Keithley 617 Service manual

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Model 617

Programmable Electrometer

Instruction Manual

Contains Operating and Servicing Information

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.

Keithley Instruments, Inc. warrants the following items for 90 days from the date of shipment: probes, cables, rechargeable batteries, diskettes, and documentation.

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 product, transportation prepaid, to the indicated service facility. Repairs will be made and the product returned, transportation prepaid. Repaired or replaced 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 product modification without Keithley’s express written consent, or misuse of

any product or part. This warranty also does not apply to fuses, software, non-rechargeable batteries, damage from battery leakage, or

problems arising from normal wear or failure to follow instructions.

THIS WARRANTY IS IN LIEU OF ALL OTHER WARRANTIES, EXPRESSED OR IMPLIED, INCLUDING ANY IMPLIED WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. THE REMEDIES PROVIDED HEREIN ARE BUYER’S SOLE AND EXCLUSIVE REMEDIES.

NEITHIZR KEITHLEY INSTRUMBNTS, INC. NOR ANY OF ITS EMPLOYEES SHALL BE LIABLE FOR ANY DIRECT, INDIRECT, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OF ITS INSTRUMENTS AND

SOmWARE EVEN IF KEITHLEY INSTRUMENTS, INC., HAS BEEN ADVISED IN ADVANCE OF THE POSSIBILITY OF SUCH DAMAGES. SUCH EXCLUDED DAMAGES SHALL INCLUDE, BUT ARE NOT LIMITED TO: COSTS OF REMOVAL AND INSTALLATION, LOSSES SUSTAINED AS THE RESULT OF INJURY TO ANY PERSON, OR DAMAGE TO PROPERTY.

Keithley Instruments, Inc. - 28775 Aurora Road - Cleveland, OH 44139 - 216-248-0400 - Fax: 216-24X-6168 - http://www.keithley.com

Model 617 Programmable Electrometer

Instruction Manual

0 1984, Keithley Instruments, Inc.

Test Instrumentation Group

Cleveland, Ohio, U.S.A.

Document Number: 617-901-01 Rev. C

SPECIFICATIONS

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

1.10

1.11

1.12

2.1

2.2

2.3

2.4

2.4.1

2.4.2

2.4.3

2.5

2.5.1

2.5.2

2.5.3

2.6

2.6.1

2.6.2

2.6.3

2.7

2.7.1

2.7.2

2.7.3

2.7.4

2.7.5

2.7.6

2.7.7

2.7.8

2.8

2.8.1

2.8.2

2.9

2.9.1

2.9.2

2.10

2.10.1

2.10.2

2.10.3

2.10.4

2.10.5

2.10.6

Introduction

Features ...................

Warranty Information ManualAddenda.. Safety Symbols and Terms Specifications Using this Instruction Manual Unpacking and Inspection Getting Started Preparation for Use Repacking for Shipment. Accessories

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SECTION 2-OPERATION

Introduction Power Up Procedure Power Up Self Test and Display Messages Front Panel Familiarization

Controls Display and Indicators TiltBan

Front Panel Programs

IEEE-488 Address Exponent Mode (Alpha or Numeric) Calibration

Rear Panel Familiarization.

Connectors and Terminals.

V,RGUARDSwitch

LineFuse..

Basic Measurement Techniques.

Warm Up Period Input Connections Making Voltage Measurements. Guarded Operation Making Current Measurements. Making Charge Measurements Resistance Measurements Using the Ohms Function As A Current Source

Using the Voltage Source

Basic Operating Procedure V/I Resistance Measurements

Analog Outputs

2v Analog Output PreampOut

Using External Feedback

Electrometer Input Circuitry

Shielded Fixture Construction External Feedback Procedure. Non-Standard Coulombs Ranges Logarithmic Currents Non-Decade Current Gains

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....... 2-2

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....... 2-7

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.. ...

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...... 2-17

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2-l 2-l 2-l

2-2 2-4 2-4 2-4 2-4 2-5 2-5 2-5 2-5 2-7 2-7

2-7 2-8

2-E Z-10 2-11 2-13 2-15 2-16 2-17

2-17 2-19 2-19 2-19 2-22 2-22 2-22 2-23 2-24 2-24 2-2.5

2.11

2.11.1

2.11.2

2.12

2.13

2.13.1

2.13.2

2.13.3

2.14

2.14.1

2.14.2

2.14.3

2.14.4

2.14.5

2.14.6

2.14.7

2.14.8

2.15

Using Zero Correct and Baseline Suppression

Zero Correct and Zero Check

Using Suppression ......................

DataStorage .............................

External Triggering. .......................

External Trigger ........................

Meter Complete ........................

Triggering Example .....................

Measurement Considerations ...............

GroundLoops

Electrostatic Interference .................

Thermal EMFs .........................

RF1 ...................................

Leakage Resistance Effects ................

Input Capacitance Effects. ................

Source Resistance .......................

Source Capacitance .....................

Engineering Units Conversion ...............

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SECTION 3-IEEE-488 PROGRAMMING

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......

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.......

3.1

3.2

3.3

3.3.1

3.3.2

3.3.3

3.4

3.4.1

3.4.2

3.4.3

3.4.4

3.4.5

3.5

3.4

3.6.1

3.6.2

3.6.3

3.7

3.7.1

3.7.2

3.7.3

3.7.4

3.8

3.8.1

3.8.2

3.8.3

3.8.4

3.9

3.9.1

3.9.2

3.9.3

3.9.4

3.9.5

3.9.6

3.9.7

3.9.8

3.10

Introduction

BusDescription

IEEE-488BUSLINES ..........................................................................

DataLines..

BusManagementLines ...........................................

HandshakeLines

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

UniIineCommands

UniversalCommands ........................................................................

AddressedCommands .......................................................................

Unaddressedcommands .....................................................................

Device-DependentCommands

CommandCodes.. ...........................................................................

CommandSequences ..........................................................................

AddressedCommandSequence

UniversalCommandSequence

Device-DependentCommandSequence

Hardwareconsiderations.. ....................................................................

Typical Controlled Systems. ..................................................................

BusConnections ............................................................................

PrimaryAddressProgramming ...............................................................

Talk-OnlyMode

Softwareconsiderations

Controller Handler Software,

Interface BASIC Programming Statements

Interface Function Codes

IEEECommandGroups

General Bus Command Programming

REN(RemoteEnable) .......................................................................

IFC(InterfaceClear)

LLO(LocalLockout) .......................................................

GTL(GoToLocaI)

DCL(DeviceClear) ........................................................................

SDC (Selective Device Clear)

GET(GroupExecuteTrigger). ...............................................................

Serial Polling (WE, SPD)

Device-Dependent Command Programming

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................................................... 3-10

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

..r

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............................. 3-16

.._ .............. 3-9

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.._

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

3-2 3-3

3-3 3-4 3-4 3-5 3-5 3-5 3-5 3-5 3-7 3-7 3-7 3-7 3-8 3-9

3-10 3-10

3-12 3-12

3-12 3-13 3-14 3-14

3-14

3-15

3-16

3-17

3.10.1

3.10.2

3.10.3

3.10.4

3.10.5

3.10.6

3.10.7

3.10.8

3.10.9

3.10.10

3.10.11

3.10.12

3.10.13

3.10.14

3.10.15

3.10.16

3.10.17

3.10.18

3.11

3.11.1

3.11.2

3.11.3

3.12

Execute(X) ...... .................

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

Range(R) Zero Correct and Zero Check (Z and C)

Baseline Suppression (N) .............

Display Mode CD).

Reading Mode (B) ............ ......

Data Store Mode ...................

Voltage Source Value (V) .............

Voltage Source Operate (0) ..........

Calibration Value (A). ...............

Non-Volatile Memory Storage (L) .....

Data Format (G) ....................

Trigger Mode (T) ...................

SRQ Mode (M) and Status Byte Format

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

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

Status(u) .........................

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

BusError.. ........................

NumberError ......................

Trigger Overrun Error ...............

Bus Data Transmission Times ...........

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

SECTION 4-APPLICATIONS

3-18

3-20

3-21

3-22

3-23

3-24

3-25

3-26

3-27

3-28

3-30

3-31

3-34

3-35

3-36

4.1

4.2

4.3

4.4

4.5

4.6

4.7

4.8

4.9

4.10

5.1

5.2

5.3

5.4

5.5

5.5.1

5.5.2

5.5.3

5.5.4

5.5.5

5.5.6

5.5.7

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

Insulation Resistance Measurements.

HighImpedanceVoItmeter

Low-Level Leakage Current Measurements DiodeCharacterization CapacitorLeakageMeasurements CapacitanceMeasurement Voltage Coefficients of High-Megohm Resistors

Static Charge Detection ........................................................

Using the Model 617 with External Voltage Sources

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SECTION 5-PERFORMANCE VERIFICATION

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

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

Initial Conditions ..........................

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

Verification Procedure ......................

Input Current Verification .................

Amps Verification .......................

Coulombs Verification. ...................

Volts Verification ........................

Ohms Verification .......................

Ohms Verification (200M0 and Gfl Ranges)

Voltage Source Verification. ...............

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4-l 4-l 4-5 4-5 4-7 4-8

4-E 4-10 4-12 4-12

5-l

5-2

5-2 5-3 5-5 5-6 5-6 5-8

iii

SECTION 6-THEORY OF OPERATION

6.1

6.2

6.3

6.3.1

6.3.2

6.3.3

6.3.4

6.3.5

6.4

6.4.1

6.4.2

6.4.3

6.5

6.6

6.6.1

6.6.2

6.6.3

6.6.4

6.6.5

6.6.6

6.7

6.6

7.1

7.2

7.3

7.3.1

7.3.2

7.4

7.4.1

7.4.2

7.4.3

7.4.4

7.4.5

7.4.6

7.4.7

7.4.8

7.4.9

7.4.10

7.4.11

7.4.12

7.4.13

7.4.14

7.4.15

7.4.16

7.5

7.6

7.7

7.7.1

7.7.2

7.7.3

7.7.4

7.7.5

7.7.6

Introduction Overall Functional Description Input Preamplifier

Input stage ......................

Gain Stage. ......................

Output stage. ....................

Ohms Voltage Source

Zero Check ......................

Additional Signal Conditioning

Ranging Amplifier ................

Multiplexer and Buffer Amplifier ....

- 2V Reference Source. ............

A/D Converter. Digital Circuitry

Microcomputer. ..................

Memory Elements. ................

Device Selection ..................

IEEE-486 Bus .....................

Input/Output Circuitry ............

Display Circuitry .................

Voltage source Power Supplies

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SECTION 7-MAINTENANCE

Introduction..

LineVoltageSelection

FuseReplacement

Lim Fuse .................................................................................

COMFuse ................................................................................

Calibration

Recommended Calibration Equipment. ........................................................

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

WarmUpPeriod ..........................................................................

CalibrationJumper

Front Panel Calibration .....................................................................

IEEE-488 Bus Calibration. ...................................................................

Calibration Sequence .......................................................................

InputOffsetAdjustment ....................................................................

InputCurrentAdjustment ...................................................................

Pemxnent Storage of Calibration Parameters

AmpsCalibration.. .......................................................................

Coulombs Calibration ...................................................................

VoltsCalibration.. ........................................................................

OhmsCalibration .........................................................................

Voltage Source Calibration ..................................................................

Additional Calibration Points ................................................................

Special Handling of Static-Sensitive Devices Disassembly Instructions Troubleshooting

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

PowerUpSelfTest .........................................................................

SelfDiagnosticProgram ....................................................................

PowerSupplyChecks ......................................................................

RelayConfiguration ........................................................................

Ranging Amplifier Gain Configuration ........................................................

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6-l

6-1 6-l 6-3 6-3 6-3 6-6 6-7 6-7 6-7 6-8 6-9

6-9 6-11 6-11

6-11 6-u

6-11 6-12 6-12 6-13 6-14

7-l

7-1

7-2

7-Z

7-2

7-2 7-3 7-3 7-3 7-3 7-4 7-5 7-5 7-s 7-6 7-4 7-7 7-8

7-a 7-10 7-10 7-U 7-12 7-12 7-12 7-14 7-14

7-14 7-15 7-15

7.7.7

7.7.8

7.7.9

7.7.10

7.7.11

7.8

7.9

A/DConverterandDisplay .................................

Input and Ranging Amplifiers

DigitalCircuitry.. .................................................

Display Board

VoltageSource ..............................................................

InputStageBalancingProcedure Handling and Cleaning Precautions

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SECTION 8--REPLACEABLE PARTS

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... 7-16

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... 7.17

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7.17

7-17 7-17 7-17 7-18

8.1

8.2 a.3 a.4 a.5

8.6

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

Electrical Parts Lists Mechanical Parts Ordering Information Factory Service.. Component Layout Drawings and Schematic Diagrams

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......

8-l 8-l 8-l 8-l 8-l 8-l

LIST OF ILLUSTRATIONS

2-l 2-2 2-3 2-4 2-5 2-6 2-7 2-a 2-9 2-10 2-11 Z-12 2-13 2-14 2-15 2-16 2-17 2-18 2-19 2-20 2-21 2-22 2-23 2-24 2-25 2-26 2-27 2-28 2-29

Model617FrontPanel..........................................

Model617RearPanel Input Connector Configuration Connections For Voltage Measurements

Meter Loading Considerations Unguarded Circuit

GuardedCircuit Guarded Input Connections CurrentMeasurements Voltage Burden Considerations. Coulombs Connections Resistance Measurement Connections Voltage Source Connections V/l Resistance Measurement Connections Typical 2V Analog Output Connections Typical Preamp Out Connections. Electrometer Input Circuitry (AmpsMode) Shielded Fixture Construction

“Transdiode” Logarithmic Current Configuration Non-Decade Current Gains Equivalent Input Impedance with Zero Check Enabled. External Trigger Pulse Specifications Meter Complete Pulse Specifications Exlemal Triggering Example Multiple Ground Points Create Ground Loop Eliminating Ground Loops Leakage Resistance Effects Input Capacitance Effects. Simplified Model of Source Resistance and Source Capacitance Effects

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2-2 2-7

2-8

2-9

2-10

2-13 2-13 2-14 2-16 2-17 2-18

2-31 2-33

2-34 2-34

3-l IEEE Bus Configuration 3-2 3-3 3-4 3-5 3-6 3-7 617 Rear Panel IEEE Connector. 3-B Contact Assignments 3-9 General Data Format 3-10 SRQ Mask and Status Byte Format. 3-11 UO Status Word and Default Values. 3-12 3-13 U2 Status (Data Condition) Format

IEEE Handshake Sequence. Commands Groups System Types IEEE-488 Connector IEEE-488 Connections

Ul Status (Error Condition) Format

.......

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

4-9 4-10 4-11 4-12

Insulation Resistance Measurement (Ungaurded)

..........

Insulation Resistance Measurement (Guarded) ............

Insuiation Resistance Measurement Using V/I Ohms Mode.

Measuring High Impedance Gate-Source Voltage ..........

Leakage Current Measurement .........................

Diode Characterization ...............................

DiodeCurves.. .....................................

Capacitor Leakage Tests

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

Capacitor Measurement. ..............................

Configuration for Voltage Coefficient Studies ...........

Farady Cup Construction .............................

Using the Model 617 with an External High Voltage Source

......

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

6-l 6-2 6-3

b-4 b-5 6-b

6-7 6-8 6-9

6-10

6-11

6-12 b-13

b-14

b-15

6-16

Test Fixture Construction

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

Connections for Amps Verification (200nA-2mA Ranges) ...........

Connections for Amps Verification (2pA-20nA Ranges) ............

Connections for Coulombs Verification ..........................

Connections for Volts Verification

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

Connections for Ohms Verification (2kQ-20MQ Ranges) ............

Connections for Ohms Verification (200MR. 2G0 and 20Gfl Ranges).

Input Impedance Verification ..................................

Connections for Voltage Source Verification ......................

Overall Block Diagram ............................

Basic Configuration Electrometer Preamplifier

.........

Electrometer Preamplifier Configuration ..............

Simplified Schematic of Input Stage

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

GainStage .......................................

Output Stage Configuration (Volts and Ohms) .........

Output Stage Configuration (Amps and Coulombs)

.....

Ohms Voltage Source Simplified Schematic ...........

Zero Check Configuration (Volts and Ohms) ..........

Zero Check Configuration (Amps and Coulombs) ......

Simplified Schematic of Ranging Amplifier ............

Multiplexer and Buffer

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

Multiplexer Phases ...............................

-2V Reference Source.

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

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

Simplified Schematic of Voltage Source Output Stage ...

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.., ..,

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

6-2 6-3 b-4

b-5

6-5 6-5

6-b

b-6 b-7

6-7

b-8

6-8 6-9 6-9

b-10

6-13

7-l 7-2 7-3 7-4 7-5

7-6 7-7 7-8 7-9 7-10 7-11

Test Fixture Construction .......................................

Calibration Jumper Location .....................................

Input Offset Adjustment Locations.

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Connections for Amps Calibration (20pA Range) ....................

Connections for Amps Calibration (20nA. 20/rA and 20mA Ranges)

Connections for Coulombs Calibration ............................

Connections for Volts Calibration ................................

Connections for Ohms Calibration (20GQ and 2OOMO Ranges) .........

Connections for Ohms Calibration (2Ok%ZOMQ) Connections for Voltage Source Calibration

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Model617ExplodedView .......................................

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7-l 7-3

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

7-9 7-10 7-10 7-13

vii

8-l Electrometer Board, Component Location Drawing. g-2 8-3

Mother Board, Component Location Drawing

Display Board, Component Location Drawing 8-4 Electrometer Board, Schematic Diagram 8-5

Mother Board, Schematic Diagram. 8-6 Display Board, Schematic Diagram

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8-11

g-13 8-17 8-19

8-21 8-27

. .

LIST OF TABLES

2-l 2-2 2-3 2-4 2-5 2-6 2-7 2-8 2-9 2-10

2-11

3-l 3-2 3-3

3-4

3-5

3-6 3-7 3-a 3-9 3-10

3-11

3-12

3-13 3-14 3-15

Display Error Messages .................................

Front Panel Program Messages

Typical Display Exponent Values ................

Ohms Function Current Output Values

Typical 2V Analog Output Values ........................

Full Range PREAMP OUT V&es ......

Data Store Reading Rates ...........

Voltage and Percent Error For Various Time Constants Minimum Recommended Source Resistance Values in Amps. ..

Engineering Units Conversion ..................

Equivalent Voltage Sensitivity of 617 Amps Ranges

IEEE-488 Bus Command Summary. .........................

Hexadecimal and Decimal Command Codes Typical Addressed Command Sequence

Typical Device-Dependent Command Sequence.

IEEE Contact Designations ................................

BASIC Statements Necessary to Send Bus Commands

Model 617Interface Function Codes. ........................

IEEE Command Groups. General Bus Commands and Associated BASIC Statements Default Conditions.

Device-Dependent Command Summary

Range Command Summary ...............................

SRQ (M) Command Parameters ............................

Bus Hold-Off Times

Typical Bus Times For Various Functions and Trigger Modes

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3-4

3-5 3-7 3-7

3-9

3-11 3-12 3-13 3-13 3-15

3-19 3-21

3-28 3-31 3-36

4-l

5-l

5-2 5-3 5-4 5-5 5-6

6-l

Diode Currents and Voltages.

Recommended Test Equipment for Performance Verification Limits for A mps Verlflcatlon Limits for Volts Verification Limits for Ohms Verification (2kn-2OMa Ranges). Limits for Ohms Verification (2COMn, 2Gn and 2OOGil Ranges) Voltage Source Verification Limits

MemoryMapping .._......................................................

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4-7

5-l 5-3 5-5

5-b

5-7 5-8

6-11

7-1 7-2 7-3 7-4 7-5 7-6 7-7 7-8 7-9 7-10 7-11 7-12 7-13 7-14 7-15 7-16 7-17 7-18 7-19

8-l a-2 8-3

8-4

Line Voltage Selection (50-60Hz). LineFuseSelection

Recommended Calibration Equipment

AmpsCalibration .............................................................................

VoltsCalibration..

OhmsCalibration .............................................................................

StaticSensitiveDevices

Recommended Troubleshooting Equipment DiagnosticProgramPhase PowerSupplyChecks Relayconfiguration Ranging Amplifier Gains

A/DConverterChecks

Preamplifierchecks .......................................................................... 7-19

RangingAmplifierChecks.......................................................................7-1 9

DigitalCircuitryChecks

DisplayBoardChecks

VoltageSourceChecks

InputStageBalancing .........................................................................

MotherBoard,PartsList .......................... .... ...... .......... .. ....

DisplayBoard,PartsList

Electrometer Board, Parts List Mechanicall’artsList

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.......................................................................... 7-16

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........................................................................ 7-21

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..................................................................... 7-15

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7-l 7-2

7-2

7-7 7-8

7-9 7-11 7-14

7-15

7-17 7-18

7-20 7-20

7-21

8-2

8-6

8-7 S-10

SAFETY PRECAUTIONS

The following safety precautions should be observed before operating the Model 617

This instrument is intended for use by qualified personnel who recognize shock hazards and are familiar with the safety precautions required to avoid possible injury. Read over the manual carefully before operating this instrument.

Exercise extreme caution when a shock hazard is present at the instrument’s input. The American National Standards Institute (ANSI) states that a shock hazard exists when voltage levels greater than 30V rms or 42.4V peak are present. A good safety practice is to expect that a hazardous voltage is present in any unknown circuit before measuring.

Do not exceed 5oOV peak between input low and earth ground. Do not connect PREAh4P OUT, COM, OI 2V ANALOG OUTPUT to earth ground when floating input.

Inspect the test leads for possible wear, cracks or breaks before each use. If any defects are found, replace with test leads that have the same measure of safety as those supplied with the instrument.

For optimum safety do not touch the test leads or the instrument while power is applied to the circuit under test. Turn the power off and discharge all capacitors, before connecting or disconnecting the instrument.

Do not touch any object which could provide a current path to the common side of the circuit under test or power line (earth) ground. Always make measurements with dry hands while standing on a dry, insulated surface, capable of withstanding the voltage being measured.

Do not exceed the instrument’s maximum allowable input as defined in the specifications and operation section.

Safe operation and good measurement practice dictates use of an external resistor when necessary to limit input currents to less than 30mA.

SECTION 1

GENERAL INFORMATION

1.1 INTRODUCTION

The Keithley Model 617 Programmable Electrometer is a

highly sensitive instrument designed to measure voltage, current, charge, and resistance. Two forms of resistance measurements are included in the standard configuration: a constant current method, and a constant voltage method that uses a built in voltage source for greater sensitivity. The measuring range of the Model 617 is between 1OpV and 200V for voltage measurements, O.lfA and 2OmA in the current mode, O.ln and 200GO (up to 1OlQ using the built in voltage source), and lOfC and 20°C in the coulombs mode. The very high input impedance and extremely low input offset current allow accurate measurement in situations where many other instruments would have detrimental effects on the circuit being measured. A 4% digit display and standard IEEE-488 interface give the user easy access to instrument data.

1.2 FEATURES

Some important Model 617 features include:

l 4% Digit Display-An easy to read front panel LED display

includes a 4% digit mantissa plus a two-digit alpha or

numeric exponent.

l Autoranging-Included for all functions and ranges. l Digital Calibration-The instrument may be digitally

calibrated from the front panel or over the IEEE-488 bus.

l Zero Correct-A front panel zero correct control allows the

user to cancel any offsets.

l Baseline Suppression-One button suppression of a

baseline reading is available from the front panel or over the

IEEE-488 bus.

l One-shot Triggering-A front panel control for triggering

one-shot readings from the front panel is included.

l Isolated IOOV Voltage Source-A built in 1OOV scwrce is

isolated from the electrometer section. The voltage source is

programmable in 50mV steps.

l Selectable Guarding-A selectable driven cable guard is in-

cluded to optimize speed.

l Standard IEEE-488 Interface-The interface allows full bus

programmable operation of the Model 617.

l Analog Outputs-Both preamp and 2V full range analog

outputs are included on the rear panel.

l 100~Point Data Store-An internal buffer that can store

up to 100 readings is accessible from either the front panel or over the IEEE-488 bus.

l Minimum and maximum data points can be stored and are

accessible from the front panel or over the IEEE-488 bus.

1.3 WARRANG INFORMATION

Warranty information for your Model 617 may be found inside the front cover of this manual. Should you need to use the warranty, contact your Keithley representative or the factory for information on obtaining warranty service. Keithley Instruments, Inc. maintains service facilities in the United States, West Germany, Great Britain, France, the Netherlands, Switzerland, and Austria. Information concerning the operation, application, or service of your instrument may be obtained from the applications engineer at any of these locations.

1.4 MANUAL ADDENDA

Information concerning improvements or changes to the instrument which occur after the printing of this manual will be found on a” addendum sheet included with this manual. Please be sure that you read this information before attempting to operate or service your instrument.

1.5 SAFETY SYMBOLS AND TERMS

The following safety symbols and terns are used in this

manual and found on the instrument:

The A should refer to the operating instructions in this manual for

further details.

The WARNING heading as used in this manual explains dangers that might result in personal injury or death. Always

read the associated information very carefully before performing the indicated procedure.

The CAUTION heading used in this manual explains hazards

that could damage the instrument. Such damage may in-

validate the warranty.

symbol on the instrument indicates that the user

l-l

1.6 SPECIFICATIONS

The following items aw included with every Model 617 shipment:

Detailed Model 617 specifications may be found immedi-

ately preceding the table of contents of the manual. Note that accuracy specifications assume that the insinxnent has been properly zero corrected, as discussed in Section 2.

1.7 USING THIS INSTRUCTION MANUAL

This manual contains all the information necessary for you to

operate and service your Model 617 Programmable Elec-

trometer. The manual is divided into the following sections:

l Section 1 contains general information about your instru-

ment including that necessary to unpack the instrument and

get it operating as quickly as possible.

l Section 2 contains detailed operating information on how to

use the front panel controls and programs, make connec-

tions, and basic measuring techniques for each of the

available measuring functions.

l Information necessary to connect the Model 617 to the

IEEE-488 bus and program operating modes and functions from a controller is contained in Section 3.

l Typical applications for the Model 617 are included ‘in Sec-

tion 4. At least one application for each of the measuring

functions is included in this section.

l Performance verification procedures for the instrument

may be found in Section 5. This information will be helpful

if you wish to verify that the instrument is operating in

compliance with its stated specifications.

l Section 6 contains a complete description of operating

theory for the Model 617. Analog, digital, power supply,

and IEEE-488 interface operation is included.

l Should your instrument ever require servicing, refer to the

information located in Section 7. This section contains in-

formation on fuse replacement, line voltage selection,

calibration. and troubleshooting.

l Replacement parts may be ordered by using the information

contained in Section 8. Parts lists as well as schematic

diagrams and component layouts are located in this section.

1.8 UNPACKING AND INSPECTION

The Model 617 Programmable Electrometer was carefully in-

spected before shipment. Upon receiving the instrument,

carefully unpack all items from the shipping carton and check

for any obvious signs of physical damage that might have oc-

curred during shipment. Report any damage to the shipping

agent at once. Retain the original packing material in case

reshipment becomes necessary.

Model 617 Programmable Electrometer Model 617 Instruction Manual. Model 6011 Triaxial Input Cable Additional accessories as ordered

If an additional instruction manual is required, order the manual package (Keithley Part Number 617-901-W). The

manual package includes an instruction manual and all perti-

nent addenda.

1.9 GElTING STARTED

The Model 617 Programmable Electrometer is a highly

sophisticated instrument with many capabilities. Although there are a number of complex aspects about the instrument,

you can use the following procedure to get your instrument

up and running quickly. For more detailed information, you should consult the appropriate section of the manual.

Carefully unpack your instrument as described in paragraph 1.8.

Locate the power cord and plug it into the rear panel power jack. Plug the other end of the line cord into an appropriate power source. See Section 2 for more complete information.

Connect the supplied triaxial cable to the rear panel input jack. Make sure the rear panel V, R GUARD switch is in the off position.

Press in the front panel POWER switch to apply power to the instrument. The instrument will power up the the autorange volts mode with zero check enabled. Thus, you could simply connect the red and black input leads to a voltage source and take a voltage reading at this point by disabling zero check. Remember that the Model 617 measures DC voltages up to 2COV.

To change to a different measuring function, simply press the desired function button. For example, to measure resistance. simply press the OHMS button.

Complete detailed operation concerning Model 617 front panel operation may be found in Section 2. If you wish to control these functions over the IEEE-488 bus, consult Section 3.

1.10 PREPARATION FOR USE

Once the instrument is unpacked, it must be connected to an

appropriate power source as described below.

l-2

Line Power-The Model 617 is designed to operate from 105-125V or 210-250V power sources. A special power transformer may be installed for 90-1lOV and 195-235V ranges.

The factory set range is marked on the rear panel of the in-

strurnent. Note that the line plug is designed to mate with the

supplied 3-wire power cord.

CAUTION Do not attempt to operate the instrument on a supply voltage outside the indicated range, or instrument damage might occur.

Line Voltage Selection-The operating voltage of the instrument is internally selectable. Refer to Section 7 for the procedure to change or verify the line voltage setting,

Line Frequency-The Model 617 may be operated from either 50 or 60Hz power sources.

IEEE-488 Primary Address-If the Model 617 is to be programmed over the IEEE-488 bus, it must be set to the arrect primary address. The primary address is set to 27 at the factory, but it may be programmed from the front panel as described in Section 3.

1.11 REPACKING FOR SHIPMENT

Before shipping, the instrument should be carefully packed in its original packing material.

Model 6011 and 6011-10 Triaxial Cables-The Model 6011 is made up of 3 feet of triaxial cable that is terminated with a

trim plug on one end and 3 alligator clips on the other end. The Model 6011-10 is a similar cable 10 feet in length. Note that the Model 6011 is supplied with the Model 617.

Model 6012 Triax to UHF Adapter-The Model 6012 allows

the Model 617 to be used with accessories having UHF type co”nectors.

Model 6lOlA Shielded Test Lead-The Model 610lA is a straight through probe and shielded lead equipped with 0.8m

(3O”) of shielded low noise cable terminated by a Tefloninsulated UHF connector. The Model 6012 must be used to adapt the Model 6101A to the Model 617 triaxial input.

Model 6103C Voltage Divider Probe-The Model 6103C extends Model 617 voltage measurement range to 30kV. The Model 6103C has a division ratio of 1OOO:l with a nominal accuracy of 5%. The probe has an input resistance of 4.5 x 10110 and is equipped with a UHF male plug. The Model 6012 adapter must be used to connect the Model 6103C to the Model 617.

Model 6104 Test Shield-The Model 6104 facilitates resistance, voltage, or current measurements with either 2- or 3-terminal guarded connections at voltages up to 1200V. The Model 6104 provides excellent electrostatic shielding and high isolation resistance. Clips plug into banana jacks, allowing custom connections. The Model 6104 has a BNC camector on one side and binding posts on the other. The Model 6147 adapter (below) is required to connect the Model 6104 to the

Model 617.

If the instrument is to be returned to Keithley Instruments for repair or calibration, include the following:

Write ATTENTION REPAIR DEPARTMENT on the shipping label.

Include the warranty status of the instrument. Complete the service form at the back of this manual.

1.12 ACCESSORIES

The following accessories are available to enhance Model 617

capabilities.

Models 1019A and 1019s Rack Mounting Kits-The Model

1019A is a fiied or stationary rack mounting kit with two front panels provided to enable either single or dual side-byside mounting of the Model 617 or other similar Keithley instrument. The Model 1019s is a similar rack mounting kit with a sliding mount configuration.

Model 6105 Resistivity Chamber-The Model 6105 is a guarded test fixture for measuring voltage and surface resistivities. The unit assures good electrostatic shielding and high insulation resistance. The complete system requires the use of an external high-voltage supply such as the Model 247 as well as the Model 617. Volume resistivity up to 105Q/cm and surface resistivity up to 1018Q can be measured in accordance with ASTM test procedures. Sheet samples 64 to 102mm (2Yz X 4”) in diameter and up to 6.4mm (IA”) thickness can be accommodated. Excitation voltages up to 1OOOV may be used.

Model 6146 Triax Tee Adapter-The Model 6147 allows the simultaneous connection of two triaxial cables to the single triaxial input of the Model 617.

Model 6147 Triax to BNC Adapter-The Model 6147 allows the Model 617 input to be connected to accessories having BNC connectors.

Model 6171 and 6172 3 Lug-to-2 Lug Adapters-The Model 6171 is a 3 lug male-to-2 lug female triaxial adapter, while the Model 6172 is a 2 lug male-to-3 lug female triaxial adapter.

1-3

Model 7008 IEEE-488 Cables-The Model 7008 cables are designed to connect the Model 617 to the IEEE-466 bus and are available in two similar versions. The Model 7008-3 is

0.9m (3 ft.) in length, while the Model 7008-6 is 1.&n (6 ft.) long. Each cable is terminated with a standard IEEE-488 connector on each end, and each connector is equipped with two metric SCTBWS.

Model 7024 Triaxial Cables-The Model 7024 cables are similar units with male triaxial connectors on each end. The Model 7024-l is 0.3m (1 ft:) in length, while the Models

7024-3 and 7024-10 are 0.9m (3 ft.) and 3.0m (10 ft.) long

respectively. These cables may be used to connect the Model 617 signal input to other equipment having similar triaxial connections.

Model 7023 Female Triaxial Connector-The Model 7023 is a

chassis mount connector that mates with the Models 6011 and 7024 triaxial cables.

Model 8573 IEEE-488 Interface for the IBM PC-The Model 8573 allows the Model 617 to be connected to and controlled from the IBM PC via the IEEE-488 bus.

1-4

SECTION 2

OPERATION

2.1 INTRODUCTION

Operation of the Model 617 may be divided into two general categories: front panel operation and IEEE-488 bus operation. This section contains information necessary to use the instrument on a front-panel basis. Note that many of these func-

tions can also be programmed over the IEEE-488 bus, as described in Section 3.

The following paragraphs contain a complete description of Model 617 front panel operation. First a complete description of each front and rear panel function is presented. Next the complete procedure for each of the measuring functions is presented, followed by a description of the built in voltage source. Finally, the analog output and guard functions are

described along with a method to apply external feedback.

2.2 POWER UP PROCEDURE

Use the procedure below to connect the Model 617 to line

power and power up the instrument.

1. Connect the female end of the power cord to the AC receptacle on the rear panel of the instrument. Connect the other

end of the cord to a grounded AC outlet.

switch. The switch will be at the inner most position when the instrument is turned on.

3. The instrument will power up in the volts function, in the autorange mode aqd with zero check enabled, as indicated by the associated front panel LEDs. All other LEDs will be off when the instrument is first turned on.

2.3 POWER UP SELF TEST AND DISPLAY MESSAGES

The RAM memory is automatically tested as part of the power up procedure. If a RAM memory error occurs, the “rr” message will remain on the display. If the instrument was not able to read the stored calibration constants and configuration, the decimal points in the two exponent digits will flash.

If such errors occur, the instrument may be partially or completely inoperative. Refer to Section 7 for more complete details.

A power up self test may be run and the software revision

level may be displayed by pressing and holding the TRIG but-

ton when the unit is first turned on. During the test, all front panel LEDs and the display segments will turn on as in the example below:

WARNING

The Model 617 is equipped with a 3-wire

power cord that contains a separate ground

wire and is designed to be used with

grounded outlets. When proper connec-

tions are made, instrument chassis is con-

nected to power line ground. Failure to use a grounded outlet may result in personal in-

jury or death because of electric shock.

CAUTION Be sure that the power line voltage agrees with the indicated range on the rear panel of the instrument. Failure to observe this precaution may result in instrument damage. If necessary, the line voltage may be changed as decribed in Section 7.

2. Turn on the power by pressing in the front panel POWER

The instrument will then display the software revision level when TRIG is released, for example:

E.4

The instrument will then enter the diagnostic mode, which is used as an aid in troubleshooting problems within the instrument. See Section 7 for details. The power must be turned off to remove the instrument from the diagnostic mode.

NOTE

If the instrument is still under warranty (less than one year from the date of shipment), and problems develop, it should be returned to Keithley Instruments for repair. See paragraph

1.11 for details on returning the instrument.

2-I

Figure 2-1. Model 617 Front Panel

PROGRAM PROGRAM

SELECT EXIT SELECT EXIT

0 0

i, i,

2.4 FRONT PANEL FAMILIARIZATION

The front panel layout of the Model 617 is shown in Figure 2-1. The front panel may be divided into two sections: controls and display indicators. The following paragraphs describe each of these items in detail.

2.4.1 Controls

All front panel controls except POWER are momentary con-

tact switches. Many control buttons include an annunciator light to indicate the selected mode. Some buttons have a secondary function that is entered by pressing the SHIFT button before pressing the desired button. All such buttons (except ADJUST) are marked in yellow. The controls are color coded into functional groups for ease of operation.

POWER-The POWER switch controls AC power to the in-

strument. Depressing and releasing the switch once turns the power on. Depressing and releasing the switch a second time turns the power off. The correct positions for on or off are marked on the front panel immediately above the POWER switch.

SHIFT-The SHIFT button adds a secondary function to some of the other front panel controls, including VOLTS, TRIG, OHMS, RECALL and PROGRAM SELECT. Note

that the shift function is entered by pressing SHIFT before the

second button rather than pressing the two simultaneously.

ELECTROMETER-The ELECTROMETER buttons control

the measuring functions, selection of instrument ranges, and such items as zero check, zero and suppression, and front panel triggering.

VOLTS-The VOLTS button places the instrument in the DC

volts measuring mode. When VOLTS is pressed, the indicator next to the button turns on, showing that the instrument is set

for that mode. Note that the Model 617 will be in this mode when it is first turned on. Pressing SHIFT/VOLTS will place

the instrument in the external feedback mode, as described in

paragraph 2.12.

OHMS--Pressing OHMS places the unit in the resistance measuring function. The indicator next to the OHMS button will be illuminated when the instrument is in this mode. Note

that there are two ways to measure resistance with the Model

617. Pressing OHMS alone will cause the instrument to measure resistance using the constant current method. Pressing the SHIFT button before pressing OHMS places the in-

2-2

strument in the V/I mode of resistance measurement, as

described in paragraph 2.8. The V/I indicator will light when the instrument is in this mode.

COUL-The Model 617 may be set up to measure charge by pressing the COUL button. The indicator next to the COUL button will illuminate when the instrument is set for this mode.

AMPS-Pressing AMPS switches the instrument to the current-measuring function. The AMPS indicator will turn on when the instrument is in this mode.

RANGE-These two buttons allow you to increment or decrement the range the instrument is in. Pressing the up ar- row button will move the instrument up one range each time it is operated, while the down arrow button will move the instrument down range one increment each time it is pressed.

Note that pressing either of these buttons will cancel autorange if that mode was previously selected. The display mantissa will remain blank until the first reading is ready to be displayed.

AUTO-The AUTO button places the instrument in the auto range mode. While in this mode, the Model 617 will switch to the best range to measure the applied signal. Note that the instrument will be in the autorange mode when it is first turned

on. Autoranging is available for all functions and ranges. Autoranging may be cancelled either by pressing the AUTO button or one of the two RANGE buttons.

ZERO CHECK-The zero check mode is used in conjunction with the ZERO CORRECT control to cancel any offsets within the instrument and is also used as a standby mode.

Pressing ZERO CHECK once will enable this mode, as shown by the associated indicator light. When zero check is enabled,

the electrometer input circuit configuration changes (see

paragraph 2.11). No readings can be be taken with zero check enabled. Pressing ZERO CHECK a second time will disable this mode. Zero check should be enabled when making connections or when changing functions.

ZERO CORRECT-The zero correct mode works with zero check to cancel electrometer offsets. If zero check is enabled, pressing ZERO CORRECT will store a new value that will be used to cancel any offset. If the range is changed while zero correct is enabled, the stored value will be scaled accordingly. Zero correct may be cancelled by pressing the ZERO CORRECT button a second time. More information on using zero correct may be found in paragraph 2.11.

may be disabled by pressing the SUPRESS button a second time, and is cancelled if the function is changed.

TRIG-The TRIG button allows you to enter the one-shot

trigger mode and trigger single readings from the front panel. To enter the one-shot mode, press SHIFT then TRIG. The SGL indicator light will show that the instrument is in the one-shot mode. Each time the TRIG button is pressed, a single reading will be processed and displayed. The displayed reading will flash when the TRIG button is pressed. The oneshot trigger mode can be cancelled by pressing SHIFT then TRIG a second time. Additional information on triggering may be found in paragraphs 2.13 and 3.10.14.

V-SOURCE-These buttons control the internal 2100V source within the instrument. More information on the using the voltage source is located in paragraph 2.8.

DISPLAY-The DISPLAY button toggles the front panel

display between the voltage source and the present display mode (electrometer or data store). Pressing DISPLAY once will switch the display from the present mode to the source

mode, as indicated by the LEDs adjacent to the display (more

information on the display is located in paragraph 2.4.2).

Pressing DISPLAY again will return the display to the

previous display mode.

ADJUST-These two buttons control the voltage source out-

put value. The up arrow button increases the voltage value in

50mV increments, while the down arrow decreases the

voltage source output in 5OmV increments. The values may

be scrolled by holding the desired ADJUST arrow in. The in-

strument will stop on the value currently displayed when the

button is released. The scrolling can be made more rapid by

pressing the SHIFT key before pressing the desire ADJUST

key. Note that the ADJUST keys are also used with certain

front panel programs, as described in paragraph 2.5. Note

that the maximum voltage values are +102.4V and

-102.35V.

OPERATE-The OPERATE button turns the actual voltage

source output on or off. Pressing the OPERATE button once

turns on the output. The LED next to the OPERATE button

will be illuminated when the source is turned on. Pressing the

OPERATE button a second time will turn off the output

(OO.oOV). Note that the OPERATE LED will flash when the

2mA current limit is exceeded.

SUPPRESS-The suppress mode allows you to cancel external offsets or store a baseline value to be subtracted from subsequent readings. For example, if you applied 1OV to the instrument and enabled suppress, that value would then be subtracted from subsequent readings. Once suppress is enabled, the value is scaled when the range is changed. Suppress

DATA STORE-The two DATA STORE buttons control the internal loo-reading data store mode of the instrument. Through these two buttons, data storage may be enabled or disabled, the storage rate may be selected, and readings may be recalled to the front panel display. Paragraph 2.12 con-

tains a complete description of data store operation.

2-3

ON/OFF--This control enables or disables data store opera-

tion. In addition, reading rates can be selected by holding the

button in when first enabling data store. When data store is enabled, the indicator light next to the ON/OFF button will be on. Minimum and maximum values are stored and up-

dated as long as the ON/OFF LED is on.

RECALL/EXIT-This single button serves to recall readings

previously stored by data store. Pressing and holding this

button causes the instrument to scroll through the pointer ad-

dresses as indicated on the display. Once the desired reading

number is displayed, releasing the button causes the actual

reading to be displayed. To exit the recall mode, press SHIFT

EXIT.

PROGRAM-A single PROGRAM button controls such

modes as IEEE address, alpha or numeric display exponent,

and digital calibration. Paragraph 2.5 further describes front panel programming.

SELECT/EXIT-This button enters the program mode to allow access to parameters described above. Pressing SELECT repeatedly causes the instrument to scroll through a program menu. To cancel the program mode, press SHIFT

and then SELECT/EXIT in that order. Note that the program mode is cancelled by pressing SELECT/EXIT after a program parameter change is made.

2.4.2 Display and Indicators

The operation of the 4% digit display and various indicators

is described below. The display updates at about three readings per second.

STATUS Indicators-These three indicators apply to operation of the Model 617 over the IEEE-488 bus. The REMOTE indicator shows when the instrument is in the IEEE-488 remote state, while the TALK and LISTEN indicators show

when the instrument is in the talk and listen states respect-

ively. See Section 3 for more information on using the Model 617 over the IEEE-486 bus.

2.4.3 Tilt Bail ’

The tilt bail, which is located on the bottom of the instru-

ment, allows the front panel to be elevated to a convenient viewing height. To extend the bail, rotate it out 90” from the bottom cover and latch it into place. To retract the bail, pull

out until it unlatches and rotate it against the bottom cover.

2.5 FRONT PANEL PROGRAMS

The Model 617 has three front panel programs that can be used to set the primary address, set the display exponent mode (alpha or numeric), or calibrate the instrument from the front panel. To select a program, press PROGRAM SELECT button repeatedly while bbserving the display. The instrument will scroll through the available programs with identifying messages. as shown in Table 2-2. When in the program

mode, the DISPLAY and DATA STORE RECALL buttons are inoperative; the data store mode may be turned off, but not on. The operation of the various programs is described in

the following paragraphs. To exit a program, press SHIFT EXIT. If a change was made, pressing SELECT alone will exit

the program.

Display-The Model 617 has a display made up of a 4% digit

signed mantissa as well as a two-digit signed exponent. The exponent can be represented either in scientific notation, or with an alphanumeric subsript such as nA. The exponent dis-

play mode can be changed with a front panel program, as

described in paragraph 2.5. Note that, when scientific nota-

tion is used, the decimal point remains fixed as in 1.9999. The

range is indicated by the exponent. In addition, the display

has a number of front panel error messages, as shown in

Table 2-l.

Display Indicators-The METER, SOURCE, and DATA LEDs indicate what the display is actually showing. When the METER LED is on, the display represents an electrometer reading. When the SOURCE LED is illuminated, the voltage source value is being displayed. A data store reading is displayed when the DATA LED is turned on. Normally, the display will be the the meter mode, but the DISPLAY and RECALL buttons will switch the display to the source and data modes respectively.

2-4

2.5.1 IEEE-488 Address

Selection of the IEEE-488 address program is indicated by the following message:

IEEE 27

Along with the message, the presently programmed IEEE-488 address (27 in this example) will be displayed. To select a new address, use the V-SOURCE ADJUST keys. When the desired value is shown in the display, press SHIFT then SELECT EXIT to return to normal operation (or if a change was made, simply press SELECT). For complete information on using the

Model 617 over the IEEE-488 bus, refer to Section 3.

Table 2-1. Display Error Messages

Message

b Err

Description

Overrange input applied (- for negative valueI.

Bus Error: Instrument programmed while npt in remote; ~ or illegal command or command option sent.*

n Err

(Number Error: Calibration or voltage source value out of ; limits.*

‘t Err

Trigger Overrun Error: Instrument triggered while processing reading from previous trigger.

“See Section 3.

Table 2-2. Front Panel Program Messages

Displays/sets IEEE primary address.

IdlSP

Sets numeric or alpha exponent.

The display in the alpha mode appears as:

dISI’m

Once the desired exponent mode is selected, press SHIFT then SELECT EXIT to return to normal operation (or simply PRO- GRAM SELECT if a change was made).

2.5.3 Calibration

CAL

Allows calibration of instrument.

2.5.2 Exponent Mode (Alpha or Numeric)

The display exponent of the Model 617 can be operated in either the alpha mode or the numeric mode. In the alpha

mode, the exponent is given in actual units such as mA. In the numeric mode, the exponent is given in scientific notation.

Table 2-3 gives typical examples. including units.

To select the exponent program, scroll through the program

menu until the following message is displayed:

dISI’

Use either of the V-SOURCE ADJUST buttons to set the ex- ponent to the desired mode. In the numeric mode, the display might show:

dISP -3

An advanced feature of the Model 617 is its digital calibration

program. The instrument can be calibrated from the front panel or over the IEEE-488 bus. To use the front panel calibration program, refer to the calibration procedures outiined in Section 7.

2.6 REAR PANEL FAMILIARIZATION

The rear panel of the Model 617 is shown in Figure 2-2.

2.6.1 Connectors and Terminals

AC Receptacle-Power is applied through the suppiied power cord to the AC receptacle. Note that the supply voltage is marked adjacent to the receptacle.

IEEE-488 Connector-This connector is used to connect the

instrument to the IEEE-488 bus. IEEE-488 function codes are

marked above the connector.

2-5

Table 2-3. Typical Display Exponent Values

I Display

IPA

Tfl

ingineering

Units

!lC

kCI

icientific Uotation

10-77-A

10-w

lo-GA

lo-3v

103Q

lO@l

low

1012sl

anocoulombr

licroamperes

Millivolts

Kilohms

Megohms

Gigohms

Teraohms

INPUT-The INPUT connector is a 2-lug triax connector to be used for all electrometer signal inputs. Note that you should not confuse a triaxial connector with the BNC type that is used for the EXTERNAL TRIGGER and ELEC-

TROMETER COMPLETE connections. Also, do not attempt

to force a 3-lug triaxial connector onto the INPUT Connector. The Models 6171 and 6172 adapters are available to make the necessary conversion.

2V ANALOG OUTPUT-The 2V ANALOG OUTPUT prc-

vides a scaled O-2V output from the electrometer (2V output

for full range input). The output uses a standard S-way bind-

ing post and is inverting in the volts and ohms modes.

PR!ZAMP OUT-The PREAMI’ OUT provides a guard cutput for voltage and resistance measurements. This output can also be used as an inverting output or with external feedback when measuring current or charge. The PREAMP OUT has a maximum output value of k3C0V and uses a standard s-way binding post.

WARNING Hazardous voltage may be present at the PREAMP OUT, depending on the input

signal.

101522

COM Terminal-The COM terminal is a 5way binding post that provides a low connection for both the 2V ANALOG OIJ’IT’LT and the PREAMP OUT This terminal is also used for input low connection when in guarded mode; COM is internally connected to input low through a lC0Q resistor. Do not connect PREAMP OUT, COM, or 2V ANALOG OUTPUT to earth when floating input.

V-SOURCE OUTPUT-The HI and LO outputs are the connections for the internal voltage source. This source can be used as a stand-alone source or in conjunction with the elec-

trometer section to make resistance measurements as high as

1owL

EXTERNAL TRIGGER INPUT-This BNC connector can be used to apply external trigger pulses to the Model 617 to trigger the instrument to take one or more readings, depending

on the selected trigger mode.

Petaohms

2-6

Figure 2-2. Model 617 Rear Panel

METER COMPLETE OUTPUT-This BNC connector prcvides an output pulse when the Model 617 has completed a reading; it is useful for triggeling other instrumentation.

Chassis Ground-This jack is a s-way biding post that is connected to instrument chassis ground. It is intended for use in situations requiring an accessible chassis ground terminal.

A shorting link is supplied and connected to the CHASSIS GROUND terminal.

2.6.2 V, !I GUARD Switch

The Model 617 has provisions for connecting a guard to the

inner shield of the input cable. Guarding is useful in the volts and ohms modes to speed up response time and minimize the effects of leakage resistance. Note that guarded operation is not recommended in amps or coulombs. The V, Q GUARD switch allows easy selection of the guarded mode of cperaticn. See paragraph 2.7.4 for more information on guarded operation.

2.6.3 Line Fuse

The LINE FUSE, which is accessible on the rear panel, pro

vides protection for the AC power line output. For infcrmaticn on replacing this fuse, refer to Section 7.

2.7 BASIC MEASUREMENT TECHNIQUES

The paragraphs below describe the basic procedures for using

the Model 617 to make voltage, resistance, charge, and current measurements.

2.7.1 Warm Up Period

The Model 617 is usable immediately when it is first turned on. However, the instrument must be allowed to warm up for at least two hours to achieve rated accuracy.

NOTE

While rated accuracy is achieved after the two hour wan-n up period, input bias current may require additional time to come to its optimum level. Allow two hours for input bias current to settle to less than 1OfA and eight hours to less than 5fA. It is preferable in sensitive applications to leave the unit on continuously.

2-7

2.7.2 Input Connections

The rear panel IivPIJT connector is a Teflon-insulated receptacle intended for all input signals to the Model 617. As shown in Figure 2-3, the center terminal is high, the inner ring or shield is low, and the outer shield is connected to instrument chassis ground. In the guarded mode, the inner shield is driven at guard potential, while the Outer shield is chassis ground.

NOTE

The input connector must be kept clean to main-

tain high input impedance.

The supplied Model 6011 input cable is designed to mate with the input connector. The other end of the Model 6011 is terminated with three alligator clips. Input high is color coded in red, input low is colored black, and chassis ground is color coded in green. Keep in mind that these connections are for

the unguarded mode. In the guarded mode, red is high, black is guard, and green is chassis ground. The COM binding post

provides a connection to input low through loOn for use in

the guarded mode.

GROUND

CAUTION

The maximum voltage between input high

and input low is ZXlV rms. DC to 60Hz sine wsve (10 seconds maximum in mA ranges). Exceeding this value may cause damage to

the instrument.

2.7.3 Making Voltage Measurements

The Model 617 can be used to measure voltages in the range of *lOpV to +2COV. In principle, the instrument operates much like an ordinary DMM, but its special characteristics allow it to make measurements in cases where an ordinary DMM would be unable to perform well. In particular, the very high input resistance of 2oOTSl (2 X 1OW) allows it to accurately measure voltage sources with high internal resistances. In contrast, an ordinary DMh4 may have an input resistance of only loMa. resulting in inaccurate measurements because of instrument loading.

Use the procedure below to make voltage measurements.

1. Turn on instrument power and allow it to warm up for two hours to reach rated accuracy.

2. Check to see that the voltage function is selected by pressing the VOLTS button. Use the autorange mode, or select the desired range with the ranging pushbuttons.

3. To achieve specified accuracy, especially on the lower ranges, it is recommended that you zero the instrument. To do so, first enable zero check and then press the ZERO CORRECT button. Correcting zero in the lowest range of any function will correct all ranges because of internal scaling.

A. UNGUARDED 6. GUARDED

I”, ii GUARD OFF)

Figure 2-3. Input Connector Configuration

NOTE

W, R GUARD ON,

It is recommended that zero check be enabled when connecting or disconnecting input signals.

WARNING The maximum common-mode input voltage (the voltage between input low and chassis ground1 is 5OOV peak. Exceeding this value may create a shock hazard.

CAUTION

Connecting PREAMP OUT, COM, or 2V ANALOG

XJTPUT to earth while floating input may

damage the instrument.

2-8

NOTE

The input circuit configuration changes with zero check enabled. See paragraph 2.11.1.

4. Connect the Model 6011 triaxial input cable or other similar cable to the rear panel INPUT jack on the instrument. For sources with high output resistance, the cable should be kept as short as possible to minimize cable capacitance.

5. If response time and leakage resistance are considerations, place the instrument in the guarded mode as described in the next paragraph.

6. Connect the other end of the cable to the voltage to be

measured, as shown in Figure 2-4. Disable zero check.

7. The reading may be obtained directly from the display.

The exponent can be placed either in the alpha or numeric

mode, as described in paragraph 2.5.

I+ I

vs= j

T- I

Figure 2-4. Connections for Voltage Measurements

TO A/D CONVERTER

Voltage Measurement Considerations: Two primary considerations come to mind when making voltage measurements. especially for voltage sources with high output resistances. For one thing, the loading effects of the measuring instrument come into play at the high resistance levels involved. Secondly, the distributed capacitance of the source, the input cable, and the input circuit of the instrument itself come into play when making these measurements.

To see how meter loading can affect accuracy, refer to Figure 2-5. In this figure there is a voltage source with a value ES and

an output RS connected to the input of the electrometer, which has its input resistance represented by RIN. The percent error due to loading can be calculated as follows:

100 RS

% ERROR = -

Rs + RIN

Thus, to keep the error under 0.1%. the input resistance must be about 1000 times the value of the source resistance. R.

At very high resistance levels, the very large time contants created by even a minimal amount of capacitance can slow

down response time considerably. For example, measuring a wurce with an internal resistance of 1OOGQ would result in an

RC time constant of one second when measured through a cable with a nominal capacitance of 1OpF. If 1% accuracy is required, a single measurement would require at least five seconds.

Basically, there are two ways to minimize this problem: (1)

keep the input cable as short as possible, and (2) use guarding.

With the first method, there is a limit as to how short the

cable can be. Using guarding can reduce these effects by up to

a factor of 1000. The Model 617 has a rear panel switch to

allow guarding to be easily applied to the input circuit: see the

next paragraph for details.

2-9

At low signal levels, noise may affect accuracy. Shielding of the unknown voltage can reduce noise effects substantially. When using shielding, the shield should be connected to input IOW.

rI /

To approach the concept of guarding, let us first review the

unguarded circuit shown in Figure 2-6. The measured signal is represented by the voltage source ES and the source resistance

RS. Cable leakage impedance is represented by 2~ The

source resistance and leakage impedance form a voltage

divider that attenuates the source voltage as follows:

ZLES

E, =

ZL + Rs

Thus, to keep the error due to leakage resistance under O.l%,

the leakage resistance must be at least 1000 times the source resistance value.

T ; / N”!

---- J

G-lJ

L-----J

Figure 2-5. Meter Loading Considerations

2.7.4 Guarded Operation

Guarding consists of using a conductor supplied by a low impedance source to totally surround the leads carrying a highimpedance signal. The output of this low-impedance source is kept at the same potential as the signal itself, resulting in drastically reduced leakage currents.

Guarding the circuit miminizes these effects by driving the

shield at signal potential, as shown in Figure 2-7. Here, a uni-

ty gain amplifier with a high input impedance and low output impedance is used. The input of the amplifier is connected to the signal, while the output is used to drive the shield. Since

the amplifier has unity gain, the potential across ZLis essentially zero, so no leakage current flows. Leakage between

the cable shield and ground may be considerable, but it is of no consequence since that current is supplied by the low impedance source, rather than by the signal itself.

2-10

Figure 2-6. Unguarded Circuit

Figure 2-7. Guarded Circuit

-I

low input offset current. The low voltage burden is achieved because the Model 617 measures current as a feedback type picoammeter, rather than the shunt method used by many DMMs.

NOTE

After measuring high voltage in volts, or following an overload condition in ohms, it may take a number of miriutes for input current to drop to within specified limits. Input current can be verified by placing the protection cap on the INPUT jack and then connecting a jumper between the COM and chassis ground terminals, With the instrument on the 2pA range and zero check disabled, allow the reading to settle until the instrument is within specifications.

NOTE

Safe operation and good measurement practice dictates the use of an external resistor when necessary to limit currents to less than 3011~4.

When the rear panel V, Q GUARD switch is placed in the ON position, guard potential is placed on the inner shield of the

triaxial cable. The other shield remains at chassis ground. Thus, it is necessary to use the COM terminal for low signal connections, as shown in Figure 2-0. For very critical measurements, a shielded, guarded enclosure should be used.

WARNING

Hazardous voltage lup to 3OOV) may be present on the inner shield when V, Q GUARD is on, depending on the input signal. A safety shield, connected to chassis ground is

recommended when making voltage

measurements over 30V or guarded resistance measurements.

NOTE

The use of guarding is not recommended in amps or coulombs.

The PREAMI’ OLJT terminal may be used for guarding in the volts and ohms modes in a similar manner. In this mode, the

preamplifier acts as a unity gain amplifier with low output impedance.

WARNING Hazardous voltage (up to 3WV) may be present at the PREAMP OUT terminal, depending on the input signal.

2.7.5 Making Current Measurements

The Model 617 can resolve currents as low as 0.1 fA

(lo--lbA), and measure as high as 2011~4 in 11 ranges. The

Model 617 exhibits low input voltage burden and extremely

To measure current with the Model 617, use the following procedure.

I. Turn on the power and allow the instrument to warm up

for at least two hours to obtain rated accuracy.

2. Select the current mode by pressing the AMPS button on

the front panel. Set V, Q GUARD to OFF.

3. To achieve rated accuracy, select the 2pA range, zero the instrument by enabling zero check and then pressing the ZERO CORRECT button. Select the desired range, or use

autoranging if desired.

4. Connect the Model 6011 or other similar cable to the rear

panel INPUT jack. Connect the other end of the circuit to be measured as shown in Figure 2-9. Shielding will be required for low-level measurements. Connect the shield to input low.

5. Disable zero check.

6. Read the current value directly from the display. The exponent may be placed either in the alpha or numeric modes, as described in paragraph 2.5.

Current Measurement Considerations: At very low levels (in the picoampere range), noise currents generated in the cable or from other sources can affect measurements. Currents generated by triboelectric effects are a primary cause of noise currents generated in connecting cables. These currents are generated by charges created at the junction between a conductor and an insulator because of friction. Coaxial and triaxial cables are especially prone to such noise currents, which are generated by cable flexing. To minimize these effects, the cable should be tied down firmly to minimize any flexing. Also, special low-noise cable, constructed with graphite be-

tween the shield and insulator, is available to minimize these

effects. However, even with low-noise cables, several tens of

femtoamps of noise currents can be generated by cable move-

ment.

2-11

Voltage burden is frequently a consideration when making current measurements. Ideally, the input voltage burden should be zero in order for the instrument to have absolutely no effect on the circuit it is measuring. If the voltage burden is too high, its effects can degrade measurement accuracy considerably.

,=-

However, if EIN has a non-zero value, the current now becomes:

To see how voltage burden can upset measurement accuracy, refer to Figure Z-10. A source, represented by ES with an output resistance RS is shown connected to the input of a picoammeter. The voltage burden is represented by a constant voltage source at the input as Em. If En\l were zero, the current as seen by the meter would simply be:

MODEL 617

Es -6~

Additional considerations include source resistance and capacitance, as discussed in paragraph 2.14.

---_ SAFETY SHIELD

WARNING: USE SAFETY SHIELD FOR SIGNALS

ABOVE 30V h!OLTSl AND OHMS

2-12

v. R

GUARD

SWITCH

INPUT AMPLIFIER

PREAMP OUT

EQUIVALENT CIRCUIT (VOLTS MODE SHOWN)

Figure 2-8. Guarded Input Connections

RANGING AMPLIFIER

TO AiD

CONVERTER

6011 CABLE

‘-jr-z-=

INPUT

MODEL 617

INPVT

INPIJT

AblPLIFIER

r------

------_

SHIELD

lRECOMMENOED

BELOW l&A,

TO AID

CONVERTER

Figure 2-9. Current Measurements

I/ = ES - EIN

L----- -1

Figure 2-10. Voltage Burden Considerations

I-----A

EQUIVALENT CIRCUT

2.7.6 Making Charge Measurements

The Model 617 is equipped with three coulombs ranges to resolve charges as low as 1OfC (10-W) and measure as high as 20nC (20 X 10-K). When the instrument is placed in one of the coulombs ranges, an accurately known capacitor is placed in the feedback loop of the amplifier so that the voltage developed is proportional to the integral of the input current in accordance with the formula: V = -$- j idt. The voltage is scaled and displayed as charge.

NOTE

After measuring high voltages in volts, or following an overload condition in ohms, it may

2-13

take a number of minutes for the input current to drop within specified limits. Input current can be verified by placing the protection cap on the INPUT jack and then connecting a jumper between the COM and chassis ground terminals. With the instrument on the 2pA range and zero check disabled, allow the reading to settle until the instrument is within specifications.

Use the following procedure to measure charge with the Model 617.

1. Turn on the power and allow a two-hour warm up period for rated accuracy.

2. Place the instrument in the coulombs mode by pressing the

COUL button. Set V, R GUARD to OFF.

3. To achieve rated accuracy, place the instrument on the 2COpC range and zero the instrument by enabling zerc~ check and then pressing the ZERO CORRECT button.

4. Select the desired range, or use autoranging, if desired.

5. Disable zero check. A small amount of zero check hop (sudden change in the reading) may be observed when zero check is disabled. If desired, enable suppress to null out

any zero check hop, which typically will be in the lo-25

count range. ’

6. Connect the Model 6011 cable to the INPUT jack. Connect the other end of the cable to the circuit being measured. as shown in Figure 2-11. For low-level measurements, shielding may be required. Note: Do not connect the circuit to the instrument with zero check enabled.

7. Read the charge value from the display. The exponent may

be placed either in the alpha or numeric modes as described

in paragraph 2.5.

6011 CABLE

0 \ RED

IN;;;T

MODEL 617

cl ---- 1

INPUT AMPLlFlER

NOTE: LEAVE OS DISCONNECTED

“NTlL ZERO CHECK DISABLED

r----i

MEASURED

CHARGE

SHIELD ,OPTIONAL)

TO A/D

CONVERTER

2-14

PREAMP OUT

EQUIVALENT C,RCUIT

Figure 2-11. Coulombs Connections

Note that the coulombs function can also be used to measure

current. The advantage of doing so is that noise in the measurement is substantially reduced because of the integrating procw. To measure current using the coulombs function, proceed as follows:

discussed in paragraph 2.8, uses the built in voltage source. With the constant current method discussed here, the instrument can resolve resistances as low as O.la and measure as high as 2COGR.

1. Place the instrument in the coulombs function and select the desired range, or use autoranging, if desired.

2. Enable zero check and connect the current to be measured to the INPUT jack (see Figure Z-9).

3. Disable zero check and note the charge measurement at the end of a specific interval of time (for example, 10 seconds).

4. To determine the current, simply divide the measured charge by the time in seconds. For example, if a charge of l2nC is seen after a lo-second interval, the current is 121010 = 1.2nA. (Using Data Store at a 10 second rate can ease data taking).

5. As an alternative Lo the above procedure, connect a chart recorder to the 2V ANALOG OUTPUT (paragraph 2.9)

and graph the measured charge. Since the current is given by I=dQ/dt, the current at any point is equal to the slope of the graph at that point, after applying the appropriate scaling factor (loOpC/V, 2CGpC range; l&/V, 2nC range; lonC/V, 2Onc range).

CAUTION CAUTION

Connecting PREAMP OUT, COM, or 2V ANALOG Connecting PREAMP OUT, COM, or 2V ANALOG OUTPUT to earth while floating input may OUTPUT to earth while floating input may damage the instrument. damage the instrument.

Charge Measurement Considerations: A primary consideration when making charge measurements is the input offset current of the integrating amplifier. Any such current is integrated along with the input signal and reflected in the final reading. The Model 617 has a maximum input offset current of 5 x lo-ISA at 23°C. This value double every 10°C. This input offset current translates into a charge of 5 X lo-15C per second at a temperature of 23OC. This value must be subtracted from the fiil reading to obtain the correct value.

When using an external voltage source, the input current

should be limited to less than 1mA by placing a resistor in series with the high input lead. The value of this resistor

should be at least: R=lOOOV (in ohms) where V is the voltage across the capacitor, or the compliance of the current being integrated.

2.7.7 Resistance Measurements

To measure resistance with the Model 617, use the following procedure:

1. Turn on the power and allow a two-hour warm-up period for rated accuracy.

2. Press the OHMS button to place the instrument in the COTrect mode.

3. For maximum accuracv, place the instrument on the 2k0

range and zero the ins&&ent by enabling zero check and

then pressing the ZERO CORRECT button.

Select the desired range, or use autoranging, if desired.

Connect the Model 6011 or similar cable to the INPUT jack. Keep the cable as short as possible to minimize the effects of cable capacitance. Connect the other end of the cable to the resistance to be measured, as shown in Figure 2-12. For measurements above lGn, it is recommended

that you use guarded connections, as described in

paragraph 2.7.4.

6. Disable zero check.

7. Take the reading from the display. The exponent may be

placed in either the alpha or numeric modes, as described in paragraph 2.5.

Resistance Measurement Considerations: When measuring high resistance values, there are two primary factors that can affect measurement accuracy and speed. Any leakage r&stance in the connecting cable or test fixture can decrease the actual resistance seen by the instrument. Also, capacitance of the cable or input circuit can slow down the response time considerably.

These two problems can be minimized by using guarding, especially when measuring r&stances above lG% Guarding is further discussed in paragraph 2.7.4. Noise pickup can also be a problem, in which case the resistor must be shielded. Connecl the shield to input low.

At low resistances, lead resistance can be a consideration. Cancel the effects of lead resistance by shorting the input leads and enabling suppress with zero check disabled. Leave suppress enabled for subsequent measurements.

The Model 617 can make resistance measurements using two different methods: the constant current method and the constant voltage method. The constant voltage method, which is

2-15

2.7.8 Using the Ohms Function As A Current

MEASURED

------

Source

The Model 617 ohms function may also be used to generate currents in decade values between InA and lOOpA. To use the instrument in this manner, simply connect the Model 6011 cable to the INPUT jack and connect the red and black alligator clips to the circuit under test. Select the resistance range in accordance with the desired current (see Table 2-4). Note that current flows from input high through input low. The

test voltage is less than 2V for all ranges 2GQ and less. except when an overload occurs, in which case the compliance is

3OQv.

Table 2-4. Ohms Function Current Output Values

Id/

6011 CABLE

-0

MDDEL 617

INPUT AMPLIFIER

-----

I-

\ :

^. ^.. I

,RECOMMENDED ASDVE 100M~l

RESISTANCE

SHIELD

2-16

COM >

EDUIVALENT CIRCUIT

Figure 2-12. Resistance Measurement Connections

2.8 USING THE VOLTAGE SOURCE

The Model 617 has a built-in voltage source that can be used

to make V/I resistance measurements. The voltage source can be adjusted between -102.35V and +102.4V in 50mV increments, and has a maximum output current of 2mA. The following paragraphs describe the basic procedure for using the voltage source as well as the method for making V/I

resistance measurements.

2.8.1 Basic Operating Procedure

Use the following procedure for connecting the voltage swrce

and adjusting its output value:

1. Connect the circuit under test to the V-SOURCE OUTPUT HI and LO binding posts, as shown in Figure Z-13. RL represents the resistive load of the circuit under test. Note that RL has a minimum value of 5OkSl at an output voltage of 1COV. This value is based on the 2mA current limit of the voltage source.

WARNING The maximum common-mode voltage (voltage between SOURCE LO and chassis ground) is +lOOV. Exceeding this value may create a shock hazard.

V-SOURCE D”TP”T

\ I

MODEL617

-0

RL = 50kR MlNlM”M AT loo”

NOTE: MAXlMLlM CURRENT = ZrnA

MAXIMUM COMMON MODE VOLTAGE (“CM) = 1oov

2. Press the DISPLAY button to observe the voltage source

V&e.

3. Press either of the V-SOURCE ADJUST buttons repeatedly to increment or decrement the source in 5ChnV increments, as required. The value may be scrolled simply by holding

the button in. The scrolling rate can be increased by press-

ing SHIFT before pressing the appropriate ADJUST but-

ton. The actual maximum and minimum values are

+102.4V and -102.35V.

4. Press OPERATE to turn the source output on. The LED adjacent to this button will illuminate when the output is

turned on. The OPERATE LED will flash if the 2nd cur-

rent limit is exceeded.

WARNING

Dangerous voltage may be present on the sourca terminals when the output is enabled.

5. To turn the source output off, simply press the OPERATE button a second time. The source output will then be programmed to OO.OLW.

Figure 2-13. Voltage Source Connections

2.8.2 V/I Resistance Measurements

The voltage source can be used in conjunction with the electrometer section of the Model 617 to measure resistances as high as lOWI. In this mode, the measured resistance is automatically calculated from the applied voltage and the measured current in accordance with the familiar formula: R

= V/I. In V/I ohms a flashing AMPS LED indicates a current

overload. Display resolution depends on the selected current range. The suppress function acts on the displayed value. If suppress is enabled in the amps function the displayed cur-

rent is suppressed. If suppress is enabled in the V/I function the displayed resistance is suppressed. To make V/I measurements while suppressing current, enable the suppress mode while in amps and then enable the V/I mode. In this case the SUPPRESS LED remains ON and the displayed resistance is calculated from the suppressed current. If the suppress mode is enabled while in the V/I mode and AMPS is pressed, suppress is cancelled but is reapplied when the V/I mode is reentered.

2-17

Use the following procedure to measure resistance with this mode:

1. Turn on the instrument and allow it to warm up for one hour to obtain rated accuracy.

2. Place the instrument in the amps mode by pressing AMPS.

3. For maximum accuracy, select the 2pA range and zero COT-

rect the instrument by enabling zero check and then zero correct in that order.

4. Select the desired range or use autoranging, if desired.

5. Connect the voltage source and INPUT jack to the measured resistance, as shown in Figure 2-14. Use the Model 6011 or other similar triaxial cable to make the input connections.

6. Turn on the source output by pressing the OPERATE button.

7. Press the DISPLAY button to return the display to the meter mode.

8. Disable zero check. The meter will now display the current being sourced through the resistor under test by the voltage sowce. To measure from a baseline current, such

as fixture leakage, enable suppress while in amps.

9. To display the resistance being measured, press SHIFT and then OHMS in that order. The V/I light will turn on indicating that the V/I ohms mode is enabled. If a displayed resistance overload occurs, the usual “OL” display message will be indicated; however, if the input current exceeds the maximum input G&e for the selected amps range, the AMPS LED will flash, as previously indicated. Note that the display can be placed in either the alpha or numeric exponent mode as discussed in paragraph 2.5.

10. To measure from a baseline resistance enable suppress while in V/T

V-SOURCE

LO HI

-0 0

MODEL 617

L-- -SELDl

IOPTlONALl

rgure z-14. v/I Hesistance Measurement Connections

V/I Resistance Measurement Considerations: The main advantage of using the constant voltage method for resistance measurements is that the effects of leakage resistance and distributed capacitance are minimized. Because of these factors, the resistance range of the instrument can be greatly increased, in the case of the Model 617, to 1016fl. However, there are certain characteristics pertaining to high resistance measurements that require discussion.

Such variation in resistance is known as rhe voltage coefficient. The Model 617 can be used to characterize such resistance changes by measuring the resistance with a number of different applied voltages. Once the variations are known, the voltage coefficient of the resistor being tested can be calculated. The method for determining the voltage coeffi-

cient of these resistors is discussed in Section 4.

A primary consideration when using this mode is to match the voltage and current ranges to optimize accuracy. In most cases, it is best use the maximum voltage value possible (except as indicated below) and set the current range accordingly. As with other Model 617 measurements, the instrument

should be placed on the most sensitive range possible without

overranging the electrometer section. Doing so will optimize the measurement for resolution and accuracy. Autoranging can facilitate range selection.

At very high resistance values, the corresponding current, as

seen by the instrument, will be extremely low. Thus, any current generated by the triaxial input cable will be reflected in the final measurement. To minimize such problems, use lownoise graphite hiaxial cable. (such as the Model 6011). Tie down the cable to avoid any triboelectric currents that might

be generated by cabling flexing. In many situations, shielding

of the circuit under test will also be required to minimize noise pickup.

Although V/I resistance measurements are much lms suscep-

tible to the effects of leakage resistance than resistance measurements made with the constant current method, there are sane cases where leakage resistance could affect V/I resistance measurements. For example, test fixture leakage paths may appear in parallel with the device beiig measured,

introducing errors in the measurement. As with other Model

617 high impedance measurements, these errors can be minimized by using proper insulating material (such as Teflon) in fixture terminal connections.

2.9 ANALOG OUTPUTS

The Model 617 has two analog outputs on the rear panel. The 2V ANALOG OUTPUT provides a scaled O-2V output with a value of 2V corresponding to full range input. The PREAMP OUT is especially useful in situations requiring buffering. These two analog outputs are discussed the the following paragraphs.

WARNING

When floating Input Low above 30V from earth ground. hazardous voltage will be

present at the analog outputs. Hazardous voltage may also be present when msasuring in ohms, or when the input voltage exceeds 30V in the volts mode.

CAUTION

Connecting PREAMP OUT, COM, or 2V ANALOG OUTPUT to earth while floating input may damage the instrument.

2.9.1 2V Analog Output

The 2V ANALOG OUTPUT provides a scaled Q2V output

that is inverting in the volts and ohms modes. Connections

for using this output are shown in Figure 2-15. For a full range

input, the output will be 2V; typical examples are listed in

Table 2-5. The 2V ANALOG OUTPUT is not corrected dur-

ing calibration. Gain errors of up to 3% may appear at this output, depending on function and range selection.

Any leakage current through cables and test fixtures can be minimized if care is taken. To cancel these effects, set up the measurement exactly as desired, but leave the resistor under test disconnected. Program the voltage source to the desired

value and turn on its output. With the instrument in the amps

mode, enable suppress to null the leakage current. Turn off the source, connect the resistor, and re-enable the voltage source. Place the instrument in the V/I ohms mode and proceed with the measurement.

High megohm resistors are somewhat curious devices, often exhibiting characteristics somewhere between those of an in- sulator and a normal re&tor. Because of these unique traits, the measured value of such a resistor will often vary with ap plied voltage.

Note that the output impedance is IOk% to minimize the ef-

fects of loading, the input impedance of the device connected to the 2V ANALOG OUTPUT should be as high as possible. For example, with a device with an input impedance of lOM0, the error due to loading will be approximately 0.1%

2.9.2 Preamp Out

The PREAMP OUT of the Model 617 follows the signal amplitude applied to the INPUT terminal. Some possible uses for thepreamp output include buffering of the input signal, as

2-19

well as for guarding in the volts and ohms modes. Connec-

tions and equivalent circuits for the preamp output are shown in Figure 2-16. Full range outputs for various functions and ranges are listed in Table 2-6. The PREAMP OUTPUT is not corrected during calibration. Gain errors of up to 3% may appear at this output, depending on function and range selection. For all volts ranges, PREAMP OUTPUT accuracy is typically Sppm.

Table 2-5. Typical 2V Analog Output Values

ZV Analog

Output Value

1.04v

1.65V

1.4 v

0.35v

1.75v

0.95v

1.25V

1.9 v

Table 2-6. Full Range PREAMP OUT Values

_-.--

Amps

Ohms*

Coulombs 1

200mV

2 v

20 v

200 v

2~4 2nA, 2/ln, 2mA.

20pA. 20nA. 20& 20mA

200pA, 200nA. 2OOfi

2 k0

20kD-2GQ

20GQ

200GQ

2OODC

200mV

20 v

200 v 200mV

20 v

200mV

20 v

1 200 v I 200mV

I 2v I

“WARNING: Open circuit voltage of 300V present at

PREAMP OUT in Ohms.

INPUT FROM

PREAMP

2-20

n/o

MODEL 617

200kR

,j-xiiL

RF = 2MR IX101

200kR ,X1)

20kR 1X0.11 2kR lXO.01 I

EQUIVALENT CIRCUIT

Figure 2-15. Typical 2V Analog Output Connections

-----I

(EXAMPLE: CHART RECORDER1

WARNING High voltage may be present between the PREAMP OUT and COM terminals depending on the input signal (see Table 2-6).

CAUTION Connecting PREAMP OUT, COM, or 2V ANALOG OUTPUT to earth while floatina inout mav damage the instrument.

- ’

Note that the output resistance is 10oR. The output resistance appears between Input Low and Analog Output Low to keep the resistor out of the loop when using external feedback elements. To keep loading errors under 0.1%. the device connetted to the PREAMP OUT should have a minimum input impedance of 1OOkQ.

Jf------

GND

MODEL 617

VOLTS

lOoR

MODEL 1683 TEST LEAD KIT

MEASURING DEVICE

>r--

EWIVALENT CIRCUITS

figure 2-16. Typical Preamp Out Connections

1000

COULOMBS

2-21

2.10 USING EXTERNAL FEEDBACK

External feedback provides a means to extend the capabilities

of the Model 617 Electrometer to such uses as logarithmic cur-

rents, non-decade current ranges, as well as non-standard coulombs ranges. The following paragraphs discuss the basic electrometer input circuitry and methods to implement these functions.

2.10.1 Electrometer Input Circuitry

A simplified diagram of the electrometer input in the amps mode is shown in Figure 2-17. An input current applied to the inverting (-) input of the op amp is nulled by a current fed back through the internal feedback network made up of Rm and CFB. Because the output of the op amp appears at the PREAMP OUT, this internal network can be replaced by an external network connected between the preamp output and Input HI connections. When using external feedback, the following factors must be taken into account:

1. The maximum current value that can be suppiied by the

preamp output is 20mA in amps (1mA in V/R).

2. The input impedance in the external feedback mode is

given by the relationship 21~ = Z@A”, where Zm is the impedance of the external feedback network, and A” is the

open-loop gain of the electrometer (typically greater than

106). Note that the input impedance is ZIN = lOM0 II 2~ when zero check is enabled.

3. The voltage at the PREAMI’ OUT terrrtinal is given by the

formula: V= -IRFB, where Rm is the value of the feedback

resistance.

4. Any feedback elements should be housed in a suitable

shielded enclosure. Insulators connected to Input HI should be made of Teflon or other high quality insulating material and should be thoroughly cleaned to maintain the high input impedance and low input current of the Model

617. If these insulators become contaminated, they can be scrubbed with methanol and then dried with clean, pressurized air.

2.10.2 Shielded Fixture Construction

Since shielding is so critical for proper operation of external

feedback, it is recommended that the shielded fixture shown

Figure 2-17. Electrometer Input Circuitry (Amps

Mode)

in Figure 2-18 be used to house the feedback element. The fixture is constructed of a Pomona #2390 shielded fixture modified with the standard BNC connectors replaced with triaxial female connectors. For convenience, a banana jack can be mounted on the box to make the necessary PREAMP OUT connection. Alternately, a wire could be ru11 through a rubber grommet mounted in a hole in the side of the box. Note that input low is connected to chassis ground within the shielded box. This connection can be made by using a small solder lug secured with a screw.

2-22

4. CONSTRUCTION

FEEDBACK

A A

IlV I-

GND) -

--v--J PoMoNAsoX -

IT:, OESCRlPTlON MFR. PART NUMBER

SHIELDED FIXTURE POMONA “2390

2 FEMALE TRIAXIAL KEITHLEY CS-181 3 SANANPl JACK WTHLEY W-9-2 4 TRlAXlAL CABLE KElTHLEY 6011 5 TRIAXIAL CABLE KEITHLEY ,024

-- ---

PARTS LIST

I I

Figure 2-18. Shielded Fixture Construction

’ ’ PREAMP OVT

\ LO

GND

TO RANGING

AMP AND AID

617 lNP”T AMP

2.10.3 External Feedback Procedure

Use the following procedure to operate the Model 617 in the external feedback mode.

1. Connect the feedback element between the PREAMP OUT 1. Connect the feedback element between th

terminal and the Input High terminal. terminal and the Input v4-h +--in=’

2. Place the instrument in LX CXKJXWZ~ x 2. Place the instrument in the external feedback mode by pressing the SHIFT then VOLTS buttons pressing the SHIFT then VOLTS buttons in that order. The AMPS and VOLTS indicators will i AMPS and VOLTS indicators will illuminate simul-

taneously in the external feedback mode taneously in the external feedback mode.

3. The display will show the voltage measured at the output of the input preamplifier (PREAMP OUT). However, the “V exponent will not appear as in the volts mode. For example, with a 150mV output the display will show:

150.00 m

4. External feedback may be temporarily digitally calibrated

as outlined in paragraph 7.4.16.

5. The external feedback mode may be cancelled by pressing one of the four functions keys (VOLTS, OHMS, COUL, or AMPS), or by pressing SHIFT OHMS to enter V/I OHMS.

2-23 2-23

2.10.4 Non-standard Coulombs Ranges

In its standard form, the Model 617 has three coulombs ranges allowing it to measure charge between 1OfC and 20nC. Different charge measurement ranges can be used by placing an external feedback capacitor between the PREAMP OUT and Inout HI and then olacing the instrument in the external feedback mode. . -

Charge is related to capacitance and voltage by the formula:

Q = CV, where Q is the charge, C is the capacitance, and V

is the voltage. The Model 617 display will read charge directly in units determined by the value of C. For example, a IFF capacitor will result in a displayed reading of lpC/V. shield the device.

A solution to these constraints is to use a transistor configured as a “transdiode” in the feedback path, as shown in Figure Z-19. Analyzing the transistor in this configuration leads to the relationship:

V = kT/q[lnI/I o- In(h&(l + h&)1

where hE is the current gain of the transistor.

From this equation, proper selection of Q1 would require a device with high current gain (h&,which is maintained over a wide range of emitter currents. Suitable devices for this application include Analog Devices AD812 and Precision

Monolithics MAT-01. Use the enclosure in Figure 2-18 to

In practice, the feedback capacitor should be greater than 1COpF for feedback stability and of suitable dielectric material to ensure low leakage and low dielectric absorption. Polystyrene, polypropylene and Teflon dielectric capacitors are examples of capacitor types with these desirable

characteristics. The capacitor should be mounted in a shielded fixture like the one in Figure Z-18.

To discharge the external feedback capacitor, enable zero check. The discharge time constant will be given by: T = (lOM0) (Cm).

2.10.5 Logarithmic Currents

The use of a diode junction in the external feedback path permits a logarithmic current-to-voltage conversion. This

relationship for a junction diode is given by the equation:

V = mkT/q h-@/I,) + IRB

where q = unit charge (1.6022X10-19). k = Boltzmann’s

constant (1.3806X10-U). and T = temperature (OK).

The limitations in this equation center on the factors I,, m and RB, I, is the extrapolated current for V,. An empirical proportional constant, m, accounts for the different character

current conduction (recombination and diffusion mechanisms) within the junction, typically varying between 1 and 2. Finally, R, constitutes the ohmic bulk resistance of the diode junction material. I0 and R, limit the usefulness of the junction diode at low and high currents, respectively. The factor m introduces non-linearities between those two extremes. Because of these limitations, most diodes have a limited range of logarithmic behavior.

Frequency compensation/stabilization is accomplished by adding a feedback capacitor, Cm. The value of this capacitor depends on the particular transistor being used and the maxi-

mum current level expected. Compensation at maximum current is required because the dynamic impedance will be minimum at this point. It should be noted that the response speed at lower currents will be compromised due to the increasing dynamic impedance, which is given by the following formula:

2 =-= KT/qI = 0.026/I (@ 25°C)

Using the above transistors, a minimum RC time constant of lC@sec at maximum input current would be used. At 11~

(m&) of lOOpA, this v&e would correspond to 0.4~F. No& that at loOnA this value would increase the RC resoonse time constant to 100msec. A minimum capacitance of 1OOpF is recommended.

Although the input signal to this particular circuit is assumed

to be a current, conversion to voltage input could be performed by placing a shunt resistor across the input. However, the nominal voltage burden of 1mV must be considered as an error signal that must be taken into account.

Further processing of the current response can be achieved by using suppress. For example, suppress could be enabled with a reference input current applied. For all subsequent currents, the natural logarithm of the ratio of the measured current to the suppressed current would then be displayed:

2-24

VDISP = VRVU) - VSUPPRESS kT/q (I* IREAD&

- In kUPPRESS&)

= kT/q(ln(

= 0.026/1(‘“( IREAD

IREAD

h’PRESS

)I @ 25°C

2.10.5 Non-Decade Current Gains

The Model 617 electrometer input uses internal decade resistance feedback networks for the current ranges. In some applications, non-decade current gains may be desirable. As shown in Figure 2-20, an external feedback resistor. R,,, can be used to serve this purpose. Limitations on the magnitude of the feedback curr,ent require that the value of RFB be

greater than loan.

NOTE

The circuit topology of Figure 2-19 works for positive input currents only. For bipolar input signals, an external offset bias must be applied or use a PNP at QL.

:“RRENT

\ . .

IOMR

Note that external feedback can be temporarily calibrated

i12% using the calibration program with the calibration

jumper in the disable position. See Section 7.

I r? I

TO RANGING

NOTE: PRESS SHIFT VOLTS TO ENTER

EXTERNAL FEEDBACK MODE

Figure 2-19. “Transdiode” Logarithmic Current Configuration

2-25

Figure Z-20. Non-Decade Current Gains

NOTE: PRESS SHIFT VOLTS TO ENTER

EXTERNAL FEEDBACK MODE

2.11 USING ZERO CORRECT AND BASELINE SUPPRESSION

The Model 617 has zero correction and baseline suppression modes that allow the cancellation of any internal offsets, or the storage of a baseline value that can be subtracted from subsequent readings.

2.11.1 Zero Correct and Zero Check

The ZERO CORRECT and ZERO CHECK buttons work

together to cancel any internal offsets that might upset accuracy. Note that the specifications listed for the instrument at the front of this manual assume that the instrument has been zeroed. Use the following procedure to zero the instrument. Note that the zero should be corrected on the range to be used, or on the lowest range of the function being used.

1. With the zero correct mode off, press the ZERO CHECK

button. Be sure ZERO CHECK light is on. In this mode,

the input signal is disconnected from the input amplifier and the input circuit is coofigured as shown in Figure 2-21. The internal preamplifier is configured to measure its own

offset when zero check is enabled.

2. Press the ZERO CORRECT button to zero the instrument. Note that if zero check is not enabled, the zeroing process will not take place. The previously stored zero parameter will be used instead.

3. To take readings, press ZERO CHECK to disable the zero check mode.

4. Readings can now be taken in the normal manner. Note

that the instrument will remain zeroed even if the instrument is upranged.

5. For maximum accuracy, the zero correction process should be repeated every 24 hours when the ambient temperature chants bv more than 1°C. or when the function is changed. .

2~ = 1003 (mAI

lOOk II 1OOOpF Cd, 1OOMO II 22OpF InA)

lOOGO n 5PF IDA,

GIN = 2OpF AMPS GIN = 2W OHMS

GIN = 2OpF

VOLTAGE C,,, = 2OpF COULOMB:

i+ = lOOk II lOOO,,F (ALL kn. 2MQ

IOOMR n 22pF (20MR. 200MR ALL GO)

Figure 2-21. Equivalent input Impedance with Zero

Check Enabled

2-26

NOTES:

1. Leave zero check enabled when connecting or disconnecting input signals, or when changing functions.

2. In V/I ohms, the display will go blank if zero check is enabled.

3. Zero will automatically be scaled when the instrument is

moved uprange.

4. Do not move the instrument down range after zerocorrecting the instrument. Re-zero the instrument after

moving downrange.

2.11.2 Using Suppression

The suppression mode allows a stored offset value to be sub-

tracted from subsequent readings. When the SUPPRESS but-

ton is pressed, the instrument will trigger a conversion and internally store the displayed value as a baseline. The SUPPRESS LED will illuminate. All subsequent readings will be the difference between the suppressed value and the actual signal level.

The baseline maintains its absolute value regardless of range.

For example, if a 1V signal is .suppressed on the 2V range, it will remain at 1V on the 20V and 2COV ranges. Only one reading for the presently selected function can be supressed; the value will be lost if the function is changed except when in the V/I ohms mode. The instrument can be toggled between V/I ohms and amps without loosing the stored value.

The suppressed readings can be as small as the resolution of

the instrument will allow, or as large as full range. Some typical examples include:

4. Press the SUPPRESS button. The triggered reading will be stored at that point. (If suppressing current in V/I ohms, press SHIFT OHMS 1.

5. Disconnect the supressed signal from the input and connect the signal to be measured in its place. Subsequent readings

will be the difference between the supressed value and the applied signal.

6. To return the instrument to the normal mode, press the SUPPRESS button. The SUPPRESS Light will go off and the instrument will be taken out of the suppression mode. The previously stored suppressed value will be cancelled.

NOTES:

1. Using suppress reduces the dynamic range of the measure-

ment. For example, if the suppressed value is -100mV on the 2COmV range, an input voltage of 1OOmV or more would overrange the instrument even though input voltages up to 199.99mV are normally within the capabilities of the 2OOmV range. If the instrument is in the autorange mode, it will move up range, if necessary.

2. Setting the range lower than the suppressed value will

overrange the display; the instrument will display the “OL” message under these conditions.

3. To store a new baseline, suppress must first be disabled and the enabled once again. The new value will be stored with the first triggered conversion.

4. Do not move the instrument down range when using sup-

press

5. If the instrument is in the V/I ohms when suppress is enabled, the displayed resistance value will be supressed (supression will be cancelled temporarily by going to amps).

6. To suppress the current in V/I ohms, enter amps and then enable suppress. Enter V/I ohms in the usual

manner.

Suppressed

Reading

+10.500 v

+2.556 nA

-12.6CihA

Applied

Signal

+18.600 v +1.8occ IL4

+4.5cnmA

Displayed

Value

+g.100 v

-0.7560 nA +17.1oomA

To use suppression, perform the following

1. Cancel suwress if uresentlv enabled

. . . .

2. Select a range and function that is consistent with the anticipated mesurement. If current is to be suppressed in

V/I ohms, select amps first.

3. Connect the signal to be supressed to the instrument input.

WARNING

The voltage on the input terminals may be

larger than the displayed value. For exampie, if a 15OVDC baseline is stored, an applied voltage of + 176V will result in a displayed value of only +25V.

2.12 DATA STORAGE

The Model 617 has an internal loo-point data store mode that

can be used to log a series of readings. The fill rate of the data store can be set to specific intervals by a parameter that is

entered when the storage mode is first enabled. Alternatively,

a special one-shot trigger mode can be used to control the fill rate from the front panel. Once data is stored, readings can be

easily recalled from the front panel.

Minimum and maximum values can also be retained for

future recall. As long as data store is enabled, maximum and minimum values are updated with each conversion.

Enter the data storage mode as follows:

1. Press and hold the DATA STORE ON/OFF button. The instrument will then scroll through the various reading rates that are listed in Table 2-7. In addition to the continuous rate, which stores readings at the conversion rate,

m me u.4 I A 3 I uxc VIY t u-r Duwm. rill then scroll through the various reading : listed in Table 2-7. In addition to the con-

which stores readings at the conversion rate,

five additional intervals from one reading per second to al intervals from one reading per second to

I ne

2-27

one reading per hour are available. A special trigger mode allows you to control the interval with the TRIG button. During the rate selection process, the display will appear as follows:

Similarly, the display will show the following for the low data point:

n=Lo

r=3

In this example, the rate parameter is 3, indicating a 1 rdg/min interval.

Table 2-7. Data Store Reading Rates

Rate

Conversion Rate (every 360mse.c)

1 Reading Per Second

1 Reading Every 10 Seconds 1 Reading Per Minute 1 Reading Every 10 Minutes

1 Reading Per Hour

L-

2. To select the desired interval, simply release the ON/OFF button when the desired rate appears in the display. The Model 617 will then begin storing readings at the selected rate. If you selected the triggered mode, one reading will be stored in memory each time the front panel TRIG button is

pushed. For rapid starts, the rate can be pre-selected by pressing

ON/OFF, releasing the button when the selected rate is displayed, and then turning off data store. Storage will then begin at the pre-selected rate the next time the ON/OFF

button is pressed.

3. When data store memory is full (after all 100 readings have been stored), the instrument will stop logging data, and the DATA LED will flash to indicate that memory is full.

4. Readings can be recalled any time (even if the instrument is still logging) by pressing and holding the RECALL button. Holding the RECALL button in causes the data pointer to be displayed. Releasing the RECALL button causes the corresponding data to be displayed. The first data point to be displayed will be the last reading stored. For example, if reading #65 was the last point, the display will show:

5. The second and third points will be the high and low data points. For example, for the high value, the display will show:

Front Panel Trigger Mode

n=65

n=HI

6. Following these three points, the remaining data points will

be displayed, beginning with the first one stored. The data

pointer will increment from 1 to the maximum point stored. For example, the tenth reading appears as:

n=lO

7. To continue recalling readings, use the RECALL button to scroll the data pointer. Scrolling becomes more rapid if the RECALL button is held in. Release the button when the desired data point is displayed.

8. The recall mode can be cancelled simply by pressing SHIFT RECALL. The instrument will then return to the normal display mode. As long as data store is not disabled and

then w-enabled, readings are retained within memory. You can return to the recall mode at any time to review data.

9. To cancel data store operation, press the ON/OFF button. The ON/OFF LED will turn off, indicating that data

store is disabled. Data is retained until data store is en-

abled once again. Thus, you can still recall data eve”

after data store is turned off.

Data Store Operating Notes:

1. Data logging continues at the selected rate during the recall until all 100 locations have been filled. Logging stops when all 100 locations are full, as indicated by the flashing DATA indicator.

2. The data store trigger mode should not be confused with the front panel trigger mode. The data store trigger mode is enabled by entering the special trigger parameter (r=6) at the beginning of the data storage process, while the front panel trigger mode is entered by pressing SHIFr TRIG.

3. If the instrument is placed in the front panel one-shot trig-

ger mode, display readings will be triggered at the data store rate interval except when r=O. For example, if the instrument is set up for 10 minute intervals, one reading will be triggered and displayed every 10 minutes. When r=O, a single reading is stored each time a” appropriate trigger is received (for example, GET in the T3 trigger mode, as described in paragraph 3.10.14)

4. The data store rate can be used to control the data output rate in the IEEE-488 talk-only mode. To use the Model 617 in this manner, place the instrument in the talk only mode (see paragraph 3.7). Now enter the data storage mode and

select the desired interval as described above. The instrument will then output readings over the IEEE-488 bus at the selected rate.

5. The storage rate in r=O and r=l may be affected if the in-

strument is in autorange and a range change occurs. Typically, it takes about 350msec per range change.

2-28

Minimum/Maximum Operation:

To use the external triggering, proceed as follows:

Minimum/Maximum operation is essentially separate from

data store except for the fact that both are enabled or disabled by the ON/OFF button. Thus, the minimum and maximum data points are continuously updated with each triggered conversion as long as the ON/OFF LED is on. Note that only range, not function, is indicated when reading maximum and minimum values. Maximum and minimum values can be obtained during the recall process, as indicated in step 4 above.

2.13 EXTERNAL TRIGGERING

The Model 617 has two external BNC connectors on the rear panel associated with instrument triggering. The EXTERNAL TRIGGER INPUT allows the instrument to be triggered by other devices, while METER COMPLETE OUTPUT allows the instrument to trigger other devices.

2.13.1 External Trigger

The Model 617 may be triggered on a continuous or one-shot

basis. For each of these modes, the trigger stimulus will depend on the selected trigger mode, which is further described in paragraph 3.10. In a continuous trigger mode, the instrument takes a continuous series of readings. A trigger stimulus in continuous triggers a new reading. In a one-shot mode, only a single reading is taken each time the instrument is triggered

The EXTERNAL TRIGGER INPUT requires a falling edge pulse at ‘ITL logic levels, as shown in Figure 2-22. The low logic level should be between O-O.&‘, and the high level

should be 2-5V. The minimum pulse width for reliable trig-

gering is approximately lO+ec. Connections to the rear panel EXTERNAL TRIGGER INPUT jack should be made with a standard BNC connector. If the instrument is in the external trigger mode, it will be triggered to take readings while in

either a continuous or one-shot mode when the negative-

going edge of the external trigger pulse occurs.

1. Connect the external trigger source to the rear panel BNC EXTERNAL TRIGGER INPUT connector. The shield (outer) part of the connector is connected to digital common. Since an internal pull-up resistor is used, a

mechanical switch may be used. Note, however, that debouncing circuitry will probably be required to avoid im-

proper triggering.

CAUTION Do not exceed 30V between digital common and chassis ground, or instrument damage may occur.

2. Place the instrument in the one-shot trigger mode by pressing SHIFT and then TRIG in that order. The instrument will indicate that it is in the one-shot mode by illuminating the SGL indicator.

3. To trigger the instrument, apply a pulse to the External Trigger input. The instrument will process a single reading each time the pulse is applied. Note that the instrument may also be triggered by pressing TRIG.

4. To return the instrument to the continuous mode, press the SHIFT and TRIG buttons in sequence.

NOTES:

1. External triggering can be used to control the fill rate in the data store mode. See paragraph 2.12 for details.

2. The Model 617 must be in the appropriate trigger mode to

respond to external triggering (the unit will be in this mode

upon power-up). See paragraph 3.10.14 for details.

3. If a trigger overrun occurs (the instrument is triggered while processing a reading from a previous trigger), it will ignore the trigger and display the following:

t En

2.13.2 Meter Complete

Figure 2-22. External Trigger Pulse Specifications

The Model 617 has an available output pulse that can be used to trigger other instrumentation. A single lTL-compatible negative-going pulse with a minimum duration of 10~sec (see Figure 2-23) will appear at the METER COMPLETE OUTPUT jack each time the instrument completes a reading. To use the meter complete output, proceed as follows:

1. Connect the Model 617 to the instrument to be triggered with a suitable shielded cable. Use a standard BNC connector to make the connection to the Model 617.

2-29

CAUTION

Do not exceed 30V between the METER COMPLETE ccmmcn (outer ring) and chassis ground or instrument damage may

OCCW.

reading. When the Model 617 finishes the reading, it triggers

the Model 705 to scan to the next channel. The process repeats until all channels have been scanned.

To use the Model 617 with the Model 705, proceed as follows:

2. Select the desired function, range, trigger mode, and other operating parameters, as desired.

3. In a continuous trigger mode, the instrument will output

pulses at the conversion rate; each pulse will occur after the Model 617 has completed a conversion.

4. In a one-shot trigger mode, the Model 617 will output a

pulse once each time it is triggered after it completes the reading conversion.

Figure 2-23. Meter Complete Pulse Specifications

2.13.3 Triggering Example

1. Connect the Model 617 to the Model 705 as shown in Figure Z-21. Use shielded cables with BNC connectors. The Model 617 METERCOMPLETE OUTPUT jack should be connected to the Model 705 EXTERNAL TRIGGER INPUT jack. The Model 617 EXTERNAL TRIGGER INPUT should be connected to the Model 705 CHANNEL READY OUTPLIT Additional connections, which are not shown on the diagram, will also be necessary to apply signal inputs to the scanner cards, as well as for the signal lines between the scanner and the Model 617.

2. Place the Model 617 in the one-shot trigger mode by pressing the SHIFT and TRIG buttons, in that order.

3. Program the Model 705 scan parameters such as first and

last channel as required. Place the instrument in the single scan mode.

4. Install the desired scanner cards and make the required input and output signal connections. See the Model 705 Instruction Manual for details.

5. If data storage is required, enter the data storage mode as described in paragraph 2.12.

6. Begin the measurement sequence by pressing the Model

705 START/STOP button. The Model 705 will close the first channel and trigger the Model 617 to take a reading. When the Model 617 completes the reading, it will trigger

the Model 705 to go to the next channel. The process

repeats until all programmed channels have been scanned.

As an example of using both the external trigger input and the meter complete output, assume that the Model 617 is to be used in conjunction with a Keithley Model 705 Scanner to allow the Model 617 to measure a number of different signals, which are to be switched by the scanner. The Model 705 can switch up to 20 2-pole channels (20 single-pole channels with special cards such as the low-current card). In this manner, a single Model 617 could monitor up to 20 measurement points.

By connecting the triggering inputs of the two instruments together, a complete automatic measurement sequence could

be performed. Data obtained from each measurement point could be stored by the data store mode of the Model.617. Alternatively, the Model 617 could be connected through

the IEEE-488 bus to a printer, which would print out the

data for each point as it is measured.

Once the Model 705 is programmed for its scan sequence, the measurement procedure is set to begin. When the Model 705

closes the selected channel, it triggers the Model 617 to take a

Z-30

2.14 MEASUREMENT CONSIDERATIONS

The Model 617 is a highly sensitive instrument that can measure extremely low signal levels. At these low signal levels, a number of factors can affect a measurement. Some considerations when making measurements with the Model 617 are discussed in the following paragraphs.

2.14.1 Ground Loops

Ground loops that occur in multiple-instrument test set-ups can create error signals that cause erratic or erroneous measurements. The configuration shown in Figure 2-25 in-

troduces errors in two ways. Large ground currents flowing

in one of the wires will encounter small resistances, either in

the wires, or at the connecting points. This small resistance results in voltage drops that can affect the measurement. Even if the ground loop currents are small, magnetic flux cutting across the large loops formed by the ground leads can induce sufficient voltages to disturb sensitive measurements.

------\

r;YPlCAL GROUND LOOP,

(CAUSES CURRENT FLOW

. IN A SIGNAL LEAD,/

POWER LINE GROUND

MODEL 705

INSTRUMENT

Figure 2-24. External Triggering Example

To prevent ground loops, instruments should be connected to ground at only a single point, as shown in Figure Z-26. Note

INSTRUMENT

that only a single instrument is connected directly to power line ground. Experimentation is the best way to determine an acceptable arrangement. For this purpose, measuring instruments should be placed on their lowest ranges. The configuration that results in the lowest noise signal is the one that should be used.

2.14.2 Electrostatic Interference

MODEL 617

COMPLETE TRIGGER

OUTPUT

INPUT

Figure 2-25. Multiple Ground Points Create a

Ground Loop

INSTRUMENT

POWER LINE GROUND

INSTRUMENT

Figure 2-26. Eliminating Ground Loop

Electrostatic interference occurs when an electrically charged object is brought near an uncharged object, thus inducing a charge on the previously uncharged object. Usually, effects of such electrostatic action are not noticable because low impedance levels allow the induced charge to dissipate quickly. However, the high impedance levels of many Model 617 Electrometer measurements do not allow these charges to decay rapidly, and erroneous or unstable readings may result. These erroneous or unstable readings may be caused in the following ways:

1. DC electrostatic field can cause undetected errors or noise in the reading.

2. AC electrostatic fields can cause errors by driving the

amplifier into saturation, or through rectification that produces DC errors.

Electrostatic interference is first recognizable when hand or body movements near the experiment cause fluctuations in

2-31

the reading. Pick up from AC fields can also be detected by observing the electrometer output on an oscilloscope. Line frequency signals on the output are an indication that electrostatic interference is present.

Means of minimizing electrostatic interference include:

vironments. The most obvious method is to keep the instrument and experiment as far away from the RF1 source as possible. Shielding the instrument, experiment, and test leads will often reduce RF1 to an acceptable level. In extreme cases, a specially constructed screen room may be necessary to sufficiently attenuate the troublesome signal.

Shielding. Possibilities include: a shielded room, a shielded booth, shielding the sensitive circuit, and using shielded cable. The shield should always be connected to a solid connector that is connected to signal low. If circuit low is floated above ground, observe safety precautions when touching the shield. Meshed screen or loosely braided cable could be inadequate for high impedances, or in strong fields. The Keithley Model 6104 Test Shield can provide shielding under many circumstances. Note, however, that shielding can increase capacitance in the measuring circuit, possibly slowing down response time.

Reduction of electrostatic fields. Moving power lines or other sources away from the experiment reduces the amount of electrostatic interference seen in the measurement.

2.14.3 Thermal EMFs

Thermal EMFs are small electric potentials generated by differences in temperature at the junction of two dissimilar metals. Low thermal connections should be used whenever

thermal EMFs are known to be a problem. Crimped or cad-

mium soldered copper to copper connections are methods

that can be used to minimize these effects.

2.14.4 RFI

If all else fails, external filtering of the input signal path may be required. In some &es, a simple one-pole filter may be sufficient. In more difficult situations, multiple-pole notch or band-stop filters, tuned to the offending frequency range, may be required. Keep in mind, however, that such filtering may have other detrimental effects (such as increased response time) on the measurement.

2.14.5 Leakage Resistance Effects

At normal resistance levels, the effects of leakage resistance

are seldom seen because any leakage resistance present is

generally much higher than the resistance levels encountered

in the circuit under test. At the high resistance levels of many

Model 617 measurements, however, leakage resistance can

have a detrimental effect on the measurement. Such leakage resistance can occur in the-circuit under test (on PC boards, for example), in the connecting cable, or even at the electrometer input itelf, especially if the input connector is not kept clean.

To see how leakage resistance can affect measurement accuracy, let us review the equivalent circuit in Figure 2-27. Es and Rs are the source voltage and source resistance respectively. The leakage resistance is represented by RL, while the voltage, as seen by the electrometer, is VM.

Radio Frequency Interference (RFI) is a general term frequently used to describe electromagnetic interference over a wide range of frequencies across the spectrum. RF1 can be especially troublesome at low signal levels, but it may also affect higher level measurements in extreme cases.

RF1 can be caused by steady-state sources such as TV or radio broadcast signals, or it can result from impulse sources, as in the case of arcing in high voltage environments. In either case, the effect on instrument performance can be consider-

able, if enough of the unwanted signal is present. The effects

of RF1 can often be seen as an unusually large offset, or, in the case of impulse sources, sudden, erratic variations in the displayed reading.

RF1 can be minimized by taking one or more of several precautions when operating the Model 617 in such en-

2-32

Rs and RL form a voltage divider that attenuates the input signal in accordance with the formula:

viq =-

Rs + RL

Thus, if RL has a value of lCOGQ and Rs is lOGQ, the actual voltage measured by the electrometer with a 1OV source would be:

10 x 1WGSl

VM =

1OGQ + 1WGQ

vp”j = 9.09v

Thus, we see that the effects of leakage resistance can be substantial, resulting in an error of almost 10% in this case.

Certain steps can be taken to ensure that the effects of leakage resistance are mimimal. The most obvious remedy to ensure that the leakage resistance itself is as high as possible. Use only good quality triaxial cable for signal connections, and make sure that the circuit under test and connectors are kept free of contamination.

Even with these steps, however, there is a limit as to how high the leakage resistance can be. In those cases, guarded input connections should be used, as described in paragraph 2.7.4.

Note that Rs is given in megohms, C is in microfarads, while t

is in seconds.

Because of the charging of GIN, the electrometer follows the exponential curve shown in Figure 2.288. At the end of one time constant (R&IN), the voltage will reach approximately 63% of its final value. At the end of two time constants

(2R5C). the voltage will reach about 86% of its final value, and so on. Generally, at least five time constants should be allowed for better than 1% accuracy.

The amount of time that must be allowed will, of course, de pend on the relative values of R5, and GIN. For example, when measuring a voltage with a source resistance of 1OGR with an input capacitance of 100pF. a time constant of 1 se cond results. Thus, at least five seconds must be allowed to achieve a better than 1% accuracy figure. Table 2-8 sum-

marizes voltage values and percentage error values for ten different time constants (T = R$ZIN).

")J = -

ESRL

Rs + RL

Figure Z-27. Leakage Resistance Effects

2.14.6 Input Capacitance Effects

Virtually any circuit has at least some small amount of distributed capacitance that can slow down the response time of high-impedance measurements. Even if the circuit itelf has minimal capacitance, cable or instrument input capacitance effects can be noticable.

As an example, assume that the Model 617 is being used to measure the value of a high-impedance voltage source, as shown in Figure 2-28. The source and source resistance are represented by E5 and R5, the input capacitance is GIN, and

the voltage measured by the electrometer is VM.

When E5 is first applied, the voltage across the capacitance

(and thus, at the electrometer input) does not instantaneously rise to its final value. Instead, the capacitance charges exponentially in accordance with the following formula:

The most obvious method to minimize the slowing effects of input capacitance is to minimize the amount of capacitance in

I I

the circuit. Using low capacitance cable and keeping the cable

as short as possible are two ways to do so. However, there is

a limit to the amount of capacitance reduction that can be achieved. In those cases, especially where high impedance levels are involved, guarded operation (see paragraph 2.7.4)

may be necessary.

While input capacitance does increase rise-time, it can help to

filter out some noise present at the input by effectively reduc-

ing electrometer bandwidth. If we assume that all input

capacitance is lumped into a single element, the half-power

(- 3dB) point of the circuit in Figure Z-28 will be:

f-3dB =

~~RsCIN

Thus, if Rs has a value of lOM’J, and CON has a value of

lCOpF, the half-power point will be 159Hz.

f-3dB

2-33

Table 2-8. Voltage and Percent Error For Various

Time Constants

/Time* 1 VM / % Error

7 IO.632 Es / 36

Figure 2-29. Simplified Model for Source

Resistance and Source Capacitance

Effects

A. CIRCUIT

0.632 ES kL

RSCIN

6. EXPONENTIAL RESPONSE

Figure 2-28. Input Capacitance Effects

2.14.7 Source Resistance

As shown in Table 2-9, a minimum value of source resistance

is recommended for each AMPS range. The reason for this

can be understood by examining Figure 2-29. Considering ef-

fects on low frequency noise and drift, Cs and CF can momentarily be ignored.

Table 2-9. Minimum Recommended Source Resis-

tance Values in Amps

Minimum Source

Range I

All pA 1

All mA

Input amplifier noise and drift appearing at the output can be calculated as follows:

Equation 1.

Output Enoise

Thus it is clear that as long as Rs>> RF, Output E,,ise = Input En,,ire. When RF = Rs, output Enoh = 2 X Input Enoie.

= Input En+ X (1 +-)

Resistance

lOOGil

1OOMQ

100 kQ

100 n

2-34

The same applies for EOS. The Model 617 will typically show

insignificant degradation in displayed performance with the

noise gain of 2 resulting from allowing Rg = Rm. Typical

amplifier input E,,ise is about 9pV p-p in a bandwidth of

0.1.1OHz. Amplifier EOS can be nulled by using suppress. The temperature coefficient of Eos is< 304~V/“C. These numbers can be used with Equation (1) to determine expected displayed noise/drift given any source resistance. Note also that the values given in Table 2-9 for minimum source resistance also represent the value of RF on that range.

When measuring leakage currents on capacitors larger than lO,OOOpF, stability and noise performance can be maintained by adding a resistor in series with the capacitor under test.

The value of this resistor should be around 1MQ. For large

capacitor values (> lpF), the value of the series limiting resistor can be made lower in order to improve settling times;

however, values below 10kR are not generally recommended.

This resistor is not critical in terms of tolerance or stability. Any carbon composition resistor will prove adequate.

2.14.8 Source Capacitance

In amps, the Model 617 is designed to accommodate up to

10,OOOpF input capacitance CC,). This limit will preclude problems in most test setups and allow extremely long input cable lengths without inducing instability or oscillations.

Increasing capacitance beyond this level may increase noise and induce instrument instability. The noise gain of the measurement circuit can be found from:

Equation 2.

Output E, = Input E, x ( 1 +$ )

where ZF =

\I (2a fRpC# + 1

and Zs =

vGziifRSCs)2 +u

Clearly as f - 0 equation (2) reduces to equation (1)

2.15 ENGINEERING UNITS CONVERSION

The Model 617 is a highly sensitive instrument with wideranging measurement capabilities. In the amps mode, for example, the unit can detect currents as low as O.lfA (lo--lbA). At the other extreme, resistances in the 1OMl (10160) range can be measured. The instrument can display its reading either in engineering units (such a mA) or in scientific notation (such as lo-3A). Table 2-10 lists engineering units and their equivalent scientific notation values.

Table 2-10. Engineering Units Conversion

Symbol 1 Prefix Exponent

/ femto- 1 lo-15

P ”

G T

pico-

“S”O-

milli-

kilo-

mega-

giga-

tera-

peta-

10-v

10-S 10-G

10-3

103 106

109

1012

1015

Refer to Table 2-11 for equivalent voltage sensitivity of 617 amps ranges.

The frequency range of interest is 0.1 to lOI& which is the

noise bandwidth of the A/D converter. The value of CF is 5pF for pA ranges, 22pF for nA ranges and 1CGOpF for pA ranges.

In general, as Cs becomes larger, the noise gain becomes larger. An application where Cs may be greater than 10,COOpF is leakage measurement of capacitors. In this case

Input E, must include the effects of the voltage source (Es) used to bias the capacitor (any noise in the source voltage will

increase the input noise).

Table 2-11. Equivalent Voltage Sensitivity

of 617 Amps Ranges

Range

2pA, 2nA. 2pA 2mA ZOpA, 20nA. ~OJLA 20mA 200pA. 2OOnA, 200pA

Sensitivity hV/count)

---.-

2-3512-36

SECTION 3

IEEE-488 PROGRAMMING

3.1 INTRODUCTION

The IEEE-488 bus is an instrumentation data bus with hardware and programming standards originally adopted by the IEEE (Institute of Electrical and Electronic Engineers) in 1975 and given the IEEE488 designation. In 1978, standards were upgraded into the IEEE-488-1978 standards. The Model 617 conforms to these IEEE-488.1978 standards.

This section contains general bus information as well as the

necessary programming information and is divided into the following sections:

1. Introductory information pertaining to the IEEE-488 bus in general is located in paragraphs 3.2 through 3.6.

2. Information necessary to connect the Model 617 to the IEEE-486 bus is contained in paragraphs 3.7 and 3.8.

3. General bus command programming is covered in paragraph 3.9.

4. Devicedependent command programming is described in paragraph 3.10. These are the most important commands associated with the Model 617 as they control most of the instrument functions.

5. Additional information necessary to use the Model 617 over the IEEE-488 bus is located in the remaining paragraphs.

3.2 BUS DESCRIPTION

The IEEE-488 bus, which is also frequently referred to as the

GPIB (General Purpose Interface Bus), was designed as a

parallel transfer medium to optimize data transfer without us-

ing an excessive number of bus lines. In keeping with this goal, the bus has only eight data lines that are used for both data and with most commands. Five bus management lines

and three handshake lines round out the complement of bus signal lines.

A typical configuration for controlled operation is shown in Figure 3-l. The typical system will have at least one controller and one or more devices to which commands are given and,

in most cases, from which data is received. Generally, there are three categories that describe device operation: controller,

talker, and listener.

Figure 3-1. IEEE Bus Configuration

The controller does what its name implies: it controls other devices on the bus. A talker sends data (usually to the con-

troller), while a listener receives data. Depending on the instrument, a particular device may be a talker only, a listener only, or both a talker and a listener.

3-l

There are two categories of controllers: system controller, and basic controller. Both are able to control other instruments, but only the system controller has the absolute authority in the system. In a system with more that one con-

troller, only one controller may be active at any given time. Certain protocol is used to pass control from one controller to

another.

The IEEE-488 bus is limited to 15 devices, including the con-

troller. Thus, any number of talkers and listeners up to that

limit may be present on the bus at one time. Although several devices may be commanded to listen simultaneously, the bus can have only one active talker, or communications would be

scrambled.

A device is placed in the talk or listen state by sending an appropriate talk or listen command. These talk and listen com-

mands are derived from an instrument’s primary address. The

primary address may have any value between 0 and 30, and is

generally set by rear panel DIP switches or programmed in

from the front panel of the instrument. The actual listen ad-

dress .value sent out over the bus is obtained by ORing the

primary address with $20. For example, if the primary ad-

dress is 27 ($lB), the actual listen address is $3B ($38 = $lB

+ $20). In a similar manner, the talk address is obtained bv OR& the primary address value with $40. With the present example, the talk address derived from a primary address of 27 decimal would be $5B ($SB = $lB -t $40)

The IEEE-488 standards also include another addressing mode called secondary addressing. Secondary addresses lie in the range of $60-$7F. Note, however, that many devices do not use secondary addressing.

3.3.1 Data Lines

The IEEE-488 bus uses eight data lines that allow data to be transmitted and received in a bit-parallel, byte serial manner. These lines use the convention DIOl-DIOS instead of the more common DO-D7. DIOl is the least significant bit, while DIOS is the most significant bit. The data lines are bidirectional (with most devices), and, as with the remaining lines, low is considered to be true.

3.3.2 Bus Management Lines

The five bus management lines help to ensure proper interface control and management. These lines are used to send the uniline commands that are described in paragraph. 3.4.1.

ATN (Attention)-The ATN line is one of the more important management lines in that the state of this line determines how information on the data bus is to be interpreted.

IFC (Interface Clear&As the name implies, the IFC line con-

trols clearing of instruments from the bus.

REN (Remote Enable&The REN line is used to place instrument on the bus in the remote mode.

EOI (End or Identify&The EOI line is usually used to mark

the end of a multi-byte data transfer sequence.

SRQ (Service Request)-This line is used by devices when

they require service from the controller.

Once the device is properly addrwed, appropriate bus transactions are set to take place. For example, if an instrument is

addressed to talk, it will usually place its data byte on the bus one byte at a time. The listening device (frequently the controller) will then read this information.

3.3 IEEE-488 BUS LINES

The signal lines on the IEEE-488 bus are grouped into three

different categories: data lines, management lines, and handshake lines. The data lines handle bus data and commands, while the management and handshake lines ensure that proper data transfer and bus operation takes place. Each bus iine.is active low, with approximately zero v&s representing a logic 1 (true). The following paragraphs describe the purpose of these lines, which are shown in Figure 3-l.

3-2

3.3.3 Handshake Lines

The bus uses handshake lines that operate in an interlocked

sequence. This method ensures reliable data transmission ms method ensures reliable data transmission

..6YA....00 ,f the transfer rate. Generally, data transfer will regardless of the transfer rate. Generally, data transfer will

occur at a rate determined by the slowest active device on the occur at a rate determined by the slowest active device on the bus

One of the three handshake lines is controlled by the source (the talker sending information), while the remaining two lines are controlled by accepting devices (the listener or listeners ret-‘..‘-- ’ S~~UZS rhe information lines are:

DAV (Data Valid&The source controls the state of the DAV line to indicate to any listening devices whether or not data bus information is valid.

x*e lines that operate in an mterlockza

0. The three handshake

NRFD (Not Ready For Data&The acceptor controls the state

of NRFD. It is used to signal to the transmitting device to hold off the byte transfer sequence.

NDAC (Not Data Accepted)-NDAC is also controlled by the accepting device.

The complete handshake sequence for one data byte in shown

in Figure 3-Z. Once data is placed on the data lines, the source checks to see that NRFD is high, indicating that all active devices are ready. At the same time, NDAC should be low from the previous byte transfer. If these conditions are not met, the source must wait until NDAC and NRFD have the correct status. If the source is a controller, NRFD and NDAC must be stable for at least 1OOnsec after ATN is set true. Because of the possibility of a bus hang up, many controllers have time-out routines that display messages in case the transfer sequence stops for any reason.

Once all NDAC and NRFD are properly set, the source sets DAV low, indicating to accepting devices that the byte on the data lines is now valid. NRFD will the” go low, and NDAC will go high once all devices have accepted the data. Each device will release NDAC at its own rate, but NDAC will not be released to go high until all devices have accepted the data byte

to its low state, and NRFD is released by each device at its

own rate, until NRFD goes high when the slowest device is

ready, and the bus is set to repeat the preocess with the next data byte.

The sequence just described is used to transfer data, talk and listen addresses, as well as multiline commands. The state of the ATN line determines whether the data bus contains data, addresses, or commands as described in the following paragraph.

3.4 BUS COMMANDS

While hardware aspects of the bus are essential, the interface would have minimal capabilities without appropriate commands to control communications among the various devices on the bus. This paragraph briefly describes the purposes of the various device commands, which are grouped into the following three general categories:

Uniline Commands-Sent by setting the corresponding bus line true.

Multiline Commands-General bus commands which are sent over the data lines with ATN true (low).

DA”’

NRFD

VALID

I I

SOURCE

ACCEPTOR

NDAC

I ,

DATA

TRANSFER

BEGINS

ACCEPTOR

DATA

TRANSFER

ENDS

Figure 3-2. IEEE Handshake Sequence

Once NDAC goes high, the source then sets DAV high to indicate that the data byte is no longer valid. NDAC is returned

Device-dependent Commands-Special commands whose meanings depend on device configuration; sent over the data lines with ATN high (false).

These bus commands and their general purposes are surnmarized in Table 3-l.

3.4.1 Uniline Commands

ATN, IFC, and REN are asserted only by the controller. SRQ

is asserted by a” external device. EOI may be asserted either

by the controller or other devices depending on the direction

of data transfer. The following is a description of each command. Each command is sent by setting the corresponding bus line true.

REN (Remote Enable)-REN is sent to set up instruments on

the bus for remote operation. Generally, REN should be sent

before attempting to program instruments over the bus.

EOI (End or Identify&E01 is used to positively identify the last byte in a multi-byte transfer sequence, thus allowing data words of various lengths to be transmitted easily.

IFC (Inter&z Clear)-IFC is used to clear the interface and return all devices to the talker and listener idle states.

ATN (Attention)-The controller sends ATN while transmit-

ting addresses or multiline commands.

SRQ (Service Request)-SRQ is asserted by a device when it requires service from a controller.

3.4.2 Universal Commands

Universal commands are those multiline commands that require no addressing. All devices equipped to implement such commands will do so simultaneously when the command is transmitted. As with all multiline commands, these commands are transmitted with ATN true.

SPD (Serial Poll Disable)-SPD is used by the controller to remove a11 devices on the bus from the serial poll mode and is generally the last command in the serial polling sequence.

3.4.3 Addressed Commands

Addressed commands are multiline commands that must be preceded by the devici listen address before that instrument will respond to the command in question. Note that only the addressed device will respond to these commands:

SDC (Selective Device Clear)-The SDC command performs essentially the same function as the DCL command except that only the addressed device responds. Generally, instruments return to their power-up default conditions when responding to the SDC command.

LLO (Local Lockou+LLO is sent to instruments to lock out their front panel controls.

DCL (Device Clear)-DCL is used to return instruments to some default state. Usually, instruments return to their power-up conditions.

SPE 6xial Poll Enable)-SPE is the first step in the serial polling sequence, which is used to determine which device has requested service.

Table 3-l. IEEE-488 Bus Command Summaw

Command Type Command Uniline REN (Remote Enable)

EOI IFC (Interface Clear) ATN (Attention) SRQ

Multiline

Universal LLO (Local Lockout)

DCL (Device Clear) SPE (Serial Poll Enable) SPD (Serial Poll Disable)

Addressed SDC (Selective Device Clear) !

GTL (Go To Local) GET (Group Execute Trigger)

Unaddressed UNL (Unlisten)

UNT Wntalk)

Device-dependent”*

GTL (Go To Local&The GTL command is used to remove instruments from the remote mode. With some instruments, GTL also unlocks front panel controls if they were previously locked out with the LLO command.

GET (Group Execute Trigger)-The GET command is used to

trigger devices to perform a specific action that depends on device configuration (for example, take a reading). Although GET is an addressed command, many devices respond to GET without addressing.

State of

ATN Line” Comments

X Set up for remote operation.

X Marks end of transmission. X Clears Interface

LOW Defines data bus contents.

X Controlled by external device.

Low Low

Locks out front panel controls.

Returns device to default conditions. LOW Enables serial polling. LOW Disables serial polling. LOW Returns unit to default conditions. LOW Sends go to local. Low Triggers device for reading. Low LOW

Removes all lineners from bus.

Removes any talkers from bus.

High Programs Model 617 for various modes.

*Don’t Care.

**See paragraph 3.10 for complete description.

3.4.4 Unaddress Commands

purposes only; the Model 617 does not have secondary addressing capabilities.

The two unaddress commands are used by the controller to remove any talkers or listeners from the bus. ATN is true when these commands are asserted.

UNL (LJnlisten)-Listeners are placed in the listener idle state by the UNL command.

UNT (Untalk)-Any previously commanded talkers will be placed in the talker idle state by the UNT command.

3.4.5 Device-Dependent Commands

The meaning of the device-dependent commands will depend

on the configuration of the instrument. Generally, these com-

mands are sent as one or more ASCII characters that tell the

device to perform a specific function. For example, the command sequence FOX is used to place the Model 617 in the volts mode. The IEEE-486 bus actually treats these commands as data in that ATN is false when the commands are transmit-

ted.

3.5 COMMAND CODES

Each multiline command is given a unique code that that is

transmitted over the bus as 7 bit ASCII data. This section

briefly explains the code groups, which are summarized in

Figure 3-3.

Note that these commands are normally transmitted with the 7 bit code listed in Figure 3-3. For many devices, the condition of DI08 is unimmxtant. However. manv devices mav reouire

, .

that DI08 has a value of logic 0 (high) to properly send commands.

Hexadecimal and decimal values for each of the commands or command groups are listed in Table 3-2. Each value assumes that DI08 has a value of 0.

Table 3-2. Hexadecimal and Decimal Command

Codes

hmmand

GIL

SDC

GET

LLO DCL SPE

SPD

LAG

TAG

UNL

UNT

Hex Value

11 14 18 19

20.3F 40-5F

3F 5F

Decimal Value

24 25

32-63

64-95

Addressed Command Group (ACG)-Addressed commands an* co*esp0n*1ng ASCII codes are listed in cohxnns WA,

. .--_. . . . . . _I.~

and O(B).

Universal Command Group (UCG)--Universal commands and values are listed in columns l(A) and l(B).

Listen Address Group (LAG)-Columns 2(A) through 3(B)

list codes for commands in this address group. For example, if the primary address of the instrument is 27, the LAG byte will be an ASCII left bracket.

Talk Address Group (TAG)-TAG primary address values and corresponding ASCII characters are listed in columns 4(A) through 5(B).

The preceding address groups are combined together to form the Primary Command Group (KG). The bus also has another group of commands, called the Secondary Command Group (SCG). These are listed in Figure 3-3 for informational

3.6 COMMAND SEQUENCES

The proper command sequence must be sent to the instrument before it will respond as intended. Universal commands, such as LLO and DCL, require only that ATN be set low when sending the command. Other commands require that the instrument be properly addressed to listen first. This section briefy describes the bus sequence for several types of commands.

3.6.1 Addressed Command Sequence

Before a device will respond to one of these commands, it must receive a LAG command derived from its primary ad- dress. Table 3-3 shows a typical sequence for the SDC command: the example assumes that a primary address of 27 is being used.

3-5

3-6

Note that an IJNL command is generally sent before the LAG, SDC sequence. This is usually done to remove all other listeners from the bus so that the desired device responds to the command.

Table 3-3. Typical Addressed Command Sequence

3.7 HARDWARE CONSIDERATIONS

Before the Model 617 can be operated over the IEEE-466 bus,

it must first be connected to the bus with a suitable cable. Also, the primary address must be programmed to the correct value, as described in the following paragraphs.

Data Bus

itep Command ATN State

2 3

UNL Set low ? 3F

LAG* stays low I 36

SDC stays low EOT 04

Returns high

ASCII Hex Decimal

63 59

“Assumes primary address=27.

3.6.2 Universal Command Sequence

Universal commands are sent by setting ATN low and then placing the command byte on the data bus. ATN would then remain low during the period the command is transmitted. For example, if the LLO command were to be sent, both ATN and LLO would be asserted simultaneously.

3.6.3 Device-Dependent Command Sequence

Device-dependent commands are transmitted with ATN false. However, a device must be addressed to listen before these commands are transmitted. Table 3-4 shows the byte se-

quence for a typical Model 617 command (FOX), which sets

the instrument for the volts mode of operation.

3.7.1 Typical Cohtrolled Systems

System configurations are many and varied and will depend on the application. To obtain as much versatility as possible, the IEEE-488 bus was designed so that additional instrumentation could be easily added. Because of this versatility,

system complexity can range from the very simple to ex- tremely complex.

Figure 3-4 shows two possible system configurations. Figure

3-4(a) shows the simplest possible controlled system. The controller is used to send commands to the instrument, which sends data back to the controller.

The system in Figure 3-4(b) is somewhat more complex in that additional instruments are used. Depending on programming, all data may be routed through the controller, or it may be sent directly from one instrument to another.

In very complex applications, a larger computer could be used. Tape drives or disks could be used to store any data generated by the instruments.

Table 34. Typical Device-Dependent Command

Sequence

Command

teP i-

2 3 4 5

UNL

LAG”

Data Data Data

*Assumes primary address = 27.

[~j~E$

MODEL 617 CONTROLLER

IA, SIMPLE SYSTEM

CONTROLLER

IS, ADDITIONAL INSTRUMENTATION

Figure 3-4. System Types

3-7

3.7.2 Bus Connections

The Model 617 is to be connected to the IEEE-486 bus through a cable equipped with standard IEEE-486 connectors, an example of which is shown in Figure 3-5. The connector is designed to be stacked to allow a number of parallel connections. Two screws are located on each connector to ensure that connections remain secure. Current standards call for metric threads, as identified by dark colored screws. Earlier versions had different screws, which are silver colored. Do not attempt to use these type of connectors with the Model 617, which is designed for metric threads.

3. Add additional connectors from other instruments, as required.

4. Make sure the other end of the cable is mouerlv connected

to the controller. Some controllers have a; IEEE-488 type connector, while others do not. Consult the instruction manual for your controller for the proper connecting method.

INSTRUMENT

Figure 3-6. IEEE-488 Connections

INSTRUMENT

INSTRUMENl

CONTROLLER

Figure 3-5. IEEE-488 Connector

A typical connecting scheme for the bus is shown in Figure 3-6. Each cable normally has the standard connector on each end. These connectors are designed to be stacked to allow a number of parallel connections on one instrument.

NOTE

To avoid possible damage, it is recommended that you stack no more than three connectors on any one instrument.

Connect the Model 617 to the cable as follows:

NOTE

The IEEE-488 bus is limited to a maximum of 15

devices, including the controller. Also, the maxi-

mum cable length is limited to 20 meters, or 2 meters times the number of devices, which ever is less. Failure to heed these limits may result in

erratic bus operation.

Custom cables may be constructed by using the information in Table 3-5 and Figure 3-8. Table 3-5 lists the contact assignments for the various bus lines,~ while Figure 3-8 shows

contact assignments.

CAUTION The voltage between IEEE-488 common and chassis ground must not exceed 30V or instrument damage may occur.

EEE 488 ,NTERFACE

ADDRESS ENTERED WITH

FRONT PANEL PROGRAM

1. Line up the connector on the cable with the connector on the rear panel of the instrument. See Figure 3-7 for connec-

tor location.

2. Tighten the screws securely, but do not overtighten them.

3-g

3OV MAX

rf;r

Figure 3-7. 617 Rear Panel IEEE Connector

Table 3-5. IEEE Contact Designations

3.7.3 Primary Address Programming

contact

Uumber

10 11 12 13 14 15 D107 16 17 18 Gnd, (6)*

19 20 21 22 23 Gnd, (111* 24

IEEE-488 Designation

DlOl

D102

D103

Di04 5 EOI 1241” 6

DAV 7

NRFD 8 NDAC 9 IFC

SRQ

ATN

SHIELD

D105

D106

D108

REN (24)’

Gnd, (7)*

Gnd, (8)”

Gnd, (9)”

Gnd, (101’

Gnd, LOGIC

Type

Data Data Data Data Management Handshake Handshake Handshake Management Management

Management

Ground

Data Data Data Data Management Ground Ground Ground Ground Ground Ground Ground

*Number in parenthesis refer to signal

ground return of referenced contact number. EOI and REN signal lines return on contact 24.

The Model 617 must receive a listen command before is will

respond to addressed commands. Similarly, the unit must receive a talk command before it will transmit its data. The Model 617 is shipped from the factory with a programmed

primary address of 27. Until you become more familiar with your instrument, it is recommended that you leave the ad-

dress at this value be&se the programming examples includ-

ed in this manual a~wme that address.

The primary address may be set to any value between 0 and 30 as long as address conflicts with other instruments are avoided. Note that controllers are also given a primary address, so you must be careful not to use that address either. Most frequently, controller addresses are set to 0 or 21, but you should consult the controller’s instruction manual for details. Whatever primary address you choose, you must make certain that it corresponds with the value specified as part of the controller’s programming language.

To check the present primary address, or to change to a new

one, use the following sequence:

1. Press the PROGRAM SELECT button repeatedly until the following message is displayed:

IEEE 27

2. This message indicates that the IEEE address program is

selected, along with the presently programmed value (in

this case, the default value of 27 is being displayed).

3. Using one of the V-SOURCE ADJUST buttons, scroll the displayed address to the desired value (the display will show special values for the talk-only mode, as described in the next paragraph).

4. Exit the program by pressing SHIFT then SELECT EXIT. The new address is now in effect, and it will remain programmed even if the power is turned off.

CONTACT 12 CONTACT 1 I

CONTiCT 24

Figure 3-8. Contact Assignments

CONiACT 13

NOTE

Each device on the bus must have a unique primary address. Failure to observe this precaution will probably result in erratic bus operation.

3.7.4 Talk-Only Mode

The Model 617 may be placed into the talk-only mode and be used with a listen-only device such as a printer. When in this mode, the instrument will ignore commands given over the bus and merely output data as requested by the listening

3-S

device. When the instrument is in the talk-only mode, the front panel TALK LED will turn on.

3.8 SOFIWARE CONSIDERATIONS

The instrument can be placed in the talk-only mode by entering one of the following parameters in the primary address program:

40 Talk only mode with prefix on data string (Example:

NDCV--1.2345E-01

41 Talk only mode without prefix on data string (Example:

-1.2345E-01

To place the instrument in the talk-only mode, perform the following steps:

1. Press the PROGRAM SELECT button so that the following message is displayed:

IEEE 27

2. Press the up arrow V-SOURCE ADJUST button repeated-

ly until the desired talk-only parameter (40 or 41) is shown.

3. To exit the program, press SHIFT then SELECT EXIT. The

unit is now programmed for the talk-only mode, and it will remain programmed in this manner even if the power is turned off.

The data output rate in the talk-only mode can be selected as follows:

There are a number of IEEE-488 controllers available, each of which has its own programming language. Also, different instruments have differing capabilities. In this section, we will discuss programming languages for two typical controllers:

the HP-85, and the IBM-PC interfaced to the bus through a Keithley Model 8573 IEEE-488 interface. In addition, interface functions codes that define Model 617 capabilities will be discussed.

3.8.1 Controller Handler Software

Before a specific controller can be used over the IEEE-488 bus, it must have IEEE-488 handler software installed. With some controllers, the software is located in ROM, and no software

initialization is required on the part of the user. With other controllers, software must be loaded from disk or tape and be properly initialized. With the HP-85, for example, an additional I/O ROM that handles interface functions must be installed. With the Keithley Model 8573 interface for the IBMPC, software must be installed and configured from a

diskette.

Other small computers that can be used as IEEE-488 con-

trollers may have limited capabilities. With some, interface programming functions may depend on the interface being

used. Often little software “tricks” are required to obtain the

desired results.

1. Press and hold the DATA STORE ON/OFF button until the desired rate is displayed, as indicated below.

Displayed r Value/Data Output Rate

r=O

Conversion Rate (Every 36Omsec)

r=l

One reading per second One reading every 10 seconds

r=2

One reading per minute

r=3

One reading every 10 minutes

r=4

One reading per hour

r=5 r=6

On reading each time TRIG is pressed

2. Press the PROGRAM SELECT button until the IEEE program message is displayed and then release the button.

Select the desired IEEE-488 talk-only parameter (40 or 41) using an ADJUST button.

3. Press SELECT EXIT to return to normal operation. The in-

strument will then enter the talk-only mode and output readings over the IEEE-488 bus at selected intervals.

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 the hardware is causing a problem when it was the software all along.

3.8.2 Interface BASIC Programming Statements

Many of the programming instructions covered in this section use examples written with Hewlett Packard Model 85 BASIC and 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 617 operation.

A partial list of HP-85 and Model 8573 statements is shown in Table 3-6. HP-85 statements have a one or three digit argw

ment that must be specified as part of the statement. The first

310

digit is the interface select code, which is set to 7 at the fac-

tory. The last two digits of those statements requiring a 3-d@ argument specify the primary address.

Those statements with a 3-digit argument listed in the table shown a primary address of 27 (the default primary address

of the Model 617). For a different address, you would, of course, change the last two digits to the required value. For example, to send a GTL command to a device using a primary address of 22, the following statement would be used: LOCAL 722.

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 727 sends the SDC command to a device with a primary address

of 27.

The Model 8573 statements, which are also listed in Table 3-6, take on a somewhat different form. Each of these statements uses the IBM BASIC CALL statement, with various variables passed as shown in the table. The command words, such as IBCLR (Interface Bus Clear) and IBSRE (Interface Bus Send Remote Enable), are, in fact, BASIC variables themselves, which must be initialized at the start of each BASIC program. In addition, you must remember not to use these keywords for any other purpose in your BASIC program.

Before using the Model 8573 examples throughout this sec- tion, you must configure the software by using the procedure below. Note that the binary handler file called GPIB.COM and the system configuration file called CONFIGSYS must be present on the DOS boot disk, as described in the Model 8573 Instruction Manual.

1. Boot up your system in the usual manner and enter

BASICA.

2. Place the Model i573 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 followine lines to the declaration file: 7 NA%=“GPIBO’:CALL IBFIND(NAS,BRDO%)

8 NA$=“DEVO”:CALL IBFIND(NA$,M617%) 9 V%=27:CALL IBPAD(M617%.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 8573 programming examples throughout this section. Also, do not use the BASIC CLEAR or NEW commands after running this program.

Table 3-6. BASIC Statements Necessary to Send Bus Commands

Action

HP-65 Statement

Transmit string to device 27. 1 OUTPUT 727;AS Obtain string iom device 27. ENTER 727; AS Send GTL to device 27. Send SDC to device 27. Send DCL to all devices.

Send remote enable. Cancel remote enable. Serial poll device 27. Send local lockout. Send GET to device. Send IFC.

LOCAL 727 CLEAR 727 CLEAR 7

REMOTE 7

LOCAL 7

SPOLL (7271

LOCAL LOCKOUT 7 TRIGGER 727 ABORT10 7

Model 6573 Statement

CALL IBWRT IM617%, CMDS) CALL IBRD lM617%, RDSI CALL IBLOC lM617%) CALL IBCLR lM617%) CMDS=CHRS (EtH14): CALL IBCMD (BRDO%, CMDS)

V% = 1: CALL IBSRE (BRDO%, V%j

V%=O: CALL IBSRE lBRDO%, V%) CALL IBRSP (M617%, SB%) CMDS=CHRS (EtHll): CALL IBCMD (BRDO%, CMDS) CALL IBTRG lM617%) CALL IBSIC (BRDO%l

3-11

3.8.3 Interface Function Codes

LE (Extended Listener Function&The Model 617 does not

have extended listener capabilities.

The interface functions codes, which are part of the

IEEE-488-1978 standards, define an instrument’s ability to

support various interface functions and should not be confus-

ed with programming commands found elsewhere in this

manual. The interface function codes for the Model 637 are

listed in Table 3-7. These codes are also listed for convenience

on the rear panel adjacent to the IEEE-488 connector. The codes define Model 617 capabilities as follows:

SH (Source Handshake Function)-SH1 defines the ability of the Model 617 to initiate the transfer of message/data over the data bus.

AH (Acceptor Handshake Function)-AH1 defines the ability of the Model 617 to guarantee proper reception of message/data transmitted over the data bus.

T (Talker Function)-The ability of the Model 617 to send data over the bus to other devices is provided by the T func-

tion. Model 617 talker capabilities exist only after the instru-

ment has been addressed to talk, or when it has been placed in

the talk-only mode.

L (Listener Function&The ability for the Model 617 to receive devicedependent data over the bus from other

devices is provided by the L function. Listener capabilities of the Model 617 exist only after the instrument has been addressed to listen.

SR (Service Request Function)-The SR function defines the ability of the Model 617 to request service from the controller.

RL (Remote-Local Function)-The RL function defines the ability of the Model 617 to be placed in the remote or local modes.

PI’ (Parallel Poll Function)-The Model 617 does not have parallel polling capabilities.

E (Bus Driver Type)-The Model 617 has open-collector bus drivers.

Table 3-7. Model 617 interface Function Codes

Code Interface Function Stil Source Handshake Capability AH1 Acceptor Handshake Capability

Talker (Basic Talker, Serial Poll, Talk Only

Mode, Unaddressed To Talk On LAG)

Listener (Basic Listener, Unaddressed To Listen On TAG)

SRl Service Request Capability

RLl Remote/Local Capability

PPO No Parallel Poll Capability

DC1 Device Clear Capability

DTl Device Trigger Capability co No Controller Capability

Open Collector Bus Drivers

TEO No Extended Talker Capabilities

LEO No Extended Listener Capabilities

3.8.4 IEEE Command Groups

Command groups supported by the Model 617 are listed in Table 3-8. Device dependent commands, which are covered in paragraph 3.10, are not included in this list.

3.9 GENERAL BUS COMMAND PROGRAMMING

DC (Device Clear Function)-The DC function defines the ability of the Model 617 to be cleared (initialized).

DT (Device Trigger Function)-The ability for the Model 617

to have its readings triggered is provided by theDT function.

C (Controller Function)-The Model 617 does not have controller capabilities.

TE (Extended Talker Function)-The Model 617 does not have extended talker capabilities.

3-12

General bus commands are those commands such as DCL

that have the same general meaning regardless of the instru-

ment type. Commands supported by the Model 617 are listed

in Table 3-9. which also lists both HP-85 and Model 8573 statements necessary to send each command. Note that commands requiring that a primary address be specified assume that the Model 617 primary address is set to 27 (its default address). If you are using Model 8573 programming examples, remember that the modified declaration file must be loaded and run first, as described in paragraph 3.8.2.

Table 3-8. IEEE Command Groups

3.9.1 REN (Remote Enable)

HANDSHAKE COMMAND GROUP

DAC= DATA ACCEPTED RFD = READY FOR DATA DAV = DATA VALID

UNIVERSAL COMMAND GROUP

ATN = ATTENTION

DCL = DEVICE CLEAR

IFC= INTERFACE CLEAR

LLO = LOCAL LOCKOUT 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: TAG=TALK ADDRESS GROUP

MTA = MY TALK ADDRESS UNT= UNTALK

OTA = OTHER TALK ADDRESS

ADDRESSED COMMAND GROUP

ACG=ADDRESSED COMMAND GROUP

GET=GROUP EXECUTE TRIGGER GTL = GO TO LOCAL SDC = SELECTIVE DEVICE CLEAR

STATUS COMMAND GROUP

RQS=REQUEST SERVICE SRQ=SERIAL POLL REQUEST STB = STATUS BYTE EOI = END

The remote enable command is sent to the Model 617 by the controller to set up the instrument for remote operation. Generally, the instrument should be placed in the remote mode before you attempt to program it over the bus. Simply setting REN true will not actually place the instrument in the remote mode. Instead the intnxnent must be addressed after setting REN true befbre it will go into remote.

To place the Model 617 in the remote mode, the controller must perform the following sequence:

1. Set the REN line true.

2. Address the Model 617 to listen.

HP-85 Programming Example-This sequence is

automatically performed by the HP-85 when the following is typed into the keyboard.

REMOTE 727 (END LINE)

After the END LINE key is pressed, the Model 617 will be in the remote mode, as indicated by the REMOTE light. If not, check to see that the instrument is set to the proper primary address (27). and check to see that the bus connections are properly made.

Model 8573 Programming Example-To place the Model

617 into the remote mode, type the following lines into the computer.

V%=l:CALL IBSRE(BRDO%,V%) (return)

CMD$=“X”:CALL IBWRT(M617%,CMD$) (return)

Table 3-9. General Bus Commands and Associated BASIC Statements

HP-85

Command Statement

REN REMOTE 7

IFC ABORT10 7 CALL IBSIC (BRDO%)

LLO LOCAL LOCKOUT 7 CMDS=CHRS (EtHlll: CALL IBCMD Front panel controls locked out.

GTL LOCAL 727 CALL IBLOC fM617%) DCL CLEAR 7 CMDS =CHRSl&H14): CALL IBCMD

SDC CLEAR 727 CALL IBCLR (M617%) GET TRIGGER 727 CALL IBTRG (M617%)

LOCAL 7 V%=O: CALL IBSRE IBRDO%. V%l Cancel LLO

Model 8573 Statement Affect On Model 617

V% = l:CALL IBSRE (BRDO%, V%)

Goes into remote when next addressed.

Goes into talker and listener idle states.

(M617%. CMDS)

Cancel remote. Returns to default conditions.

(M617%, CMDS)

Returns to default conditions.

Triggers reading in T2 and T3 modes.

3-13

The instrument will go into the remote mode when the return key is pressed the second time.

After the return key is pressed, the instrument will return to the local and talker idle states.

3.9.2 IFC (Interface Clear)

The IFC command is sent by the controller to place the Model

617 in the local, talker and listener idle states. The unit will respond to the IFC command by cancelling front panel TALK panel controls except POWER will be inoperative. REN must or LISTEN lights. if the instrument was previously placed in one of those modes.

To send the IFC command, the controller need only set the

IFC line true for a minimum of 100~sec.

HP-85 Programming Example-Before demonstrating the 2. Place the LLO command on the data bus

IFC command, turn on the TALK indicator with the following statements:

REMOTE 727 (END LINE)

ENTER 727;A$ (END LINE)

At this point, the REMOTE and TALK lights should be on. The IFC command can be sent by typing in the following statement into the HP-85: After the second statement is entered, the instrument’s front

ABORT10 7 (END LINE)

3.9.3 LLO (Local Lockout)

The LLO command is used to remove the instrument from the local operating mode. After the unit receives LLO, all its front

be true for the instrument to respond to LLO. REN must be set false to cancel LLO.

To send the LLO command, the controller must perform the following steps:

1. Set ATN true.

HP-85 Programming Example-The LLO command is sent

by using the following HP-85 statement:

REMOTE 7 (END LINE)

LOCAL LOCKOUT 7 (END LINE)

panel controls will be locked out.

After the END LINE key is pressed, the REMOTE and TALK

lights will turn off, indicating that the instrument has gone into the talker idle state.

Model 8573 Proarammina Example-Place the instru-

ment in the remote-and talkeractive slates with the following

statements:

V% =l:CALL IBSRE(BRDO%,V%) (return)

CMD$=CHR$(&H5B):CALL IBCMD(BRDO%,CMD$)

bfum)

After the return key is pressed the second time, the instrument should be in the remote and talker active states, as indicated by the respective indicators.

To send IFC, enter the following statement into the IBM-PC:

CALL IBSIC(BRDO%) (return)

Model 8573 Programming Example-To send the LLO

command from the IBM-PC, type in the following statement:

V% =l: CALL IBSRE (BRDO%, V%) (RETURN)

CMD$=CHR$(&Hll):CALL IBCMD$(BRDO%,CMD$)

(return)

After the return key is pressed, Model 617 front panel con-

trols will be locked out.

3.9.4 GTL (Go To Local) and Local

The GTL command is used to take the instrument out of the

remote mode. With some instruments, GTL may also cancel LLO. With the Model 617, however, REN must first be placed false before LLO will be cancelled.

To send GTL, the controller must perform the following se-

quence.

3-14

1. Set ATN true.

2. Address the Model 617 to listen.

3. Place the G-l-L command on the bus,

controls. Now enter the following statement into the HP-85 keyboard:

CLEAR 7 (END LINE)

HP-85 Programming Example--Place the instrument in

the remote mode with the following statement:

REMOTE 727 (END LINE)

Now send GTL with the following statement:

LOCAL 727 (END LINE)

When the END LINE key is pressed, the front panel REMOTE

indicator goes off, and the instrument goes into the local mode. To cancel LLO, send the following:

LOCAL 7 (END LINE)

Model 8573 Programming Example--Place the instru-

ment in the remote mode with the following statements:

V%=l:CALL IBSRE(BRDO%,V%) (return)

CMD%=“X”:CALL IBWRT(M617%,CMD$) (return)

Now send GTL with the following statement:

CALL IBLOC(M617%) (return)

After return is pressed, the REMOTE indicator turns off, and

the instrument goes into the local mode. To cancel LLO, send the following:

V%=O: CALL IBSRE (M617%, V%) (return)

When the END LINE key is pressed, the instrument returns to

the default conditions listed in Table 3-10.

Model,8573 Programming Example-Place the unit in the

amps function, and cancel autorange with the front panel controls. Now enter the following statement into the IBM computer:

CMD$=CHR$(&H14):CALL IBCMD(BRDO%.CMDS)

(return)

When the return key is pressed. the instrument returns to the default conditions listed in Table 3-10.

3.9.6 SDC (Selective Device Clear)

The SDC command is an addressed command that performs essentially the same function as the DCL command. However, since each device must be individually addressed. the SDC command provides a method to clear only a single, selected instrument instead of clearing all instruments simultaneously, as is the case with DCL. When the Model 617 receives the SDC command, it will return to the power-up default conditions listed in Table 3-10.

Table 3-10. Default Conditions*

3.9.5 DCL (Device Clear)

The DCL command may be used to clear the Model 617 and return it to its power-up default conditions. Note that the DCL command is not an addressed command, so all instruments equipped to implement DCL will do so simultaneously. When the Model 617 receives a DCL command, it will return to the default conditions listed in Table 3-10.

To send the DCL command, the controller must perform the following steps:

1. Set ATN true.

2. Place the DCL command byte on the data bus

HP-85 Programming Example-Place the instrument in

the amps mode and cancel autorange with the front panel

Default /

Mode

Function

Range RO Zero Check Cl Zero correct 20

Suppression

Value

Trigger T6

Voltage Source operate

Read Mode

Data Format

Display

Data store

SKI Mode

EOI and Bus Hold-off

DO Q7

MOO

Prefix, no suffb

Terminator Y(CR LFN=:l CR LF

‘IStatus Upon Power-Up or After DCL or SDC)

Obtained with UO command

3.15

To transmit the SDC command, the controller must perform

the following steps:

When the END LINE key is pressed, the instrument will process a single reading.

1. Set ATN true.

2. Address the Model 617 to listen.

3. Place the SDC command on the data bus.

HP-85 Programming Example-Using the front panel con-

trols, place the instrument in the amps mode and cancel autorange. Enter the following statement into the HP-85:

CLEAR 727 (END LINE)

After END LINE is pressed, the instrument returns to the power up default conditions listed in Table 3-10.

Model 8573 Programming Example-Place the instru-

ment in the amps function and cancel autorange with the front panel controls. Now enter the following statement into

the IBM-PC:

CALL IBCLR(M617%) (return)

After the return key is pressed, the instrument returns to the

default conditions listed in Table 3-10.

3.9.7 GET (Group Execute Trigger)

Model 8573 Programming Example-Type in the follow-

ing statements to make sure the instrument is in the remote and correct trigger modes for purposes of this demonstration:

V% =l:CALL IBSRE(BRDO%,V%) (return)

CMD$-‘T3X”:CALL IBWRT(M617%.CMD$)(retum)

Now send GET to the instrument with the following statement:

CALL IBTRG(M617%) (return)

When the return key is pressed, the instrument will process a single reading.

3.9.8 Serial Polling (SPE,SPD)

The serial polling sequence is used to obtain the Model 617 status byte. The status byte contains important information about internal functions, as described in paragraph 3.10.15. Generally, the serial polling sequence is used by the controller

to determine which of several instruments has requested ser-

vice with the SRQ line. However, the serial polling sequence may be performed at any time to obtain the status byte from

the Model 617.

GET may be be used to trigger the Model 617 to take readings if the instrument is placed in the appropriate trigger mode (more information on trigger modes may be found in paragraph 3.10.14).

To send GET, the controller must perform the following steps:

1. Set ATN true.

2. Address the Model 617 to listen.

3. Place the GET command byte on the data bus.

HP-85 Programming Example-Type in the following

statements into the HP-85 keyboard to place the instrument

in remote and enable the correct trigger mode for this

demonstration:

REMOTE 727 (END LINE)

OUTPUT 727: ‘T3X” (END LINE)

Now send the GET command with the following statement:

TRIGGER 727 (END LINE)

The serial polling sequence is conducted as follows:

1. The controller sets ATN true.

2. The controller then places the WE (Serial Poll Enable)

command byte on the data bus. At this point, all active devices are in the serial poll mode and waiting to be ad-

dressed.

3. The Model 617 is then addressed to talk.

4. The controller sets ATN false.

5. The instrument then places its status byte on the data bus.

at which point it is read by the controller.

6. The controller then sets ATN true and places the SPD

(Serial Poll Disable) command byte on the data bus to end the serial polling sequence.

Once instruments are in the serial poll mode, steps 3 through 5 above can be repeated by sending the correct talk address for each instrument. ATN must be true when the address is transmitted and false when the status byte is read.

HP-85 Programming Example-The HP-85 SPOLL state-

ment automatically performs the sequence just described. To demonstrate serial polling, type in the following statements

into the HP-85

3-16

REMOTE 727 (END LINE)

S = SI’OLL(727) (END LINE)

DISP S (END LINE)

When the END LINE key is pressed the second time, the computer conducts the serial polling sequence. The decimal value of the status byte is then displayed on the computer CRT when the END LINE key is pressed the third time. More information on the status byte may be found in paragraph 3.10.15.

Model 8573 Programming Example-Use the following

sequence to serial poll the instrument and display the decimal value of the status byte on the computer CRT:

V%=l:CALL IBSRE(BRDO%,V%) (return)

CALL IBRSP(M617%,SB%) (return)

PRINT SB% (return)

When the return key is pressed the second time, the serial polling sequence is conducted. The status byte value is

displayed when the return key is pressed the third time.

3.10 DEVICE-DEPENDENT COMMAND PROGRAMMING

IEEE-488 device-dependent commands are used with the Model 617 to control various operating modes such as function, range, trigger mode, and data format. Each command is made up of a single ASCII letter followed by a number representing an option of that command. For example, a command to control the measuring function (Volts, Ohms, Amps, Coul) is programmed by sending an ASCII “F” followed by a number representing the function option. The IEEE-488 bus actually treats these commands as data in that ATN is false when the commands are transmitted.

A number of commands may be grouped together in one str-

ing. A command string is usually terminated with an ASCII “X” character, which tells the instrument to execute the cornmand string. Commands sent without the execute character

will not be executed at that time, but they will be retained

within an internal command buffer for execution at the time the X character is received. If any errors occur, the instrument will display appropriate front panel error messages and generate an SRQ if programmed to do so.

Function (F); Range (R); Zero Check (C); Zero Correct (Z); Suppress (N); Trigger(T); Voltage Source Operate (0): Read Mode (B); Display Mode (D): Data Storage (Q): SRQ Mode

CM): EOI and Bus Hold-off (K); and Terminator (Y). Thus to force a particular command sequence, you would follow each command with the execute character, as in the example string, ClXZlXCOX, which can be used to zero correct the instrument.

These programming aspects are covered at the end of this

paragraph.

Device-dependent commands can be sent either one at a time,

or in groups of several commands within a single string.

Some examples of valid command strings include:

FOX Single command string. FOKlDOROX Multiple command string. T6 X Spaces are ignored.

Typical invalid command strings include:

HlX Invalid command, as H is not one of the instrument commands. F9X Invalid command option because 9 is not an option of

the F command.

If an illegal command (IDDC), illegal command option UDD-

CO), is sent, or if a command string is sent with REN false,

the string will be ignored.

Devicedependent commands that control the Model 617 are listed in Table 3-11. These commands are covered in detail in

the following paragraphs. The associated programming ex-

amples show how to send the commands with both the HP-85 and the IBM-IW8573.

NOTE

Programming examples assume that the Model 617 is at its factory default value of 27.

In order to send a devicedependent command, the controller

must perform the following steps:

Commands that affect the electrometer section (F, R, C, Z, N, T, and A) will trigger a reading when the command is executed. These bus commands affect the Model 617 much like the front panel controls. Note that commands are not necessarily executed in the order received; instead, they will be executed in the same order as they appear in the status word:

1. Set ATN true.

2. Address the Model 617 to listen.

3. Set ATN false.

4. Send the command string cwer the bus one byte at a time.

317

NOTE

REN must be true when sending devicedependent commands to the instrument, or it will ignore the command and display a bus error message.

General HP-85 Programming Example-DDevice-

dependent commands may be sent from the HP-65 with the following statement:

oul-PuT 727; A5

A$ in this case contains the ASCII characters representing the command string.

General Model 8573 Programming Example-Use the

following general syntax to send device-dependent commands from the IBM-PC:

CALL IBWRT(M617%,CMD5)

Again, CMD$ contains the command letters to program the instrument. Remember that the modified declaration file must be loaded and run before using any of the programming examples.

3.10.1 Execute (Xl

The execute command is implemented by sending an ASCII

“X” over the bus. Its purpose is to direct the Model 617 to ex-

ecute other device-dependent commands such as F (function)

or R (range). Usually, the execute character is the last byte in the command string (a number of commands may be grouped together into one string); however, there may be certain circumstances where it is desirable to send a command string at one time, and then send the execute character later on. Command strings sent without the execute character will be stored within an internal command buffer for later execution. When the X character is finally transmitted, the stored commands will be executed, assuming that all commands in the previous string were valid.

HP-85 Programming Example-Enter the following

statements into the HP-85 keyboard:

Modal 8573 Programming Example-Enter the following

statements into the IBM computer:

V%=l:CALL IBSRE(BRDO%,V%) (return)

CMD$=“X”:CALL IBWRT(M617%,CMD$) (return)

When the retmn key is pressed the second time, the X

character is transmitted to the instrument, although no mode changes occur because no other commands are transmitted. Note that the instrument remains in the listener idle state after

the command is transmitted because IBWRT automatically sends UNT (Untalk) and UNL (Unlisten) at the end of the transmission sequence.

3.10.2 Function IF)

The function command allows you to select the type of measurement made by the Model 617. The parameter options associated with the function command set the instrument to measure voltage, current, resistance, charge, external feedback, or V/I ohms. When the instrument responds to a function command, it will be ready to take a reading once the front end is set up. The function may be programmed by sending one of the following commands:

FO=Volts Fl = Amps F2 = Ohms F3 = Coulombs F4=Extemal Feedback F5=V/I Ohms

Upon power-up, or after the instrument receives a DCL or SDC command, the FO (Volts) mode will be enabled.

HP-85 Programming Example-Place the instrument in

the current function with the front panel AMPS button and

enter the following statements into the HP-85 keyboard:

REMOTE 727 (END LINE)

OUTPUT 727;“FOX” (END LINE)

When END LINE is pressed the second time, the instrument changes to the volts mode, as indicated by the associated

LED.

REMOTE 727 (END LINE)

OUTPUT 727;“X” (END LINE)

When the END LINE key is pressed the second time, the X character will be transmitted to the instrument. No mode changes will occur with this example because no other commands were sent. Note that the instrument remains in the listener active state after the command is transmitted.

3-18

Model 8573 Programming Example--Place the instru-

ment into the current mode with the front panel AMPS button. Now type the following statements into the computer keyboard:

V% =l:CALL lBSRE(BRDO%,V%) (return)

CMD$=“FOX”:CALL IBWRT(M617% ,CMD$) (return)

When the return key is pressed the second time, the instrument changes to the volts function.

/lode xecute

:unction

lange

:ero Check

:ero correct

laseline Suppression

display Mode

leading Mode

)ata Store

loltage Source

falue roltage Source )perate Calibration Value

: .^.^ P”l:b.-^ri^^

Table 3-11. Device-Dependent Command Summary

Command

X Execute other device-dependent commands.

Description

FO Volts Fl

Amps F2 Ohms F3 Coulombs

External Feedback F5 V/I Ohms

: External V/I

Volts Amps Ohms Coulombs Feedback Ohms

RO Auto Rl 200mV R2

2 V 20 pA 20 kR 2nC 2V 20Tfl R3 20 V 200 pA 200 k0 R4

200 v

Auto Auto Auto Auto

2 PA

2 kR 2OOpC 200mV 2OOTQ

20 nc 20 v 2TR

2 nA 2MQ 20 nC 20 v

200GLl R5 200 V 20 nA 20M0 20 nC 20 v R6 200 V 200 nA 200MQ R7 R6 R9

200 V 2 /LA 2GO 200 V 20/~A 20GS2

200 V 200 PA 200G0 RlO 200 v 2mA 200GSI Rll 200 V 20mA 200GQ

20 nC 20 v 2G0 20 nC 20 v

200MR 20 nC 20 v 20 nC 20 v 20 nC 20 nC

20 v

200 kR

200 kQ

R12 Cancel autoranging for all functions

co Cl

Zero Check Off

Zero Check On zo Zero Correct Disabled Zl Zero Correct Enabled

NO Suppression Disabled

Nl Suppression Enabled DO Electrometer

Voltage Source BO Electrometer El 82

Buffer Reading

Maximum Reading 83 Minimum Reading 84

Voltage Source

00 Conversion rate 01

One Reading Per Second a2 One Reading Every 10 Seconds Q3 One Reading Per Minute Q4 One Reading Every 10 Minutes

One Reading Per Hour

Q6 Trigger Mode

Q7 Disabled

V+ nnn.nn or Voltage Source Value: - 102.35V to + 102.4V, 50mV

increments

V+n.nnnnE+n

00 Source Output Dff (OV) 01 Source Output On (Programmed Value)

A+ nnn.nn or Calibrate Function and Range

An.nnnE+n

I4 Ph.-,. P”liL.....i.... P^..^.^^.^ i.. hl\,D Ah”

Paragrapl

3.10.1

3.102

3.10.3

Auto

20G$l

20MR

2MR

3.10.4

3.10.5

3.10.6

3.10.7

3.10.8

3.10.9

3.10.10

3.10.11

2 ‘1n ‘I?

3-19

Table 3-11. Device-Dependent Command Summary (Cont.)

Mode 3ata Format

Trigger Mode

SRQ

EOI and Bus Hold Off

Terminator

Status Word

-r-

Command

Ml6

M32

YfLF CR) YICR LF)

YIASCII)

GO Gl

TO Tl M T3 T4 15 T6 T7 MO Ml

KO Kl K2 K3

YX IJO

Description

Reading with Prefix (NDCV - 1.23456E+OO)

Reading without Prefix f - 1.23456E+OO)

Reading with Prefix and Buffer Suffix (if in Bl) (NDCV-1.23456E+OO, 012)

Continuous, Trigger by Talk One-Shot, Trigger by Talk Continuous, Trigger by GET One-Shot. Trigger by GET Continuous, Trigger by X One-Shot, Trigger by X Continuous, Trigger by External Trigger One-Shot, Trigger by External Trigger

Disable SRQ Reading Overflow Buffer Full Reading Done Ready Error Enable EOI and Bus Hold-off On X Disable EOI, Enable Bus Hold-off On X Enable EOI, Disable Bus Hold-off On X

Disable both EOI and Bus Hold-off On X Terminator = LF CR Terminator = CR LF Terminator = ASCII Character

No Terminator

Send Status Format: 617 FRRCZNTOBGDQMMKYY

Error Conditions

Data Conditions

Paragraph

3.10.13

3.10.14

3.10.15

3.10.16

3.10.17

3.10.18

3.10.3 Range (RI

The range command gives the user control over the sensitivi-

ty of the instrument. This command, and its options, perform

essentially the same functions as the front panel AUTO and up and down range buttons. Range command parameters and the respective ranges for each measuring function are summarized in Table 3-12. The instrument will be ready to take a reading after the range is set up when responding to a range command.

Upon power up, or after receiving a DCL or SDC command,

the instrument will be in the RO (autorange) mode.

3-20

HP-85 Programming Example-Make sure the instrument

is in the autorange mode and then enter the following

statements into the HP-85:

REMOTE 727 (END LINE)

OUTPLJT 727;“R3X” (END LINE)

When the END LINE key is pressed the second time, the in-

strument cancels the autorange mode, and enters the R3 range instead.

Model 8573 Programming Example-Make sure the in-

strument is in the autorange mode. Now enter the following statements into the IBM-PC keyboard:

V% =l:CALL IBSRE(BRDO%.V%) (return)

CMD$=“R3X”:CALL IBWRT(M617%,CMD5) (return)

When the return key is pressed the second time, the instru-

ment cancels the autorange mode and switches to the R3

Et”ge.

3.10.4 Zero Correct and Zero Check (2 and C)

The zero correct and zero check commands work together to

cancel any internal offsets that might upset accuracy. If the instrument is placed in the zero correct mode with zero check enabled, it will store a new offset value to be used for subsequent readings. If the instrument is zero corrected with zero check disabled, the previously stored zero value will be used instead, Note that the specifications at the front of this manual assume that the instrument has been properly zeroed. Zero correct and zero check commands include:

CO = Zero check off

Cl = Zero check on

ZO=Zero correct off Zl = zero correct on

Use the following procedure to zero the instrument:

1. With zero correct off, place the instrument in zero check by sending ClX.

2. Zero correct the instrument by sending ZlX.

3. Disable zero check by sending COX. Readings can then be taken in the usual manner.

HP-85 Programming Example-Enter the following lines

into the HP-85 computer:

REMOTE 727 (END LINE)

OUTPUT 727;“ClXZlXCOX” (END LINE)

When END LINE is pressed the second time, the instrument is

first placed in zero check, the unit is zero corrected, and the

zero check mode is then disabled.

Model 8573 Programming Example-Enter the following

statements into the IBM computer:

V% =l:CALL IBSRE(BRDO%,V%) (return)

CMD$=“ClXZlXCOX”:CALL IBWRT(M617%,CMD$)

(return)

The instrument will be ready on reading done (zero correct)

or when the front end is set up (zero check). Upon power up, or after receiving a DCL or SDC command, the unit will be in the Cl and ZO modes (zero check on and zero correct off).

Table 3-12. Range Command Summary

T-

Command

R3 R4 R5 R6 R7 R8 R9

RlO

Rll R12

Volts

Auto

200mV

2 v

20 v 200 v 200 v 200 v 200 v 200 v 200 v 200 v 200 v

:ancel Auto

Amps

Auto

2 PA

20 pA

200 pA

2 nA

20 nA

200 nA

2 PA

20 fi

200 pA

2mA

20mA

Cancel Auto

The zero check and zero correct sequence will be performed when the return key is pressed the second time.

Range

Ohms

Auto

2 kG

20 kC

200 kR

2MC

20MR

200MC

2GR

20GR 200GQ 200GO 200GO

Coulombs

Auto

2oopc

2nC 20nC 20nC 20nC 20nC 20nC 20nC 20nC 20nC 20nC

Cancel Auto

External

Feedback

Auto

200mV

2v 20 v 20 v 20 v 20 v 20 v 20 v

20 v 20 v 20 v

Cancel Auto

V/I’

Ohms

Auto

200Tt-l

20TR

2TC

200GR

20GQ

2GC

200MR

20Mt-l

2Mtl 200 kR 200 kR

Cancel Auto

*Full range value based on 100V/10,000 displayed counts of current.

3-21

3.10.5 Baseline Suppression (N)

HP45 Programming Example-To enable baseline sup-

pression, type in the following lines:

The baseline suppression mode allows a stored offset value to be subtracted from subsequent readings. When the suppression mode is enabled with the appropriate command, the in-

strument will internally store the baseline value with the next triaered conversion. All subsequent readings will be the dif-

f&&e between the stored b&line value and the actual

signal level. For example, if 1OOmV is stored as a baseline, that value will be subtracted from the following readings. See

paragraph 2.11.2 for a complete description.

To use baseline suppression, perform the following steps:

1. Cancel baseline suppression by sending NOX if already enabled.

2. Select a range and function consistent with the expected measurement,

3. Connect the signal to be used as a baseline to the instrument input.

WllmuIuc

..-..I....U

The voltage present on the input terminals

may be larger than the displayed value. For

example, if a 150VDC baseline is stored. an applied voltage of +175V will result in a

displayed reading of only +25V

REMOTE 727 (END LINE)

CXJTl’UT 727;“Nlx” (END LINE)

When the END LINE key is pressed the second time, the baseline suppression mode is enabled.

Model 8573 Programming Example-Type the following

commands into the HP-85 keyboard in order to enable baseline suppression:

V% =l:CALL IBSRE(BRDO%,V%) (return)

CMD$=“NlX”:CALL IBWRT(M617%,CMD$) (return)

The baseline suppression mode will be enabled when the return key is pressed the second time.

3.10.5 Display Mode IDI

The two parameters associated with the display mode com-

mand control whether the front panel display shows the elec- ?r the front panel display shows the elec-

trometer reading or the voltage source value. Thus, this com- lmg or the voltage source value. Thus, this command performs essentially the same function as the front ms essentially the same function as the front panel DISPLAY button. The two display command .AY button. The two display command

parameters are:

4. Enable baseline suppression by sending NlX over the bus. The baseline will be stored when the command is executed.

5. Disconnect the baseline signal from the instrument and connect the signal to be measured in its place. Subsequent readings will be the difference between the baseline and the applied signal.

NOTES:

1. Baseline suppression reduces the dynamic range of the measurement. For example, if the stored baseline value is 1oOmV on the 200mV range, an input voltage of 1COmV or more would overrange the instrument even though voltages up to 199.99mV are normally within the capabilities of the 2oOmV range. If the instrument is in the autorange mode, it will move up range if necessary.

2. Setting the range lower than the stored baseline value will overrange the instrument.

3. Accurate control over when the baseline is actually stored may be achieved by placing the instrument in a one shot

trigger mode. Once the desired baseline value is connected to the instrument, the baseline can be stored by sending

NIX.

4. Function changes cancel baseline suppress. Refer to paragraph 2.11.2 for details concerning suppress.

DO=Electrometer Dl = Voltage source

Upon power up, or after receiving a DCL or SDC command, the instrument will be in the DO (electrometer) mode.

NOTE

When in the Dl mode, sending an electrometer command (F, R, C, Z, N, or T) will cause the

instrument to revert to the DO (electrometer)

mode.

To program the desired display mode over the bus, you need only send the appropriate command string. For example,

DlX would be transmitted to view the voltage source value

on the display.

HP-85 Programming Example-Using the front panel

DISPLAY button place the display in the electrometer mode.

Now type in the following lines:

REMOTE 727 (END LINE)

OUTPUT 727;“DlX” (END LINE)

3-22

When the END LINE key is pressed the second time, the display shows the voltage source value.

Model 8573 Programming Example-Momentarily power

down the instrument and then enter the following lines into the IBM computer:

V% =l:CALL IBSRE(BRDO%,V%) (return)

CMD$=“DlX”:CALL IBWRT(M617%,CMD$) (return)

Note that the instrument changes from the electrometer dispiay mode to the voltage source display mode when the return key is pressed the second time.

3.10.7 Reading Mode (B)

The reading mode command parameters allow the selection of the source of data that is transmitted over the IEEE-488 bus. Through this command, you have a choice of data from

the electrometer, voltage source, data store reading, or minimum and maximum values. Note that the commands associated with data store are always available; however the suffix of the reading string will show Ooo if data store is disabled, as in NDCV +12345E+CO,000. Minimum/maximum values returned will be the last values stored, unless

these parameters are requested after a DCL, in which case unuseable readings will be returned.

sending the B2 or B3 commands. Note that the maximum and minimum values are updated at the maximum reading rate while data store is enabled. See paragraph 3.10.8 for a complete description of data storage.

The voltage source value is returned in a similar manner bv sending B4X. Once the desired reading mode has been selected, the data string can be read by addressing the instru- ment to talk and reading the bvtes in the strinrt in the normal

manner.

HP-85 Programming Example-Use the following se-

quence to read the voltage source value and display it on the computer CRT:

OUTPUT 727;“B4X” (END LINE)

ENTER 727; A$ (END LINE)

The second command above changes the reading mode to access the voltage source, while the third and fourth statements acquire the reading and display it on the CRT.

Model 8573 Programming Example-To display the

voltage source value on the computer CRT, enter the follow-

ing program statements into the IBM computer:

REMOTE 727 (END LINE)

DISP A$ (END LINE)

Parameters associated with the reading mode include:

BO=Electrometer Bl=Data store reading

B2=Maximum reading B3 = Minimum reading B4=Voltage source value.

Upon power up, or after receiving a DCL or SDC command, the unit will be in the BO (electrometer) mode.

When in BO, normal electrometer readings will be sent. In a continuous trigger mode, readings will be updated at the conversion rate (one reading every 36Omsec. In Bl, readings will be taken from consecutive data store locations, beginning with the oldest reading and progressing to the newest reading until all readings currently stored have been read. Once all

readings have been requested, the unit will cycle back and

begin again. These readings may be accessed even if data

store is still taking place.

While data store is enabled, the maximum (most positive) and

minimum (most negative) readings may also be requested by

V% =l:CALL IBSRE(BRDO%,V%) (return)

CMD$=“B4X”:CALL IBWRT(M617%,CMD$) (return)

RD$=SPACE!§Q5):CALL IBRD(M617%,RD$) (return)

PRINT RD$ (return)

The second statement above programs the reading mode to access the voltage source value. The third statement addresses

the instrument to talk and reads the data string from the instrument, while the fourth statement mints the data strine on the computer CRT.

3.10.8 Data Store Mode

The data store commands enter the data storage mode and allow you to store up to 100 readings with internal memory

of the Model 617. By entering an appropriate parameter, readings may be stored at one of six intervals between the conversion rate and one reading per hour. Either during or after the storage process, readings, including maximum and minimum values, may be recalled by using the B command as described in the last paragraph.

Once the unit has logged all 100 readings, the instrument will stop data storage until another Q command is sent to enable

3-23

data store cmce again. Note that the instrument may be programmed to generate an SRQ when memory is full, as

described in paragraph 3.10.15.

The available storage intervals include:

QO= Conversion rate (one reading every 360msec) Ql =One reading per second Q2 = One reading every 10 seconds Q3 = One reading per minute Q4 =One reading every 10 minutes QS = One reading per hour. Q6=Trigger mode (TRIG button) Q’I=Data store disabled

In addition to the various rates, data store can be used at a rate determined by the TRIG button (Q6 mode). When in this mode, one reading will be stored in memory each time

TRIG button is operated.

Upon power up, or after a DCL or SDC command. the

data

store will be disabled (Q7 mode.)

NOTES:

1. To use data store on a one-shot basis with other trigger stimuli. ulace the instrument in the 00 mode and select the desired one-shot trigger mode (paragraph 3.10.14).

2. In Qo and Ql, the storage rate may be decreased if the instrument is in autorange and a range change occurs.

HP-85 Programming Example-Enter the program below

to enable data store operation and obtain and display 100 readings on the computer CRT:

PROGRAM COMMENTS

10 DIM A$ [ZS] 20 REMOTE 727 Send remote enable 30 OUll’UT 727;“QOX” Enable data store at

conversion rate.

40 S = SPOLL(727)

Serial poll the 617. 50 IF NOT BIT(S.1) THEN 40 If not full, wait. 60 OUTPUT 727;“BlG2X” Set read mode to data

store.

70 FORI = 1TO100 Loop 100 times.

80 ENTER 727:A$ 90 DISP AS

100 NEXT I

Get a reading. Display it.

Loop back and get next readine.

fill (lines 40 and 501, turn on the data store output (line 60). and then request and display all loo readings(lines 70-100).

Model 8573 Programming Example-To demonstrate

data store operation, load the modified DECL.BAS file and enter the program lines below:

PROGRAM

10 NA$=“GPIBO”:CALL IBFIND

(NA$,BRDO%)

20 NA$=“DEVO”:CALL IBFIND

(NA$,MblZ$

30 V% =27:CALL IBPAD

(M617%.V%)

40 V%=l:tiALi IBSRE

COMMENTS

Find the board descriptor. Find the instrument descriptor. Set primary address

to 27.

Send remote enable.

(BRDO%,V%)

50 CMD$=“QOX”:CALL IBWRT

(M617%,CMD$)

60 CALL IBRSP(M617%,SB%)

70 IF (SB% AND 2) = 0 THEN

Enable data store at conversion rate. Get status byte. If not full, wait.

80 CMD$=“BlGZX”:CALL

Turn on data store.

IBWRT(M617%,CMD$)

90 FORI = 1TOlOO

100 RD$=SPACE$(25):CALL

IBRD(M617%,RD$) 110 PRINT RD$ 120 NEXT I

Display the reading.

Go back and get another.

130 V % = 0:CALL IBONL

Close the board file.

(BRDO%,V%)

140 CALL IBONL(M617%,V%)

Close the instrument

.~.

Press the IBM F2 key to run the program. Data store is enabled (line 50). the program waits for memory to fill (lines 60

and 70), the output is turned on (line 80), and all 100 readings are then requested and displayed (lines 90-120).

3.10.9 Voltage Source Value (VI

The voltage source value command allows you to program

the built-in voltage source of the Model 617 to between

- 102.35V and + 102.4V in 50mV increments. Normally, the voltage source output is updated at the beginning of each electrometer conversion (every 160msec); however, you can force an immediate update by applying an appropriate trigger

stimulus to force the start of a new conversion (see paragraph

3.10.14 for more information on triggering).

After entering the program, press the HP-85 RUN key. The

program will enable data store (line 30), wait for memory to

3-24

The voltage swrce value is programmed by sending the V

command letter followed by a maximum of 5% digits representing the voltage value. The unit will round off the programmed values to 5OmV minimum increments. Either nor-

mal or scientific representation may be used as indicated

below:

Vnmum (normal convention) Vn.nnnnE+n (scientific notation)

Upon power up or after a DCL or SDC, the source output will be programmed to oO.oOV.

Some equivalent examples of these two conventions are shown below:

N0IlIlal Scientific

V25

v99.1 vo.05 v-11

V2SEfl V0.99E+2

V50E-3

V-1X2+1

Note that merely programming the swrce value does not ap-

ply the voltage to the voltage source ourput terminals. The

output must be separately programmed on or off as described

in the following paragraph.

3.10.10 Voltage Source Operate (0)

The voltage source operate command performs essentially the same operations as the front panel OPERATE button. The parameters included with this command are:

Oo=Source output off (Output =OV) Ol=Source output w-, (Output = programmed value)

Upon power up, or after receiving a DCL or SDC command, the instrument will be in the 00 (Source off) mode.

Keep in mind that the voltage swrce has a maximum current output of 2mA: the OPERATE LED will flash if this value is exceeded.

WARNING

Hazardous voltage may be present on the

voltage source terminals, depending on the

programmed value.

HP-85 Programming Example-Enter the following state-

ments into the HP-85 to program and display the swrce and turn the output on:

HP-85 Programming Example-To program the voltage

saxce to a value of -loV, press the front panel DISPLAY

button to view the source value and enter the following state-

ments into the computer:

REMOTE 727 (END LINE)

OUTPUT 727;‘DlV-10X” (END LINE)

When the second slakment is executed, the source value is programmed for a value of -lOV.

Model 8573 Programming Example-Momentarily power

down the instrument and then select the voltage source with

the front panel DISPLAY button. Now enter the following

statements into the IBM computer:

V% =l:CALL IBSRE (BRDO%,V%) (return)

CMD$=“DlV-lOX”:CALL IBWRT(M617%, CMD$)

baml)

The voltage scwrce will be programmed to a value of -1OV

when the second statement is executed.

REMOTE 727 (END LINE)

OIJTRJT 727:“DlV6Olx” (END LINE)

When the command string is sent Lo the instrument, the display mode is changed to view the source value, the source voltage is programmed to +6V, and the source output is turned on.

Model 8573 Programming Example-Enter the following

statements into the IBM computer:

V% =l:CALL IBSRE(BRDO%,V%) (return)

CMD$=“DlV601X”:CALL lBWRT(M617%,CMD$)

(return)

When the command string is sent to the instrument, the display will change to the source mode, the scurce value will be programmed to a value of +6V, and the source output wilI be turned on.

3.10.11 Calibration Value (A)

One advanced feature of the Model 617 is its digital calibra-

tion capabilities. Instead of the mire difficult method of ad-

3-25

justing a number of potentiometers, the user need only apply

an appropriate calibration signal and send the calibration

value over the bus. The calibration command may take on either of the following forms:

Ann.nnn An.nnnnE+n

Thus, the following two commands would be equivalent:

Al9 A1.9E+l

In this example, the nominal value for the 20V range is being used. Note that only as many significant digits as necessary need be sent. In this case, the exact calibration point is assumed to be 19.000 even though only the first two digits were

actually sent.

If the calibration value is outside the allowed range (? 6% of

nominal value), a number error will occur, as indicated by the following message:

n Err

The calibration value is sent to the instrument when the second statement is executed.

3.10.12 Non-Volatile Memory Storage IL)

The Model 617 uses non-volatile (NV) RAM to store calibra-

tion parameters. Once the instrument has been calibrated, as described in the last p&graph, the NVRAM storage command should be sent to permanently store these parameters. This procedure is performed by sending the following sequence: LlX. NVRAM storage will take place when the instrument receives this command over the bus. Note that NVRAM storage may be disabled by changing the position of a calibration jumper, as described in Section 7. If the jumper is in the enabled position, all calibration must be properly done, or calibration of all functions and ranges will be affected.

NOTE

Do not perform the following programming exam&s unless actual NVRAM storaee is desired. Uniess proper calibrating para&te;s have~been previously programmed, inadvertent use of this command could affect instrument accuracy.

Once all functions and ranges have been calibrated, permanent storage of calibration parameters must be performed, as described in paragraph 3.10.12.

NOTE

The proper calibration signal must be connected

to the instrument before attempting calibration.

See Section 7 for complete details on calibrating

the instrument either from the front panel or over the bus.

HP85 Programming Example-The following statements

can be used to calibrate the instrument on the 2oOV range:

REMOTE 727 (END LINE)

OUTPUT 727;“A190X” (END LINE)

When the second statement is executed, calibration of the

2OOV range is performed, assuming that the correct calibra-

tion value is applied to the instrument.

Model 8573 Programming Example-Use the following

statements to send the 2COV range calibration value to the in-

strument:

V%=l:CALL IBSRE(BRDO%,V%) (return)

CMD$=“AlQOX”:CALL IBWRT(M617%,CMD$) (return)

HP-85 Programming Example-Use the following

statements to perform NVRAM storage:

REMOTE 727 (END LINE)

OUTPUT 727;“LlX” (END LINE)

NVRAM storage will be performed when the second statement is executed.

Model 8573 Programming Example-Perform NVRAM

storage with the following Model 8573 statements:

V% =l:CALL IBSRE(BRDO%,CMD$) (return)

CMD$=“LlX”:CALL IBWRT(M617%,CMD$) (return)

NVRAM storage is performed when the second statement is executed.

3.10.13 Data Format (G)

Through the use of the G command, the format of the data

the instrument sends over the bus may be controlled as

foIlows:

GO= Send reading with prefix. Example:NDCV-1.23456E

+OO

3-28

Gl =Send reading without prefix. Example: -l.Z3456E+OO

GZ=Send reading with prefix and suffix when in BI (data

store) mode. Example:

NDCV-1.23456E+OO,023. In this example, memory loca-

tion 23 is being accessed.

Upon power up, or after the instrument receives a DCL or SDC command, the instrument will be in the GO mode.

Figure 3-9 further clarifies the general data format. Note that the prefix defines a normal or overflow reading as well as the

measuring function. The mantissa is always 5~2 digits,

although the most significant digit will assume a value of 2 under overload conditions, except for a current overload in V/I ohms. In V/I ohms, all zeroes will be returned when a current overload condition occurs. Keep in mind that the B command affects the source of the data. See paragraph 3.10.7 for complete details.

If the B4 (voltage source) mode is enabled, the VSRC prefix

will be sent.

Model 8573 Programming Example-Type in thefollow-

ing statements to place the instrument in the G1 mode:

V% =l:CALL IBSRE(BRDO%,V%) (return)

CMD$=“BOXGlX”:CALL IBWRT(M617%,CMD$) (return)

RDB=SPACE5(2O):CALL IBRD(M617%,CMD$) (return)

PRINT RD5 (return)

When the second statement is executed, the instrument will be placed in the Gl &de. The last two lines obtain the data string from the instrument and display it on the CRT. Note that the prefix is absent from the data string. The instrument may be returned to the prefix mode by repeating the above procedure with the GO command.

3.10.14 Trigger Mode (T)

Triggering provides a stimulus to begin a reading conversion within the instrument. Triggering may be done in two basic ways: in a continuous trigger mode, a single trigger stimulus is used to restart a continuous series of readings. In a oneshot mode, a single reading will be processed each time the appropriate trigger simulus is given.

DATA STORE

N = NCIRMAL

0 = OVERFLOW

“NE” *1.23456 E+m. 011 CR LF

DC”= VOLTS DCA = AMPS OHM=OHMS DCC = CO”LOMBS DCX= EXTERNAL

Figure 3-9. General Data Format

HP-85 Programming Example-To place the instrument in

the Gl mode and obtain a reading, enter the following statements into the HP-85 keyboard:

OUTPUT 727; “BOXGlX” (END LINE)

ENTER 727;A$ (END LINE)

When the second statement is executed, the instrument will change to the Cl mode. The last two statements acquire data

from the instrument and display the reading string on the

CRT. Note that no prefix appears on the data string. The

above procedure can be repeated with the GO command to re-

turn to the normal prefix mode.

MANTISSA

(5% DIGITS1

REMOTE 727 (END LINE)

DISP A5 (END LINE)

EXPONENT TERMlNATOR

LOCATION

,B,. G2 ONLY,

““SW replaces NDC”

when reading V-Source CB4)

The Model 617 has eight trigger modes as follows:

TO=Continous Mode, Triggered by Talk Tl =One-shot Mode, Triggered by Talk

T2=Continous Mode, Triggered by GET T3 = One-shot Mode, Triggered by GET T4=Continous Mode, Triggered by X T5=Oreshot Mode, Triggered by X Tb=Continous Mode, Triggered with External Trigger Ti’=One-shot Mode, Triggered with External Trigger

Upon power up, or after the instrument receives a DCL or

SDC command, the T6 (continous mode, external trigger)

mode will be enabled.

The trigger modes are paired according to the type of stimulus that is used to trigger the instrument. In the TO and Tl modes, triggering is performed by addressing the Model 617 to talk. In the T2 and T3 modes, the IEEE-488 multiline GET command performs the trigger function. The instrument execute (X) character provides the trigger stimulus in the T4 and T5 modes, while a trigger pulse applied to the rear panel EXTERNAL TRIGGER INPUT, triggers the instrument in the T6 and T7 modes.

NOTES:

1. A trigger stimulus will abort the present reading conversion and immediately begin another.

3-27

2. The front panel TRIG button will trigger the instrument regardless of the selected trigger mode, unless LLO is in ef-

fect.

3. Serial polling usually addresses the instrument to talk. This talk command will trigger the instrument in the TO and Tl

modes.

HP-85 Programming Example-Place the instrument in

the one-shot on talk mode with the following statements:

REMOTE 727 (END LINE)

OUTPUT 727:“TlX” (END LINE)

One reading can now be triggered and the resulting data ob-

tained with the following statements:

ENTER 727;A!$ (END LINE)

DISP A$ (END LINE)

In this example, the ENTER statement addresses the Model

617 to talk, at which point a single reading is triggered. When the reading has been processed (360msec later), it is sent out

over to the bus to the computer, which then displays the result.

Model 8573 Programming Example--Place the instru-

ment in the Tl mode with the following statements:

V%=l:CALL IBSRE(BRDO%,V%) (return)

CMD$=“TlX”:CALL IBWRT(M617%,CMD$) (return)

The instrument can now be addressed to talk to trigger a con-

version, and the resulting data displayed with the following statements:

The Model 617 can be programmed to generate an SRQ

under one or more of the following conditions:

1. If an overrange condition occurs.

2. When the data store memory is full (100 readings).

3. If a reading is completed.

4. When the instrument is ready to accept bus commands.

5. If an error occurs. The nature of the error can then be determined with the Ul command, as described in paragraph 3.10.18 (use Ul to restore SRQ after an error occlm )

Upon power up, or after a DCL or SDC command is received, SRQ is disabled.

SRQ Mask-The Model 617 uses an internal mask to determine which conditions will cause an SRQ to be generated. Figure 3-10 shows the general format of this mask, which is made up of eight bits. The SRQ has the same general format as the status byte (described below) except for the fact that bit

6 is not used in the SRQ mask.

SRQ can be programmed by sending the ASCII letter “M” followed by a decimal number to set the appropriate bit in the SRQ mask. Decimal valu&s for the various bits are sununarized in Table 3-13. Note that the instrument may be programmed for more than one set of conditions simultaneously. To do so, simply add up the decimal bit values for the required SRQ conditions. For example, to enable SRQ under reading overflow and buffer full conditions, send M3X. To disable SRQ, send MOX. This command will clear all bits in

the SRQ mask.

RD$=SPACE$(20):CALL IBRD(M617%,RD$) (return)

PRINT RD$ (return)

Each time the IBRD function is called, the instrument is addressed to talk, at which time it is triggered. When the conversion is complete (360msec later), the reading is sent out over the bus to the computer, which then displays the resulting data.

3.10.15 SRQ Mask IM) and Status Byte Format

The SRQ command controls which of a number of conditions within the Model 617 will cause the instrument to request service from the controller by asserting SRQ. Once an SRQ is generated, the status byte can be checked to determine if the Model 617 was the instrument that asserted SRQ, and, if so,

what conditions caused it to do so. Note that additional data and error conditions can be checked by using the Ul and U2 commands, as described in paragraph 3.10.18.

3.28

Table 3-13. SRQ (MI Command Parameters

Reading Overflow

Data Store Full

Status Byte Format-The status byte contains information

relating to data and error conditions within the instrument. The general format of the status byte (which is obtained by using the serial polling sequence, as described in paragraph

3.9) is shown in Figure 3-9. Note that the various bits cor~es-

pond to the bits in the SRQ mask as described above.

I= ROS BY 617

-I

lSTAT”S BYTE ONLY)

I= ERROR

1= READY I= READING DONE

1 =REAOING

OVERFLOW

1 = DATA STORE

Figure 3-10. SRQ Mask and Status Byte Format

Bit 6 provides a means for you to determine if SRQ was asserted by the Model 617. If this bit is set, service was requested by the instrument. Bit 5 flags a Model 617 error con-

dition, which can be further checked with the Ul cornmand. If this bit is set, one of the following errors has occurred:

1. An illegal device dependent command (IDDC) or illegal device dependent command option (IDDCO) was transmitted.

2. The instrument was programmed when not in remote.

3. A trigger overrun has occurred (the instrument was trig-

gered while processing a reading from a previous trigger).

4. A number error has occurred (calibration or voltage source

values were out of limits).

Keep in mind that you can program the instrument to assert SRQ under any of these conditions simply by setting bit 5 in the SRQ mask (M32X). Paragraph 3.10.18 describes how to

use the Ul command to obtain information on the type of error from the instrument. The LJl command is used to clear the error bit and restore operation of SRQ on error after the error byte is read.

The bits in the status (serial poll) byte have the following meanings:

Reading Overflow (Bit O&Set when an overrange input is applied to the instrument (except when a current overload oc-

curs in V/I ohms). Cleared when a non-overflowed reading is

available. Data Store Full (Bit 1)-&t when all 1OO readings in data

store have been taken. Cleared by reading a stored reading

over the bus (B1X).

Reading Done (Bit 3)--S& when the Model 6l7 has completed the present reading conversion. Cleared by re-

questing a reading over the bus.

Ready (Bit4)-Set when. the instrument has processed all previously received commands and is ready to accept addi-

tional commands over the bus.

Error (Bit 5)-Set when an error condition occurs, as described above. Cleared by reading the error word with the U1 command. RQS (Bit 6)--S& if the Model 617 has asserted SRQ.

Bits 2 and 7 are not used, and are always set to 0.

Note that the status bite should be read to clear the SRQ line once the instrument has generated an SRQ. All bits in the status byte will be latched when the SRQ is generated. Bit 6 (RQS) will be cleared when the status byte is read.

Even with SRQ disabled, the status byte can be read to determine appropriate instrument conditions. In this case, bits 0, 1, 3, and 4 will be continuously updated to reflect current instrument status; however, bit 5 (the error bit) will latch and remain so until the U1 status word (paragraph 3.10.18) is read, even if no SRQ occurs.

HP-85 Programming Example-Enter the following pro-

gram into the HP-85:

PROGRAM

10 REMOTE 717 @ CLEAR 7

20 OUTPUT 727;“M32X”

30 OUTPUT 727;“KSX”

40 S = SPOLL(727)

50 DISP”B7 B6 85 84 83 B2 Bl

RW’

60 %R 1=7TO 0 STEP -1

70 DISP BIT (S.1):

80 NEXT I 90 DISP

100 END

Once the program is entered and checked for errors, press the HP-85 RUN key. The computer first places the instrument in remote (line 10) and then programs the SRQ mode of the instrument (line 20). Line 30 then attempts to program an illegal command option, at which point the instrument generates an SRQ and sets the bus error bit in its status byte. The computer then serial polls the instrument (line 40). and then displays the status byte bits in proper order on the CRT. In this example, the SRQ (B6) and error (B5) bits are set because of the attempt to program an illegal command option (KS). Other bits may also be set depending on instrument status.

COMMENTS

set up for remote

operation, clear

instrument.

Program for SRQ on

error.

Attempt to program illegal option. Serial poll the instrument. Identify the bits.

Loop eight times. Display each bit posi-

tion.

3-29

Model 8573 Programming Example-Load the modified

DECL.BAS file into the IBM computer (see the Model 8573 Instruction Manual) and add the lines below:

PROGRAM COMMENTS

KO=Send EOI with last byte; hold off bus until commands

processed on X

Kl=Do not send EOI with last byte; hold off bus until com-

mands processed on X K2=Send EOI with last byte; do not hold off bus on X IW=Send no EOI with last byte; do not hold off bus on X

10 NA$=“GPIBO” :CALL IBFIND Find the board

(NA$,BRDO%) descriptor.

20 NA$= “DEVO” :CALL IBFIND Find the instrument

(NAS,M617% ) descriutor.

30 V% =27:CALi IBPAD

(M617%,V%)

40 V% = l:CALL IBSRE

(BRDO%,V%):CALL

Set phmary address to 27. Send remote enable,

clear instrument.

IBCLR(M617%)

50 CMDS = “M32X” :CALL

IBWRT(M617%,CMD$l

60 CMD$=“KSX”:CALL IBWRT

(M617%,CMD$l

70 PRINT”B7 B6 B5 B4 83 B2 Bl

Program for SRQ on aTor. Attempt to program illegal option. Identify the bits.

80” 80 MASK % = 128 90 CALL IBRSP(M617%,SB%)

Define bit mask. Serial poll the instmmerit.

100 FORI =1TO8

110 IF (SB% AND MASK%)=0

THEN PRINT “0”; ELSE

Loop eight times.

Mask off the bits

and display them.

PRINT “1 “; 120 MASK%=MASK%/2 130 NEXT I 140 PRINT 150 V% =O:CALL

Close the board file.

IBONL(BRDO%,V%)

160 CALL IBONL(M617%,V%) Close the instrument

file.

Upon power up, or after the instrument receives a DCL or

SDC command, the KQ mode is enabled.

The EOI line on the IEEE-486 bus provides a method to positively identify the last byte in a multi-byte transfer sequence. 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 input sequence

to hang 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. The purpose of the hold off is to ensure that the front end FETs and

relays are properly configured before taking a reading. Keep in mind that all bus operation will cease-not just activity

associated with the Model 617. 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 3-14 lists hold off times for a number of different

commands. Since a NRFD hold off is employed, the handshake sequence for the X character is completed.

To run the program press the F2 function key. After placing the instrument in remote (line 40). the program then sets the

SRQ mode (line 50). An attempt is made to program an illegal

command option (line 60). at which point the instrument generates an SRQ and sets the error and RQS bits in its status byte. Other bits may also be set depending on instrument status. Lines 70-90 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 100-130 are used to generate the binary equivalent of the status byte value.

3.10.16 EOI and Bus Hold-off Modes (K)

The K command allows control over whether or not the instrument sends the EOI command at the end of its data string, and whether or not bus 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:

3-30

HP-85 Programming Example-To program the instm-

ment for the K2 mode, enter the following statements into the HP-85:

REMOTE 727 (END LINE)

OUTPUT 727;“K2x” (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 8573 Programming Example-To place the instm-

ment in the K2 mode, enter the following statements into the IBM computer:

V%=l:CALL IBSRE(BRDO%,V%) (return)

CMD$=“KZX”:CALL IBWRT(M617%,CMD$) (retom)

The Model 617 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.

Table 3-14. Bus Hold-off Times

Model 8573 Programming Example-Use the following

statements to reverse the default terminator sequence:

Bus Held Off

Commands On X Until:

F. R, C

2. N

All Others

Note: NRFD will be held off until each byte is recognized

NVRAM Storage Completed (13msec) 617 Front End Configured (20msecl Value Taken (36Omsec)

When X is recognized

(1.60msec in continuous trigger mode; Imsec in

one-shot trigger model.

3.10.17 Terminator (Y)

The terminator sequence that marks the end of the instrument’s data string or status word can be programmed by sending the Y command followed by an appropriate ASCII character. The default terminator sequence is the commonly used carriage return, line feed (CR LF) sequence (CR=ASCII 13: LF=ASCII 10). The terminator will assume this default value upon power’up, or after the instrument receives a DCL or SDC command.

The terminator sequence may be changed by sending the desired one or two characters after the Y command. However, the capital letters (A-Z) cannot be used as terminators.

V%=l:CALL IBSRE(BRDO%,V%) (return)

CMD!§=“Y”+CHR$(lO)+CHR$(13)+“X”:CALL

IBWRT(M617%,CMD$) (return)

The terminator sequence will be reversed when the second statement is executed.

3.10.18 Status NJ)

The status command allows access to information concerning instrument ooeratinz modes that are controlled bv other device-dependent c&mands such as F (functionj’and R (range). Additional parameters of the status command allow data and error conditions to be accessed. Status commands include:

UO=Send status word. Ul=Send instrument error conditions. UZ=Send instrument data conditions.

When the command sequence UOX is transmitted. the instrument will transmit the status word instead of its normal data string the next time it is addressed to talk. The status word will be transmitted only once each time the UO command is given. To make sure that correct status is transmitted, the status word should be requested as soon as possible after the command is transmitted.

Special command sequences will program the instrument as follows:

1. Y(LF)(CR)X = (LF CR) (two terminator characters)

2. Y(CR)(LF)X = (CR LF) (two terminator characters)

3. YX = (no terminator)

HP-85 Programming Example-To reverse the default (CR

LF) terminator sequence, type the following lines into the computer:

REMOTE 727 (END LINE)

OUTPUT 727;“Y”;CHR$(lO);CHR!§(l3);“X” (END LINE)

When the second statement is executed, the normal terminator sequence will be reversed; the instrument will terminate each data string or status word with a (LF CR) sequence.

The format of UO status is shown in Figure 3-11. Note that the

letters correspond to modes programmed by the respective device-dependent commands. The default values in the status

word (upon power up or after a DCL or SDC command) are

also shown in Figure 3-11.

Note that al1 returned values except for those associated with

the terminator correspond to ihe programmed numeric values. For example, if the instrument is presently in the R3 range, the second (R) byte in the statLls word will correspond to an ASCII 3. The returned terminator characters are derived by ORing the actual terminator byte values with $30.

For example, a CR character has a decimal value of 13, which equals $OD in hexadecimal notation. ORing this value with $30 yields $3D, or 6110, which prints out as an ASCII equal sign (= ). This terminator conversion step is necessary to convert the standard terminators into displayable form, as they will not normally print out on a computer CRT.

3-31

617 F RR

O=VOLTS

1= AMPS

2=OHMS 3=COULOMBS 4=XFDElK 5=“,I

RANGE

“Ok* AnyIS Ohms Coulombs XFDSK 00 = A”:0 A”fO ANO AU10 A”W AU10 01 = 200mV 02= 2” 20 pA 20 k* 2nC 2 v 20TR 03 = 20 V 200 pA 200 kR 20°C 20 ” 2Tfl 04 = 200 v 2 “A 2MO 20nC 20 ” 20Gll 05 = 200 v 20 nA 20MR 20°C 20 ” 20GQ 06 = 200 V 200nA 200MR 20nC 20 ” 2GR 07 = 200 V 2 PA 2GR 20nC 20 v 200MR 08 = 200 v 20&A 20GR 20°C 20 ” 20MR 09 = 200 V 200gA ZOOGO 20nc 20 v 2MQ

10 = 200 v 2mA ZOOGR 20nc 20 v 200 k0 11 = 200 v 20mA 200GfI 20nc 20 ” 200 id2 12 = Auto off for all functions

2 PA

2kcl zoo$c

ZERO CHECK O=OFF

,=ON

ZERO CORRECT

O=OFF

l=ON

SUPPRESS

O=OFF

l=ON

TRIGGER A 0 = CONTINUOUS. TALK

1= ONE-SHOT, TALK 2= CONTINUOUS, GET 3=ONE-SHOT. GET 4=CONTINUOUS. EXTERNAL 5=ONE-SHOT. X 6=CONTINUOUS. EXTERNAL 7=ONE-SHOT, EXTERNAL

2OOmV 2OOTtl

“/I

ulM K YY CR LF )BGDOI

TERMINATOR ASCII

=:CRLF

:= LFCR

k EOI: BUS HOLD-OFF

O=EOI + HOLD-OFF

1 =NO EOI + HOLD-OFF 2=EOI + NO HOLD-OFF 3=NO EOI + NO HOLD-OFF

-sm

OO=DISASLEO 01= READING OVERFLOW OZ=DATA STORE i=“LL

08=READING DONE

16=READY 32 = ERROR

DATA STORE O=CONVERSION RATE

1= 1 RDGISEC 2=1 RDGilO SEC 3= 1 RDGIMIN 4=1 RDG/lO MIN 5=1 RDG,HR B=TRIG SUTTON 7 = DISABLED

DISPLAY 0= ELECTROMETER

1 =VOLTAGE SOURCE

DATA PREFIX

O=PREFIX. NO SUFFIX

1 = NO PREFIX OR SUFFIX Z=PREFIX AND SUFFIX ,IF Bl,

READ MODE

0= ELECTROMETER

I= DATA STORE

2=MAXIMUM

3= MINIMUM

4=VOLTAGE SOURCE

VOLTAGE SOURCE OPERATE O=OFF

l=ON

332

Figure 3-11. UO Status Word and Default Values

The Ul command allows access to Model 617 error conditions in a similar manner. Once the sequence UlX is sent, the instrument will transmit the error conditions with the format shown in Figure 3-12 the next time it is addressed to talk in the normal manner. The error condition word will be sent only once each time the Ul command is transmitted. Note that the error condition word is actually a string of ASCII characters

representing binary bit positions. An error condition is also flagged in the status (serial poll) byte, and the instrument can be programmed to generate an SRQ when a” error condition

OCCWS. See paragraph 3.10.15. Note that all bits in the error condition word and the status byte error bit will be cleared when the word is read. In addition, SRQ operation will be restored after an error condition by reading Ul.

617 Oil O/l 0,

I= IDDCO-

0 0

000 CR LF

,LWAYS ZEROES

TERMINATOR

(DEFAULT

SHOWN1

In a similar manner, the U2X sequence allows access to instrument data conditions. When this command is transmitted, the instrument will transmit the data condition word shown in Figure 3-13 the next time it is addressed to talk. This information will be transmitted only once each time the command is received. As with the Ul error word, the U2 word is made up of ASCII characters representing binary values. Unlike the Ul error word, however, the LIZ data condition word will not be cleared when read; thps, instrument status in the U2 word is always current.

000 CR LF

.LWAYS !EROES

TERMINATOR

,DEFAULT

1 = DATA STORE J

2 (ZERO CORRECT) 0= OFF

l=ON

617 Oil 0 Oil o/1 0.

MODEL

NUMBER

PREFIX

FULL

VALUES

1= NO REMOTE -

1 1 = NUMBER ERROR

Figure 3-12. Ul Status (Error Condition) Format

The various bits in the error condition word are described as

follows:

IDDC-Set when a” illegal device dependent command

(IDDC) such as HlX is received (“H” is illegal).

IDDCO-Set when a” illegal device-dependent command op-

tion (IDDCO) such as T9X is received (“9” is illegal).

No Remote-Set when a programming command is received when REN is false.

NOTE

The complete command string will be ignored if

an IDDC. IDDCO or no remote error occurs.

N (SUPPRESS1

O=OFF

l=ON

1 =TEMPORARY CALlSRATlON-

1 =“OLTAGE SOURCE

OVER I-LIMIT

Figure 3-13. U2 Status (Data Condition) Format

The various bits in the data condition word include:

Data Store Full-Set when all 100 readings have been stored in the data store memory.

Z and N-Represents the same information as the corresponding zero correct (Z) and suppress (N) bytes in the UO status word.

Temporary Calibration-Set when new calibration parameters not yet stored in NVRAM have been received, or if power-up recall of NVRAM data was in error. Cleared when NVRAM storage is performed.

Voltage Source I-limit-Set when the 2mA current limit of

the voltage source has been exceeded.

Trigger Overrun-Set when a trigger is received when the instrument is still processing a reading from a previous trigger.

Number Error-Set when a” Out of range calibration or voltage source value is received.

HP-85 Programming Example-Enter the following pro-

gram into the computer to obtain and display instrument

status, the error condition word, and the data condition word.

3-33

PROGRAM COMMENTS

10 REMOTE 727

Send remote enable. 20 DIM AS 1251 30 OuTPIJT 727:“UOX” Send UO command. 40 DW”mdlFRRCZNTOBGD Display UO word values

QMMKYY”

50 ENTER 727;A$

Obtain UO status from in-

strument.

60 DISP A$ 70 OUTPUT 727;“Ulx”

80 ENTER 727;A$

Display UO status word

Send U1 command.

Get error condition

word. 90 DISP A$

Display error condition

word.

100 OUTPUT 727:“U2X” 110 ENTER 727;A!J

120 DISP A$

Send U2 command.

Get data condition word.

Display data condition

word.

130 EmR 727:A$ 140 DISP A$

Get normal reading.

Display normal reading.

150 END

80 PRINT RD$ 90 CMD$=“UlX”:CALL IBWRT

(M617%,CMD5)

100 RD$=SPACE$(ZS):CALL IBRD

(M617%,RD$)

1.10 PRINT RD$

120 CMD$=“UZX”:CALL IBWRT

(M617%,CMD$)

130 RD$=SPACE$(2S):CALL IBRD

(M617%,RD$)

140 PRIh’T RD$

150 RD$= SPACE$(25):CALL IBRD

(M617%,RD$)

160 PRINT RD$

170 V% =O:CALL IBONL

(BRDO%,V%)

180 CALL IBONL (M617%,V%)

Display status word. Send Ul command.

Get error condition word. Display error condition word. Send IJ2 command.

Get data condition word. Display data condition word. Get normal reading.

Display normal reading. Close the board file.

Close the instrument file.

After entering the program, run it by pressing the HP-85 RUN key. The program will place the unit in remote (line 10). send the UO command (line 30). and then obtain and display the status word (lines 50 and 60). Th e Ul command is mitted (line 70). z

md the error condition word is thj en obtained

then trans-

and displayed (lines 80 and 90). Line 100 sends the U2 command, and the data condition word is then obtained and displayed (lines 110 and 120). To show that status is transmitted only once, a normal reading is then requested and displayed (lines 130 and 140).

Model 8573 Programming Example-Obtain and display instrument status, the error condition word, and the data condition word as follows: load the modified D--’ - IS file ‘tCL.LI~

from disk (see the Model 8573 Instruction Manual) and add

the lines from the program below:

PROGRAM

COMMENTS

10 NA!J= “GPIBO” :CALL IBFIND Find the board

(NA$,BRDO%) descriptor.

20 NA$=“DEVO”:CALL IBFIND Find the instrument

(NA!f+M617%)

30 V% =27:CALL IBI’AD

(M617%,V%)

40 V%=l:CALL IBSRE

descriptor. Set primary address to 27. Send remote enable.

(BRDO%,V%)

50 CMD$=“LIOX”:CALL IBWRT Send UO command.

(M617%,CMD$)

60 PRINT”mdlFRRCZNTOBGD Identifv word bvtes.

QMMKYY”

70 RD$=SPACE$QS):CALL IBRD Get status word

(M617%,RD$) from instrument.

Press the conmuter F2 function kev to run the moeram. The

. ”

instrument is placed in remote (line 40). programmed to access the UO status word (line 50). and that status word is then obtained and displayed (lines 70 and 80). The Ul command is then transmitted (line 90). and the error condition word is then obtained and displayed (lines 100 and 110). Line 120 then sends the U2 command, and the data condition word is obtained and displayed in lines 130 and 140. To show that status is transmitted only once, a normal reading is then requested and displayed (lines 150 and 160).

3.11 Front Panel Messages

The Model 617 has a number of front panel messages associated with IEEE-488 programming. These messages are intended to inform you of certain conditions that occur when sending device-dependent commands to the instrument.

The following paragraphs describe the front panel error messages associated with IEEE-488 programming.

3.11.1 Bus Error

A bus error will occur if the instrument receives a device dependent command when it is not in remote, or if an illegal

device-dependent command (IDDC) or illegal device dependent command option (IDDCO) is sent to the instrument.

Under these conditions, the complete command string will be

rejected and the following message will be displayed:

b Err

3-34

In addition, the error bit and pertinent bits in the Ul word will be set (paragraph 3.10.15 and 3.10.18) and the instmment can be programmed to generate an SRQ under these conditions (paragraph 3.10.15).

A no remote error can occur when a command is sent to the instrument when the REN line is false. Note that the state of REN is only tested when the X character is received. An IDDC error can occur when an invalid command such as HlX is transmitted (this command is invalid because the instrument has no command associated with that letter). Similarly, an IDDCO error occurs when an invalid option is sent with a valid command. For example, the command T9X has an invalid option because instrument has no such trigger mode.

HP-85 Programming Example-To demonstrate a bus er-

ror, send an IDDC with the following statements:

REMOTE 727 (END LINE)

OUTPUT 717:“HlX” (END LINE)

When the second statement is executed, the bus error message appears on the display for about one second.

Model 8573 Programming Example-Type in the follow-

ing statements to demonstrate a bus error by sending an IDDCO:

V% =l:CALL IBSRE(BRDO%,V%) (rehxn)

CMD$=“HlX”:CALL IBWRT(M617%,CMD$) (return)

When the second statement is executed, the instrument will display the number error message for about one second. This error occurs with this example because an attempt is made to program a voltage value of 125V, which is outside the range of the voltage source (-102.35V 5 V 5 +102.4V).

Model 8573 Programming Example-To display the

number error, enter the following lines into the IBM computer:

V%=l:CALL IBSRE(BRDO%,V%) (return)

CMDB=“DlVl25X”:CALL IBWRT(M617%,CMD$)

(return)

The number error message will be displayed for about one se-

cond when the second statement is executed. The number er-

ror occurs with this example because of the attempt to program a voltage of 125V, which is above the range of the voltage source (-102.35V 5 VI +102.4V).

3.11.3 Trigger Overrun Error

A trigger overrun error occurs when the instrument receives a

trigger while it is still processing a reading from a previous

trigger. Note that only the overrun triggers are ignored and will have no effect on the instrument except to generate the

message below. When a trigger overrun occurs, the following

front panel message will be displayed for approximately one

second:

t Err

The bus error message will be displayed for about one second when the second statement is executed.

3.11.2 Number Error

A number error occurs when an out of range value is sent to the instrument when programming the voltage source, or when sending calibration values over the bus. Under these conditions, the instrument will display the following error message:

“Err

The command string will be accepted, but calibration or voltage values will remain unchanged.

HP-85 Programming Example-Enter the following lines

to display a number error:

REMOTE 727 (END LINE)

OUTPUT 727;“DlV125X” (END LINE)

HP-85 Programming Example-To demonstrate a trigger

overrun error, enter the following statements into the HP-85

keyboard:

REMOTE 727 (END LINE)

OUTPUT 727;‘T3x” (END LINE)

TRIGGER 727@TRIGGER 727 (END LINE)

Note that the trigger overrun message is displayed with the

third line above is executed.

Model 8573 Programing Example-Enter the following

statements into the computer to demonstrate the trigger over-

run message:

V%=l:CALL IBSRE(BRDO%,V%) (return) CMD$=“T3X”:CALL IBWRT(M617%,CMD$) (return) CALL IBTRG(M617%):CALL IBTRG(M617%) (return)

The trigger overrun error message will be displayed when the third line above is executed.

3-35

Table 3-15. Trigger to Reading-Ready Times

3.12 Bus Data Transmission Times

ErrIN

Time (msec

365 780

204, 200nA. 20nA

1;;; &A 2~

l20nC. 2nC

l2oopc

20kS200GQ

2kL-I

Notes:

1. Conditions: Input is on range, HP-85 controller.

2. Preamp settling time (to 12%) is 2 seconds on preamp ranges (2,20,20OpA), and must be taken into account by

the user.

3. Volt time/error also apply to external feedback.

4. V/I time/error is the same es the applicable current range.

365 365 780 780 365 780 365 780

% of step Input

1 f

.Ol .lO

.Ol

55 (2)

.lO

25 (2)

.Ol .lO .Ol .lO

A primary consideration is the length of time it takes to ob-

tain a reading once the instrument is triggered to make a conversion. The length of time will vary somewhat depending on the selected function and trigger mode. Table 3-15 gives typical times

3-36

SECTION 4

APPLICATIONS

4.1 INTRODUCTION

Applications for the Model 617 are many and varied and will depend on the user’s needs. Basically, the Model 617 can be used to make many of the same measurements in the range of ordinary DMMs; however, special characteristics such as high input resistance and high sensitivity give the instrument much better capabilities than those of the ordinary DMM.

For example, the typical input resistance for an ordinary DMM is on the order of lOM0. In contrast, the Model 617 has an input resistance of greater than ZOOTQ (2 x 10143). The Model 617 can detect currents as low as O.lfA (lo-16A), while a typical DMM might be limited to current measurements in the pA range.

In this section, then, we will discuss some possible applications for the Model 617 Electrometer. Keep in mind that these examples are only representative of what is possible with this highly sophisticated instrument, and by no means exhaust the possible uses for the unit.

4.2 INSULATION RESISTANCE MEASUREMENTS

constant. The voltage developed across the test resistance will, of course, depend on the value of the insulation resis- tance. The Model 617 measures the generated voltage and

calculates the resistance value accordingly. The low compliance voltage of the Model 617 ( < 2V on 2G0 range and

lower, except <3OOV during overload) keeps error due to

voltage coefficient small.

For resistance measurements above 1080, or for cables longer than three feet, guarded measurements are recommended, as shown in Figure 4-2. In this case, the rear panel V, R GUARD switch is used to internally apply a guard signal to the inner shield on the connecting cable. The guard is carried through to the inner shield of the test fixture. The inner shield must be insulated from the outer shield, which is a safety shield. Incidentally, a shielded fixture is recommended for both unguarded and guarded configurations for measurements above 107n if stable readings are to be expected (in the unguarded mode, the shield should be connected to input IOW).

With the constant current method just discussed, the Model 617 can make rneasurenients as high as 200GR. However, the insulation resistance of such materials as polyethylene may lie above this range. By using the Model 617 to make resistance measurements in the constant-voltage mode, measurement range can be extended up to 10160. Also, for a given resistance range, the V/I mode will be faster.

At the moderate impedance levels of many circuits, insulation resistance is seldom a consideration, as it is generally many orders of magnitude above the highest impedance encountered in the remainder of the circuit. At very high impedance levels, however, insulation resistance can be a consideration, since it can lower effective circuit impedance considerably. Since typical insulation resistances run in the range

of lOlo-lOM2, their values lie above the measurement range of ordinary instruments. The high resistance measurement range of the Model 617, however, gives it capabilities to measure such high resistances.

A typical test configuration for making insulation resistance

measurements is shown in Figure 4-l. In this case, the constant current method is used. Using this method, insulation resistances up to 2WGfI can be measured. As the term irn-

plies, the tet current through the unknown resistance is kept

A typical configuration for using the Model 617 in this manner is shown in Figure 4-3. Here, the built in voltage source of the instrument is used to force a current, I, through the unknown resistance, R. The insulation resistance is then automatically calculated by the Model 617 as follows:

R=-

where I is the current through the resistance as measured by

the instrument, and V is the programmed voltage.

Note that COM is connected to input LO thru 1OGQ and appears in series with the resistor under test. This resistance is below the resolution of the instrument on ranges above 2MSl.

4-l

MODEL 6147

,&R:;;,, ,A

INPUT

MODEL 4801

00 00

-0 cl

617 SET TO OHMS

r-----l

4-2

EQUIVALENT CIRCUIT

Figure 4-l. Insulation Resistance Measurement (Unguarded)

INPUT

6011 CABLE

r---

OFF m ON

VR GUARD - ’ u

-----_

617 SET TO OHMS, “. ff GUARD ON

I-----

WARNING: SAFETY SWELO RECOMMENDED FOR GUARDED

COM 617 PREAMP

)I’

If---l

RESISTANCE MEASUREMENTS ABOVE 30GR. UP TO 300” MA,’ SE PRESENT ON GUARD

L--J--

SAFETY

SHIELD

A/D CONVERTER

SIGNAL GUARD

EQUIVALENT CIRCUIT

Figure 4-2. Insulation Resistance Measurement (Guarded1

4-3

MODEL 6147 TRIAX TO BNC ADAPTER

MODEL 4601 CABLE

---_

r----

00 00

V-SOURCE OUTPUT

\Lo\J ,o, F

\ ’

6104 TEST FIXTURE

----__

617 SET TO “II OHMS

POMONA MODEL 4666 PATCH CORDS

617 PREAMP

Ryj+” &&&y&&

MODEL 6104

TEST FIXTURE

A/D CONVERTER

BLACK

SHIELDED

4.4

z V-SOURCE

EQUIVALENT CIRCU,T

Figure 4-3. Insulation Resistance Measurement Using V/I Ohms Mode

For example, assume that the applied voltage is 1OOV. and the measured current is 1pA. The resistance is calculated as follows:

The percent error due to voltmeter loading in this circuit can be given as:

100

R =-=_=

IPA

Since the user has fine control over the internal voltage source

(-102.35V to +102.4V in 5OmV steps), the resistance at a given applied voltage can be easily determined. Such control can give rise to voltage coefficient studies, as described later in this section.

In addition to the measurement of insulation resistances, this basic method can be used to measure unwanted leakage resis-

tances. For example, leakage resistance between PC board

traces and connectors can be made with either of the two methods above, depending on the resistance values involved.

10140

4.3 HIGH IMPEDANCE VOLTMETER

The input resistance of the Model 617 in the volts mode is greater than ZOOTQ. Because of this high value, the Model 617 can be used to make voltage measurements in high impedance circuits with a minimum of loading effects on the circuit.

Consider the situation where a circuit designer must measure

the gate-to-source voltage of a precision JFET amplifier that

has a gate impedance of 1COMQ. Further assume that the re-

quired accuracy of this measurement is 1%

% ERROR =

Suppose, for example, a typical DMM with a 1OMR input resistance were used to make this measurement. The error because of meter loading would be:

% ERROR =

Even if a DMM with an input resistance of 1OW were used, the error would still be:

% ERROR = x 100% = 9.1% error

Such a large error would not be tolerable in this case because of the 1% accuracy requirement. However, since the Model 617 has an input resistance of 200TR. its error in this example would be:

%ERROR = x 100% = O.oooo5% error

which would be dominated by the instrument’s specified accuracy.

Rs + RIN

1OOMQ

1OOMR + lOMQ

1OOMQ

lC0MQ + 1GO

lWM0

1OOMQ + 2OOTQ

x 100%.

x 100% = 91% elm2

The set-up for this measurement is shown in Figure 4-4. The

gate-source voltage is represented by VGS, while the effective gate impedance is represented as Rs. The input resistance of the voltmeter is given as RN.

A. MEASUREMENT

CONFIGURATION

B. EWIVALENT CIRCUIT

Figure 4-4. Measuring High Impedance Gate-

Source Voltage

Thus, the input impedance of the Model 617 would be more

than adequate for this situation, because the error due to meter loading is substantially better than the required 1% value stated earlier. In addition, the 4~ digit resolution of the instrument allows the designer sufficient precision to make use of the high input impedance.

4.4 LOW-LEVEL LEAKAGE CURRENT MEASUREMENTS

Many devices exhibit low-level leakage currents that may require measurement. Typically, such leakage currents might lie in the nA (lo-9A), pA (lo-“A) or even the fA (lO-lsA) range. The Model 617 is an ideal instrument for such current measurements because it can detect currents as low as O.lfA.

An example of a situation requiring low current measurement

is shown in Figure 4-5. In this example, the gate leakage current of a JFET is to be measured. Although the device manu-

4-5

facturer may specify the current value, it is often desirable to

verify the specification for a particular sample of the device. Then too, the specified leakage current might be at a higher voltage than required. For example, the specified leakage current might be 11~4 with an applied voltage of 25V, while that figure might be much less at an operating value of 1OV.

An added bonus of using the Model 617 in this situation is

that the instrument has a built in voltage source. Thus, the voltage source could be programmed to the desired value or values, and the leakage current could be measured for each voltage. In this manner, leakage current characterization

MODEL 6147 TRIAX

TO BNC ADAPTER

MODEL 4801 CABLE

studies could be perfomed with only a single measuring in-

strument, rather than requiring a separate voltage source.

As shown in Figure 4-5, a shielded test fixture such as the Keithley Model 6104 should be used to keep the measurement quiet and stable. A good quality low-noise cable, such as the Model 4801 connected through a Model 6147 adapter should be used to connect the current input to the instnnnent.

Forward and reverse diode currents could be measured in a similar manner. The forward leakage current (measured with

\ II

‘--Il.::

V-SOURCE OUTPUT

LO HI

6104 SHIELD

------

\ \

617 SET TO AMPS

POMONA MODEL 4686 PATCH CORDS

617 PREAMP

r-l

r----

--1

TEST FIXTURE

-~~~~~~~--AID

Figure 4-5. Leakage Current Measurement

>LO

-+>H’

- V-SOURCE

the built-in voltage source set to less than 0.6V) can be

measured using the Model 617 without regard to input voltage burden. High capacitance diodes such as zener devices

will present no problem, since the Model 617 is unaffected by stray capacitance up to O.OlpF.

4.5 DIODE CHARACTERIZATION

When the Model 617 is placed in the ohms mode, constant current values between In4 and lC@A are available at the INPUT jack high and low terminals, as shown in Table 4-l.

(Input high sources the current). These currents can be used to plot the I-V (current-voltage) characteristics over a substantial range.

Table 4-I. Diode Currents and Voltages

Diode

Range

2kQ. 20kfI

200 kCl

2MQ

ZOMR

200MQ

2GR, 20GQ, 200GD

*R = displayed resistance.

Current Diode Voltage (VP

lOOpA V=(lOO x 10-61 (f?)

lOpA V=( 10 x 10-q (RI

. lOOnA V=(lOO x 10-q (RI

1OnA V=( 10 x 10-q (RI

1nA V=( 1 x 10-?(R)

v=( 1 x 1041 (RI

MODEL 6147 TRIAX

TO BNC ADAPTER BNC CABLE

‘I

INPVT

MODEL 4601

617 SET TO OHMS

EQUIVALENT CIRCUIT

6104 SHlELD

r-1

617 PREAMP

r-----

l--L---i

KEITHLEY MODEL 6104

SHIELDED TEST FIXTURE

Figure 4-6. Diode Characterization

4-7

Figure 4-6 shows the basic circuit configuration for using the Model 617 in this manner. A decade current, 1, is forced

through the diode under test. The current will develop a for-

ward voltage drop, VF, across the diode. The voltage across

the diode can be calculated by muldplying the displayed resis-

tance by the test current (see Table 4-4). For example, assume

that a resistance reading of 50kR is measured with the instru-

ment on the 2OOkR range. The voltage across the diode is: lOpA X 50kR = 0.5V.

Figure 4-7 shows several examples for typical diodes. The curves were drawn from data obtained in the manner just described.

WARNING

Up to 300V may be present between the

high and low terminals in ohms.

4.6 CAPACITOR LEAKAGE MEASUREMENTS

necessary to folly charge the capacitor, typically 1ORC. Once the test is completed, the voltage source should be turned off to allow the capacitor to discharge.

The leakage current can be directly read from the Model 617

display during the test procedure. If the leakage resistance value is required instead, the instrument can be placed in the V/l ohms mode, and the instrument will directly display the leakage resistance value, with no calculations necessary on

the part of the user.

This basic procedure could be used to test a number of capacitors on an automated basis. A test fixture that holds a

number of capacitors could be constructed, and a Keithley

Model 705 or Model 706 Scanner could be used to select among the various devices to be tested. For a higher degree of automation, both the scanner and the Model 617 could be controlled from a computer via the IEEE-488 bus. In this way, measurements that would otherwise be tedious and time consuming could be conducted on a more routine basis.

An important parameter associated with capacitors is their leakage currents. Once the leakage current is known, the insulation resistance can be calculated. Ideally, a capacitor should have no leakage current, and thus infinite leakage resistance. However, capacitors, like all practical devices, are not ideal, so these parameters can become important, especially to circuit design and component engineers. The amount of leakage current in a given capacitor depends on its dielectric as well as the applied voltage. Ceramic dielectric capacitors typically have leakage currents in the nA to pA range, while polystyrene and polyester dielectric devices exhibit much lower leakage currents-generally in the fA range. (These values are for test voltages in the 1COV range).

The basic configuration for this test is shown in Figure 4-8. The Model 617 voltage source is used to impress a voltage

across the capacitor, C. The resulting leakage current is then measured by the electrometer section of the Model 617.

The resistor R is necessary to limit current to a safe value in case the capacitor is shorted, and it also helps to reduce noise. Typically a value of about 1Mn should be used, although that value can be decreased for larger capacitor values. However,

values under lOk0 are not recommended. Refer to paragraph 2.14.8.

At the start of the test, the Model 617 should be placed in the

amps mode and on the 2011~4 range. The voltage source is then programmed to the desired voltage, and the output turned on. Once the required soak time has passed, the instrument can be placed on the proper current range to make the current measurement. The soak time is the period

4.7 CAPACITANCE MEASUREMENT

The coulombs function of the Model 617 provides a quick and easy method of measuring capacitance values of capacitors, cables, and connectors. It is especially useful in cases of cables and connectors because of the very small values of charge that can be measured.

The basic method involves using the voltage source to apply a step voltage across the capacitor, as shown in Figure 4-9. Since charge is to be measured, the Model 617 should be in

the coulombs function to make the measuremenl. Just prior to turning on the voltage source, zero check should be dis-

abled and the charge suppressed. Then, turn on the voltage source and note the final charge value.

The capacitance can then be computed as follows:

cc-..-

where: AQ = Q2 (final charge)-Q1 (initial charge

assumed to be 0)

AV = V, (step voltage) -VI (initial voltage, assumed to be 0)

4-8

,$‘A

DIODE

CVRRENT

(II

lOO”A -

---l--

0.2

0.6

Figure 4-7. Diode Curves

-.--!

T-- - - - - -, SHIELD

RECOMMENDED R VALUES:< IOOpF-10nF 1MR

IOnA-l+F 1OOkR

ideal instrument to obtain data to determine the voltage co-

efficient because of its built-in variable voltage source and its

highly sensitive picoammeter section.

The basic configuration for making voltage coefficient

measurements is shown in Figure 4-10. The voltage, Vs, is applied to the resistor under test by the voltage source of the instrument. The current is measured by the electrometer input

of the instrument. The! resulting current can then be used to calculate the resistance. If the instrument is in the V/I ohms mode, the resistance will be calculated automatically.

Figure 4-8. Capacitor Leakage Tests

RECOMMENDED R VALUES: < lOO,+lOnF IMR

Figure 4-9. Capacitor Measurement

As an example of the above procedure, assume that an unknown capacitor is to be measured. If the step voltage is 1LXW. and a AQ value of 2°C is obtained, the capacitance value is:

2°C

Cc---

4.8 VOLTAGE COEFFICIENTS OF HIGH-MEGOHM RESISTORS

= 20pF

1OQv

,OnF.l,J 1OOkll

Two resistance readings at two different voltage values will be required to calculate the voltage coefficient. The voltage coefficient in %/V can then be calculated as follows:

100 CR,--R,)

Voltage Coefficient (%/V) =

R,(AV)

where: R, is the resistance with the first applied voltage. R, is the resistance with the second applied voltage. AV is the difference between the two applied voltages.

As an example, assume that the following values are obtained:

R, = 1.01 x IOW RZ = 1 x loWI

AV = 5V

The resulting voltage coefficient is:

X0(1 X 108)

Voltage coefficient (%/VI =

1 x lolo

Note that the voltage coefficient of a particular device may apply only across the selected voltage range, and may, in fact, vary with different voltage increments in the same approximate range.

= 0.2%/V

High megohm resistors (above 10%) often exhibit a change in resistance with applied voltage. This resistance change is characterized as the voltage coefficient. The Model 617 is an

4-10

Keithley 617 Service manual

Specifications and Main Features

Frequently Asked Questions

User Manual