), minus ( - ), decimal point or the number 1. Otherwise it

will be ienored.

2. Characters 2, 3 and 4 on the left display and 2, 3, 4 and 5 on the right display will accept any displayable ASCII character. Any character not displayed will appear as a “d” segment. A “d” segment is shown as follows:

3. The maximum number of characters for the displays that can be sent is nine. The first four characters are shown on

the left display. The last five characters are shown on the right display.

4. Depending on the program more than one message may be

displayed.

12345

After the second statement. the Model 228 displays the present memory location on its front panel display and transmits the data string to the computer. After the fourth statement, the present memory location with the prefix is displayed on

the computer CRT.

As another example we will illustrate the D4 (display message) mode. Read the following paragraphs and do the programming example.

The ASCII message is, of course, limited to the display of the seven segment LEDs on the front panels of the Model 228. Both front panel displays may be used to display the message.

The message may be controlled with the following commands:

D4aaaaaaaX=The command is D4 while the letter “a” represents an ASCII character (up to seven characters may be sent). DO, Dl, D2 or D3=Takes the Model 228 out of the message display mode (D4) and into the display mode that is programmed.

NOTE For the following notes, refer to the display numbering sequence shown.

HP-85 Programming Example-To display the message “For self test send JO,” enter the following program into the HP-85:

PROGRAM

10 REMOTE 711 20 OUTPUT 7ll;“D4 FORSELFX” 30 WAIT loo0 40 OUTPUT 711; “D4 TEST X” 50 WAIT loo0

OUTPUT 7ll; “D4 SENDX” 70 WAIT 1000 80 OUTPUT 711; “D4 JOX” 90 WAIT 5COO

IOU

GOT020

110 END

NOTE

Make sure there is a space in the program be-

tween D4 and the message. Othewise an erratic display will result.

When RUN key on the HP-85 is pressed the Model 228 displays the following message:

Display operation may be restored by entering the following statement into the HP-85:

COMMENTS

Set for remote. Display FORSELF. Wait on second. Display TEST. Wait one second. Display SEND. Wait one second. Display JO. Wait 5 seconds. Repeat.

OUTPUT 711:“DOX” (END LINE)

4-15

Model 8673 Programming Example-To display the mes-

sage “HELLO,” enter the following program into the IBM PC: 10 DIM A$ I601

PROGRAM

10 V% =l:CALL IBSRE

(BRDO%,V%)

20 CMD$=“DQ HELLO”:CALL

IBWRT(M228%,CMD$)

After the return key is pressed the second time the Model 228

displays HELLO, Display operation may be restored by entering the following statement into the IBM PC.

CMD$=“DOX”:CALL IBWRT(M22E%,CMD$)

COMMENTS

Set up for remote

operation.

Display HELLO.

4.5.2 Memory Control Mode (PI

The following three commands set the Model 228 to single

step cycle or continuous memory control mode. PO=The PO command sets the Model 228 to the single step

memory control mode. The single step memory control mode allows the user to step through the programmed memory lo-

cations one at a time upon sending the PO command. One location per I’2 command.

I’1 =The I’1 command sets the Model 228 to the single cycle memory control mode. The single cycle mode allows one complete cycle through the programmed channels.

P2=The P2 command sets the Model 228 to the continuous

memory control mode. The continuous mode allows a continuous cycle through the programmed memory location.

HP-85 Programming Example-The following example illustrates the Pl (single cycle) memory control mode.

PROGRAM

20 REMOTE 713 30 OUTPUT 711;“BlX”

(END LINE)

40 OUTPUT 711;“V5IlWlx”

(END LINE)

50 OUTPUT 711;“B2X”

(END LINE)

60 OUTPUT 7ll;“VlOIW2X”

(END LINE)

70 OUTPUT 711;“B3X”

(END LINE)

80 OUTPUT 711;“V25IlW3x”

(END LINE)

90 OUTPUT 711;“PlX”

(END LINE)

100 OUTPUT 711:“DOGOX”

(END LINE)

110 OUTPUT 711;“TOX”

(END LINE)

120 ENTER 711;A$ (END LINE) Obtain start on talk. 130 DISP A$

140 END

After entering the program, press the HP-85 RUN key to run

the program. After the RUN key is pressed, the Model 228 steps through memory locations 1,2 and 3. The Model 228 also displays the programmed voltage for each of the memory locations. Since the program specifies the single cycle mode, the memory locations are stepped through only once. To do so continuously, program P2 in line 90 instead of Pl. The HP-65 screen displays the full buffer contents for memory location 3. This is because the TALK statement (Line 120) tells the instrument to send its data string. Since the Model 228 is presently on memory location 3, that data is sent wer the bus.

COMMENTS

set up for remote operation. Set memory location

001. Set 5V, 1A and 1 second dwell time in memory

location 001. Set memory location

002. Set 1oV. 1A and 2 second dwell time in memory location 002. Set memory location

003. Set 25V, 1A and 3 second dwell time in memory location 003.

Set single cycle mode. Set for volts display and

buffer location with prefix sent. Set for start on talk.

Display data string.

4-16

Memory Location 1 = Voltage, Current, Dwell Time, Modulation on or off, Sink on or off.

Memory Location 2 = Voltage, Current, Dwell Time, Modulation on or off, Sink on or off.

Memory Location 3 = NDCV + 2.5COE + 1, ODCI +

~.OIXIE+O,W+~.OOOE+O,B+~.~~~E+~.

To run the program press the F2 function key. After placing the instrument in remote (line 40), the program sets memory locations 1,2 and 3 for various parameters. Lines 110 and 120 set the instrument for buffer location output, single cycle mode, start on talk trigger mode and volts display mode. Lines 130 and 140 obtain the data string and displays it on the IBM CRT. Lines 1.50 and 160 close the board and instrument file.

Modal 8673 Programmlng Example-The following pro-

gram illustrates the single cycle memory control mode (Pl)

over the bus using the IBM PC and the Model 8573 IEEE-488 interface. Load the modified DECL.BAS file into the IBM computer (see Model 8573 Instruction Manual) and add the following lines.

PROGRAM

10 NA$==“GPIBO”:CALL IBFIND

(NA$, BRDO%)

20 NA$==“DEVO”:CALL IBFIND

(NA$,MZtS%)

30 V% = 11:CALL IBPAD

(M228%,V%)

40 V% -1:CALL IBSRE

(BRDO%,V%)j

50 CMD$=“BlX”:CALL IBWRT

(M228%,CMD$)

60 CMD$=“VSIlWlX”:CALL

IBWRT(MZ28%, CMD$)

70 CMD$=“BZX”:CALL IBWRT

(M228%,CMD$)

80 CMD$=“V5IlWZX”:CALL

(M228%, CMD$)

90 tiMD$=‘“B3X”:CALL IBWRT

(M228%,CMD$)

100 CMD$=“V2511W3X”:CALL

(M228%,CMD$)

110 CMD$=“POGOX”:CALL IBWRT

(M228%,CMD$)

120 CMD$=“TODOX”:CALL IBWRT Select start on talk

(M228%,CMD$)

130 RD$=SPACE(60):CALL IBRD

CM228 % ,RD$) 140 PRINT RD5 150 V% =&CALL IBONL

(BRDO%,V%)

160 CALL lBONL(M228%,V%)

COMMENTS

Find the board descriptor. Find the instrument descriptor.

Set primary address to 11 Set remote enable.

Select memory location 1. Set 5V. 1A and 1 second dwell time. Select memory location 2

Set lOV, 1A and 2 second dwell time. Select memory location 3 Set 25V, 1A and 3

second dwell time. Selects butfer loca-

output and single cycle mode.

and volts display

mode.

Obtain data string.

Display data string.

Close the board

file.

Close the instru-

ment file.

4.5.3 Prefix (G)

When addressed to talk, the instrument will send a data string containing information about the programmed current, voltage, dwell time and memory location. This data string can be sent with or without a prefix. The prefix (G) commands and their format are described as follows:

GO=Present Buffer Location Output. Sending the GO command allows the data to be sent with a prefix as follows:

NDCV+n.nnnEfn, Ifn.nnnErtn, Wfn.nnnE*n, B+n.nnnE+n Voltage, Current, Dwell Time, Memory Location

Gl=Present Buffer Location Output. Sending the Gl command allows the data to be sent without a prefix as follows:

+n.nnnE+n, fn.nnnEfn, +n.nnnEfn, +n.nnnEfn

G2=Full Buffer Output. Sending the G2 command allows all

of the data in all 100 buffer locations to be sent with a prefix. The format is as follows:

NDCVfn.nnnEfn, I-tn.nnnE+n, W*n.nnnEfn, B+l.OOOE+2

NDCV&n.nnnE*n, I*n.nnnE&n, W*n.nnnE*n,

B+l.COE+2

G3=Full Buffer Output. Sending the G3 command allows all

of the data in all 100 buffer locations to be sent without a prefix. The format is as follows:

fn.nnnEtn, +n.nnnEfn, fn.nnnEfn, fn.nnnEfn

‘&.n;nE.;t;, +n..nnnE_+n, fn.nnnEfn, +l.OOE+2

4-17

G4=Present Voltage and Current Buffer Output. Sending the

G4 command allows the voltage and current data that is pres-

ent on the output to be sent with a prefix. The formatis as

follows:

prefix is desired in the data string, change line 60 to read as follows:

60 OUTPUT 711:“GlDOX”

NDCVfn.nnnE*n, I*n.nnnEfn, W*n.nnnEfn, B+n.nnnE*n

G5=Present Voltage and Current Buffer Output. Sending the G5 command allows the voltage and current that is present on the output to be sent without a prefix. Also, present output mode values are sent (operate or standby). The fonnat is as follows:

*n.nnnE*n, *n.nnnEfn, ztn.nnnE&n, +n.nnnEen

HP-86 Programming Example-The following program sends the data string over the IEEE bus. In order to obtain the data string from the instrument, the controller must perform

the following sequence:

1. Set ATN true.

2. Address the Model 228 to talk.

3. Set ATN false.

4. Input the data string one byte at a time.

NOTE Press the END LINE key after each line is entered.

PROGRAM COMMENTS

10 DIM A$ (1001

Dimensions A$ for 100 characters.

20 REMOTE 711

Set instrument up for

remote operation. 30 CLEAR 7 40 OUTPUT 7ll;“BlX”

Clear the instrument.

Selects memory location

50 OUTPUT 711;“V1011W10X”

Set 1OV. IA and 10

second dwell time. 60 OUTPUT 711;“GODOX”

Programs the volts

display mode and the

Buffer location with

prefix mode. 70 ENTER 711: A$ 80 DISP A$

Obtain data strinn.

Display data st&. 90 END

Once the program is entered, press the HP-85 RUN key to start the program. The data string appears on the HP-85 CRT. The Model 228 is programmed for lOV, 1A 10 second dwell time the prefix mode and the volts display mode. If no

The Gl command programs the instrument to drop the prefix from the data string.

Model 8573 Programming Example-The following pro-

gram sends the data string over the IEEE bus. In order to ob-

tain the data string from the instrument, the controller must

perform the following sequence.

1. Set ATN true.

2. Address the Model 228 to talk.

3. Set ATN false.

4. Input the data string one byte at a time.

NOTE Load the modified DECL.BAS file into the IBM computer (see the Model 8573 Instruction Manual) and add the following lines. Press the return key after each line is entered.

PROGRAM

10 NA$=“GPIBO”:CALL IBFIND

(NA$,BRDO%)

20 NA$=“DEV(Y’:CALL IBFIND

(NA$,M228 % )

30 V%=ll:CALL IBPAD

(M22E%,V%)

40 V%=l:CALL IBSRE

(BRDO%,V%)

50 CMD$=“BlX”:CALL IBWRT

(M228%,CMD$)

60 CMD$=“V’lOIlWlOX”:CALL

IBWRT(M228%,CMD$)

COMMENTS

Find the board descriptor. Find the instrument descriptor. Set primary address to 11. Send remote enable Select me”lory location 1. Set 1OV. 1A and 10 second dwell time.

70 CMD$=“GODOX”:CALL IBWRT

M228 % ,CMD$)

Set volts display mode and buffer

output with prefix

mode.

80 RD$=Sl’ACE$(50):CALL

Obtain data string.

(M228%,CMD$)

90 PRINT RD$

Display data String.

loo V% =O:CALL IBONL

Close board file.

(BRDO%,V%)

110 CALL IBONL(M228%,V%)

Close instrument file.

Once the program is entered, press the F2 function key to run SRQ may be programmed by sending the ASCII letter ‘WI” the program. The Model 228 is programmed for lOV, lA, 10 second dwell time volts display mode and the buffer location

output with prefix mode. If the prefix is not desired, change more’ than one set of conditions simultaneously. To do so, line 70 to:

70 CMD$=“GlDOX”:CALL

IB!WRT(M228%,CMD$)

The Gl command programs the instrument to drop the prefix

from the data string.

followed by a decimal number to set the appropriate bits in the mask. Note that the instrument may be programmed for

simply add up the decimal bit values for the required SRQ conditions. For example, to enable SRQ under illegal devicedependent command option, send MlX. To disable SRQ, send MOX. This command clears all bits in the SRQ mask.

4.6.4 SRQ Response Mode (Ml

The bus response mode determines whether or not the Model 228 requests service from the controller through the SRQ line.

SRQ ON ERROR

Table 4-9 lists the conditions that cause an SRQ. Note that the instrument can be programmed for one or more conditions simultaneously.

SRQ ON READY

SRO ON END OF DWELL TlME

SRD ON END OF SVFFER

-. J

Table 4-9. SRQ Mask Commands

IDDC.

SRQ

ommand

MO* Ml M2 M3 M4 M5 M6 M7 MB M9 Ml0 Ml1 Ml2

Ml3 Ml4

Ml5

“MO Disables SR(I.

SRQ Mask-The Model 228 uses an internal mask to d&t.mine which conditions cause an SRQ to be generated. Figure 4-5 shows the general format of this mask, which is made up of eight bits. The SRQ has the same general format as thh status byte except that bit 6 is npt used in the SRQ mask.

End of

hrell Time bead\

ind of

hfier F

X X

IDDCO

I h

lo Remotf

Figure 4-5. Format of SRQ Byte

Figure 4-6 shows the format of the SRQ mask byte. Bits within the mask can be controlled bv sendine the ASCII character “M” followed by a decimal number f&n 0 to 15.

B7 B6 85 84 83 82 Bl BO

N/A IN/A IN/A/O/l IO/l IO/l /O/l IO/l

I-

Figure 4-6. Format of SRQ Mask

Status Byte Format-The status byte format byte contains information relating to data and error conditions within the in-

strument. The general format of the status byte (which is ob-

tained by the serial polling sequence) is shown in Figure 4-5.

Note that the various bits correspond to the bits in the SRQ

mask.

Bit 6 provides a means to determine if an SRQ was asserted by the Model 228. If this bit is set, service was requested by the instrument. Bit 5 flags a Model 228 error condition, If this bit was set, one of the following errors have occurred.

1 1 1 1 -DISABLE SRD

~ DWELL TIME

4-19

1. An illegal device-dependent command (IDDC) or illegal Model 8573 Programming Exampledevice-dependent command option (IDDCO) was sent. The instrument was not in remote when programmed.

2. Ready when the Model 228 is ready for operation.

3. If the end of the buffer (program memory) is encountered when running a program.

4. When the end of the present programmed dwell time is

reached during program execution.

Load the modified DECL.BAS file into the IBM zl DECL.BAS file into the IBM

computer (see the Model 8573 Instruction

Manual) and add the following lines. Press the I the following lines. Press the

return kev after each line is entered.

NOTE the Model 8573 Instruction !ach line is entered.

PROGRAM

Note that the status byte should be read to clear the SRQ line once the instrument has generated an SRQ. All bits in the status byte are latched when the SRQ is generated. Bits are cleared when the status byte is read. Even with SRQ disabled,

the status byte can be read to determine appropriate instru-

ment conditions. In this case, bits 2, 3, 4 and 5 are con-

tinuously updated to reflect current instrument status; however, bit 5 (the error bit) latches and remains latched until the status byte is read, even if no SRQ occurs.

10 NA$=“GPIBO”:CALL IBFIND

(NA$,BRDO%)

20 NA$=“DEVO”:CALL IBFIND

(NA5.M228%)

30 i,‘% =ll:CALi IBPAD

(M228%,V%,)

40 V% =l:CALL IBSRE

(BRDO%,V%)

50 CMD$= “MlX”:CALL IBWRT

(M228%,CMD$)

HP-85 Programming Example-Enter the following pro-

gram into the HP-85:

60 CMD$=“RPX”:CALL IBWRT

(M228 % ,CMD$)

70 PRINT”87 B6 85 B4 B3 B2 B7

NOTE After each line is entered press the END LINE key.

BO” 80 MASK% =128 90 CALL IBSRP(M228 % ,SB % )

100 FOR1 =ltot3

PROGRAM

10 REMOTE 711 20 OUTPUT 711;“MlX” 30 OUTPUT 711;“R9X” 40 S=SPOLL(711)

COMMENTS

set up for remote operation. Program for SRQ on error. Attempt to program illegal option. Conduct serial poll.

110 IF (SB% AND MASK%) =0

THEN PRINT “0”; ELSE PRINT

1,” I,

120 ~ASK%=MASK%/~ 130 NEXT I 140 PRINT 150 V% =O:CALL IBONL

(BRDO%,V%)

160 CALL IBONL(M228%,V%) 50 DISP”B7 B6 B5 B4 B3 B2 Bl BO” Identify the bits. 60 For I=7 to 0 STEP -1 70 DISI’ BIT (S.1):

80 NEXT I 90 DISP

100 END

Loop eight times. Display each bit p&i&

After the program is entered, press the F2 function key to run

the program. After placing the instrument in remote and setting SRQ (line 501, line 60 attempts to program the instrw ment into a range that does not exist (R9). At which point the instrument generates an SRQ and sets the error and SRQ bits in its status byte. Other bits may also be set depending on in-

After the program is entered, press the HP-85 RUN key to run

the program. The computer places the instrument in remote and then programs the SRQ mode of the instrument. Line 30 attempts to program an illegal option (R9), at which point the

instrument generates an SRQ and sets the bus error bits in its

strument status. Lines 70, 80 and 90 display the bit positions, set the mask value to the most significant bit and serial poll the instrument. Since the status byte is in decimal form, lines 100, 110, 120 and 130 are used to generate the binary

equivalent of the status byte value. status byte. The computer serial polls the instrument and displays the status byte bits in proper order on the CRT. In this example, the SRQ (B6) bits are set because of the attempt to program an illegal command option. Other bits may be set depending on instrument status.

COMMENTS

Find the board descriptor. Find the instrument descrmor. Set p&uy address

11. Send remote enable. Program for SRQ on error. Attempt to program illegal command option. Identifv the bits

Defind bit mask.

Conduct serial poll.

LOOD eight times.

Mask orf the bits and display them

Close the board file. Close the instrument file.

420

4.5.5 Trigger Modes (T)

Triggering is used to tell the Model 228 to intitiate the memory control mode sequence (single step, single cycle or continuous). The trigger stimulus may come from commands sent over the bus, through the external trigger input or by the front panel START/STOP key. Triggering may be used to either start the memory control mode sequence or stop the sequence. The trigger modes are as follows:

TO=Start on Talk. In the TO mode, talk commands initiate the memory control mode sequence.

228 steps through the programmed memory locations. To send a GET command, enter the following statement into the HP-85:

TRIGGER 711 (END LINE)

Model 8673 Programming Example-Set the Model 228 to the default conditions by entering the following statements

into the IBM computer:

V%=l:CALL IBSRE(BRDO%,V%) (return)

CALL IBCLR(M228%) (return)

Tl=Stop on Talk. In the Tl mode, talk commands stop the memory control mode sequence.

T2= Start on GET. In the T2 mode, a GET command (Group Execute Trigger) initiates the memory control mode sequence.

T3=Stop on GET. In the T3 mode, a GET command stops

the memory control mode sequence.

T4=Start on X. In the T4 mode, an execute command in-

itiates the memory control mode sequence.

T5=Stop on X. in the T5 mode, an execute command stops

the memory control mode sequence.

Tb=Start on External Trigger-In the T6 mode, an external

trigger pulse initiates the memory control mode sequence.

T7=Stop on External Trigger-In the T7 mode, and external

trigger pulse stops the memory control mode sequence.

HP-55 Programming Example-Set the instrument to its

default conditions by entering the following statements into

the HP-85:

REMOTE

CLEAR 7 (END LINE)

The default conditions include the trigger mode to be set for the T6 mode. Enter the following statement to set the Model 228 to the T2 trigger mode.

OUTPUT;“T2X” (END LINE)

After the END LINE key is pressed, the Model 228 is placed in the T2 mode (Start on GET). When a GET command is sent by the controller to the Model 228, the instrument goes into the selected memory control mode. For example; if memory locations 1 through 25 are programmed for various values of voltage current and dwell time and the single cycle mode is selected, then when the GET command is received, the Model

711

(END LINE)

The default conditions include the Model 228 set to the T6 trigger mode. To set the Model 228 to the T2 mode enter the

following statement into the IBM computer:

CMD$=‘T2X”:CALL IBWRT(M228%,CMD$) (return)

After the return key is pressed, the Model 228 is set to the T2 trigger mode (Start on GET). When a GET command is sent by the controller to the Model 228, the selected memory control mode is initiated. For example, if memory locations 1 through 25 are programmed for various values of voltage, current and dwell time and the single cycle memory control mode is selected, then when GET is received the Model 228 steps through the programmed memory locations. To send GET, enter the following statement into the IBM computer:

CALL IBTRG(M228%) (return)

4.5.6 Programmable Terminator (Y)

The Model 228 uses special terminator characters to mark the end of its data string. To allow a wide variety of controllers to be used, the terminator can be changed by sending the appropriate command over the bus. The default value is the commonly used carriage return, line feed (CR LF) sequence. The terminator assumes this default value upon power up, receiving DCL or SDC command.

The terminator may be programmed by sending the ASCII character Y followed by the desired terminator character. Any ASCII character except one of the following may be used:

1. All capital letters

2. All numbers

3. Blank

+ - / , and e.

4-21

Special command characters will program the instrument for special terminator sequences as follows:

l. Y(ASCI1) any ASCII except preceding list.

2. Ymn = Two terminator characters.

3. Yn = One terminator character.

4. Y(DEL) -

No terminator character.

I=stores the current (I) value into the present memory loca-

tion.

V=stores the voltage (V) value into the present memory loca-

tion.

W=stores the dwell time (W) value into the present memory

location.

B-selects the memory location.

NOTE

Most controllers use the CR or LF character to

terminate their input sequences. Using a nonstandard terminator may cause the controller to hang up unless special programming is used.

HP-86 Programming Example-Enter the Following statements into the HP-85. To reverse the default CR LF terminator sequence, type the following lines into the HP-85:

REMOTE 7ll (END LINE)

OUTPUT 7ll;“Y”;CHR$(lO):CHR!$(l3):“X” (END LINE)

When the END LINE key is pressed the second time, the nor-

mal terminator sequence is reversed. The instrument ter-

minates each data string or status word with a LF CR se-

quence.

Model 8573 Programming Example-Use the following statements to reverse the default terminator sequence.

V%=l:CALL IBSRE(BRDO%,V%) (return)

CMD$=“Y”-CHR$(10)+CHR!$(13)+“X”:CALL IBWRT

(M228% ,CMD$l (return)

A complete summary of input commands along with the for-

mat of each is shown in Table 4-10. The parameter of each

command (except memory location) may be entered in direct

or scientific notation as long as the allowable range for each command is not exceeded. Some examples of the various command formats are as follows:

Desired Result

1.5A Current 25V Voltage 250msec Dwell Time

Notes

1. An IDDCO (Illegal Device-Dependent Command Option)

error occurs if the input command parameter is outside of the legal range. A front panel error message indicates this

error. The instrument may also be programmed to

generate an SRQ if such an error occurs, as described in

paragraph 4.5.4.

2. Dwell time accuracy is valid only if the IEEE bus is idle.

3. The input command for memory location truncates any

valid variation. For example, if the command is B1.9; then the Model 228 truncates anything to the right of the decimal point. This means that the Model 228 selects memory location 1.

Command Variations

11.5; 115E-1; I.l5E+l V25; V2.5E+l; V250E-1 W250E-3; W.25; W25E-2

The terminator sequence will be reversed when the second statement in executed.

4.5.7 Inputs (I, V, W and B)

The input commands control the current (I), voltage (V), dwell time (W) and the memory location (B). The input commands that affect Model 228 operation are as follows:

4-22

Table 4-10. Input Command Summary

Dwell Time (Wl Value .OZaec to 1000sec

HP-ES Programming Example-The following program sets up the Model 228 output according to the values entered from the HP-85 keyboard. Press the END LINE key after each line is entered.

PROGRAM

10 REMOTE 711

COMMENTS

Set for rem&e operation.

20 DISP”ENTER MEM

STEP”

30 INPUT B$

tion

Enter desired memory loca-

(Example: location l=Bl) 40 DISP” ENTER 1” 50 INPUT I$

Enter desired current.

(Example: 2.5A = 12.5) 60 DISP”ENTER V” 70 INPUT V$

Enter desired voltage.

(Example: 2.5V = V2.5) 80 DISP”ENTER W”

Enter desired dwell time.

(Example: 250msec = W.25)

90 OUTPUT 711;“ROFOX”,

“B”,B$,“I”,1$,“V”,V$,

Output to IEEE bus, address

11.

-w.W$‘~

100 GO TO 20

Repeat.

110 END

After entering the program, press the HP-65 RUN key to start the program. The program prompts the operator for inputs at

the appropriate points in the program. Each parameter of a memory location is entered. To stop the program press the PAUSE key.

Model 8573 Programming Example-The following pro-

gram sends a command string to the Model 228 and displays

the instrument data string on the IBM CRT.

NOTE Load the modified DECL.BAS file into the IBM computer (see the Model 8573 Instruction Manual) and add the following lines.

PROGRAM

10 NA$=“CPIBO”:CALL IBFIND

(NA!J,BRDO%)

COMMENTS

Find the board descriptor.

20 NA$=“DEVO”:CALL IBFIND Find the instrument

(NA$,M228%)

30 V% =ll:CALL IBPAD

(MZZS%,V%,)

40 V%=l:CALL IBSRE

(BRDO%,V%)

50 INPUT”COMMAND”;CMD$

descriptor. Set primary address to 11. Send remote enable. Prompt for com-

mand string.

60 IF CMD$=“EXIT” THEN 140 See if program is to

be stopped.

70 IF CMD$=” ” THEN 50 If null command

string go back and get another.

80 CALL IBWRT

(M228%,RD$)

Address Model 228

to listen and send command string.

90 RD$= SPACF$WO)

Assign reading in-

put buffer.

lo0 CALL IBRD

M228%,RD$)

Address Model 228 to listen and input

data string.

110 RD$=LEFT$

(RD$,IBCNT%)

120 PRINT RD$

Trim string to

proper size. Display reading on CRT.

130 GOT0 50

140 V%=O:CALL IBONL

(BRDO%,V%)

Repeat. Close the board file.

150 CALL IBONL (M228%,V%) Close the instrument

file.

160 END

After entering the program press the F2 function key to run

the program. The CRT prompts the operator for the desired commands and then displays the data string on the CRT.

4.6.8 Function IFI

The function commands control the actual output of the Model 228. These commands perform the same operation as

the front panel OPERATE/STANDBY key. The output may

be controlled by bus commands as follows:

death. Always turn the instrument to standby, let It cool down and then turn It off before coming Into contact with the output

terminals of the Model 228.

4.5.9 Range (RI

FO (Standby)-The output terminals are programmed to +4

counts on the present range. Refer to paragraph 2.2.1 for

details concerning the standby mode.

Fl (Operate)=The output terminals are programmed to the present value of voltage and current.

HP-66 Programming Example-Using the front panel OPERATE/STANDBY key, place the instrument in the standby mode and enter the following statements into the

HP-85:

REMOTE 711 (END LINE)

OUTPUT 711;“FlX” (END LINE)

When the END LINE key is pressed the second time, the front

panel OPERATE LED turns on and the instrument is placed in

the operate mode. Do not leave the instrument in the operate mode unattended. Always place the instrument in standby after the measurement or test is completed.

WARNING Do not come into contact with any live circuit that could cause esrsonal injury or

The range commands set the maximum allowable cwcent that

may be programmed into the instrument. ‘Table 4-11 shows the range commands. Upon power up, or after a DCL or

SDC, the RO (AUTO) mode is enabled.

1. On a given range, the source parameter can be no longer than that range will allow.

2. If an under range command is given, a zero source value is stored.

3. If an overrange command is given, the instrument responds with a front panel IDDCO (Illegal DeviceDependent Command Option) error as described in paragraph 4.5.4.

HP-85 Programming Example-The following program sets the Model 228 to the 1V. 10A range and then gives an input command of 75OmV. The program stops at this point and

prompts the user to continue the program. Once the program

is running again the controller sends an illegal devicedependent command option (5V) to the instrument. Then the program displays an IDDCO on the instrument as well as on the HP-85 CRT.

NOTE

After entering each line press the END LINE key.

Table 4-11. Range Commands

Maximum Output

lV, IOOmA lV, 1A IV, IOA lOV, lOOmA lOV, IA lOV, IOA lOOV, lOOmA lOOV, 1A

Minimum step

lmV, lOpA lmV, IOOfi lmV, ImA 10mV. ~OJLA lOmV, lOOti lOmV, 1mA lOOmV, lOpA lOOmV, lOOhA

PROGRAM

COMMENTS

PROGRAM COMMENTS

10 REMOTE 7ll@ CELAR

Set up for remote operation and clear the screen.

20 CLEAR 7ll 30 OUTPUT 7ll;

“RJMIDOX”

Return to the default condi-

ti”“S

Set the Model 228 to the lV, 1OA range turn on SRQ and display Volts, Amps.

40 OUTPUT 7ll;‘Y.75v”

Program the Model 228 to

75Omv.

50 DISP” PRESS CONT” 60 PAUSE 70 OUTPUT 7l1;‘115x”

Attempt to program illegal

voltage on this range.

80 S = SPOLL (7’ll) 90 IF BIT(S,S) AND BIT(S,l)

Conduct serial poll.

Check for IDDCO.

= 1 THEN DISP’YLLEGAL COMMAND OPTION”

100 OUTPUT 711;“ROX”

Set to autorange.

110 END

After entering the program, press the RUN key. The program

sets the Model 228 to the lV, 10A range and programs for a voltage of 75OmV. Press the CONT key and observe that the

instrument displays IDDCO. The IDDCO is also displayed

on the CRT because the status byte was checked by the computer when the error IDDCO bits were set.

10 NA!J=“GPIBO”:CALL IBFIND

(NA$,BRDO%)

20 NA$=“DEVO”CALL IBFIND

(NA$,M228 % )

30 V% =ll:CALL IBPAD

(M228%,V%)

40 V% =l:CALL IBSRE

Find the board descriptor. Find the instrument descriptor. Set primary address to 11. Set remote enable.

(BRDO%,V%)

50 CALL IBCLR(M228%)

Set to default conditions.

60 CMD$=“R3MlXDO”:CALL Set to IV, 10A

IBWRT(M228%,CMD$) range turn on SRQ

and disolav Volts.

Amps. . .

70 CMD$=“V,75X”:CALL IBWRT Program the

(M228 % ,CMD$)

80 CMD$=“V5X”:CALL IBWRT

750mV. Attempt to program

(M228%,CMD$) illegal voltage on

this range.

90 CALL IBSRP

Conduct serial poll.

(M228%,SB%) 100 PRINT SB% 110 CMD$=“ROX”:CALL IBWRT

Disolav data. Set-to autorange

(M228%,CMD$) 120 V% = :CALL IBONL

Close board file.

(BRDO%,V%) 130 CALL IBONL Close instrument

(M228%,V%)

file.

It is important to note that the commands in line 70 would be valid if the instrument were set to the proper range. This is

taken care of automatically in the RO mode, since the instrw ment changes to the appropriate range, depending on the commanded value. To demonstrate this point, change line 30

to OUTPUT 7ll; ‘ROMlX” and run the program again. This time the commands in line 70 are accepted by the insrument since it remains in the autorange mode.

Model 8673 Programming Example-The following program sets the Model 228 to the IV, 10A range and then gives an input command of 750mV. The program stops at this point and prompts the user to continue the program. Once the program is running again the controller sends an illegal command option (5V) to the instrument. Then the program displays an IDDCO on the instrument as well as on the CRT.

NOTE

Load the modified DECL.BAS file into the IBM cornouter (see the Model 8573 Instruction Maiual) anh add the following lines. After each

line is entered press the return key.

After entering the program, press the F2 function key to run the program. The program sets the Model 228 to the 1V. 10A range and sets 750mV. Then the program attempts to set the instrument to 5V. This value is outside of the selected range

and causes the IDDCO message to be displayed on the instrument. A serial poll is conducted and an SRQ reveals the IDDCO. The computer also displays the data.

It is important to note that the commands in line 80 would be

valid if the instrument were set to the proper range. This is

taken care of automatically in the RO mode, since the instru-

ment changes to the appropriate range depending on the com-

manded value. To demonstrate this point, change line 60 to:

60 CMD$=“R3MlX”:CALL

Run program,

IBWRT(M228%,CMD$)

This time the commands in line 80 are accepted by the instru-

ment since it remains in the autorange mode.

4-26

4.5.10 External Modulation (A, C)

HP-86 Programming Example-To enable the sink mode over the bus, enter the following statements into the HP-85:

The external modulation mode may be enabled or disabled over the bus. In external modulation, an external AC signal is

applied to the external modulation connector and therfore the

output. Current or voltage may be modulated as can be seen by the front panel LEDs (MODULATE V and MODULATE I). The commands for external modulation are as follows:

AO-Turn off voltage modulation. Al-Modulate voltage.

CO-Turn off current modulation. Cl-Modulate current.

HP-86 Programming Example-To turn on the modulate current function enter the following lines into the HP-85:

REMOTE nl (END LINE)

OUTPUT 711;“AlX” (END LINE)

After the END LINE key is pressed the second time, the

Model 228 is placed in the modulate current mode.

Model 8573 Programming Example-To turn on the modulate current function enter the following lines into the IBM computer.

REMOTE 711 (END LINE)

OUTPUT 711;“SlX” (END LINE)

After the END LINE key is pressed the second time, the Model 228 is placed in the sink mode. The front panel SINK ONLY LED turns on. The Model 225 high power supply is decreased and the instrument can dissipate full power continuously at 50°C with no derating.

Model 8573 Programming Example-To enable the sink mode over the bus, enter the following statements into the IBM computer:

V% =l:CALL IBSRE(BRDO%,V%) (return)

CMD$=“SlX”:CALL IBWRT(M228%,CMD$) (return)

After the return key is pressed the second time, the Model 228 is placed in the sink mode. The front panel SINK ONLY LED turns on. The Model 228 high power supply is decreased and the instrument can dissipate full power continuously at 50°C with no derating.

4.5.12 Status Word Kl)

V% =1:CALL IBSRE(BRDO%,V%) (return)

CMD$=“AlX”:CALL IBWRT(MZZS%,CMD$) (return)

After the return key is pressed the second time, the Model 228 is placed in the modulate current mode.

4.5.11 Sink Mode (S)

The Model 228 may be operated in the sink mode. That is, power is delivered to the Model 228. The sink program allows

the instrument to decrease the high power supply and still operate as an active load. With the supply reduced, the

Model 228 can dissipate full power continuously at 50°C with

no derating. Refer to paragraph 3.13.4 for details concerning the sink mode. The commands to enable the sink mode are as

follows: SO=Disable sink mode.

Sl=Enable sink mode.

The status word command allows access to information concerning various operating modes of the instrument. When the UO command is given, the instrument outputs the status word

the next time it is addressed to talk. The status word is sent instead of the normal data string. The status word is sent only once each time the UO command is given. The command for

the status word to be sent is as follows: Uo=Send Status Word. The format is the Model number

(228) followed by five bytes representing the modes and func-

tions of the Model 228. Information concerning all modes except for SRQ are one byte in length.

Ul=Send Error Status Word. The format is the model number (228) followed by five bytes representing the various errors.

Figure 4-7 shows the general format of the error status word. The figure shows the errors of the word. Figure 4-8 shows the

general format of the status word. The figure shows the default values. The letters correspond to modes programmed by the respective device-dependent commands.

4-26

Note that all returned values except for those associated with the terminator correspond to the programmed numeric values. For example, if the instrument is presently in the R3

range, the R byte in the status word will correspond to an

ASCII 3.

Notes

1. The status word should not be confused with the SRQ status byte. The status word contains a number of bytes pertaining to the various operating modes of the instrument. The status byte is a single byte that is read by using the serial polling sequence and contains information on SRQ status and error or data conditions.

2. To make sure proper status is returned, the status word should be read immediately after sending the command. Otherwise, instrument status may change, resulting in erroenous status information.

3. The status word is sent only once each time the status command is given. Once the status is read, the instrument sends the normal data string the next time it addressed to talk.

4. The SRQ status information contains several bytes. These bytes assume the decimal value previously set by the SRQ mode command.

5. After step 4, the Model 228 goes through the autocalibration cycle and displays the CAL message.

6. After step 6, the Model 228 is ready for operation.

NOTE The self test (J) over the bus, performs the exact same sequence as Program 6. The messages are also the same. Refer to paragraph 3.11.6.

4.5.14 EOI and Bus Hold-Off Modes (K)

The K command controls whether the instrument sends the EOI command at the end of its data string: and whether busy activity is held off (through the NRFD line) until all commands sent to the instrument are internally processed once the instrument receives the X character. K command options include:

KO=Send EOI with last byte; hold off bus on X.

Kl=Do not send EOI with last byte; hold off bus on X.

K2=Send EOI with last byte; do not hold off bus on X.

HP-85 Program’ming Example-To output the status word

enter the following program into the HP-85:

NOTE After each line is entered, press the END LINE key.

4.5.13 Self Test (J)

The letter J is the command that programs the Model 228 to go through many of the testing routines that are automatically performed upon power up. When the J command is sent the following routines are performed:

1. All of the front panel LEDs turn on. This is a display test. The user can note inoperative display segments or individual LEDs by observing the front panel.

2. During the display test, the Model 228 performs a check on the RAM circuitry and a cyclic redundancy check (CRC) on the ROM circuitry. If a problem is found with either of these two tests, then the appropriate messages are displayed and the J byte in the status word is set.

3. After steps 1 and 2, the Model 228 displays the present

software level.

4. After step 3, the Model 228 displays the present primary

address.

K3=Send no EOI with last byte; do not hold off bus on X.

PROGRAM

10 REMOTE 711 Set up for remote operation. 20 CLEAR 7 30 OUTPUT 7ll;“UOX” 40 ENTER 711;A$ Obtain data string. 50 DISI’ A5 60 END

After the program is entered into the computer, press the HP-85 RUN key to run the program. After pressing the RUN key, the Model 228 outputs the status word. In this case, the status is transmitted to the controller with a prefix.

NOT REMOTE

COMMENT8

Clear the Model 228.

Output status word.

Display data string. End of program.

Figure 4-7. Error Status Word

427

TERMINATOR ICRIILFI -

-ISiNK IDFFI

- ISOURCE IOFFI -

-VSOURCE (OFF)--, ) 1 )

-VSlNK IDFFl-

1 1

228 D F G J

DISPLAY ID=O) VOLTS/AMPS

FUNCTION IF=01 STANDBY

PREFIX lG=O) BUFFER LOCATION OUTPUT

SELF TEST

[DEPENDENT ON TESTI

SEND EOI

SINGLE CYCLE MODE tP=O)

AUTORANGE IR=Ol

Figure 4-8. Status Word Format

Model 8573 Programmlng Example-To output the status word enter the following program into the IBM computer.

NOTE

Load the modified DECL.BAS file into the IBM

computer (see the Model 8573 Instruction

tianual) and add the following lines. After each

line is entered press the return key.

PROGRAM

10 NA$=“GPIBO”:CALL IBFIND

(NA$,BRDO%)

20 NA$=“DEVO”:CALL IBFIND

(NA!§,M228 % )

30 V% =ll:CALL IBPAD

(Mzz6%,V%)

40 V% =l:CALL IBSRE

(BRDO%;V%)

50 CMD$-“UOX”:CALL IBWRT

(M225%,cMD$)

60 RD$=SPACE(50):CALL IBRD

(M228%.RD$)

70 PRINT RD$ 80 V%=O:CALL IBONL

(BRDO%,V%)

90 CALL IBONL

(M228%,V%)

COMMENT8

Find the board descriptor. Find the instrument descriptor. Set primary address

to 11.

Send remote enable. Output status word.

Obtain data string.

Display data string.

Close the board file. Close the instrument

file.

ACSMMOOOOOOOO~ ACSMMOOOOOOOO~

SRO DISABLED IM=01 SRO DISABLED IM=01

PREVIOUSLY PREVIOUSLY

PROGRAMMED PROGRAMMED

VALUES OF VALUES OF

TRIGGER CT=61

STOP ON X

After the program is entered, press the F2 function key to run the program. After pressing the F2 key the Model 228 outputs the status word and it is displayed on the CRT.

Upon power up, or after the instrument receives a DCL or

SDC command, the KO mode is enabled.

The EOI line on the IEEE-488 bus provides a method to positively identify the last byte in a multi-byte tranfer se-

quence. Keep in mind that some controllers rely on EOI to terminate their input sequences. In this case, suppressing EOI

with the K command may cause the controller’s input sequence to hang up unless other terminator sequences are used.

The bus hold off mode allows the instrument to temporarily

hold up bus operation when it receives the X character until

it processes all commands sent in the command string. Keep

in mind that all bus operation will cease, not just activity associated with the Model 228. The advantage of this mode is that no bus commands will be missed while the instrument is processing commands previously received.

The hold off period depends on the commands being processed. Table 4-12 lists hold off times for a number of different

commands. Since a NRFD hold off is employed, the hand-

shake sequence for the X character is completed, and no bus

hang up occurs under these conditions.

MEMORY MEMORY LOCATION #I LOCATION #I

4-28

HP-g6 Programming Example-To program the instru-

ment for the K2 mode, enter the following statements into the HP-85:

Device-dependent commands are sent as a string of several ASCII

characters.

include:

Some examples of valid command strings

REMOTE

OUTPUT 7ll;‘KZX” (END LINE)

When the second statement is executed, the instrument will be

placed in the K2 mode. In this mode, EOI will still be transmitted at the end of the data string, but the bus hold-off mode will be disabled.

Model 8673 Programming

ment in the K2 mode, enter the following statements into the IBM computer:

V% =l:CALL IBSRE(BRDO%,V%) (return)

CMD$=“IUX”:CALL IBWRT(M228%,CMD$) (return)

The Model 228 will be placed in the K2 mode when the second statement is executed. The EOI mode will be enabled, but the bus hold off will be disabled.

711 (END LINE)

Example-To

place the instru-

Table 4-12. Hold OFF Times

Command

V. 1, B. W

Time to SRQ on Reedy

200msec

to SRQ on Ready.

FOX = Single command string. FOM2POR4X=Multiple command string. R7 X= Space is ignored.

Some examples of invalid command strings are:

@OX=Invalid command; @ is not a command.

D6X=Invalid command option; 6 is not an option of the D command.

The numbers after the command are each interpreted as a decimal integer. For example:

TOl.OX is interpreted as TlX

Figure 4-9 shows the front panel error messages used Model 228. The message in Figure 4-9A results from an illegal device-dependent command (IDDC), while the message in Figure 4-9B results from an illegal device-dependent command option (IDDCO). The no remote message in Figure 4-9C results from attempting to program the

it is not in the remote mode.

instrument when

by the

All other device dependent 175msec to SRQ on Ready. commands (A, C, D, etc.)

NOTE: Times are typical and very depending on the actual

commands and options sent.

4.6 FRONT PANEL ERROR MESSAGES

The process of programming the Model 228 involves the proper use of syntax. Syntax is defined as the orderly systematic arrangement of programming commands or languages. The Model 228 must receive value commands with the proper syntax or the instrument quence.

1. Ignore the entire command string in which the invalid command appears.

2. Set appropriate bits in the status byte.

3. Generate an SRQ if programmed to do so.

4. Display an appropriate front panel error message.

goes through the

following se-

(r-Liz--

[*p-&E-q

Figure 4-S. IEEE Display Error Message

4-29

4.6.1 IDDC Error

An IDDC emor results when the Model 228 receives an in-

valid command such as 5X. This command is invalid because no such letter exists in the instrument’s programming language.

HP-86 Programming Example-To demonstrate an IDDC error, enter the following statements into the HP-85:

REMOTE 711 (END LINE)

OUTPUT 7ll;“$X” (END LINE)

When the END LINE key is pressed the second time, the error message in Figure 4-BA is displayed on the Model 228 front panel for about one second. The instrument then returns to the previous mode.

Model 8573 Programming Example-

V% =l:CALL IBSRE(BRDO%,V%) (return)

CMD$-“R9X”:CALL IBWRTfM228%,CMD$) (return)

When the return key is pressed the second time, the error in Figure 4-88 is displayed for about one second. The instrument then returns to the previous mode.

4.6.3 No Remote Error

A front panel no remote error message is displayed if the Model 228 is not in the remote mode when it receives a command over the bus. If an attempt is made to program the instrument when it is not in the remote mode, the no remote message in Figure 4-K is displayed on the front panel for about one second.

Model 8573 Programming Example-To demonstrate an IDDC error, enter the following statements into the IBM computer:

V% -l:CALL IBSRE(BRDO%,V%) (return)

CMD$=“Q2X”:CALL IBWRT(M228%, CMD5) (return)

When the return key is pressed the second time, the error message in Figure 4-8A is displayed on the Model 228 front panel for about one second. The instrument then returns to the previous mode.

4.6.2 IDDCO Error

An illegal device-dependent command option (IDDCO)

results when the Model 228 receives an invalid command such as D7X. This command option is invalid because no option of 7 exists for the command D.

HP-86 Programming Example-To demonstrate an IDD-

CO error, enter the following statements into the HP-85:

REMOTE 711 (END LINE)

OUTPUT 7ll;“R9X” (END LINE)

HP-85 Programming Example-To make sure the instrument is not in the remote mode, enter the following into the HP-85:

LOCAL 7 (END LINE)

Now enter the following programming statement into the keyboard:

OUTPUT 7ll;“DlX” (END LINE)

When the statement is executed, the no remote error message in Figure 4-K is displayed on the front of the instrument for

about one second. The instrument then returns to the

previous mode.

Modal 8573 Programming Example-To make sure the instrument is not,in the remote mode, enter the following into the IBM computer:

CALL IBLOCfM228% )

Now enter the following programming statement into the kevboard:

V%=l:CALL IBSRE(BRDO%,V%) (return)

When the END LINE key is pmssed the second time, the error

message in Figure 4-8B is displayed for about one second. The When the statement is execute, the no remote error message

instrument then returns to the previous mode. in Figure 4-8C is displayed on the fr’ont panel of the instru-

ment for about one second. The instrument then returns to the previous mode.

4-30

SECTION 5

PERFORMANCE VERIFICATION

5.1 INTRODUCTION

Performance verification may be performed upon receipt of

the instrument to ensure that no damage or &adjustment has occurred during transit. Verification may also be performed whenever there is question of the instrument’s accuracy.

NOTE For instruments that are still under warranty (less than 12 months since date of shipment), whose performance falls outside specifications at any point, contact your Keithley representative or the factory.

5.2 ENVIRONMENTAL CONDITIONS

Verification should be performed at an ambient temperature of 18”-2&?°C and less than 70% relative humidity, unless otherwise indicated.

5.3 RECOMMENDED TEST EQUIPMENT

5.4 INITIAL CONDITIONS

The Model 228 must be turned on and allowed ten minutes for warm up. If the instrument has been subjected to extremes of temperature, allow sufficient time for internal temperature to reach normal operating conditions as specified in paragraph 5.2. Typically, it takes one hour to stabilize a unit that is 10°C (1&3°F) out of the specified range.

5.5 PERFORMANCE VERIFICATION PROCEDURE

Use the following procedure to verify the accuracy of the

Model 228. If the Model 228 is out of specification, check the test configuration. If the test configuration is properly set up, then check the test equipment’s calibration date. If the test equipment is in calibration, proceed to Section 7 Maintenance, unless the Model 228 is under warranty.

WARNING Verification should be performed by qualified personnel using accurate and

reliable test equipment.

Table 5-l lists all the test equipment required for verification. If alternate equipment is used, the alternate equipment

specifications must be at least as good as the specifications listed in Table 5-l.

Table 51. Recommended Test Equipment

Digital Multimeter lOO.OOmV f0.016% 197

(Current Shunt)

o.ln*0.02% o.orn f0.0256

5.5.1 Voltage Mode Verification (IV, IOV and IOOV)

1. Connect the Model 228 and the Model 197 as shown in Figure 5-l.

2. Set the Model 197 to the 2VDC range.

3. Program the Model 228 to output l.OCOV, lOOmA.

4. Verify the reading on the Model 197 to be within the limits listed in Table 5-2.

5. Set the Model 228 to standby.

6. Set the Model 197 to the 20VDC range.

7. Program the Model 228 to output lO.CW, lOOmA.

8. Verify the reading on the Model 197 to be within the limits listed in Table 5-2.

9. Set the Model 228 to standby.

10. Set the Model 197 to the 200VDC range.

11. Program the Model 228 to output lOO.OOV, lOOmA

12. Verify the reading to be within the limits listed in Table 5-2.

13. Set the Model 226 to standby.

14. Repeat steps 2 through 13 using negative output.

5-l

Table 5-2. Output Voltage Verification

Model 197

Model 228

Range

1V +l.OOOV, IOOmA

IOV +lO.OOV, IOOmA

1OOV +lOO.OV, lOOmA

1OV

1OOV

output

-l.OOOV, lOOmA

-lO.OOV, lOOmA

-lOO.OV, lOOmA

Allowable Readings

@m~C-28~C + ,998 to + 1.002 +9.9e to + 10.02

+99.8 to + 100.2

- ,996 to - 1.002

-9.98 to - 10.02

-99.6 to - 100.2

“ECT

BOARD

7. Program the Model to output l.OCOA, 1V.

8. Verify the reading on the Model 197 is within the limits listed in Table 5-3.

9. Set the

10. Set the Model 197 to the 2OOmVDC range.

11. Program the Model 228 to output lO.WA, 1V.

12. Verify the reading on the Model 197 is within the limits listed in Table 5-3.

13. Set the

14. Repeat

Model 228 to standby.

Model 228 to standby. steps 2 through 13 with

negative output.

Table 5-3. Output Current Verification

Model 197

Model 228 Allowable Readings

Range lOOmA +.lOOOA, 1V +.0998to +.1002

1 A +l.OOOA, 1V +.998 to +1.002

10 A +lO.OOA, IV +9.94 to +10.06

lOOmA -.lOOOA, 1V -.0998to -.1002

1 A -l.OOOA, IV

output @ WC-28T

A -1O.OOA. IV

-.998 to -1.002

-9.94 to -10.06

Figure 5-1. Output Voltage Configuration

5.5.2 Output Current Verification

1. Set up the configuration shown in Figure 5-2.

2. Set the Model 197 to the 200mVDC range.

3. Program the Model 228 to output lOOmA 1V.

4. Verify the reading on the Model 197 is within the limits listed in Table 5-3.

5. Set the Model 228 to standby.

6. Set the Model 197 to the 200mVDC range.

MODEL 2575

CURRENT

Figure 5-2. Outwt Current Configuration

SHUNT

MODEL 197

6-2

SECTION 6

THEORY OF OPERATION

6.1 INTRODUCTION

This section contains an overall functional description of the

Model 228. The information is supported by simplified schematics and block diagrams to aid in understanding of this complex instrument. This section is divided into the following parts:

1. The switching power supply and linear power supply are described in paragraph 6.2.

2. The analog board and the A/D converter are described in paragraph 6.3.

3. The digital board is described in paragraph 6.4.

4. The display board is described in paragraph 6.5.

Detailed schematics and component layout drawings are located at the end of the instruction manual. Figure 6-l is a block diagram of the Model 228.

L----l I

6.2 POWER SUPPLY

The power supply is comprised of two power supplies: the

switching power supply and the linear power supply. The switching circuitry of the switching power supply is powered by the linear supply and the linear supply is powered by the AC line. The switching power supply is designed for lower power consumption and to reduce the physical size of the

transformers.

6.2.1 Linear Power Supply

The linear supply is comprised of T305, CR308, CR309,

CR310, VR303, VR304 and associated resistors and capacitors. The AC line voltage is applied to the primary of T305 through S302 and 5301. CR308 and CR309 rectify the signal of T305’s secondary. VR303 and VR304 regulate

SWITCHING

POWER SVPPLY

ANALOG CONTROL

\ /

OUTPUT

OUTPUT VOLTAGE/

CURRENT SENSlNG

A/D CONVERTER

Figure 6-I. Model 228 Block Diagram

INTERNAL STATUS

6-l

*voltage for the positive and negative five volt supplies. Capacitors C334, C336, 035 and C343 filter the supplies. Capacitor C333 filters the +9V digital supply. abruptly turned off at lW,CCO times a second.

+175V and -175V. R309, R310, C306 and C308 limit the

voltage spikes that are caused when current through T303 is

6.2.2 Switching Power Supply

The switching power supply is a push-pull type supply

operating at a constant frequency of 50kHz with a variable

duty cycle. The description of the switching power supply is

divided into three sections; Primary DC supply, Switching

Circuitry and Filtering.

Primary DC Supply

The AC line voltage is applied to RT301 and CR301 through

5301 and F301. CR301, C304, C305, C340 and C341 convert

the AC line voltage into DC voltage. RT301, negative

temperature coefficient thermistor, limits the turn on current.

Inductors (chokes) L310 and L311 along with C304, C305,

C340 and C341 form pie filters that attenuate 50kHz swit-

ching noise from getting into the power line.

A safety circuit (crowbar) comprised of Q301, VR301 and

R304 open the line fuse (F302) if the improper line voltage is

applied. R302 and R303 are used as bleeder resistors to

discharge the 350V that is charged on C304, C305, C340 and

~341 after power is turned off.

Switching Circuit IJ302 is the heart of the switching circuitry. U302 has in inter-

nal clock and reference. This component controls the 50kHz pulses that determine the amount of energy that is produced by the supply. The two outputs of II302 (pin 11 and pin 8) are buffered by U303 and U304 before driving T302. T302 in turn

drives the power switching FETs Q302 and Q303. The +15V supply is sensed (R327, R329, R331 and U302) and held at 15V by varying the duty cycle of the power switching FETs, Q302 and Q303.

Filtering

The current on the secondary on transformer T303 is rectified

and filtered before it is used by the Model 228 circuitry. The rectifiers are CR303, CR304, CR305, CR306 and CR307. R304, C309, R315, C318 limit the voltage spikes that are caused when current through T303 is abruptly turned off lW,OCO times a second. C310, C311, C319 and C320 along with L301, L.304, L306 and L308 comprise low pass filter which allows the outputs to be regulated.

L302, L303, L305, L307, L309, C314, C323, C324 and C315 attenuate the switching noise and ripple voltage on the output. R316, R317, R318 and R319 provide a minimum load to

the power supply secondaries. The minimum load is required to prevent the supply from oscillating or losing regulation.

6.3 ANALOG CONTROL

U103A supplies a signal which drives the output in the polari-

ty programmed by the operator. Comparators UlO6 through UlO9 supply a signal which balances the signal from U103A when the output approaches a programmed limit. The

*voltage limits are set with a zero to +l.OlOV signal from the voltage DAC (Vdac) UllO. The acronymn DAC means Digital to Analog Converter. The *current limits are set with a zero to +l.OlOV signal from the current DAC (Idac) Ulll.

The positive limits (IJ107 and U109) are sensed by comparing

the (DAC voltage) with the (feedback voltage) and attempting to keep feedback voltage less than or equal to the DAC voltage. The negative limits NJ106 and UlOg) are sensed by comparing the (DAC voltage ffeedback voltage) with ground and attempting to keep (DAC voltage +feedback voltagekgreater than or equal to zero or -(feedback voltage) less than or equal to (DAC voltage). Refer to Figures 6-3 and 6-4.

The soft start of the supply is controlled by C332 and R334. The supply is disabled by shorting C334 with Q304. The disable signal may come from one of two places: the analog board or the curre@ sense circuit (T304, R312, R313, R314, R320, C317, C328, CR302 and U301). The signal disables the supply for a short time when the FET (4302 and Q303) current is too high.

4302 and 4303 are isolated from the secondary by T302 and act as switches. Only one FET is on at a time. This switches

the voltage on T303 pin 2 (referenced to pin 11) between the

6-2

Ull2 scales the output voltage for -1.OlOV to +l.OlOV for

the A/D converter and the voltage limit comparators IJ108

and U109.

U113 (X10 amplifier) scales the output current for -1.OlOV

to + l.OlOV for the A/D converter and the current limit corn-

parators U106 and U108. U115 senses which comparator

NJ106 through U109) is controlling the output for the

microprocessor.

VOLTAGE SENSING

SETTING DAC

OUTPUT

CURRENT SENSING

I ;

\ /

/ AMPLIFIER

OUTPUT

AMPLIFIER

CURRENT

SETTING DAC

POLARlTY SELECT

OUTPUT VOLTAGE OUTPUTCURRENT

DAC VOLTAGES

SUPPL,’ VOLTAGES

HEAT SINK TEMPERATURES

Figure 6-2. Analog Control

MULTIPLEXER

-7

AID CONVERTER

-I COMPARATOR \I

Figure 6-3. A/D Converter

I I

OUTPUT

RELAY

-r

X10 AMPLIFIER

f "OUT

FULL SCALE

VOLTAGE FEEDBACK

Figure 6-4. Voltage Sensing

The output amplifier is a two stage voltage amplifier and a

three stage current amplifier (Refer to Figure 6-5). Overall voltage gain is set by R114/R109 at 18. R115 and Cl02 decrease the gain to 5 at higher frequencies to maintain control loop stability. R107, ClOl, Rll3 and Cl04 also aid stability from oscillation.

VR104 and VR105 limit the maximum current through QllO/Qlll and Qll5/Qll6 to prevent secondary break-

down when attempting to source more than about 1.5A while the instrument is programmed for sink only. CR116 and CR118 allow the output to source 1OA at low voltages without shorting the higher voltage supplies when the output exceeds the low voltage supplies (base-collector diode of 4112 through Qll4, Qll7 and Qll9).

CR117 and CR119 act much the same as CR116 and CR118 except when the Model 228 is programmed for sink only.

Sink only removes the f 15V at 10A supplies from the output using relays K301 and K302. Cl03 and R153 improve stability from oscillation when very large capacitors load the output. This is done by bypassing the pole caused by the output

resistance and load capacitor.

The A/D converter (U122) is a single chip 4% digit A/D con-

verter. The clock which is provided by U123 allows 2% times

the normal frequency for this chip to increase the conversion

rate to about six per second. The one volt reference is provid-

ed from a 6.2V zener that is internal to the current DAC

(Ulll). Refer to Figure 6-6.

Multiplexers U117 and U119 switch the input of the A/D con-

verter to the signal to be measured. R162, Rlbl, R127 and R128 divide the power supply sense voltage down to below the -12V capability of the A/D converter.

EXTERNAL CURRENT

MONITOR OUPUT

CURRENT FEEDBACK

t * IV FULL SCALE,

Figure 6-6. Current Sensing

R120 and CR121 are temperature sensors that are mounted

to the output amplifier heat sinks and provide lpA/“Kelvin.

With R151 and R158 (1kR resistors), lmV/ “Kelvin (296mV at

23’C) is available to the A/D converter. There are three temperatures that are of key importance to the Model 228:

-5O”C-This temperature displayed on the front panel in-

dicates the sensors are unplugged or broken.

+90”C-This temperature displayed on the front panel in-

dicates that the instrument should switch to the sink only pro-

gram to reduce output transistor temperature.

+lOO%-This temperature message on the front panel indicates that the power supply should be disabled since this temperature should never be reached during normal opera-

tion.

Data is taken from the A/D converter by ANDing the

“BUSY” and “CLOCK” signals. This provides 10,001 + (zero

to 20,000 pulses) for zero volts to two volts.

The analog and digital section are isolated from each other by opto-isolators NJ419 through U422) and also by seperate power supplies. Data from analog circuits is shifted serially

out of U409 into U114, U104, U103, UlO2 and UlOl shift registers. When U114 pin 12 (Status Select) is low data from the A/D converter (pulses) pass through U120 (and Ull6G and U422) to U409 where they are counted. When status select is high, strobe pulses from U409 shift data from U120 into U409.

6-4

The A/D starts a conversion when its run/hold line is pulsed

(signal from U114 pin 14). Normally, this happens six times per second. However, the A/D converter may be stopped during self test, IEEE-488 communications or when the output is being updated often (e.g. the memory function is used with very fast dwell times).

POSITIVE OUTPUT

CURRENT

The analog reset circuitry is comprised of R164, CR115, Cl28

and U124. When line power is switched off or interrupted this circuitry detects the interuption. The switching power supply is temporarily turned off (U124B) and the output of the Model 228 is switched to an open circuit by disabling the cur-

‘rent shunt relays (K104, K105 and KlO6). A flip-flop formed

by U121B and Ul2lC holds the reset condition until cleared

by the microprocessor (pulse on the strobe line).

CURRENT GAIN

EMITKR FOLLOWER

NEGATIVE

OUTPUT

CURRENT

VOLTAGE

Figure 6-6. Output Amplifier

6-5

6.4 DIGITAL BOARD

The Model 228 is controlled by the internal microprocessor. This section briefly describes the operation of the various sections of the microprocessor and associated digital circuitry. For more complete circuit details refer to schematic 228-146 at the end of this manual.

The microcomputer centers around the 6809 high density N-MOS microprocessor (U410). It is an eight bit microprocessor with direct addressing up to 64k bytes of memory. Timing for the microprocessor is accomplished by the use of Y401; a 4MHz crystal. Internally this frequency is divided down by four to obtain a bus operating frequency of 1MHz.

The software for the microprocessor is stored in EPROMs U413 and U414. The software revision level is displayed in the power up sequence. U412 and U411 are CMOS Random Access Memory (RAM). Partial address decoding is used in this system. The function selected is determined by the state of All, A12, A13, Al4 and Al5 address lines. These address lines determine which is selected by the decoders. The decoders are U403, U407, U404, and U102. Only one of the following devices (ROM, RAM, VIA, etc) will have access to the data bus at any one time.

The digital circuitry is optically isolated from the analog cir-

cuitry by U419 through U422 and the associated circuitry.

The output signals consist of SHIFT, DATA, STROBE and

STATUS. These signal lines permit serial communication to the analog circuitry.

The battery back up circuitry turns on when power is turned off. The battery power is connected to all the RAM circuitry. This retains the data in the buffer locations when power is shut down. When power is lost, transistors Q402 and 4401 turn off and the battery voltage is routed through diode CR402 to the RAM circuitry.

U415, U416 and U408 comprise the IEEE-466 interface bus circuitry. U415 is the main interface chip. U408 and U416 are the bus transceivers.

U423 (on the digital board) detects loss of power and resets the microprocessor. This prevents writing to the battery backed up memory of U411 and U412.

6.5 DISPLAY BOARD

The display information is sent through display latch U417

(SE1 through SE7). The information is updated at a 1kHz

rate. This means each digit is begins by presenting new segment information to display latch and sending a clock pulse on I’AO. The clock pulse to U204 shifts a digit enable bit to the next digit to be enabled. Every 12 times the display is updated, a digit enable bit is generated at PA1 and goes to the data input of the shift

of the display digits. The appropriate LEDs are also activtaed. Refer to the block diagram of Figure 6-7.

When each of the first 6 digits are selected, a row of switches are also selected. The row (Sl through S5 is then read by the

microprocessor through U409 inputs PA3-I’A7).

for lmsec. Each update

The external trigger circuitry consists of U409, CR401, R401,

R402 and R403. U409 is protected by the circuit formed by CR401, R401 through R403.

= SEGMENT _

DATA - LEDS

LEDS

fip

KEY

DATA -- -/-

-- J- J-

--/- -- -_/- -/- -/-

Figure 6-7. Display and Keyboard

DIGIT SELECT

6-716-E

Keithley 228 Service manual

Specifications and Main Features

Frequently Asked Questions

User Manual