Keithley 485 Service manual

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Page 1

Model 485

Autoranging Picoammeter

Instruction Manual

Contains Operating and Servicing Information

Page 2

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 WARRAN-IY

This warranty does not apply to defects resulting from product modification without Keithley’s express written consent, or misuse of any product or pwt. 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 LlBU 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.

NEITHER KBITHLEY INSTRUMENTS, 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 SOFTWARE 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: 216-248-6168 * http://www.keithley.com

Page 3

Model 485 Autoranging Picoammeter

Instruction Manual

0 1984, Keithley Instruments, Inc.

Test Instrumentation Group

Cleveland, Ohio, U.S.A.

January 1990, Sixth Printing

Document Number: 485-901-01 Rev. F

Page 4

SPECIFICATIONS

ACCURACY I1 YEAR,

lW28~C

RANGE

2nA

200

RESOLUTION

“A 1 PA “A 10 pA

O.lpA

2 PA 100 PA

!A 1 nA

200

,‘A 10 “A

2mA

,NP”T VOLTAGE BURDEN: Less than 200&V. RANQING: Manual or autoranging. AUTORANGING TIME: Average 250ms per range. SmLlNG TIME AT DISPLAY: Less than 1 second to within 2 co”nts on

fixed range. CONVERSION PERIOD: 300,“s. TEMPERATURE COEFFICIENT 10°-160C B 26°-50”C,: f10.1 x BP-

plicable sccuracy specification) per OC. MAwMUM COMMON MODE VOLTAGE: 30V rms. DC to 60Hz sine

100 “A

* l%rdg + countslt

0.4 + 4

0.4 + 1

0.2 + 1

0.15 + 1

0.1 + 1

0.1 +1

WWB.

ANALOG OUTPUT:

Output Voltage: + IV = - 10000 co”ntf.. mept + 1OOmV = - 10000

mints 0” 2nn range.

OUtput tIea,*tance: 10000.

REL: Pushbutton allows zeroing of an range readings. Allows relative

readings to be made with respect to baseline value. Front panel ~nnuncistor indicates REL mode.

DATA STORE and MINIMAX: 100 reading storage capacity: records data

at one of six selectable rates from 3 readings/second to 1 reading/hour, or by manual triggering. Also detects and stores maximum and minimum readings comin”““sIY while in the data store mode.

LOG: Displays logarithm (base 101 of the absolute value of the measured C”F

rent Iexamples: -3.000 = *ImA; -6.301 = +O.$Al.

IEEE-488 BUS IMPLEMENTATION (Option 48631

MULTILINE COMMANDS: DCL, SDC, GET, GTL, “NT. UNL. SPE. SPD. UNILINE COMMANDS: IFC, REN EO,. SRC. ATN. INTERFACE FUNCTIONS: SHl. AH,, T5. TEO. L4, LEO. SRI, RL2,

PPO. DCl, DTI, CO, El.

PROGRAMMABLE PARAMETERS: Zero Check. Range, REL. LOG, Trig-

ger, Calibration. EO,, SRO, Status. 0”tp”t Format. Terminator.

ANALOG REJECTION

RISE TIME RATIO

I10 .SO%, IS0 or EOHz, INPUTt

60ms 60iTlS

6rnS

3ms 3ms

lms lms

GENERAL

DISPLAY: 4% digit LCD, 0.5” height: polarity. range and staf”s indication. OVERRANGE INDICATION: “OL” displayed. CONNECTORS:

Input: ENC. Analog Output: Banana Jacks.

OPERATING ENVIRONMENT: 0-50.X. less than 70% R.H. up to 35’C:

linearly derate 3% R.H./OC up to 5OOC. STORAGE ENVIRONMENT: -25O to +BO”C POWER: lOF,-125V or 210.250V (switch selected,. go-llOV available.

SO-6OHr. 12 VA. DIMENSIONS, WEIGHT: 65mm high Y 235mm wide x 275mm deep.

(3%” x 9%” x lO%“,.

Net Weight: 1 .Skg I4 Ibs.)

ACCESSORIES AVAILABLE:

Model 1010: Model ,017: Model 1664: Mods, 1758: Model 4801: Model 4603: Model 4653: Model 7006-3: Model 7006-6: Model 6573:

NORMAL MODE

7OdB 7OdB 350Vdc 65dB 350Vdc

6FdB 350Vdc 65dB 5O”dc 65dB 5OVdc

55dB

Single Rack Mounting Kit Dual Rack Mounting Kit

Hard Shell Carrying Case Rechargesble Battery Pack Low Noise Input Cable (4ft.l. BNC to ONC

Low Noise Cable Kit

IEEE-486 Interface

IEEE-466 Digital Cable 13ft.b IEEE-468 Digital Cable 16 ft.1 IEEE-488 Interface for IBM PC

MAXIMUM

CONTINUOUS

350”dC

5OVdc

Specifications subject to change without notice.

Page 5

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

SECTION l-GENERAL INFORMATION

Introduction. Getting Started Unpacking and Inspection

Specifications

Warranty Information.

Manual Addenda Safety Symbols and Terms Optional Accessories

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l-1 1-l

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

2.1

2.2

2.2.1

2.2.2

2.2.3

2.3

2.4

2.4.1

2.4.2

2.4.3

2.4.4

2.5

2.6

2.7

2.7.1

2.7.2

2.7.3

2.7.4

2.75

2.7.6

2.7.7

2.8

2.8.1

2.8.2

2.8.3

2.8.4

2.8.5

SECTION Z-BENCH OPERATION

introduction ...............................................................................

PreparationforUse

Line Power ..............................................................................

Battery Pack Power .......................................................................

BatteryCharging

TntBail ....................................................................................

Model 485 Familiarization

Display

FrontPanelControls

InputConnector ..........................................................................

AnalogOutputConnectors

Error Messages

EnvironmentalCondition .....................................................................

BasicBenchMeasurements

Power-Up ...............................................................................

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

Current Measurements ....................................................................

RelativeMode

LOGMode ...............................................................................

Inverting Analog Output ...................................................................

MIN/MAXand 100 Point Data Store

MeasurementConsiderations

SourceResistance ........................................................................

SourceCapacitance

LeakageResistance .......................................................................

ZeroTimeStability

Groundingconsiderations

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2-l 2-l 2-l 2-l 2-l

2-1 2-l 2-l 2-2 2-2 2-2 2-2 2-3

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

2-5 2-6 2-6 2-6 2-7

2-8 2-8 2-8

2.9

2.9.1

2.9.2

2.9.3

2.9.4

2.9.5

3.1

3.2 i::

3.5

Applications

Op Amp Offset Current

FET Gate Leakage and Channel Current. Insulation Leakage Currents and High Resistance. Phototube, Photodiode and Beam Currents Resistivity Tests

SECTION 3-PERFORMANCE VERIFICATION

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

Environmental Conditions Recommendrsd Test Equipment Initial Conditrons Verification Procedure

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3-l 3-l

,. 3-l

3-1 3-l

Page 6

4.1

4.2

4.3

4.3.1

4.3.2

4.3.3

4.3.4

4.3.5

4.4

4.4.1

4.4.2

4.4.3

4.4.4

4.5

4.6

4.7

5.1

5.2

5.3

5.4

5.4.1

5.4.2

5.4.3

5.4.4

5.4.5

5.5

5.6

5.6.1

5.62

5.63

5.6.4

5.6.5

5.7

5.8

5.9

TABLE OF CONTENTS (CONT.)

SECTION 4-THEORY OF OPERATION

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

Overall Functional Description. ................................................................

AnalogCircuitry ............................................................................

Current-to-Voltage Converter ...............................................................

Multiplexer ............................................................................

InputBufferAmplifier .....................................................................

-2VReferenceSource .....................................................................

AIDConverter.. ......................................................................... 4-3

Digital Circuitry .............................................................................

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

Address Decoding ........................................................................

PIA .....................................................................................

DisplayBoard.. ..........................................................................

Digital Calibration ...........................................................................

PowerSupply ..............................................................................

Model 1758 Battery Option ...................................................................

SECTION 5-MAINTENANCE

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

Top Cover Removal/Installation ...............................................................

Battery Pack (Model 1758) Installation

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

Recommended Calibration Equipment.

CalibrationJumper ........................................................................

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

Calibration Procedure. .....................................................................

CalibrationStorage ........................................................................

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

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

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

Self Diagnostic Program ...................................................................

Power Supply and Battery Pack (Model 1758) Checks

A/D Converter and Display .................................................................

SignalConditioning .......................................................................

Input Amplifier NJ105) Balancing ..............................................................

LineFuseReplacement ......................................................................

Special Handling of Static Sensitive Devices.,

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4-2

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

4-l 4-l 4-l 4-1

4-2 4-3

4-4 4-4

4-4

5-I 5-l 5-l 5-l 5-1

5-2

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

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

6.1

6.4

6.5

SECTION B-REPLACEMENT PARTS

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

ReplaceableParts ...........................................................................

Ordering Information ........................................................................

FactorySen/ice .............................................................................

Component Location Drawings and Schematic Diagrams

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

6-l 6-l 6-l 6-l 6-l

Page 7

LIST OF ILLUSTRATIONS

2-1 2-2 2-3 2-4 2-5 2-6 2-7 Z-8 2-9

2-10 3-l 4-l 4-2 4-3 4-4 4-5

5-I

5-2

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

Model485FrontPanel ....................................................................... 2-2

Model 465 Inverting Analog Output Simplified Model for Input Signal Conditioning

Test Fixture Guarding ....................................................................... 2-8

LeakageTestSetUpUsingModel6104 ........................................................ 2-8

Op Amp Input Offset Currents Measurement

F5T Gate Leakageand Channel Currents Measurement.

Insulation Leakage Currents end High Resistances Measurement .................................... 2-9

Set Up to Measure Photomultiplier, Photodiode end Beam Currents .............................. ,, 2-9

ResistivityTestSetUp

Shielded Test Fixture ........................................................................ 3-2

Simplified Block Diagram ..................................................................... 4-l

Current-to-Voltage Converter

Simplified Schematic of the Multiplexer

Simplified Schematic of the Input Buffer Amplifier AIDConverter

Segmentldentification

JumperLocations ...........................................................................

Model485MiscelianeousParts

Display Assembly Mother Board, Component Location Drawing. Dwg. No. 485-100

Mother Board, Schematic Diagram, Dwg. No. 485-106., .......................................... 6-9

Display Board, Component Location Drawing, Dwg. No. 485.110 ................................... E-13

Display Board, Schematic Diagram, Dwg. No. 485-116

Model 1758 Battery Peck, Component Location Drawing, Dwg. No. 1758-100 ......................... 615

Model 1758 Battery Peck, Schematic Diagram, Dwg. No. 1768-106 ................................. 6.16

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2-7

2-8 2-9

Z-IO

4-2 4-2 4-2 4-3

5-4 5-7

6-2 6-3 6-7

6-14

iii

Page 8

LIST OF TABLES

2-1 2-2 2-3 3-1 3-2 5-1 5-2 5-3 5-4 5-5 5-6 5-7 5-8 6-1 6-2 83 8-4

Error Messages.. ..........................................

Range, Accuracy and hlaximum Allowable Inputs Equivalent Input Resistance With Zero Check Enabled

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

RangeAccuracy ...........................................

Range Calibration ..........................................

Recommended Troubleshooting Equipment

TroubleshootingModes .....................................

Power Supply Checks and Battery Pack (Model 1758) Checks

A/DConverterChecks ......................................

DisplayBoardChecks ......................................

OffsetJumparSetUp ......................................

Static Sensitive Devices ....................................

Mother Boerd, Parts List ....................................

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

Model 1758 Battery Pack, Parts List ...........................

Model485SperePartsList ..................................

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

6-4 6-13 6-15 6-17

Page 9

SAFETY PRECAUTIONS

The following safety precautions should be observed before operating the Model 485.

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 30V rms between the input connector shell and earth ground.

Inspect the test leads for possible weer, 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 3mA.

Page 10

Model 485 Addendum

me following idormation is supplied as a supplement to tfi manual k order to prmide the user with the latest tiprovements. It is recommended that vefication tio~tion k added to Section 3 of the Model 485 Instiction Manual and c&bration tifomatimr be added to Section 5.

~is addendum contatis complete procedures for vefi@g and cahhatig the Model 485 ustig the WltMq Model 2& Cdibmtor/Somce. Complete sepmate pmcedmes a pmtided for @otig di@ti calibration horn either the hont panel or over the IEEE+8 bus. Dgitd ctibration over the bus is automated ustig a BASIC pro~am mn @ the W 85 computer.

PA-2w Rev. A / 149

Page 11

PERFORMANCE VERIFICATION USING MODEL 263 ~LIBRATOR/SOURCE

Use of the Model 263 to verify ac~aq specifications of the Model 485 stip~ies the prored~ by etiating the need for user desi~ed _nt somces. The quipment

fisted h Table >1 of the manual is not needed.

Idetiy performance verification shotid be perfomed when the tis~ent k first received to emm that no daage or chmge h calibration has ocmed dtig ship ment. It may&O be perfomed when fi~ent acwa~ is swpe~ Orfo~w~ c~bration. E perfmrnance on any of the rmges ia outside the specified tits, ctibrate the titiment.

NOTE

Mthe

~ent does not meti spedicatiom md is stfl under warrmty ~ess thm Q months stice date of shipment), con~d your ~lMey mpmsentative Orthe factory b detetie the atimr to &

t&en.

2. Tm on the Models 485 and 263, and allow them to wm up for one hour. The Model ~ may be operated from either ~ie power or battery pack power, as long as the batteq pack has been fu~y charged..

Veficatirur Prncedw

Weed as fo~ows to verify the accuraq of the Model 485:

1. On the Model 485, press ZERO CHECK and select the M rmge.

2. With an open input, adjust the ZERO pot for .0000 *1 cmrnt on the display.

3. Comect the Model 263 to the Model 485 as shown in Fi~e 1. Make sue the cdlbrator is in standby.

4. Relesae ZERO CHECK on the Model 485.

5. Using the AMPS (adive) c~nt source, program the

Model 263 to output 1.90~nA and verify that the reading is within the Itits h Table 1,

6. Using Table 1 as a guide, check the rest of the current

ranges by applying the a~ropriate current and verifying that the reatig is within the allowable limits.

Etimenti Condltiom

M measurements shodd be made at m mbient temperature b~een M“ md 28°C (&” to 82°~ with a relatiw humidity less thm 70°h.

Irritid

Conditimra

Before perfofig the verification procedure, m&e sure the Models 485 md 263 meet the fo~owtig conditiom:

1 E the tis~ents have been subjed b tempmams

blow M°C (&°F) Orabom 28°C (82°F), dow sufficient tie for the titruments to reach temperahs tithti the rmge. GenerWy, it tskes one hour to stabtie m irrs~ent that is M“C (MOF)outside of the specfied range.

Table 1. Range Accumcy

263 Output

(AMPS)

1.90M0 A

19.0000 M

190.WO A

1.90000 PA

19.0000 ~A

190.000 @

1.9oooofl

*Includes Model 263 error.

Allowable Reading*

(M”C -28°C)

1.8933 to

B.936 to

M9.69 to

1.8976

28.986

to to

E9.86 to

1.8986 to

1.9067

19.064

190.31

1.9024

19.014

lW.14

1.9014

Page 12

MODEL 4W BNC TO TRIW ADAPTER

MODEL 263

Rgum 1. Model 485 Verification Connections

MODEL 485

Page 13

CALIBRATION USING MODEL 263 CALIBRATOWSOURCE

me fo~oting pua~aphs ptide detded pmcedwes for c~bratig the Model 485 Picommeter using the Model 263 Wbrator/Some. M but one of the cfibratimr adjmtienta ~e digiti md ~ & done km the ~nt pmel m over the ~EE~ bus.

TOc~brate the tis~ent bm the tint pmel, pefiom the fo~otig pmedures, muitig pma~aph ‘TEEE= BW Cfibration”. TO ctibate the Model 485 over the =4 bus, pdom the foflwtig pmedmes, ornitig pmagaph ‘Tmnt ~el Mbration”.

Environmental Conditions

C~bration shmdd be pefiomed under labrato~ ccm&tiom hatig m -bient tempera~ of 23 +l°C md a relative hufidity of less tha 70%. With both the Model 485 and 263 on, dow them to wam up for one hem. K either ina~ent has ken subjected to mtieme temperatim or hufidity, dow at least one ad~tiond how for the titiment to stabike before be@tig the ctibration procedw.

NWE

Cfibration can be stopped at ay tie md ody those ranges out of spwificatimr need be cdbra~d.

Calibmtion Stomge Enable

The Model 485 mmt be in cfibratimr storage enable to stem cfihation comtita h NVRAM. E the instiment k not placed h ti mode, subsequent ctibration W be lost when the ~

~g steps tO enable cab~mtiOn stOrage.

1. Mthe Model 485 is presently rm, * it off.

2. We holtig k the S~/CLR button, - the ina~ment back on.

3. When the “CA~ message is displayed, mle=e the ~/CLR button. The ina~ent ti ~ to the rmrmd diapl~ mode md the stotig of cdibratimr cons~ts is now enabled.

at k bd off. @fiOm the fOflw-

Required Equipment

The fo~-g item (one of each) me necess~ ti ctihate the Model ~:

1. WitMq Model 263 Cti&ator/Some.

2. Trim to Tri= Cable (suppfied with 263)

3. kiW~ Model W Mde BNC to Pemde Tfi Adapter.

N~: The fo~owtig ad~tiond item@ be nwces~ if c~bration is to be petioned over the ~E4 bus.

4. KiMey Model 4853 EEE48 Intetiace tisti~ed h the Model 485.

5. ~ 85 Computer eqtipped tik ~ 82937 GP~ kterface md 1/0 ROM.

6. KltMey Model 7008 ~E cable.

Front Panel Calibmtion

Petiom the foE- steps to dbrate the Model& tim the front pmek .

1. On the Model 485, depress ZERO C~CK and select the M rmge.

2. With m open tiput, adjust the Z~O pot for.~ AI count on the display.

N~E

Q104, U105, RIU, Rl14 or RIB hwe been replaced, the pico-der may not zero. See paa&aph 5.7 h the Model& btition Manual fur the pmcedti to bdmce the tiput amp~er.

3. Comect the output of the Model 263 ~hatur/Sowe to the tiput of the Model 485 as show h Fi~ 2. M*e sue the ctibrator is h standby.

4. On the Model 485, press the R~ arrd ~G pwhbuttmrs stidtanemrsly md hold k unti the message

“CAH is &played. Release the buttons. The tit is now h the c~bration mode m kdicated by the “~~ annunciator.

5. Release Z~O HCK on the Model 485.

6. Pro&mn the Model 263 to output .m nA. Use the

AMPS (active) -ent some.

7. The Model& maybe displaying a smfl offset (=1 count). TOcmcel this offset, press ML rm the Model 485 to zem the display.

8. Pro~a the Model 263 to output 1.900W nA.

9. Adjust the display of the Model 485 to read l.~ uatig the S~/CLR md RCL httons. The STO/CLR button hcrements the displayed reading and the R~ button demments the displayed reatig.

Page 14

MODEL 4W BNC TO TRl~ ADAPTER ~

MODEL 263

MODEL 485

Rgum 2. Model 485 Catibmtion Connections

10. Ustig Table 2 as a guide, repeat the basic pmcedme the ~E48 bus ustig the Model 263 C~brator/Sowe. oufltied h steps 5 thmuxh 9 to ctibrate the rest of the

-ent range; of the M;del 485.

11. TOatom A:bration comtmta md ~t the ctibration mode, simti~eously press the ~ md LOG buttom UM the message “Stofl is &played. E titead the

message “ouf’ is displayed, then ctihation storage 2. Make sue the =488 adtiess of the Model 2@ is set was not embled md cahbatimr crmstits W be lost when the Model N is tied off.

Table 2. Model 485 Range Calibtion

263 titput

Cumnt

1.90000 d

485 Readtig

19.0000A

190.000 A Lm &

19.0000@

190.000 @

1.9W d

IEEE-488 Bus Calibmtion

1. Comect the Models 263 md 485 to the GP~ titefiace of the HP 85 computm. The Model 485 mti have a Modd &53 ~488 htefiace tistied.

to 8 md the adhss of the Model 4853 is set to 22.

3. Enter the c~iration pm~m tito the HP 85 computer.

4. TO‘dbmte the titiment, stiply press the R~ key

on the computi. The -m wfl prompt for the Only marmd adjustimt md then automatically cdbrate d the mmnt rmges of the Model 485.

5. The pm-@ prompt for storage of the c~tiation constita me 330). ~ ptides the user the opportity to stop at this petit to avoid pemment cAha-

tiOn. me Ctibation con~ts WM ~ lost when the Model 485 is tied off.

6. Stomge of c~bmtion comtits is pefimed mrhe 350

of the pmga md is tidcated by the “Stofl message on the Model 485. H btead the message “out” k displayed, c~iratiorr storage was not enabled md c~bmtion com~ts w~ be lost when the Model &

is ~ed off,

Z After c~bration is completed, it is mcomended that

you somce a mnt fmm the Model 263 to each rmge

at k h~ scale b verify acwacy.

Pdom the fofltig steps to dbrate the Model 485 mr

Page 15

10 CLEAR 722 @ CLEfiR

NAIT 1020

OUTPUT 722 ; “CIRIX” 42 BEEP @ DISP 50 DIsP

S0 DISP “IF DISPLAY WILL NOT ZERO, PRO- CEEO TO P6RAGRAPH 5.7 IN THE 48 SMANUAL. 70 OISP 80 DISP ,’PRESS ‘CONT’ KEY ON THE HP 85 TOCONTINUE. “ 90 P6USE

100 CLEAR @ BEEP 110 DISP “CONNECT ?G3 OIJTPUT TO 485 INPUT (SEE FICURE 2) ~ ~

120 DIS?

130 OISP “PRESS ‘CONT’ TO CONTINUE. “

140 PAUSE

152 06Th 1, .0000000019,2,.000000019,3, .00000019,4, .0000019,5,.000019,6, .00019,7,

160 CLEAR 170 CLEAR 708 180 OUTPUT 708 ; “F1R4UI . gE-gx,

190 OUTPUT 722 ; “COX,, 200 FOR 1=4 TO 10

210 REAO J

~ZO OUTPUT 722 ~ ,,R,, ;J; ,,x, ! 485; ~e~ect ~ange,

230 OUTPUT 708 ; R; I; ,X< ! 265; select range. 240 OUTPUT 708 ; “Z101X” ! 263; output zero amp5. 2S0 WAIT 3000 260 OUTPUT 722 ; “ZIXS’ ! 485; enable REL to 270 REAO J@ WAIT 2000

~sO OUTp UT 708 ; ,,zOx,, ! ~E~; 290 Wfl IT 2000

300 OUTPUT 722 ; “V’’; J; “X,” ! 485; send calibration value. 310 OUTPUT 722 ; “ZOX” ! 485; disable REL. 320 NEXT I 330 BEEP @ OISP “TO STORE C6L CONSTANTS, PRESS ‘CONT’ . “ 340 PAUSE

‘AOJUST ‘ZERO’ POT ON 495 FOR

! 485; set to 2nA range and enable ZERO CHECK.

.0000 +/-1 COUNT. “

! 263; program for 1.9nA.

! 4S5; disable ZERO CHECK.

cancel Of

source programmed outpu

5et .

350 OUTPUT 722 ; ‘“LOX,’ ! 485; store cal constants.

560 CLEhR @ BEEP 370 DISP “CfiLIBRATION COMPLETE”

380 END

485 CALIBRATION PROGRAM

Page 16

MODEL 485 AUTORANGING PICOAMMETER

Features:

l 4% Digit LCD Display l Fast Autoranging l Bench or Portable l Digital Calibration l 100 Point Data Store l O.lpA Sensitivity l Analog Output l LOG/Relative Functions l Min/Max Reading Hold

Options:

l Model 1758 Rechargeable Battery Pack l Model 4853 IEEE-488 Interface

Page 17

SECTION 1

GENERAL INFORMATION

1.1 INTRODUCTION

This instruction manual contains the necessary information for operating and maintaining the Model 485 Autoranging

Picoammeter and the Model 1758 Rechargeable Battery Pack. The information is divided into the following sections:

1. Section 1 contains general information and provides guidelines for using this manual. Important safety information is also presented here.

2. Section 2 contains detailed operation information for the Model 485.

3. Section 3 contains the information needed to verify the

accuracy of the Model 485. Performance verification can be done upon receipt of the unit or whenever the basic accuracy is in question.

4. For the more technically oriented, information on theory of operation, maintenance and servicing is contained in Section 4 through 6.

NOTE

The Model 4853 IEEE-488 interface comes supplied with its own instruction manual.

1.2 GElTlNG STARTED

Perform the following steps in sequence to acquaint yourself

quickly and safely with the basic operation of the Model 485.

Verify that the Model 485 was not damaged in transit, as explained in paragraph 1.3.

Carefully read the safety precautions and warnings found preceding this section and the first two sections (General

Information and Bench Operation) of this manual. Referring to paragraph 2.2.1 (Line Power) set the line

voltage switch and plug the power cord into a properly grounded cutlet. If the optional battery pack is installed the charge circuitry will be activated.

Acquaint yourself with the controls and display of the

Model 485 as follows:

A. Turn on the Model 485 by pressing in the ON/OFF

pushbutton. All the zeroes will be displayed briefly.

B. Select autoranging by pressing in the AUTO pushbut-

ton. The nA and AUTO annunciators will be displayed. Pressing any of the other range pushbuttons will put the Model 485 in manual ranging as indicated by the absence of the AUTO annunicator.

C. Engage the ZERO CHECK pushbutton and note that

the ZERO CHECK annunciator turns on. Release the ZERO CHECK button.

D. Select LOG by pressing the LOG pushbutton. The

LOG annunciator will turn on. Press the LOG button

again to take the Model 485 cut of the LOG measurement mode.

E. REL (relative) can be used in the linear measurement

mode or the logarithm measurement mode. The stored REL level will be subtracted from all subsequent measurements. Press the REL pushbutton and note that the REL annunciator turns on.

F. To activate the 100 point DATA STORE with

MinIMax, press end hold in the STO/CLR pushbut-

ton. When the reading rate r = 0 is displayed let go of

the button. The ST0 annunciator will turn on. Press the RCL pushbutton and the last data point will be displayed briefly followed by the reading (data). Other date points can be displayed by holding in the RCL button. Turn off the DATA STORE by pressing the STO/CLR pushbutton again.

5. When you are comfortable with the controls of the Model 485, go on and make the desired measurements using

Section 2, Bench Operation as a guide.

1.3 INSPECTION

The Model 485 Bench Picoammeter was carefully inspected,

both mechanically and electrically, before shipment. Upon receiving the Model 485, check for any obvious signs of physical damage that might have occurred during shipment. Report the damage to the shipping agent immediately. Retain

the original packing materials in case reshipment becomes

necessary. The following items are included with every Model

485 order:

l Model 485 Autoranging Picoammeter l Model 485 Instruction Manual l Additional accessories as ordered.

If an additional instruction manual is required, order then manual package (Keithley Part Number 486-901-00). The manual package includes an instruction manual and all pertinent addenda.

1.4 SPECIFICATIONS

Detailed Model 485 specifications may be found immediately preceding the table of contents of this manual.

1.5 WARRANTY INFORMATION

Warranty information may be found on the inside back cover

of this manual. Should it be necessary to exercise the warran-

ty, contact your Keithley representative or the factory to

determine the correct course of action. Keithley Instruments maintains service facilities in the United States, West Germany, Great Britain, France, the Netherlands, Switzerland

1-l

Page 18

and Austria. Information concerning the application, cperaticn or service of your instrument may be directed fc the ap-

plications engineer at any of these locations. Check the inside

front cover of this manual for addresses.

Model 1684 Hard Shell Carrying Case-Hard vinyl case,

IOOmm x 300mm x 350mm (4 x 13 x 14 inches) has a fit-

ted foam insert with room for the Model 485, instruction

manual end small accessories.

1.6 MANUAL ADDENDA

Information concerning improvements or changes to the in-

strument which occur after the printing of this manual will be

found on an addendum sheet included with this manual. Be

sure to review these changes before attempting to operate or service the instrument.

1.7 SAFETY SYMBOLS AND TERMS

The following safety symbols and terms are used in this

manual or found on the Model 485.

The symbol should refer to the operating instructions in this manual.

The WARNING heading in this manuel explains dangers that

could result in personal injury or death. The CAUTION heading in this manual explains hazards that

could damage the instrument.

1.8 OPTIONAL ACCESSORIES

The following accessories can be used with the Model 485.

Model 1010 Single Reck Mounting Kit-Use to mount

one Model 485 in e standard 5% x 19” rack.

on the instrument indicates that the user

Model 1768 Rechargaable Battery Pack-Provides six hours minimum operation from full charge, recharges within

10 hours end is field installable.

Model 4801 Input Cable-A low noise coaxial cable four feet (1.2m) in length with a male BNC connector on each

end.

Model 4803 Low Noise Cable Kit-Consists of 50 feet

(15.2m) of low noise coaxial cable, 10 male BNC connectors,

and five female chassis mount BNC connectors.

Model 4863 IEEE-486 Interface-Field installable prcgram-

mable option provides isolated data output. Switchselectable talk only or addressable modes. Mounts within and powered by the Model 485.

Model 7008 IEEE-488 Digital Cable-Useful for ccnnecting the Model 4853 to the IEEE-488 bus. The Model 7008-3 is

0.9m 13 ft) in length and has a standard IEEE-488 connector at each end. The Model 7008-6 is 1.8m (6 ft) in length.

Modal 8673 IEEE-486 Interface for IBM PC-Field in- stallable programmable option provides data output for the

IBM PC. Mounts within and powered by the IBM PC.

Model 1017 Dual Reck Mounting Kit-Use to mount two

Model 486’s in a standard 5% x 18” rack.

l-2

Page 19

SECTION 2

BENCH OPERATION

2.1 INTRODUCTION

This section contains the information needed to prepare and operate the Model 485 as a bench picoammeter. Bench operation consists of using the Model 485 to perform basic

current measurements. Data store operation is also covered. The capabilities of the Model 485 can be enhanced with the addition of the Model 4853 IEEE-488 interface. IEEE operstion is covered in the Model 4853 Instruction Manual.

2.2 PREPARATION FOR USE

2.2.1 Line Power

The Model 485 is provided with a three-wire line cord which

mates with third-wire grounded receptacles. Connect the in-

strument to AC line power as follows:

1. Set the LINE VOLTAGE switch on the back of the instrument to correspond to line voltage available. Ranges are 105-125V or 210-250V 50/60Hz AC.

CAUTION

Connect only to the line voltage selected.

Application of incorrect voltage can

damage the instrument.

2. Plug the power cord into a properly grounded outlet.

WARNING Ground the instrument through a properly grounded receptacle before operation.

Failure to ground the instrument can result in severe injury or death in the event of short circuit or malfunction.

NOTE

Although the Model 485 is specified at 50Hz and 60Hz the instrument may be operated at 400Hz

and 440Hz. Add one count to instrument specifications under this condition.

2.2.3 Battery Charging

After the Model 1758 Banery Pack is installed in the Model

485 it can be charged and recharged as follows:

1. Connect the instrument to line power as described in paragraph 2.2.1.

2. With the power switch off, the battery charge circuitry is automatically energized to charge the battery at the maximum rate. When the battery pack is first installed, or if it is completely discharged, allow it to charge for ten hours.

NOTE

For maximum battery efficiency only charge the battery pack after it has become discharged and only charge until it is fully charged I,10 hours). Continuous charging over long periods of time will not damage the batteries but, useful life will gradually decrease. This loss is not permanent and may be restored by cycling the battery pack through several complete charge/discharge cycles. The battery pack is capable of 500 to

1000 charge/discharge cycles before replace-

ment is needed.

Do not make measurements with the BAT annunciator on as the readings may be erroneous.

3. When the Model 485 is in use on line power, the banely charger maintains a trickle charge on the battery pack.

2.3 TILT BAIL

The Model 485 is equipped with a tilt bail which makes it possible to elevate the instrument to a convenient viewing

position. To change the bail position, pull out the bail handle from each side of the case until it rotates freely; rotate the bail to the desired position and release the bail to allow it to lock

into place.

2.4 MODEL 485 FAMILIARIZATION

2.2.2 Battery Pack Power

The Model 485 may also be operated from rechargeable sealed nickel-cadmium batteries contained in the optional

Model 1758 Rechargeable Battery Pack. The battery pack will operate the Model 485 for up to six hours. The BAT ennunciator will turn on when the banely charge is insufficient to

maintain eccurate readings. Refer to Section 5, paragraph 5.3 for installation procedures.

The following paragraphs and Figure 2-l provides a brief

description of the display, front panel controls and connec-

tors.

2.4.1 Display

The Model 485 has a 4% digit liquid crystal display (LCD). The minus sign is displayed. The plus sign is implied by the absence of the minus sign. The following annunciators are

displayed on the LCD.

2-l

Page 20

BAT-Low battery indicator for the Model 1758.

nA. uA or mA-Nanoamos. Microamos or Milliamos

selected.

RMT IRemote)-Model 485 being controlled over the

IEEE-488 bus (Model 4853 installed).

CAL-Model 485 in calibration mode.

AUTO-Autorange selected.

REL-Relative selected.

LOG-Logarithm selected. ZERO CHECK-Zero Check selected. BTO- Data being stored.

RCL-Data being recalled. RCL flashes when buffer is full during store cycle.

1. STO/CLR-Pressing this button initiates the storage sequence. Pressing the button a second time shuts off the data store when in r=Othrough r=5. When in r=6, pressing this button stores one reading.

2. RCL-Pressing and holding this button in scrolls the data pointer. To read the data at a particular point, simply release the button.

Range Pushbuttons

1. Auto-This pushbutton selects autoranging.

2. Manual ranging is accomplished by depressing the appropriate range button.

2.4.2 Front Panel Controls

ON/OFF-Pressing in this pushbutton turns the Model 485 on. Releasing (out) this pushbutton turns the instrument off.

ZERO CHECK and ZERO-This pushbutton and trimpot are

used to zero the instrument’s internal offsets. REL (Relative)-This pushbutton is used to cancel measurement offsets or store the input signal as a reference level.

Pressing this button again shuts REL off. LOG-This pushbutton selects the logarithm function. The displayed current measurement is expressed as the logarithm

(base IO) of the measured current referenced to one ampere.

Pressing this button again shuts LOG off. DATA STORE-Has MlNlMAX and 100 point reading storage capachY; records data at one of seven selectable rates. Records minimum and maximum conversion during

the period the data store is active at the rate of 3/set.

ITHLEY 485 AUTORANGING PICOAMMETER

i_J

2.4.3 Input Connector

The input connector is a standard BNC type.

2.4.4 Analog Output Connectors

A voltage level that is proportional to the incoming current can be monitored using the analog output banana jacks located on the rear panel.

2.5 ERROR MESSAGES

Table 2-1 lists the error messages associated with basic front panel operation. Note that the instrument has a number of other messages that are discussed in the appropriate sections of this manual.

4 \

2-2

Figure 2-l. Model 485 Front Panel

Page 21

Table 2-l. Error Messages

Display Message Comments

im RAM Error

IpEz

kiir-

2.6 ENVIRONMENTAL CONDITIONS

All measurements should be made at an ambient temperature within the range of O°C to 50°C, and with a relative humidity

of 0% to 70% up to 35OC. For instruments above 35OC

derate humidity 3% per OC up to 50°C. If the instrument has

been subjected to extremes of temperature, allow sufficient

time for internal temperatures to reach environmental condi-

tions. Typically, it takes one hour to stabilize a unit that is

10°C IlEaF) out of specified temperature range.

2.7 BASIC BENCH MEASUREMENTS

Basic measurement techniques for using the Model 485 to measure DC current are covered in the following paragraphs.

Also included is the operation of the MinIMax and 100 point

data store. A summary of range, accuracy and maximum

allowable input information is given in Table 2-2.

Calibration Error Model 485 locks up, but operation can be restored by pressing

INVRAM Failure) any one of the four momentary pushbuttons. If restored, calibration

Overrange Overrange input applied to the Model 485. Leading minus sign

Model 485 locks up. See Section 5 for troubleshooting information.

is invalid as indicated by the flashing “CAL” annunciator. See Sec-

tion 5 for troubleshooting information.

indicates that input signal has a negative value.

WARNING

Before operating the Model 485, observe

the safety precautions found preceding

Section 1. Failure to observe these and other safety precautions found in this manual could result in severe injury or death.

WARNING

Do not exceed 30V RMS between input low and power line ground or a shock hazard will result. Also, current inputs that exceed 3mA may be erroneously displayed as a”

on-scale reading.

CAUTION

Do not exceed the maximum input limits

shown in Table 2-2.

Table 2-2. Range, Accuracy and Maximum Allowable Inputs

Maximum Accuracy Source

Flli;lry i *l%Reading + Counts1

Range

2mA

1.9999 nA

19.999 nA

199.99 nA

1.9999 pA

19.999 pA 0.1 + 1

199.99 pA 0.1 +1

1.9998mA

2 nA

20 nA

200 nA

22$

200 PA

IOTE:

Current above maximum will result in an “OL” display.

,. Source resistances lower than these may result in higher instrument noise and drift.

i. Maximum Transient Overload Voltage: IOOOV with a series 1OOkB resistor. Safe

operation and good measurement practice dictates use of an external resistor when necessary to limit input currents to less than 3mA.

Maximum volts-hertz product (common mode): 108V.H~

lB°C -28OC (Note 2) (Note 3)

0.4 + 4

0.4 + 1

0.2 + 1

0.15 + 1

0.1 +1

Minimum

Recommended Maximun

Allowablt

Resistance

1OOMB 350v 1OOMB 350v

10MB 350v

1MB 350v

100 kC 5ov

10 kB 5ov

1 kKl 5ov

Input

2-3

Page 22

2.7.1 Power-Up

NOTE

The software revision level of the Model 485 can be disolaved uoon oower-uo bv runnino the diagnostic program. See .Section 5, Maintenance, for more information.

Turn on the Model 485 by pressing in the ON/OFF switch. The following will occur automatically:

1. Reset- All zeroes will be briefly displayed before going into the measurement mode.

2. RAM Test-If this test fails the Model 485 will lock up with zeroes displayed.

3. NVRAM Test-This test determines if the calibration constants are properly read from NVRAM. If this test fails the display will show the error message “cErr”.

Refer to Table 2-1 for more information pertaining to error messages.

CAUTION

During power up and power down, using

AC line or battery pack, a current surge

15mA, 5V maximum) can appear at the INPUT of the Modal 455. Protect any circuitry

that would be damaged by these levels by

making circuit connections only after turning on the Model 485. Disconnect these circuits before turning off the Model 485.

2.7.2 Zero Check

The instrument should be properly zeroed (after one hour warm-up) before making any current measurements. Only the 2nA current range needs to be zeroed. To check or adjust

zero, proceed as follows:

1. Select the 2nA range.

2. Turn off REL and LOG if they are on.

3. Depress the ZERO CHECK pushbutton. Momentary or locking action can be achieved depending on how far the button is depressed. To adjust zero, place the pushbutton

in to the lock position.

4. Adjust zero level trimpot via access hole on front panel for a zero indication on the digital display.

5. Release the ZERO CHECK button.

In normal operation, the equivalent input resistance of the

485 picoammeter is equal to or less than the maximum

burden voltage (2OOfiV) divided by the maximum range current. This does not hold while in zero check or overload con-

ditions because the feedback to the input node is broken.

Values of input impedance for normal operation and zero check/overload are shown in Table 23.

NOTES

1. When zero is properly adjusted, the input voltage burden for an on-range reading will be less than or equal to 2OOpV.

2. The REL feature can be used instead of the ZERO pot to zero the display. However, REL then cannot be used to cancel a measurement offset or establish a reference level.

Table 2-3. Equivalent Input Resistance With Zero

Check Enabled

:urrent Maximum Effective Impedance In

Range

2 nA 1OOkD 9MGll230pF

20 nA

200 nA

2::: 100 10 D a 900k08230pF 100kGll0.01~F

200 pA lOkDUO.OlpF

2mA 0.: IY Ik9ljO.Ol~F

2.7.3 Current Measurements

1. Zero the instrument as described in paragraph 2.7.2.

2. Select a current range that is appropriate for the expected input level or select autorange.

3. Connect the source to the INPUT connector on the front panel. Low-noise cable and connector accessories de-~ scribed in Section 1 should be used as required. Measurement considerations are discussed in paragraph 2.8. A summary of range, accuracy and input overload information is given in Table 2-2.

4. Read the input current on the digital display. Overrange is

indicated by an “OL” message.

2.7.4 Relative Mode

When the relative mode is selected with an on-scale reading on the display the following occurs:

1. The REL annunciator is displayed.

2. The next reading is stored.

3. The stored reading is then algebraically subtracted from all subsequent readings and displayed.

A REL level can be established for the linear measurement mode or the logarithm measurement mode and is effective only in that mode. Changing modes will not affect a REL level already established. However, if another REL level is set fin the other measurement mode) the previous REL level will be cancelled. For example, place the Model 485 in the logarithm mode (LOG annunciator on) and select the 2pA range. With an open input, note the approximate -10.0 reading on the display. Press the REL button and note that the REL annunciator is on and that display is zeroed. Select the linear measurement mode by pressing the LOG button (LOG annunciator off). Note that the REL annunciator is off, indicating that there is not a REL level established for the linear measurement mode. Switch back to the LOG mode and note

Input Resistance Zero Check/Overload

IOkD 9MDjj230pF

IkD 5MCll230pF

2-4

Page 23

that the REL level is still there. Again, go back to the linear

measurement mode (LOG off) and set a REL level of lfi. the REL annunciator will turn on. Switch back to the LOG mode

and note that the REL annunciator is off, indicating that the

REL level for the LOG mode is cancelled. Once a REL level is established for a measurement mode, that

stored level will be the same regardless of what range the

Model 485 is on. For example, if + IMA is established es the

AEL level on the 20/~A range, + IpA will also be the REL level

on the 2mA range.

It is important to note that the use of REL reduces the dynamic range of measurements by that level. For instance, assume that the REL level is + IpA and the Model 485 is manually set to the 26 range. The maximum positive displayed reading (before overranging), would be

+0.9999& This is because the A/D converter would be seeing 1.9999fl (maximum) from the input. Thus, the dynamic range of measurement is -1.9999fi to +0.9999fi

(2.9998fi) as compared to the normal -1.9999fi to + I .9999/rA (3.9998$1. The dynamic range of measurement

has been reduced by l& The effects on dynamic range can

be reduced by selecting a higher range or using autorange.

2.7.6 LOG Mode

The Model 485 can make logarithm measurements refer-

enced to a 1A current level or to other current levels with the use of the REL feature.

The following examples compute the expected LOG readings for various current levels applied to the Model 485:

A. InA

LOG reading = LDG +$LOG reading = -9.000

B. 0.5&A

LOG reading = LOG LOG reading = -6.301

C. -1mA

LOG reading = LOG I+1 LOG reading = -3.000

To make LOG measurements reference to lA, proceed as follows:

A. Zero the instrument, if required, as described in

paragraph 2.7.2. B. Select auto range on the Model 486. C. Connect the source to the Model 485. D. Press the LOG button. E. Take the LOG reading from the display.

2. Log measurements using other reference currents:

LOG measurements, referenced to other current levels, can be read directly from the display of the Model 485 by utilizing the REL feature and an accurate current source.

I I

0.5fi

I I

The basic procedure for using the LOG mode is to select auto

range and press the LOG button (LOG annunciator on). To get out of the LOG mode, press the LOG button again. The

LOG annunciator will turn off.

Because the logarithm of a negative number is undefined, the logarithm is taken with the absolute value of the measured current.

NOTE

LOG measurements must always be made on

the lowest Dossible ranae (without overranging).

Readings dn high ranges will not allow Optimum calculations of the logarithm. When in doubt,

use Auto Range.

1. Log Measurements with IA reference currant: The LOG measurement mode displays the absolute value of

the logarithm (base 101 of the input current referenced to

IA. The following equation illustrates this relationship:

LOG Reading = Log

Using this reference &rent, the LOG riading span is from

-13.0 (fO.lpA) to -2.699 (1tI.9999mAl.

Applied Current

To make LOG measurements referenced to another cur-

rent level, proceed as follows: A. Z.&o the instrument, if required, as described in

paragraph 2.7.2. B. Set the Model 485 to auto range. C. Input the reference current to the Model 485. D. With the Model 485 in the LOG mode, press the REL

button. The REL annunciator will turn on and the

display will zero. E. Remove the reference current source from the Model

485.

F. The Model 485 is now set up to make LOG

measurements referenced to that current level. Simply

input the current to be measured and take the reading

from the display.

2.7.6 Inverting Analog Output

Two banana jacks, accessible from the rear panel, permit monitoring or recording of the output from the current-to-

voltage converter within the Model 485. Since the Model 465

is a feedback picoammeter, as shown in Figure 2-2, the input current is forced through the feedback resistor and an in-

2-5

Page 24

verted analog output voltage is developed by the operational amplifier. The feedback (Rangel resistors are selected such that voltage for an on-scale reading on the 2nA range will be

between zero and k200mV. The output voltage for the rest of the ranges will be between zero and f2V. The relationship between the analog output signal and the digital display is as follows:

2nA Range: 10000 counts = -1OOmV. or -1OFVIcount

20nA-2mA Ranges: 10000 counts = -IV or -lOO~V/count

The analog ouput is input protected up to 20V RMS and during an input current overload the analog output is clamped to a maximum voltage swing of approximately *4V. Although protected up to 20V to prevent instrument damage, a voltage

applied to the analog output could cause an erroneous

display, rather than the “OL” message.

Since the output of the current-to-voltage converter is

bipolar, the inverting analog output can also be used to

measure low frequency AC current which falls within the specified analog rise time. The inverting analog output resistance is 1 .Ol kD; 9lOD in series with the signal leads and

1OOD in series with the ground lead.

Typical Analog Output Accuracy:

Linearity: < 0.1% full scsle

Gain Accuracy: k 1%

Output Resistance: +5%

Ff+ ‘Efif

Figure 2-2. Model 485 Inverting Analog Output

2.7.7 Mm/Max and 100 Point Data Store

The data store can save up to 100 readings and store the minimum and maximum readings recorded during the period

that the data store is active. The 100 points of data are stored

at one of six selectable rates. Manuel data entry (r = 6) is also available. Readings for minimum and maximum are sampled at the rate of three per second regardless of the selected rate. The minimum and maximum readings are continuously updated while in the data store mode. The procedure for operating the data store is as follows:

1. Connect the desired measurement configuration to the Model 465. Make sure that the controls of the Model 485

are set appropriately.

2. Storing Data: A. Press and hold the STO/CLR pushbutton. The follow-

ing reading rates will scroll on the display: r = 0 I3 rds/sec) r = 1 (1 rdglsecl

r = 2 (1 rdg/lO secj r = 3 II rdglmin) r = 4 (I rdg/lO mini r = 5 (I rdglhr)

r = 6 (I rdg every time ST0 button is pressed)

NOTE There is no need to select a rate if just minimum/maximum readings are desired. Momentarily press the STO/CLR button to start

the store.

6. Release the STO/CLR pushbutton when the desired reading rate is displayed. The ST0 annunciator will

turn on and data will be stored at the selected rate.

NOTE The date store cycle can be terminated at any time by doing the following:

A. If in r=6 mode, press the RCL button and

the STO/CLR button.

6. If in any other r mode, only press the STO/ CLR button.

With the data store off, data is retained and can be recalled at

any time as long as the instrument remains on.

3. Data Retrieval: Data can be retrieved at any time, but a flashing RCL annunciator indicates that the maximum

number of readings (100) have been stored. A. Press and hold in the RCL pushbutton. The display will

scroll through the date points and MlNlMAX (LO/HI). The first data point displayed will be the last stored reading. The next two data points will be the HI and LO readings made during that store cycle. Notice that the longer the RCL pushbutton is held in the faster the data points will scroll on the display.

B. Release the RCL pushbutton at the desired data point

and note the reading (data) on the display. The data pointer can be incremented by steps of one by momentarily holding in the RCL pushbutton.

4. Shut off the data store by pressing the STO/CLR

pushbutton. All stored data will be retained until a new

store cycle has commenced.

2.6 MEASUREMENT CONSIDERATIONS

This section describes the effects of source resistance, capacitance, noise and leakage resistance on the measurement. Other measurement considerations are also discussed.

Minimum and maximum values of these source parameters

are defined, at which point a significant degradation of the measurement can begin to occur. Compensation methods

are described to minimize these effects. Refer to Figure 2-3 for the following discussion.

2-6

Page 25

2.8.1 Source Resistance

Increasing capacitance beyond this level may increase noise

and induce instrument instability. The noise gain of the

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

is recommended for each range. The reason for this can be understood by examining Figure 2-3. Considering effects on low frequency noise and drift, CS and CFB can momentarily

measurement circuit can be found from: Equation 2.

Output en = Input en x(1 +

be ignored. where ZF =

Input amplifier noise and drift appearing at the output can be

calculated as follows:

Equation 1.

Output enOiSe = IflpUt enOjSe

x(1+ -@)

Thus it is clear than as long as RS>>RFB, Output enoNe fz

Input enoNe. When RFB = RS, Output enojse = 2 x input

enoise, The same applies for eos.

, , cFB

I I

RFB

(1 Es

Slrm

WVV

lOon

T--

ANALOG 10,OOOpF is leakage measurement of capacitors. In this case OUTPUT

TO A/D

CONVERTER

Figure 2-3. Simplified Model for Input Signal

Conditioning

RFB

and ZS =

42a fRSCSP+ 1 j

Clearly ss f -0

equation (2) reduces to equation (I).

The frequency range in interest is O.lHz to IOHz which is the noise bandwidth of the AID convener. The value of CF is 22OpF for nA ranges and O.OlpF otherwise.

In general, as CS becomes larger, the noise gain becomes larger. An application where CS may be greater than

Input en must include the effects of the voltage source (ES) used to bias the capacitor. The Keithley Model 230 is recommended for this application.

When measuring leakage currents on capacitors larger than

10,OOOpF. stability and noise performance can be maintained by adding a resistor in series with the capacitor under test. The value of this resistor shoulde be around 1 MB. For large capacitor values (z lrFj, the value of the series limiting resistor can be made lower in order to improve settling times: however, values below 1OkD are not generally recommended.

Model 485 will typically show insignificant degradation in displayed performance with the noise gain of 2 resulting from allowing RS = RFB. Typical amplifier input enOjSe is about 5@ p-p in a bandwidth of 0.1.IOHz. Amplifier ECS can be

nulled with front panel ZERO adjustment, but available

resolution limits this adjustment to about 5V. The temperature coefficient of ECS is < 2OpV/“C. These

numbers can be used with Equation 111 to determine ex-

pected displayed noise/drift given any source resistance.

Remember that 1 displayed count = lOO$/ except on 2nA range where 1 displayed count = lO@V. Note also that the

values given in Table 2-2 for minimum source resistance also

represent the value of RFB on that range.

2.8.2 Source Capacitance

The Model 485 is designed to accomodate up to 10,OOOpF in-

put capacitance ICS). This limit will preclude problems in most test setups and allow extremely long input cable lengths

without inducing instabiliw or oscillations.

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

A second-order advantage to using this limiting resistor is sdded protection to Model 485 in the event of capacitor failure.

2.8.3 Leakage Resistance

The effect of leakage currents should be considered when

making small current measurements with high impedance

sources. Leakage current and its effects can be minimized by

using high resistance insulation in the test circuits and guerding. Since the Model 485 is a feedback picoammeter, it is ef-

fectively guarded at the input. The effect of leakage paths on the measurement can be further minimized by using a gusrd-

ed text fixture as shown in Figure 2-4. In the configuration

shown, the current through the component under test will

not be shunted significantly by either leakage resistance path. If a high voltage supply is used to make high resistance leakage measurements, it is suggested that a series current

2-7

Page 26

limiting resistor be used to prevent exceeding the maximum

overload input limit of the Model 455 in the event the item

under test is shorted.

2.5.4 Zero Time Stability

The typical zero time stability of the Model 455 is less than

one count per week, exclusive of temperature effects.

SHORT

CIRCUIT

CURRENT -

LIMITER

TEFLON

INSULATOR

VVV’I

Figure 2-4. Test Fixture Guarding

2.5.5 Grounding Considerations

Input LO (outer ring of input connector) should be connected

to a potential at the source which is within 30V RMS of

power line ground of the Model 455 or the equipment near it. Connection to power line ground is not made internally in order to avoid possible ground loops.

MODEL 485

2.5 APPLICATIONS

The following applications can be automated to various degrees with the use of programmable equipment over the IEEE-455 bus. The Model 455 becomes fully programmable with the addition of the Model 4553 interface. Programmable sources are available from Keithley and other manufacturers. The documentation that is provided with the Model 4553 includes example programs using various controllers.

The Model 455 may be used in conjunction with the Model

6104. The Model 6104 is a guarded and shielded test box for 2-terminal or 3-terminal connections. The Model 6104 pro-

vides excellent electrostatic shielding and high isolation

resistance for the component under test. Clips plug into banana jacks allowing the user to fashion modified connec-

tions to suit the component to be tested.

The Model 6104 is useable with the Model 455 picoammeter and Keithley voltage supplies, such as the Model 230. When connected together as a system, using the cable and connector options, they form a complete test facility for measuring leakage current and other low current parameters for various test applications. A possible test set up is hewn in Figure 2-5. The measurement sample would be connected between Jl and J7 or J6.

EXT. SOURCE

MODEL

BLhK [ j4 45 j

CASE

Figure 2-5. Leakage Test Sat Up Using Modal 6104

2.9.1 Op Amp Input Offset Currents

As the parameters of new BIFET, BIMOS, and FET op amps

approach the parameters of the ideal op amp, such characteristics as the input offset current are breaking

through the 1pA level. Use the Model 455 to measure these

low level currents as shown in Figure 2-6. Note the connection of Model 455 input low.

2-5

Figure 2-6. OP Amp Input Offset Currents

Measurement

Page 27

2.9.2 FET Gate Leakage and Channel Currants

Analog switches, multiplexer circuits, sample and hold circuits, integrators, LED drives, and many other circuits have errors generated by either gate leakage or channel leakage in

FET-based components. For understanding the design limita-

tions of a component or for tight component selection use the Model 485 as shown in Figure 2-7.

Figure 2-7. FET Gate Leakage and Channel Currents

Measurement

2.9.3 Insulation Leakage Currents and High Resistance

In precise low power, low current circuitry, stray leakage cur-

rents can adversely affect circuit performance. Since leakage current is a non-linear function of voltage, the expected voltage level must be applied.

Leakage resistance of 10% can be determined with the

Model 485 and a voltage source of 1OOV. Using this tech-

nique, you can evaluate high resistance materials or insulation leakage of capacitors, PC boards, switches, or connectors under normal environmental conditions and under elevated temperature and humidity conditions. (see Figure Z-8).

Figure 2-S. Insulation Leakage Currents and High Resis-

tances Measurements

2.9.4 Phototube. Photodiode and Beam Currents

Photomultiplier tubes and other light detection devices require precise measurement of a wide range of currents (see Figure 2-9). Beam currents used for ion implantation, surface

phenomena studies, and atomic structure analysis using scanning electron microscopy are in the picoamp to nanoamp range. The Model 485 has the accuracy and sensitivity to make these measurements with routine ease. In addition, for

these applications it is convenient to cancel out dark currents,

using the Model 485’s “REL” feature. To present data in a logarithm format, simply touch the “LOG” button. Use the

AUTO ranging feature to cover a broad dynamic range.

SCANNING

ELECTRON

MICROSCOPE

Figure 2-9. Setup to Measure Photomultiplier, Photodiode and Beam Currents

2-9

Page 28

2.9.5 Resistivity Tests

The Model 485 may be used along with the Model 6105 to perform resistivity tests. The Model 6105 is a guarded test fix-

ture for measurement of surface and volume resistivities. The

chamber is designed in accordance with ASTM Standard Method of Test Electrical Resistance of Insulating Materials, D257-66. The Model 6105 can be used in conjunction with

the Model 485 and a high voltage power supply, such as the

Modal 247.

MODEL* MODEL

32418 4801

CABLE

m M~uHF~+C[~

NOT TO

EXCEED IOOOV

*Supplied with Model 247

Figure 2-10. Resistivity Test Set Up

Resistivity can be determined by measuring the current

through a sample with a known voltage impressed. The

Model 6105 can accomodate non-rigid sheet samples 2% inches (63mm) to four inches (102mm) in diameter and % inch (6mml thick with excitation voltages up to IOOOV. The Model 6105 has a UHF connector for the bias supply and a

BNC output to the Model 485. A test hook up using the

Model 247 power supply is shown in Figure 2-10.

CABLE

2-10

Page 29

SECTION 3

PERFORMANCE VERIFICATION

3.1 INTRODUCTION

This section contains information necessary to verify that the

Model 485 performance is within specified accuracy Model

485 specifications may be found at the front of this manual.

Ideally, performance verification should be performed when the instrument is first received to ensure that no damage or change in calibration has occurred during shipment. The verification procedure may also be performed whenever instrument accuracy is suspect or following calibration. If performance on any of the ranges is outside specified limits, calibration can be performed as described in Section 5.

NOTE If the instrument does not meet specifications and it is still under warranty (less than 12 months since date of shipment), contact your Keithley representative or the factory to determine the action to be taken.

3.2 ENVIRONMENTAL CONDITIONS

All measurements should be made at an ambient temperature

between 18e and 28OC (65” to 82OFl with a relative humidity less than 70%.

3.3 RECOMMENDED TEST EQUIPMENT

Equipment for verifying the performance of the Model 485 is

listed in Table 3-I. Alternate equipment may be used as long as the equipment accuracy is at least as good as the specifications listed in Table 3-1. Information needed to build the test fixture can be found in Figure 3-1.

3.4 INITIAL CONDITIONS

Before performing the verification procedures, make sure the Model 485 meets the following conditions:

1. If the instrument has been subject to temperatures below 18eC (65OF) or above 28°C (82eFj. allow sufficient time for the instrument to reach temperatures within the range. Generally, it takes one hour to stabilize an instrument that is 10°C (18°F) outside of this range.

2. Turn on the Model 485 and allow it to warm up one hour. The instrument may be operated from either line power or

battery pack power, as long as the battery pack has been

fully charged as described in paragraph 2.2.3.

3.5 VERIFICATION PROCEDURE

The following paragraphs give the basic verification procedure for checking accuracy.

To properly check the accuracy of the Model 485, precision current sources are necessary. These precise currents are obtained by using the DC calibrator and measured resistors in a shielded test fixture, as shown in Figure 3-1.

Proceed as follows to check the accuracy of the Model 485:

NOTE

Record the following measurements and calculations in Table 3-2. Use a pencil so that the

table can be reused.

1. Using the Keithley Model 191 or 192, measure and record the resistance of the lOk0, 100kD. IMg and IOMD

resistors.

2. Using the Guildline Model 9520, measure and record the

resistance of the lOOMD, 1GD and 1OGB resistors.

3. Calculate and record the required DC calibrator setting for

each range as follows: DC Calibrator Setting: V = I (Required Current) x R

(Measured Resistor)

4. Depress ZERO CHECK and select the 2nA range.

5. With an open input, adjust the ZERO pot for .OOOO+ 1 count on the display.

8. Set the Model 485 to the appropriate range.

7. Connect the DC calibrator to the test fixture.

8. Connect the test fixture to the input of the Model 485 using a low-noise coaxial input cable, such as the Keithley Model 4801.

9. Using Table 3-2 as a guide, install the appropriate resistor in the test fixture, set the DC calibrator to the calculated setting and check all the ranges of the Model 485.

10. Reverse the + and - test leads at the DC calibrator and repeat all checks with negative current.

3-1

Page 30

Table 3-I. Recommended Test Equipment

Description DC Calibrator

Resistor

Resistor Resistor Resistor Resistor Resistor Resistor DMM Teraohmmeter

Shielded Test Fixture

INPUT ;

FROM I

DC CALIBRATOR,

+> :

&t---l

PARTS LIST

A = Resistor:

1OGll for 2nA range, Ksithley P/N R-319-100 IGll for 20nA range, Ksithley P/N R-29910 lOOMa for 200nA range, Keithlsy P/N R-299.IOOM 1OMn for 2@ range, Keithley P/N W29910M 1MG for 20+ range, Ksithlsy P/N R-299-IM 1OOkSl for ZOO&A range, Keithlsy P/N R-298lOOk~

IOkQ for 2mA range, Keithley P/N R-299.10k B = One BNC connector. Kslthley PIN CS-44 C = Three banana jacks, Ksithlsy P/N’s BP-11-O. BP-11-2,

D = Two banana jacks. Keithley P/N BJ-3 E = Two test clips, Ksithlsy P/N BP-9

Specification 19v; f0.002%

IOGO; *2% 1Gl-l; f2%

100MD; f 1% IOMD; fO.l% IMD; kO.l% IOOkn; fO.l% 1OkD; fO.l%

20kD20MD; rtO.O8%

IOOMD; f0.03596 1Gi-i; f0.05% 10GD; f0.07% (see Figure 3-l)

r------------------.

D.E

‘C

i------------------------J

BP-11-5

Figure 3-I. Shielded Test Fixture

METAL TEST BOX

,~~l\~h~h<. D.E

Keith& R-289-IOOM Keithley R-299-10M Keithley R-299-IM Keithley R-298-100k Keithley R-298-10k

Keithley 191 or 192

Guildline 9520

- l-

-----7

I ’ BNC

I OUTPUT I

I B I- <

I MODEL 495

I I

3-2

*v = (Ii

Required

Current (I)

I .9000nA

19.000nA

190.00nA

I .9000 pA

19.000 @

190.00pA

1.9000mA

where:

V = Calibrator Setting

I = Required Current

R = Measured Value of Resistor

Required

Resistor

1OGSl

IGD

100Mi-l

10MD

1MD

100 kD

IO kC

Table 3-2. Range Accuracy

Calculated*

DC Calibrator

Setting lVl

Allowable

Readings

V18°C -28°C)

1.8920 to 1.9080

18.923 to 19.077

189.61 to 190.39

1.8971 to 1.9029

18.980 to 19.020

189.80 to 190.20

1.8980 to 1.9020

Page 31

SECTION 4

THEORY OF OPERATION

4.1 INTRODUCTION

This section contains an overall functional description of the

Model 485. Information pertaining to the Model 1758 Battery Pack option is also included. Detailed schematics and component layout drawings are located at the end of this instruction manual.

4.2 OVERALL FUNCTIONAL DESCRIPTION

Basically the Model 485 is a 4% digit f20.000 count autoranging picoammeter with seven DC current ranges. A simplified block diagram of the Model 485 is shown in Figure 4-I. The heart of the Model 485 is a transresistance amplifier

(current-to-voltage converter) followed by an AID converter that translates the conditioned analog input signals into a form useable by the microcomputer.

CURRENT TO

VOLTAGE

CONVERTER

RANGE

--O RESISTORS

2mA RANGE

2nA-2004 RANGES

4.3 ANALOG CIRCUITRY

The following paragraphs contain a description of the

current-to-voltage converter, multiplexer, buffer amplifier,

-2V reference and A/D converter circuits. These circuits may be found on schematic diagram number 485106 located at

the end of this manual.

4.3.1 Current-to-Voltage Converter (Transresistance Amplifier)

The current-to-voltage converter is shown in simplified form

in Figure 42. Operational amplifier U105 is connected as a feedback xl amplifier with selectable feedback resistors. In this configuration, the linear transfer function of U105 is

-llin)R = V,. On all but the 2nA range, the feedback resistance is selected such that a full scale current input will

c MUX

INPUT

AMP

-2v

REFERENCE

RANGE CONTROL

Figure 4-1. Simplified Block Diagram

MICROCOMPUTER

RANGE/ FEATURE

SWITCHES

4-I

Page 32

result in a 2V output from the converter f-(2mA) x 1 kD = -2Vl. On the 2nA range, the fullscale output is 200mV I-2nAt x IOOMD = -2OOmVl. The maximum output voltage from the converter for an on-scale reading is *1.9999\1 If 199.99mV for the 2nA range).

Actuating the ZERO CHECK pushbutton shorts the feedback resistance of U105 which results in the offset of U106 being presented at its output. The ZERO pot is used to eliminate the offset of the amplifier.

RANGE

RESISTORS

INPUT POT

4.3.2 Multiplexer

The multiplexer connects one of four signals to the buffer

amplifier; two possible signal lines, zero or the reference. The multiplexer, shown in Figure 4-3, is made up of 4 JFETS which are controlled by the microprocessor through Ulll. The FETs are driven by U102 and part of U103. The drivers

convert the digital signals of the microprocessor to signals

useable by the FETs.

All ranges, except the 2mA range, are fed to Q106 of the

multiplexer. The 2mA range uses a line that senses the signal

before the range FET IQlOl) and feeds it directly to the

multiplexer lQ105L The sense line is needed because of the

relatively high resistance of the range FET (6OD) as compared to the resistance of the feedback resistor flkD).

ZERO

Figure 4-2. Current-to-Voltage Converter

TO MULTIPLEXgR

Figure 4-3. Simplified Schematic of the Multiplexer

INPUT FROM

MuLT’pLEF=-l sy;

. ..-

ilERT!R

Ordinarily, F5T switching creates transients which could be

seen in the final measurement. These effects are minimized in

the Model 485 through the use of software generated delays

and by signal-ground differenatial measurements.

4.3.3 Input Buffer Amplifier

The input buffer amplifier provides the necessary isolation

between the input signal and the AID converter. The

amplifier is a noninverting, low noise, high impedance circuit with xl gain for the 20nA-2mA ranges and x10 gain for the 2nA range. The amplifier gain is controlled by the

microprocessor. Figure 44 shows the simplified schematic of the input buffer amplifier.

4-2

RlZ2F

1okn

1kQ

FROM Ulll (PSO)

Figure 44. Simplified Schematic of the Input Buffer

Amplifier

Page 33

4.3.4 -2V Reference Source

The Model 485 current measurements are based on compar-

ing the unknown signal with an internal -2V reference voltage. During each measurement cycle the microprocessor samples the unknown and uses it along with a zero measurement and -2V signal measurement to compute the unknown voltage.

The -2V reference is made up of a highly stable zener diode (VR103). an op-amp and a resistive voltage divider. U107 and

RI22 A, B, C act as a constant current source to minimize the

zener voltage variations. RI18 C, D is then used to divide

down the -6.35V zener voltage to approximately -2V.

The output of U107 I-N) is used as a reference voltage for the A/D converter and as a negative supply for various

components.

propriate multiplexer FET is turned on. The actual delay period depends on the selected range and function.

Once this occurs the signal from the buffer amplifier is added to the offset from Rl22H. This converts the bipolar signal from the buffer t +2V) to a &polar input for the integrator.

The integrator ramps up until it just passes the charge-

balance comparator threshold voltage. When thejsing edge of 03 occursfrom U116 or when U115goes low, Qgoes high

forcing ICB into the integrator input. Since ICB is much greater than the current through Rl22G and Rl22H the integrator output voltage will ramp in the negative direction. The integrator will continue ramping downward until U115B goes low. Each time the output U117A goes high it is gated

(inside the microprocessor) with the microprocessor’s inter-

nal clock and these pulses are counted. Once U117A goes

low the process repeats itself.

4.3.5 AID Converter

The Model 485 uses a combination constant frequency

charge balance, single slope analog-to-digital converter. A simplified schematic of the A/D used in the Model 485 is shown in Figure 4-5 with an associated output waveform.

The charge balance phase begins when the input enable line

is set high. This occurs at the end of a software-generated

delay period that allows the signal to settle after the ap-

R120A

‘I .5v

The charge balance phase continues for IOOmsec. At the end of the charge balance phase, the output of the integrator is

resting at some positive voltage. Since the integrator output is connected to the noninverting input of the UllOA, its output will stay high until the integrator ramps negative. During

single slope 0109 is turned off and R120l-i is connected to

+5V. The single slope comparator is then gated with the microprocessor’s internal clock and counted. Once the comparator output goes low the microprocessor stops counting

and can compute the reading.

SINGLE SLOPE

CHARGE BALANCE

UllOB

INPUT ENABLE/ DISABLE

Figure 4-5. AID Converter

U116

4-3

Page 34

4.4 DIGITAL CIRCUITRY

Model 485 operation is controlled by the internal microcomputer. This section briefly describes the operation of the

various sections of the microcomputer and associated digital

circuitry. For complete circuit details refer to schematic diagram number 485108 at the end of this manual.

4.4.1 Microcomputer

The microcomputer (MPU) centers around the 146805E2

CMOS microprocessor. It is an 8 bit microprocessor with direct addressing of up to 8k bVtes on a shared address and data bus.

In order to drive the display correctly four voltages are obtained from R121. The clock required bY U201 is obtained from U118.

The display board also houses the special function keys: LOG, REL, STO/CLR and RCL.

4.5 DIGITAL CALIBRATION

The Model 485 uses digital calibration to eliminate calibration

potentiometers in the instrument. The constants that the Model 485 uses are stored in a nonvolatile electrically

alterable read only memory fU1231, and are read on power-up

of the instrument. There is one constant for each range.

Timing of the microprocessor is accomplished by the use of YIOI; a 32788MHz crystal. Internally this frequency is di-

vided down bY 5 to obtain a bus operting frequency of

855.38kHz. This is present on the address strobe of U120 (pin

8) and supplies timing to all other parts of the instrument through the binary divider U116.

The software for the MPU is stored in U113 (PROM). Temporary storage is provided by Ul12. U112 is used to store the calibration constants on power up and as RAM for the microprocessor’s in-house functions. It also stores readings for the data logger. U123 is the NVRAM and is used to store

the calibration constants which are moved to the RAM

KJ112) on power up.

4.4.2 Address Decoding

Ullg is used to latch in the address that is on the bus when the address strobe of VI20 goes high and presents it to the

PROM full31 during data strobe.

4.4.3 PIA

Ulll provides for most of the control of the instrument. It controls all ranging hardware, AID converter, and data output and input for the IEEE option.

4.4.4 Display Board

The LCD display is driven by a flat pack LCD controller chip U201 and it communicates to the microprocessor through

four control lines. During power-up the microprocessor configures U201 to drive the triplexed display.

4.6 POWER SUPPLY

Fuse FlOl is the LINE FUSE which is internally accessible. SlOl is the power ON/OFF switch, and S102 selects 115V or

230V operations bY placing the transformer primary windings

in parallel or series.

TlOl, the power transformer has two secondary windings; one for the Model 485 and the other for the IEEE option

(Model 4853). The bridge rectifier (CRIOI) functions as a

fullwave rectifier for both the plus and minus supplies. RI25

limits current to the 12V zener fVR106) and to the batteries (if installed) for charging. The zener acts as a pre-regular to the

+ 5V regulator.

4.7 MODEL 1758 BAlTERY OPTION

Maximum battery charging rate is acieved when the instrument is connected to line power and the ON/OFF switch is off. Fullwave rectified voltage from CR101 is applied to RI02 and BTlOl to charge the batteries. 0101 acts as a current sink if the charging current rises above 150mA. The batteries are of the quick recharge o/pe and will charge in 8 to 10 hours. With the instrument turned on the batteries will trickle charge at approximately 40mA.

With the battery peck installed, the negative supply is generated using a CMOS voltage inverter (U1011. The output of the inverter is applied to CR101 and Cl01 for filtering.

Low battery detection is accomplished by the comparator

fU102) and the microprocessor. A voltage level of 8.8V across ET101 signals the end of useful battery life. The trip level for the comparator is set by R103 and R104.

4-4

Page 35

SECTION 5

MAINTENANCE

5.1 INTRODUCTION

This section contains installation, calibration and service information for the Model 485 and 1758 Battery Pack.

WARNING

The procedures described in this section ere for use only by qualified service personnel. Do not perform these procedures

unless qualified to do so. Many of the steps

covered in this section may expose the in-

dividual to potentially lethal voltages that could result in personal injury or death if normal safety precautions are not observed.

5.2 TOP COVER REMOVAL/INSTALLATION

The top cover of the Model 485 must be removed in order to move the calibration jumper, service the unit or to install the

Model 1758 battery pack and/or the Model 4853 IEEE-488 in-

terface. Proceed as follows:

WARNING Service by qualified personnel only. Disconnect the line cord and all other sources end cables before removing the top cover.

1. Turn off the power, disconnect the line cord and remove all test leads from the terminals of the Model 485.

2. Turn the unit over and remove the four screws from the bottom of the case.

3. Turn the unit over again and separate the top cover from the rest of the unit.

4. To reinstall the top cover, position the tilt bail properly into

the bottom cover and reverse the above procedure.

5.3 BAlTERY PACK INSTALLATION

Refer to Figure 6-l and perform the following procedure to install the battery pack:

WARNING Service by qualified personnel only. Disconnect line cord and remove all test leads from the terminals of the Model 485.

1. Remove the top cover as explained in paragraph 5.2.

2. Remove the four screws securing the shield to the mother board.

3. Position the battery board as shown in Figure 6-l and secure it to the shield using two supplied screws. The

screws are fed through the shield into the battery board

fasteners.

4. Place the battery pack in the bracket end position it on the shield as shown. Feed the two screws through the shield into the bracket and tighten.

CAUTION

Do not allow the battery leads to short together or damage to the batteries may occur.

5. Carefully place the shield (with battery pack) back into the Model 485 and replace the four screws securing it.

6. Connect the ribbon cable from the battery board to the

male connector (marked BAT) on the mother board.

CAUTION

Make a close visual inspection to ensure

that the connector is properly mated or

damage to the instrument may result.

7. Connect the red battery lead to the + RED terminal pin on

the battery board. Connect the black battery lead to the

-BLK terminal pin on the battery board.

8. Reinstall the top cover as explained in paragraph 5.2.

9. Charge the battery pack per instructions in paragraph

2.2.3.

NOTE

The IEEE interface.IModel4853) cannot be used

on battery power.

5.4 FRONT PANEL CALIBRATION

Calibration should be performed every 12 months, or if the performance verification procedures in Section 3 show that the Model 485 is out of specification. If any of the calibration procedures in this section cannot be performed properly, refer to the troubleshooting information in this section. If the problem persists, contact your Keithley representative or the factory for further information.

The entire calibration procedure may be performed without having to make any internal adjustments.

5.4.1 Recommended Calibration Equipment

The same equipment that is used in the performance verification procedure is used to calibrate the Model 485. This equip-

ment is listed in Table 3-1. The information needed to build

the shielded test fixture is provided in Figure 3-l.

5-I

Page 36

5.4.2 Calibration Storage Enable

The CAL LOCK switch of the Model 495 must be in the calibration storage enable position in order to store calibration constants into NVRAM. If the switch is not placed in the enabled po sition, calibration will be lost when the instrument is turned off.

The access hole for the CAL LOCK switch is located to the left of the ON/OFF power switch. CAL LOCK is a two position (IN and OUT) pushbutton switch. To enable calibration storage, insert a small-bladed screwdriver into the access hole in the front panel

and set the pushbutton switch to the innermost position.

5.4.3 Environmental Conditions

Calibration should be performed under laboratory conditions having an ambient temperature of 23 f3OC and a relative humidity of less than 70%. With the instrument on, allow it to warm up for one hour. If the instrument has been sub-

jected to temperatures outside this range, or to higher

humidity, allow at least one additional hour for the instrument to stabilize before beginning the calibration procedure.

NOTE Calibration can be stopped at any time and only selected ranges can be calibrated if needed.

5.4.4 Calibration Procedure

Perform the following steps to calibrate the Model 485:

NOTE

Record the following measurements and

calculations in Table 5-l. Use a pencil so that the

table can be used again.

1. Using the Keithley Model 181 or 192, measure and record the resistance of the lOkC, lOOkg, 1MC and 1OMD resistors.

2. Using the Guildline Model 9520, measure and record the resistance of the lOOMg, lG9 and 1OGg resistors.

3. Calculate and record the required DC calibrator setting for

each range as follows (Refer to Table 5-l): V = I (Required Current) x R (Measured Resistor)

4. Depress ZERO CHECK and select the 2nA range.

5. With an open input, adjust the ZERO pot for .OOOO* 1

count on the display.

NOTE If Q104, U105, R113, RI14 or R115 were changed, the instrument may not zero. See paragraph 5.7 for instructions on balancing the input amplifier offset.

8. Connect the DC calibrator to the test fixture. Make sure that the calibrator is in standby.

7. Connect the test fixture to the input of the Model 485 us-

ing a low-noise coaxial input cable (such as the Keithley

Model 4801).

8. Press in the REL and LOG pushbuttons simultaneously

until the message “CAL” is displayed. Release the but-

tons. The unit is now in the calibration mode as indicated

by the “CAL” annunciator.

9. With the Model 485 in the calibration mods, perform the following procedure using Table 5-1 as a guide.

A. With the DC calibrator in standby, install the ap-

propriate resistor in the the test fixture.

8. Set the Model 485 to the appropriate range. C. Set the DC calibrator to output the calculated voltage

level needed to generate the required current.

D. Adjust the display accordingly with the use of the

STOlCLR and RCL buttons. The STO/CLR button increments the displayed reading and the RCL button decrements the displayed reading.

5.4.5 Calibration Storage

To store the calibration constants, simultaneously press REL and LOG until the message “stof is displayed. The instrument will return to normal operation.

If however, the message “out” is displayed, the CAL LOCK switch is in the disable (OUT) position. The CALannunciator on the display will blink indicating that calibration is temporary and

will be lost when the instrument is turned off.

NOTE

If calibration was inadvertently performed with CAL LOCK in the disable (OUT) position, calibration constants can be stored by performing the following steps:

1. Place the CAL LOCK switch to the enable (IN) posi-

tion (see paragraph 5.4.2).

2. Simultaneously press REL and LOG until “CAL” is displayed. This places the instrument back into the calibration mode.

3. Simultaneously press REL and LOG until “star” is displayed.

Page 37

Table 5-1. Range Calibration

1 Rewired

lOGi i 19v

IGO i 19V

1OOMD ~

19v

lOM9 / 19v

IMQ

19v

100 kD 19v

10 kD 19v

‘V = (1) NV where:

V = Calibrator Setting

I = Required Current

R = Measured Value of Resistor

5.5 CALIBRATION OVER IEEE-488 BUS

The calibration procedure can be automated by using pro-

grammable equipment over the IEEE-488 bus. The Model 485 becomes fully programmable with the addition of the Model

4853 interface. Programmable sources are available from

Keithley and other manufacturers. The documentation that is provided with the Model 4853 includes example programs using various controllers.

-r

Measured

Value of

Calculated*

DC Calibrator

Resistor (RI j Setting IV)

leadinc

485

1.9000

19.000

190.00

1.9000

19.000

190.00 19000

5.6.1 Recommended Test Equipment

The success or failure in troubleshooting the Model 485 depends not only on the skill of the technician, but also relies heavily on accurate, reliable test equipment. Table 52 lists the equipment and specifications recommended for troubleshooting the Model 485. Other equipment such as logic analyzers, capacitance meters, etc. could also be helpful in difficult situations.

5.6 TROUBLESHOOTING

The troubleshooting instructions contained in this section are

intended for qualified personnel having a basic understanding of analog and digital circuitry. The individual should also be experienced at using test equipment as well as ordinary troubleshooting procedures. The information presented here

has been written to assist in isolating a defective circuit or cir-

cuit section; isolation of the specific component is left to the technician.

NOTE

Avoid touching the PC board or its component

parts. Handle the PC board by its edge.

Table 5-2. Recommended Troubleshooting Equipment

MFG

Keithley

Five-function DMM with 0.05% basic

Description

Model 175 DC accuracy, 1OMD input impedance

Tektronix

Dual-trace, triggered-sweep oscillo- Digital and analog waveform checks.

Model 2213 scope, DC to 6OMHz bandwidth.

5.6.2 Self Diagnostic Program

To use the self diagnostic program, hold in the LOG button and turn on the Model 485. The following will occur:

1. All LCD digits and annunciators will turn on.

2. The sofhvare revision level will be displayed (i.e. Al).

3. The sequential display test will run.

4. The Model 485 will go into the troubleshooting test mode.

If the LOG button is released the instrument will flag either RAM or NVRAM self test failures, should they occur. If neither RAM nor NVRAM fails, the instrument will default to

the troubleshooting test mode.

use

Power supply and DC voltage checks, analog

signal tracing, continuity, static logic levels.

5-3

Page 38

RAM Test-If the RAM test fails, the Model 485 will lock up with all zeroes displayed. Replacing U112 may correct problem.

Non-Volatile RAM Test-If the NVRAM test fails, the

following message will be displayed.

This is a sufficient message indicating that the instrument is

probably not properly calibrated since calibration constants are stored in the non-volatile RAM. The Model 488 will lock

up at this point if the test fails, but operation may be restored

for troubleshooting by pressing any front panel momentary

button. The flashing “CAL” annunciator will indicate that the

unit failed the NVRAM test.

ctrr

1. The “a” segments of the digits, and the LOG and CAL annunciators are displayed.

2. The “b” segments of the digits are displayed.

3. The “c” segments of the digits are displayed.

4. The “d” segments of the digits, and the m, ZERO CHECK and RMT annunciators are displayed.

5. The “e” segments of the digits, minus sign end the REL, and A annunciators are displayed.

6. The “f” segments of the digits, end the AUTO and BAT annunciators are displayed.

7. The “g” segments of the digits, and the RCL and n annunciators are displayed.

8. The decimal points, most significant digit and the ST0 and A annunciators are displayed.

At this point try calibrating the instrument with the constants already entered by simultaneously pressing in the REL and

LOG buttons until “CAL” is displayed, and then again until

“Stor” is displayed. If error gets corrected, indicating that the

NVRAM is probably good, a full calibration will be needed. If the error persists try replacing the NVRAM chip (U123). Again, the Model 485 must undergo a complete calibration

after the problem is corrected.

Sequential Display Test-Segments and annunciators are sequentially displayed in eight steps. Use Figure 5-1 for segment identification. The steps are as follows:

I I

Figure 5-1. Segment Identification

Troubleshooting Test Modes-The troubleshooting mode

is designed to switch on various switching FETs, relays and logic levels to allow signal tracing through the instrument.

The first displayed mode will reflect the function and range.

For example, assume that “OAl” is displayed. The “1” cor-

responds to the 2nA range, and the “0” is the test number. The test number can be changed by pressing in the LOG button. Table 53 lists the test modes for all ranges.

To update the test mode, select the new range and hold in the LOG button until range number changes.

Troubleshooting consists of selecting the desired test mode and using the data found in Table 5-3 to signal trace the circuit.

NOTES:

1. When a different range is selected the LOG button must be pressed and held in to update the display with the corresponding test mode.

2. Do not use AUTO or ZERO CHECK in the self-diagnostic mode.

3. To get out of the self-diagnostic mode, cycle power.

5-4

Page 39

Table 5-3. Troubleshooting Modes

Test

Range

2 nA

20 nA

200 nA

2 4

20 /LA

200 pa

2mA

NOTES: 1. Range

Mode

OAl

IA1 2Al 3Al

OA2

2 3A2

OA3

lA3 2A3 3A3

OA4

lA4 2A4 3A4

OA5

IA5

z: OA6

lA6 2A6 3A6

OA7 lA7 2A7 3A7 j

2. Range FETs (QlOl, 0102 and 0103) are turned off by -7V on gates.

3. Multiplexer FETs (0105, Q106, Q107 and QI08l are turned off by -7V on gates.

4. + 5V on pin 9 of U103C selects x10 gain. OV selects xl gain.

5. Logic level 1 = 5V. Logic level 0 = OV.

Range

Relay

Closed

[Note 1)

none none none none

K102 K102 K102 K102

KlOl KlOl KIOI KlOl

KlOl

KlOl KIOI

KlOl KlOl KlOl

slays are

Range

FET On

INote 21

none none none

"One

none none none none

none none none

"On.5

Q103 Q103 Q103 Q103

none none none none

Q102 Q102 0102 Q102

0101 0101 0101 QlOl

)I and Kl

Multiplexer

FET On

INote 3)

0106 Q107 0108 0107

Q106 Q107 0108 Q107

Q106 Q107 Q108 Q107

0106 0107 Q108 Q107

Q106 Q107 Q108 Q107

a105 Q107 0108

0107

Lmplifiel

Gain

RJlO4)

(Note 4)

x10 x10

XT Xl

xl xl xl xl

xl xl

xl xl xl xl

I-

PA0

Range Control

Logic Levels On Ulll

(Note 5)

1 1

0 0 0

1 1

-L--l--

1 1 1

0 0 0

1 1

0 :

0 0 0

0 0 1

0 1

0 0 1

: 0

i 0 0

0 1 0

i 1 i

0 1 0

0 0 0 0

0 0

: 0 0 0 0 0

0 0

t 1

0 0

1 0 0 1 0 1 : 1

: 0

PBI

1 1 1 1

1 1

z 0 0

i 0

1 1 1 1

1 1

1 1 1 1

5-5

Page 40

5.6.3 Power Supply and Battery Pack (Modal 1766)

Checks

Table 5-4 shows the various checks that can be made to the

power supplies within the Model 465 and 1758. In addition to the normal voltage checks, it is a good idea to check the various supplies with an oscilloscope to make sure no noise is present.

Table’ 6-4. Power Supply Checks and Battery Pack (Modal 1758) Checks

5.6.4 A/D Converter and Display

Make sure the A/D converter and display are operating properly before attempting to troubleshoot the signal conditioning circuit. Check these circuits using the information in Table 5-5

and 58.

Step Item/Component

1 S102 Line Switch

2 FlOl Line Fuse

3 Line Cord

Required Condition

Set to 115 or 230V as required. Continuity.

Plugged into line receptacle;

-I-

Remarks

5102 externally accessible from rear panel.

power on.

4 U121** Input (TPl)

5 U121”’ Output (TP31 6 U122 Input fTP2) 7 U122 Output fTP4) 8 VR103 9 U107pin 8

lo* QlOl base

+12v flO% +5v f5%

-20v to -14v

-lov flO%

-8.25V to -8.45V

-7v f5%

0.W while charging (power

+ 5V regulator input.

+ 5V regulator output. Negative supply input. Negative supply output. Reference zener diode. Low noise negative supply. Current sink.

switch off).

ll* Battery’ Pack

Line cord disconnected, battery pack charged,

power switch on. 12* UlOl pin 8 13* U102 pin 7

z 8.8V

+5V with batteries charged.

Voltage inverter. Voltage comparator

‘These items are located on the Model 1758 (if installed).

**If U121 is replaced, be sure that the device is properly seated on the mother board so that it will not touch

the IEEE board (if installed).

Table 5-6. A/D Converter Checks

Item/Component\ Required Condition

Remarks

/Turn on Dower: select 2mA

range. Engage ;ero check.

U120, pin 38

3.2788MHz Clock U118, pin 10 655.38kHz Clock U116, pin 6 81.92kHz Clock U116, pin 5 U118, pin 7 U116, pin 12 U115, pin 6

40.98kHz Clock

163.84kHz Clock

1.28kHz Clock +5V to -0V pulse train,

Crystal (YlOl)

Address Strobe

Synchronous Clock for AID Synchronous Clock for A/D Stnchronous Clock for AID Integrator timebase and real time interrupt. Charge balance synchronization signal.

3pec duration every 22Gec. U109, pin 8 Integrator Ramp UllOB, pin 6 -1.5v Ul 106, pin 7

Variable pulse train OV to + 5V. U117A. pin 6 Variable pulse train, OV to + 5V.

U108B. pin 15 U108B, pin IO

Variable pulse train, OV to f5V.

=5msec positive going pulses.

Comparator Reference Comparator Output Reference current generator.

Control line for charge balance/single

slope.

U117B. pin 9

IOOmsec positive going pulse.

Control line for integrator.

5-6

Page 41

Table 5-6. Display Board Checks

;tep Item/Component Required Conditions

1 Turn on power; select the 2mh range.

Engage zero check 2 P1006, pin 5 3 P1006, pin 6 4 P1006, pin 7 +5v +5%

5 P1006, pin 2 81.92kHz Display Clock 6 P1006, pin 1 OV to + 5V Pulses 7 P1006, pin 12 8 P1006, pin 13

9 P1006, pin 14 + 5v to ov Pulses

10 LCD 11 Connector (P1008) Check that connector is not reversed.

12 Strip Connectors* Check that they are positioned properly.

*See Figure 6-2.

5.6.6 Signal Conditioning

The circuit can be checked by using the diagnostic program

(troubleshooting modes). See paragraph 5.4.2.

5.7 INPUT AMPLIFIER (U1051 BALANCING

Part changes in the input section of the Model 485 may make it necessary to balance the offset of the input amplifier. If the instrument cannot be zeroed, as explained in paragraph

2.7.2, perform the following procedure:

+ 3.33v Vlcdl + 1.66V Vlcd2

OV to + 5V Pulses OV to + 5V Pulses

Check that LCD is positioned properly.

If reversed, display test will run, then

display will blank.

Remarks

Power to display.

Data From pp Data From pp Data From pp Data From pp

a104

WARNING Disconnect line cord and remove all test leads from the terminals of the Model 485.

1. Remove the top cover as explained in paragraph 5.2.

2. Remove the shield. Four screws secure it to the mother board.

3. Referring to Figure 5-2, locate jumpers WlOl and W102 on the mother board. If the jumpers have been cut or removed, replace them with new ones.

4. Connect the line cord and turn the power on.

5. Select the 2nA range and zero check.

6. Center the front oenel ZERO pot and note the offset present on the display.

7. Follow Table 5-7 and cut the appropriate jumper.

8. Disconnect the line cord and install the shield and top cover.

Figure 5-2. Jumper Locations

Table 6-7. Offset Jumper Set Up

5.6 LINE FUSE REPLACEMENT

The line fuse is located internally in the Model 485. For exact fuse location, refer to Figure 6-l. To replace the fuse proceed

as follows:

6-7

Page 42

WARNING

Disconnect the line cord and all other

sources before removing the top cover.

1. Remove the top cover as explained in paragraph 5.2.

2. If the Model 4853 IEEE-488 interface is installed it must be removed to gain access to the fuse. The IEEE board is

secured to the mother board by a support post at the rear, and a connector on the left side. To remove, lift board up

until it disengages from the connector and support post.

3. Replace the blown fuse with the following type: 1/8A,

25OV, 3hG. Slo-Blo (Keithley P/N FU-20).

CAUTION

Do not use a fuse with a rating higher than

specified or instrument damage may occur.

If the instrument persistently blows fuses, a problem may exist within the instrument. If

so, the problem must be rectified before

continuing operation.

4. If the IEEE interface was installed, reinstall as follows: A. Position the Model 4853 loosely on the rear standoff.

WARNING

Do not push down on the seven terminal, female connector fJ1006L The male connector pins will pass through JIOOB and

may cause personal injury.

B. Guide the pins of PI008 into J1008 and firmly push

down on that end of the board to mete the connec-

tors.

Push down on the other side of the IEEE board until it

snaps onto the rear standoff. Make sure the board is

seated properly on the front stand off.

5. Reinstall the top cover es explained in paragraph 5.2.

6.8 SPECIAL HANDLING OF STATIC SENSITIVE DEVICES

may be sufficient to destroy these devices if they are not handled properly. Table 5-8 lists the static sensitive devices in

the Model 485. When handling these devices, use the follow-

ing precautions to avoid damaging them.

1. The ICs listed in Table 58 should be transported and handled only in containers specially designed to prevent

static build-up. Typically, these parts will be received in static-protective containers until ready for installation.

2. Remove the devices from their protective containers only at a properly grounded work station. Also ground yourself with a suitable wriststrap.

3. Handle the devices only by the body; do not touch the pins.

4. PC boards must be grounded to bench while inserting devices.

5. Use only antistatic type solder suckers.

6. Use only grounded soldering irons.

Table 5-8. Static Sensitive Device

-I

Schematic

Designation

UlOl. U102. U103. U108

UiO6 Ulll u112 u113 u114 u115 U116

u117

U118

u119

u120

u101*

*Part of Model 1758

(eithley

‘art No.

IC-283 IC-354 LSI-61 LSI-53 LSI-52 IC-143 IC-341 IC-348 IC-337 IC-351 IC-338 LSI-60 IC-340

CMOS devices are designed to operate at very high impedance levels for low power consumption. As a result, any normal static charge that builds up on your person or clothing

Page 43

SECTION 6

REPLACEABLE PARTS

6.1 INTRODUCTION

This section contains replacement parts information, component location drawings and schematic diagrams for the

Model 485 and Modal 1758.

6.2 REPLACEABLE PARTS

Parts are listed alpha-numerically in order of their circuit designation. Table 6-1 contains a parts list for the mother board. Table 6-2 contains a parts list for the display board. Table 6-3 contains a parts list for the Model 1758 Battery

Pack. Miscellaneous replaceable parts list are not listed in a table but can be identified in Figures 6-1 and 6-2. Table 6-4 contains a complement of spare parts that can be ordered to maintain up to 10 Model 485’s for approximately one Year.

6.3 ORDERING INFORMATION

To place an order, or to obtain information concerning

replacement parts, contact Your Keithley representative or

the factory. See the inside front cover for addresses. When

ordering include the following information:

1. Instrument Model Number

2. Instrument Serial Number

3. Part Description

4. Circuit Designation (if applicable)

5. Keithley Part Number

If an additional instruction manual is required, order the manual package (Keithley Part Number 485-901-00). The manual package includes an instruction manual and all pertinent addenda.

6.4 FACTORY SERVICE

If the instrument is to be returned to the factory for service, please complete the service form which follows this section and return it with the instrument.

6.5 COMPONENT LOCATION DRAWINGS AND SCHEMATIC DIAGRAMS

Figure 6-3. Display Board, Component Layout Figure 6-4. Model 1758 Battery Pack, Component Layout Figure 6-5. Mother Board, Component Layout Figure 6-6. Mother Board, Schematic Diagram

Figure 6-7. Display Board, Schematic Diagram

Figure 6-8. Model 1758 Battery Peck, Schematic Diagram

6-1

Page 44

LINE CORD

*REAR PANEL

LABEL MC-365

6-2

‘NOT SHOWN

SNC CONhECTO&JHAiDLE

CS-249

Figure 6-I. Model 485 Exploded View

OVERLAY

465-309

‘CONDENSED OPERATlNG

INSTRUCTIONS MC-366

Page 45

Figure S-2. 0’

-----MASK

STRrP Pnr*..-

‘%% Assembly

Page 46

Cl06 Cl07 Cl08 Cl09 Cl10 Cl11 Cl 12 Cl13 Cl14 Cl 15 Cl16

Cl 17 Cl18 Cl19 Cl20 Cl21 Cl22 Cl23 Cl24

Table 6-1. Model Board, Parts List

Description

Not Used Capacitor, .OlsF, 5OV, Metal Polycarbonate Not Used Capacitor, 22OpF, 5OOV. Polystyrene Capacitor, lOpF, 1OOOV. Ceramic Disk Capacitor, lOOpF, IOOOV, Ceramic Disk Capacitor, .I/IF, 5OV. Ceramic Film Capacitor, .lsF, 5OV. Ceramic Film Capacitor, lpF, 5OV. Metal Polycarbonate Capacitor, lOpF, 25V. Aluminum Electrolytic Capacitor, .OlpF, IOOV, Metal Polypropylene

Capacitor, .lpF, 5OV. Ceramic Film

Capacitor, .lkF, 5OV, Ceramic Film Capacitor, .IpF, 5OV, Ceramic Film Capacitor, 22pF. lOOOV, Ceramic Disk Capacitor, 22pF, 1OOOV. Ceramic Disk Capacitor, .IpF, 5OV. Ceramic Film Capacitor, 15OOrcF. 25V, Aluminum Electrolytic Capacitor, 4.7rF. 25V. Aluminum Electrolytic Capacitor, 4.7cF. 25V, Aluminum Electrolytic Capacitor, 4.7pF, 25V. Aluminum Electrolytic Capacitor, 25OpF. 25V. Aluminum Electrolytic Capacitor, .l!F, 5OV. Ceramic Film Capacitor, .1&F, 5OV, Ceramic Film

Location Keithley

Sch* Pcb Part No.

c3-1 C? c-201-.01

C4-1 C5 C-138-220~

85-l C5 C-64-10~ 05-l C3 C-64-100~ D5-1 D3 C-237-.1 D5-1 D3 C-237-.1

E3-1 C3 C-335-1 G4-1 C2 C-314-10

El-2 D3 C-306-.01 85-2 D5 C-237-.1 D6-2 E5 C-237-.1

E3-2 E4 C-237-.1

E6-2 F5 C-64-22~

F3-2 F4 C-237-.1

Fl-2 E3 C-3141500

Gl-2 E3 C-3144.7

Hl-2 E3 C-3144.7 Hl-2 E3 C-314-4.7

Gl-2 D3 C-314-220

Bl-1 D4 C-237-.1

E4-1 F2 C-237-.1

CR101

FlOl

JlOOl J1002 J1003 J1006 J1009

KlOl K102 K103

PI004 PI008

QlOl a102 a103 Q104 a105 Cl106 Q107

QIOB

QlOi a110

cl111

Bridge Rectifier, VM18

Fuse, 25OV, l/BA, 3AG, Slo-Blo

Connector, BNC, Female Connector, Modfied Connector, Modified Socket Connector, Male, lo-Pin

Relay, RI Relay, 5V Relay, 5V

Connector, Modified Connector, Modified

JFET, N-Channel, 2N4392 JFET, N-Channel JFET, N-Channel, J210

Transistor, MP-831-1010 JFET, N-Channel, J210 JFET, N-Channel, J210 JFET, N-Channel, J210 JFET, N-Channel, J210

FET, N-Channel Transistor, NPN, Silicon, 5818 Transistor, NPN, Silicon, 5818

Fl-2 03 RF-52

El-2 F3 FU-20

Al-l A5 CS-249

E41 F2 28316 E4-1 F2 29316

Sev F5 SO-70 Sev

82-l C5 RL-70 U-1 C5 RL-70

C5-1 C5 RL-70

El-2 I2 175-316

Sev

D2-1 C3 TG-169 D2-1 C3 TG-130 D3-1 C3 TG-167 Cl-1 C4 TG-156

Fl-1 82 TG-167 Fl-1 C2 TG-167 F2-1 C2 TG-167 F3-1 C2 TG-167

82-2 D2 TG-128

C2-1 C4 TG-138

D3 CS-389-4

E2 175321

6-4

RlOl

R102 R103 RI04

Resistor, lkfl, O.l%, lW, Wirewound Resistor, IOOkfl, 5%, lf4W. Composition Resistor, llkD, 0.1%. l/lOW, Metal Film Resistor, IOOkD, 5%, 1/4W, Composition

C2-1 C4 R-249-lk D2-1 C3 R-76-IOOk C2-1 C4 R-263-11 k D3-1 C3 R-76-IOOk

Page 47

Table 6-I. Mother Board, Parts List iCont.1

Circuit

Desig.

R105 RI06 RI07 R108 I3109 RI10 RI11 R112 R113 R114 RI15

R116 RI17 RI18 Fill9 R120 R121 R122 R123 R124 RI25 R128 R127 RI28 R129 RI30

Description

Resistor, IOOkD, O.l%, l/lOW, Metal Film Resistor, l.lMD, O.l%, 1/8W Resistor, IlMD, 0.7%, IW, Cermet Film Resistor, 99M61, 0.5%, 1/4W, Metal Oxide Resistor, IOMO, 10%. 1/4W, Composition Resistor, 220kD, 5%. 1/4W, Composition Resistor, 49912, 1 %, 1/8W, Composition Resistor, 243B, 1%. 1/8W, Composition

5OOD, IO%, 3/4w, Pot

Resistor Set, 260kC. 0.1% Resistor Set, 280kC. 0.1% Resistor, IOkC, 5%. ll4W. Composition Resistor, 9100, lo%, 1W. Composition

Thick Film Resistor Network

Resistor, IOOkD, 5%. 1/4W, Composition Thick Film Resistor Network Thick Film Resistor Network Thick Film Resistor Network

Resistor, lOOk0, 5%. 1/4W, Composition

Resistor, 10MC. lo%, 1/4W, Composition

Resistor, 27C, lo%, 2W. Composition

Resistor, 8.06k0, l%, 1/8W, Composition

Resistor, 1.24kC, I%, 1/8W, Composition

Resistor, 47k61, 5%, 1/4W, Composition

Resistor, 1000, 5%, ‘IW, Composition

Resistor, 5.lkD, 5%. 1/4W, Composition

Location

Sch* Pcb

c3-1 c4 c3-1 c4 D4-1 84 c4-1 c5

85-l C5

B5-1 C5 c5-1 c4 D5-1 D4

U-1 B5 c5-1 c3 D5-1 D3

E3-1 C3

E4-1 C3

Sev C2

El-l 83

Sev C3 Sev E3

SW c2 El-l C3 F8-2 F5 Fl-2 E3

Gl-2 E3 G2-2 E3

H5-2 D3 E4-1 E2 C4-1 85

Keithlev Part Nd.

R-263-IOOk R-176-l.lM R-302-1 1 M R-269-99M R-76-IOM R-76-220k R-88-499 R-88-243 RP-89-500 R-306 R-306 R-76-10k R-2-910 TF-169 R-78-IOOk TF-172 TF-173 TF-171 R-76-IOOk R-76-10M R-3-27 R-88-8.08k R-881.24k R-76-47k R-76-100 R-78-5.lk

SlOl 5102

TIOI

UlOl lJ102 u103 u104 u105

U106

u107

U108 u109 UllO Ulll u112 u113 u114 u115 U116

Pushbutton Switch Station

Line Switch

Transformer, Power (105-125V, 210-25OV)

Triple 2-Channel Analog Multiplexer, CD40538C Triple Z-Channel Analog Multiplexer, CD4053BC Triple 2Channel Analog Multiplexer, CD4053BC

Programmable Op Amp, TLC271 Linear Op Amp LM308AN Hex Inverter, 74HC04

Programmable Op Amp, TLC271 Triple 2Channel Analog Multiplexer, CD40538C Op Amp, TLOGICP

Dual Voltage Comparator, LM393

Peripheral Interface Adapter, 65C21

1024 x 4 Bit Static CMOS RAM 8k x 8 UV Erasable PROM Triple 3-Input OR Gate, CD4075BE Triple 3-Input NAND Gate, MM74HClO

12 Stags Binary Counter, 40408

Sev 83

El-2 F3

Fl-2 D2

SW c3 Sev c2 Sev C2

F2-1 C2

D5-1 C3

SW D4

F4-1 C2

SW D2 82-2 c3 c2-2 c3 C4-2 D3 A8-2 D5 C6-2 D5

SW E3 Sev E4

D3-2 E4

SW-455 SW-318

TR-201

IC-283 K-283 IC-283 IC-347 K-203 K-354 IC-347

IC-283 IC-227 ICI-343 LSI-61 LSI-53

485-800-**

ICI43 IC-341 IC-348

6-5

Page 48

Circuit I

Desig.

u117 U118 u119 u120 u121 u122

U123

Table 6-l. Mother Board, Parts List (Cont.1

Description

/ Dual D FlipFloe, 74HC74

Quad 2-Input NAND Gate, 74HCoo Tri-State Octal D Latch, 74HC373 CMOS 8-Bit Microprocessor, 146805E2

Regulator, +5V, lA, 7805 3-Terminal Adjustable Regulator, LM337L

18 x 16 Bit Serial Nonvolatile Static RAM, X2443P

Location Keithley

Sch’ Pcb Part No.

D3-2 E3 I(3337

Sev

D6-2 E5 IC-338

SW HI-2 E2 IC-93 G2-2 E3 IC-345 H5-2 D3 IC-353

D4 IC-351

F5 LSI-60

VRlOl

VR102 VR103 VR104

VR105

VR108

WI01 WI02 WI03

YlOl

“-

“Lone and page number e.g. BZ-1 corresponds to zone B2 on page 1 of schematic.

**Order same software as presently installed. For example, if Al is the displayed software, order 485-800-A?.

Diode, 2.3V-2.9V, lN702A Diode, 2.3V-2.9V, lN702A Diode, Zener, 6.35V. 400mW. lN4577 Diode, Zener, 5.1V, 400mV. lN751 Diode, Zener, 12V. lN963B Diode, Zener, 12V, 5W. IN5349

Jumper Jumper Calibration Jumper

) Crystal, 3.2768MHr

~_.

E4-1 C3 DZ-33 E4-1 C3 DZ-33

F4-1 C3 DZ-58 G4-1 C2 DZ-59 Hl-2 D3 DZ-54 H2-2 E3 DZ-72-1

C5-1 C4 J-3 D5-1 C4 J-3 H6-2 D4 CS-476

E6-2 F5 ) CR-21

6-6

Page 49

;

Page 50

Page 51

I 1

> I III III iii G

Page 52

Table 6-2. Display Board, Parts List

Circuit Dasig.

DS-201 Liquid Crystal Display P1006 u201 LCD Controller/Driver

I III’ ----

Description

Cable Assembly (14 Conductor)

,,r-----~--~-~-------~-----,II,,

Location Keithley

Pcb Sch Part No.

E2 D3 DD-35

C4 C4 CA-g-3 rkl al I SI&Q

Figure 6-5. Display Board, Component Location Drawing, Dwg. No. 485-110

6-13

Page 53

6-14

Figure 6-6. Display Board, Schematic Diagram Drawing, Dwg. No. 465-116

Page 54

Table 6-3. Model 1768 Battery Pack, Parts List

Circuit

Desig.

BTlOl Cl01

Cl02 CR101

JlOlO JlOll

P1009 RlOI

R102 RI03 R104 RI05

RTlOl cl101 UlOl

u102

Description

Battery Assembly, 9.6V sealed rechargeable Ni Cad

Capacitor, 250~F. 25VDC. Aluminum Electrolytic Capacitor, lOpF, 25VDC, Aluminum Electrolytic

Rectifier, Schottky Barrier, 1 N5620 Pin

Pin Cable Assembly, 10 Conductor Resistor, 4.7B, lo%, lf2W. Composition

Resistor, 4.7g, 5%, 1/4W, Composition Resistor, 30.lkD. l%, 1/8W, Metal Film

Resistor, 39.2kg, 1%. 1/8W, Metal Film

Resistor, 1.2Mg. 5%. ll4W. Composition PTC Thermister Transistor, NPN, High Voltage (TIP-49) Voltage Converter, 517661

Voltage Comparator, LM393

Heat Sink (used on UlOll

Standoff (Battery Board to Shield)

Battery Bracket

E2 C3 R-l-4.7 El C2 R-764.7 E3 E3 R-88-30.1 k

Figure 6-7. Battery Pack, Component Location Drawing. Dwg. No. 1758-100

6-16

Page 55

I-

Page 56

Table 6-4. Model465 Spare Parts List

my.

TG-167

0103; aio< ~106

Q107,Q108

TG-128 QlO9

K-347

K-283 UlOl, u102. u103,

u104,u107

U108

IC-353 U123 IC-354 U106

1 1

IC-351 U118 1 1 1 1

k 1 1

6-17/6-18

Page 57

Service Form

Model No.

Serial No.

Date

Name and Telephone No.

Company

List all control settings, describe problem and check boxes that apply to problem.

Cl Intermittent

0 IEEE failure Q Front panel operational

Display or output (check one) m Drifts

0 Unstable 0 Overload

0 Calibration only 0 Data required

(attach any additional sheets as necessary)

Show a block diagram of your measurement system including all instruments connected (whether power is turned on or not).

Also, describe signal source.

CI Analog output follows display

0 Obvious problem on power-up a All ranges or functions are bad

Q Unable to zero 0 Will not read applied input

0 Certificate of calibration required

a Particular range or function bad; specify

0 Batteries and fuses are OK 0 Checked all cables

Where is the measurement being performed? (factory, controlled laboratory, out-of-doors, etc.)

What power line voltage is used7

Relative humidity?

Any additional information. (If special modifications have been made by the user, please describe.)

Other’?

Ambient temperature?

Keithley 485 Service manual

Specifications and Main Features

Frequently Asked Questions

User Manual

SPECIFICATIONS

TABLE OF CONTENTS

LIST OF ILLUSTRATIONS

LIST OF TABLES

SAFETY PRECAUTIONS

Model 485 Addendum

MODEL 485 AUTORANGING PICOAMMETER

1.1 INTRODUCTION

1.3 INSPECTION

1.4 SPECIFICATIONS

1.5 WARRANTY INFORMATION

1.6 MANUAL ADDENDA

1.7 SAFETY SYMBOLS AND TERMS

1.8 OPTIONAL ACCESSORIES

2.1 INTRODUCTION

2.2 PREPARATION FOR USE

2.3 TILT BAIL

2.4 MODEL 485 FAMILIARIZATION

2.5 ERROR MESSAGES

2.6 ENVIRONMENTAL CONDITIONS

2.7 BASIC BENCH MEASUREMENTS

2.6 MEASUREMENT CONSIDERATIONS

2.5 APPLICATIONS

3.1 INTRODUCTION

3.2 ENVIRONMENTAL CONDITIONS

3.3 RECOMMENDED TEST EQUIPMENT

3.4 INITIAL CONDITIONS

3.5 VERIFICATION PROCEDURE

4.1 INTRODUCTION

4.2 OVERALL FUNCTIONAL DESCRIPTION

4.3 ANALOG CIRCUITRY

4.4 DIGITAL CIRCUITRY

4.5 DIGITAL CALIBRATION

4.6 POWER SUPPLY

5.1 INTRODUCTION

5.2 TOP COVER REMOVAL/INSTALLATION

5.4 FRONT PANEL CALIBRATION

5.5 CALIBRATION OVER IEEE-488 BUS

5.6 TROUBLESHOOTING

5.6 LINE FUSE REPLACEMENT

6.1 INTRODUCTION

6.2 REPLACEABLE PARTS

6.3 ORDERING INFORMATION

6.4 FACTORY SERVICE

6.5 COMPONENT LOCATION DRAWINGS AND SCHEMATIC DIAGRAMS