Keithley 602 Service manual

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MODEL 602 INSTRUCTION MANUAL

Instruction Manual

Solid-State Electrometer

Model 602

Publication Date: June 1963 Document Number: 29111 Rev. C

Contains Operating and Servicing Information for the

Model 602 Solid-State Electrometer

01975, Keithley Instruments, Inc.

Cleveland, Ohio, U.S.A.

Document Number 29111

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 we warranted for the balance of the original warranty period, or at least 90 days.

LIMITATION OF WARRANTY

This warranty does not apply to defects resulting from pmduct modification without Keithley’s express written consent, or misuse of

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

problems arising from normal wear or failure to follow instructions.

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

NEITHER KEITHLEY 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

SPECIFICATIONS

AS A VOLTMETER: RANGE: .OOlV full scale to 1OV in nine’lX and 3X ranges. ACCURACY: f 1% of full scale on all ranges exclusive of noise and drii. ZERO DRIFT: Less than Im” per 24 hours, Ikss than 150@ per OC. METER NOISE: *25&J maxim”m with input shoned on most sensitive

IN?~?iMPEDANCE: Greater than lo’% shunted by2OpF. Input resistance AS iN AMMETER:

RANGE: lCr14A full scale to 0.3A in twenty-eight 1X and 3X ranges. ACCURACY: 12% of full scale on 0.3 to 10”A ranges using the mallest

available multiplier setting; *t4% of full scale on 3 x lo-l2 fo 10-14A

ranoes. METER NOISE: Less than f3 x 10-16A. OFFSET CVRRENT: Lens than 5 x 10-15A.

AS AN OHMMETER: RANQE: 7000, full scale to 10% in twent+hree linear IX and 3X ranges. ACCURACY: *3% of full scale on 100 to l@Q ranges using the largest

available multiplier stting; f5% of full scale on 3 x 109 to 1O’jn ranges. AS AN COULOMBMETER:

RANGE: lo-‘? full scale to 10dC in fifteen IX and 3X ranges. ACCURACY: f5% of full scale on all ranges. Dritt due fo offset current

does no, exceed 5 x 10.=C per second. AS AN AMPLIFIER:

tNPUT IMPEDANCE: Greater than 10’40 shunted by2OpF. input resistance

may a,so be ~&cted in decade steps from 10 fo lO”O. OUTPUTS: Unitygain output and either voltage or cment recorder o”tp”t. UNITY-QAIN OUTPUT: At DC, o”tp”t is equal to input within 10 ppm. ex-

clusive of noise and drib?. for o”tp”t currents of lOO@ or less. Up 10 ImA

may be drawn for input voltages of 10” or less. Output polarity is same as input p&dry.

VOLTAGE RECORDER OUTPUT: *lV for full-scale input. Internal

resistance is g1M1. Output polarity is opposite input polarity. Gain: 0.1. 0.33, a.. to 1000. Frequmw Response lwithin 3db): DC to 40kHr 81 a gain of 1 and

lo&, &e&g to DC to 1OOHz at maximum gain. Full o”tp”t response limited to 3kHz on any gain.

Noise: Less than 3% ms of full scale at gain of 1000. decreasing 10 less

than 0.5% ar gains below 10.

CURRENT RECORDER OUTPUT: i ImA for full-scale input. variable

f6% wtih 14OOll recorders.

GENERAL ISOLATION: Circuit ground to chassis ground: Greater than l@Q shunted

by .0016~F. Circuit ground may be floated up to f 15OOV with wpecf to chassis ground.

Polarity: Meter *witch seIects lefvzero Ipositive or negative) or center-zero

scales. Meter witch does nof reverse polarity of o”fp”tS.

CONNECTORS: Input: Teflon-insulated tdaxial Bendix 33050-Z. Low:

Binding post. Voltage or currem o”tp”t: Amphenol 60.PCZF. Unity-gain

o”tp”1, chassis ground: Binding posts.

BATTERY CHECK: Condition of all baneries may be checked with front

paw co”trok.

BATTERIES: Six 2N6 lor 246. VS306. NEDA 16021: one RM-1W. 1000 DIMENSIONS. WEIGHT: Overall bench size 10% in. high x 7 in. wide x

11 ‘h in. deep 1276 x 175 x 2gOmm). Net weight. 13 pounds l57kgl.

ACCESSORIES SUPPLIED: Model 6011 Input Cable: 30” triaxial cable

with friaxial connector and 3 alligator clips. Mating o”tp”f connector.

TABLE OF CONTENTS

Paragraph

SECTION l-GENERAL DESCRIPTION

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.8.1

1.82

1.8.3

1.8.4

1.8.5

1.8.6

1.8.7

2.1

2.2

2.3

2.4

2.5

2.6

2.6.1

2.6.2

2.6.3

2.7

2.7.1

2.7.2

2.8

2.8.1

2.6.2

2.8.3

2.9

2.9.1

2.9.2

2.9.3

2.10

2.11

2.12

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

Model 602 Features. ....................

Warranty Information ...................

ManualAddenda

Safety Symbols and Terms. ..............

Safety Precautions

Specifications .........................

Optional Accessories. ...................

SECTION Z-OPERATION

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

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

Rear Panel Terminals. ..................

Input Connections .....................

Preliminary Procedures. ................

Voltage Measurements. ................

Off-Ground Voltage Measurements .......

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

Resistance Measurements ..............

Charge Measurements .................

Recorder Outputs .....................

Unity-Gain Output .....................

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

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

Model 6101A Shielded Probe ...........

Model 6103C Divider Probe

Model 6104Test Shield. ...............

Model 6105 Resistivity Chamber ........

Model 2503 Static Detector Probe.

Model 6011 Input Cable ...............

Model 6012 Triax-to-Coax Adapter ......

Normal Method Voltage Measurements Guard Method Voltage Measurements

Low Impedance Source ..............

FEEDBACK Switch Set To NORMAL ...

FEEDBACK Switch Set To FAST ......

Normal Mode IO.3 to lO~‘4A Ranges) ....

Fast Method (Current Below lo-=A) ....

Galvanometric Method ...............

Normal Constant Current Method ......

Fast Constant Current Method. ........

Voltmeter-Ammeter Method (To 10%)

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

......

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

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

Title Page

.........

...... ..

.........

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

2-1 2-l 2-l 2-l 2-4 2-5 2-5 2-5 2-5 2-5 2-5 2-5 2-6

2-6 2-6 2-7 2-7 2-7 2-8 2-8 2-8 2-9 2-9

......

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

......

3.1

3.2

3.3

3.4

3.4.1

3.4.2

3.5

3.5.1

3.5.2

3.6

SECTION 3-THEORY OF OPERATION

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

Voltmeter Operation ...................

Voltmeter Circuit ......................

Ammeter Operation. ...................

Normal Method .....................

Fast Method. .......................

Ohmmeter Operation ..................

Normal Method .....................

Guarded Method ....................

Coulombmeter Opration ................

......

,,....

......

.,....

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

......

3-l

3-1

3-l 3-1 3-l

3-2 3-2

3-2

4.1

4.2

4.2.1

4.2.2

4.3

4.4

4.5

4.6

4.7

4.8

4.9

4.10

4.10.1

4.10.2

4.10.3

4.10.4

4.11

4.12

4.13

4.14

4.14.1

4.14.2

4.15

4.16

SECTION 4--SERVICING INFORMATION

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

Calibration

RecommendedEquipment

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

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

CalibrationSchedule ..........................................................................

Preliminary Procedures Mechanical Meter Set and Meter Zero Calibration

Tracking Check and 1MA Output Calibration

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

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

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

NoiseCheck ...................................................................................

OffsetCurrentCheck DrinCheck

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

High-Megohm ResistorVerification. AccuracyCheck

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

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

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

VoltageAccuracyCheck .......................................................................

CurrentAccuracyCheck .......................................................................

ResistanceAccuracyCheck

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

ChargeAccuracyCheck .......................................................................

Unity-GainCheck

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

FrequencyResponseCheck ......................................................................

CommonModeRejectionCheck ..................................................................

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

Servicing Schedule ...........................................................................

Par&Replacement Procedures To Guide Troubleshooting Servicing High Impedance Circuitry

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

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

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

41 4-l 4-l 4-l 4-l 4-2 4-2 4-2

z 4-3 4-3 43

4-4 zl

4.4 45

4.2 4-6

5.1

5.2

5.3

5.4

5.5

5.6

5.7

SECTION S-REPLACEABLE PARTS

Introduction

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

PartsList .....................................................................................

OrderingInformation ............................................................................

FactoryService ................................................................................

Special Handling of Static Sensitive Devices ComponentLocationDrawing

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

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

SchematicDiagram.........................,.,.............,,..,............................... o-1

5-l 5-l 51 5-l 51 51

LIST OF FIGURES

Figure

Model 602 Front Panel Controls

2-1

Model 602 Rear Panel Terminals

2-2

Triaxiallnput ..........................................................

2-3

Error Due to Ammeter Resistance.

2-4

Measuring Current by the Galvanometric Method,

2-5

Measuring Resistance by the External Voltage Method

2-6 2-7 Divider Curcuits ccross Model 602 Output for Driving 50 and 10OmV Recorders

Measuring Potential of Hich Resistance Source with 0.025% Accuracy.

2-8

Block Diagram of Model 602 in Voltmeter Mode

3-1

Block Diagram of Model 602as a Picoammeter

3-2

Block Diagram of Model 602for Normal Method Measuring Resistance

3-3 4-l Model 602 Case to LO Isolation Check

Model 602 Unity-Gain Test Set-Up.

4-2

Model 602 Chassis, Side View.

5-1

RANGE Switch, S102, Component Location Drawing

5-2

MULTIPLIER Switch, S106, Component Location Drawing

5-3

Model 602, PC186, Component Location Drawing

5-4

Model 602, PC127, Component Location Drawing

5-5

Model 602, Schematic Diagram, Dwg. No. 21174E

5-6

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

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

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

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

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

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

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

Title

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

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

.........

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

.........

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

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

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

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

LIST OF TABLES

...

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

Page

.........

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

......... 2-4

......... 2-6

......... 2-7

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

......... 2-9

.........

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

......... 4-2

......... 4-4

.........

......... 53

.........

......... 5-9

2-2

3-l

5-2

57 5-7

Table 2-l Color Coding of Alligator Clips for Model 6011 Input Cable ... 2-2 Multiplier Switch Positions for Checking

4-1 Recommended Test Equipment .........................

4-2 Model 602 Internal Controls. 4-3 Coulomb Ranges Accuracy Check 4-4 Model 602 Troubleshooting. 5-l Model 602 Static Sensitive Devices 5-2 Model 602 Replaceable Parts List

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

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

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

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

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

Title

......

..,...

Page

2-l 2-4 4-l

4-2 4-4 4-5 5-l 54

iii/iv

SECTION 1

GENERAL DESCRIPTION

1.1 INTRODUCTION 1.3 WARRANTY INFORMATION The Keithley Model 602 Electrometer is a completely solid-

state, battery operated instrument, which measures a wide

range of DC voltage, current, resistance and charge. The Model 602’s input resistance of greater than 10’4R is the result of extensive instrument development with high input impedance transistors. The Model 602 has all the capabilities of conventional VTVMs, but can also make more measure-

ments without loading circuits.

The Model 602 has nine voltage ranges from O.OOlV full scale to lOV, 28 current ranges from 10’4A full scale to 0.3A. 23

linear resistance ranges from 1000 full scale to 1OtQ. and 15

charge ranges from lo-‘SC full scale to lo-aC. The Model 602 offers complete line isolation and excellent

off-ground measuring capability. Up to 1500V may be applied instrument which occur after the printins o! this manual will

between the input low terminal and the case, and stage be found on an addendum sheet included .-:ith this manual.

operation is assured with the case grounded. A triaxial con- Be sure to review these changes before ar:en:$ing to operate

nectar allows complete guarding of the high impedance input or service the instrument. terminal.

The Model 602 employs matched insulated-gate field-effect

transistors followed by transistor differential amplifier stages

and a compliritentary-output stage. A large amount of

negative feedback is used for stability and accuracy.

1.2 MODEL 602 FEATURES

1. The Model 602 has excellent zero stability which permits accurate measurements with minimal adjustment. Short term zero drift is less than 50& per hour. Zero offset due to temperature change is less than 15O/rV per OC after 30 minute warm-up period. This offset, however, can easily be compensated for with the front panel zero controls.

2. Fast warm-up is an inherent characteristic of the Model

602. It can be operated 30 minutes after warm-up on the

most sensitive range and almost immediately on less sensi-

tive ranaes.

3. Low offset current 5 X lo-IsA, minimizes zero offset with high source resistance and permits maximum resolution

when measuring current and charge.

4. The 1000 hour life of the batteries enables usage in long term experiments without interruptions for recharging.

Battery life is maintained even when the 1OmA recorder output is used. For further convenience, battery condition is readily checked on the panel meter.

5. Excellent overload protection without degradation of performance is obtained by use of a unique input circuit. The

Model 602 Electrometer will withstand damage and has good recovery.

Warranty information may be found inside the front cover of this manual. Should it become necessary to exercise the warranty, contact your nearest Keithley representative or the factory to determine the correct course of action. Keithley

Instruments maintains service facilities in the United States,

West Germany, Great Britain, France, the Netherlands,

Switzerland, and Austria. Information concerning the appli-

cation, operation, or service of your instrument may be directed to the applications engineer at any of these locations. Check the inside front cover of this manual for addresses.

1.4 MANUAL ADDENDA

Information concerning improvements or changes to the

1.5 SAFETY SYMBOLS AND TERMS

The following safety symbols and terms are used in this

manual or found on the Model 602.

The symbol

should refer to the operating instructions in this ;nanual.

The symbol

tential of 1OOOV or more may be present on the terminaltsl.

Standard safety precautions should be observed when such dangerous voltages are encountered.

The WARNING heading in this manual explains dangers that could result in personal injury or death.

The CAUTION heading in this manual explains hazards that could damage the instrument.

1.6 SAFETY PRECAUTIONS

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

2. Excercise extreme caution when a shock hazard is present at the instrument’s input. The American National

Standards Institute (ANSI) states that a shock hazard ex-

ists when voltage levels greater than 30V rms or 42.4V

peak are present. A good safety practice is to expect that hazardous voltage is present in any unknown circuit before measuring.

on the instrument indicates that the user

on the instrument indicates that a po-

l-l

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

4. 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.

5. 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.

6. Exercise extreme safety when testing high energy power circuits (AC line or mains, etc). Refer to the operating section.

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

1.7 SPECIFICATIONS

Detailed Model 602 specifications may be found immediately preceding this section.

Three-Terminal Connections-The GUARD output on the Model 602 Electrometer can be used for resistance measurements where the effects of cable capacitance may be significant. Connect the unknown between INPUT and EXT terminals. Connect the EXT terminal to the GUARD output on the electrometer. Use the electrometer in fast mode for ohms measurement.

I.E.4 Model 6105 Resistivity Chamber

The Model 6105 is a guarded test fixture for measurement of surface and volume resistivities. The chamber is designed in accordance with ASTM Standard Method of Test for Electrical Resistance of Insulated Materials, D257-66. The Model 6105 can be used in conjunction with an electrometer and voltage supply.

Resistivity can be determined by measuring the current through a sample with a known voltage impressed. The measurement can be made most conveniently when a set of

electrodes are used which can be calibrated in terms of surface or volume resistivity. The Model 6105 has been designed for use with a Keithley electrometer and an optional high voltage supply such as the Model 247.

1.8 OPTIONAL ACCESSORIES

The following optional accessories can be used with the

Model 602 to provide additional convenience and versatility.

1.8.1 Model 8lOlA Shielded Probe The Model 6010A is a shielded cable with a needle point

probe and 30 inches of low noise cable terminated by a UHF connector.

I.E.2 Model 8103C Divider Probe The Model 6013C is a shielded cable with a needle point

probe and 30 inches of low noise cable terminated by a UHF connector. The probe includes a 1OOO:l voltage divider with a

4.5 X 1OW input resistance. Accuracy is f5% at 30kV.

1.8.3 Model 8104 Test Shield

The Model 6104 is a shielded test box for two-terminal or three-terminal connections. The INPUT terminal is Teflon@ insulated.

Two-Terminal Connections-Resistance measurements can be made conveniently using the INPUT and GROUND terminals on the test box. Connect the electrometer to the BNC output. Use the electrometer in normal mode for ohms measurement.

1.8.5 Model 2503 Static Detector Probe Model 2503 is designed to detect voltage due to charge on

relatively small surface areas. Solid coaxial 13mm (% inch) diameter tube used with 89mm (3% inch) head, 89mm (3% inch) coupler, 25mm (one inch) adapter and two 90° angle adapters which may be placed at various junctions along the tube. It gives a 10,OOO:l & 10% divsion ratio when used with Model 610C and held 6mm (‘/ inch) away from a charged plane of at least 13mm (% inch) diameter. Output is a UHF male plug.

I.E.8 Model 8011 Input Cable The Model 6011 is a low-noise triaxial cable, 30 inches long,

terminated by three color-coded alligator clips. This cable mates directly with the triaxial input. The cable is fabricated using a Keithley connector (P/N CS-141) and low-noise cable (P/N SC-22).

The Model 6011 may be used for measurements which require a triaxial connection, especially when the input LO is floated above CASE ground.

I.E.7 Model 6012 Triax-to-Coax Adapter The Model 6012 is an adapter for mating the triaxial input and

UHF (coax) type connectors. Permits using Models 220,602, 614, 616 and 619 with all Keithley electromete accessories having UHF type connectors.

l-2

2.1 INTRODUCTION

SECTION 2

OPERATION

connected to case ground, only if the shorting link on the rear panel is connected.

A layout of the Model 602 front panel controls is contained in

Figure 2-1, while Figure 2-2 contains a layout of the rear panel terminals. See the following paragraphs for Model 602 front panel controls and rear panel terminals.

2.2 FRONT PANEL CONTROLS

Range Switch-Selects the mode to be measured: voltage, current, resistance or charge.

Multiplier Switch-Determines full scale voltage sensitivity and can be used to multiply current, resistance and charge ranges on the range switch.

METER Switch-Checks battery condition, turns instrument off, disconnects meter, selects meter polarity, sets instrument for center zero operation.

ZERO Control-Allows precise meter zeroing. ZERO CHECK Switch-Zeroes meter on any range.

FEEDBACK Switch-Determines the feedback connections within the instrument.

INPUT Connector-Connects input to source. Connector is a Teflon” insulated triaxial connector.

LO Terminal-Provides connection to input low.

2.3 REAR PANEL TERMINALS COARSE ZERO Switch-Extends the zeroing capability of

the front panel ZERO controls. lMA/IV Switch-Selects the Model 602 output: 1mA or

1V. Must be in 1V position if the output is connected to a load of more than 2kQ.

IMA CAL Control-Varies the output from 0.95 to 1.05mA.

OUTPUT Connector-Connects output to monitoring

device.

Xl OUTPUT and OHMS-GUARD Terminals-For guard-

ed measurements and for use as an extremely linear

preamplifier.

LO Terminal-Provides an alternate connection to input

low.

CASE GND Terminals-Connects to Model 602 cabinet and outside shell of input connector.

2.4 INPUT CONNECTIONS The Model 602 INPUT connector is a TeflonO insulated

triaxial connector. The center terminal is a high impedance terminal, the inner shield is a low impedance terminal and the outer shield is case ground (See Figure 2-3). The LO terminal, below the connector, is connected to the inner shield. It is

The Model 6011 Input Cable is supplied with the instrument, Table 2-1 indicates the color coding of the alligator clips. The high impedance terminal is shielded by the inner braid of the triaxial cable up to the miniature alligator clip. If the unshielded clip causes pick-up from nearby electric fields, remove the clip, and connect the shielded lead directly to the source.

Table 2-l. Color Coding of Alligator Clips For Modal

8011 Input Cable

Lead Heavy wire with

red clip cover.

Thin wire with black clip cover.

Thin wire with green clip cover.

When working with a high impedance source carefully shield the input connection and the source since any variation in the electrostatic field near the input will cause definite meter disturbances.

Use high resistance, low loss material (such as, Teflon@ , polyethylene of polystyrene) for insulation. The insulation

leakage resistance of test fixtures and leads should be several orders of magnitude higher than the internal resistance of the source. Excessive leakage reduces the accuracy of reading

from high impedance sources. The triaxial or coaxial cables

used should be a low noise type which employs a graphite or

other conductive coating between the dielectric and the sur-

rounding shield braid. The Model 6011 input cable ensures

good input connections. When working with a high impedance source, any change in

the shunt capacitance of the input circuit will cause disturbances in the reading. Make the measuring setup as rigid as possible, tie down connecting cables to prevent vibrations.

A continuous vibration may appear at the output as a

sinusoidal signal, and other precautions may be necessary to

isolate the instrument and connecting cable from the vibra-

tions.

Clean, dry connections and cables are very important to maintain the value of all insulation materials. Even the best insulation will be com-

promised by dust, dirt, solder flux, films, oil or water vapor. A good cleaning agent is methyl alcohol, which dissolves most common dirt without chemically attacking the insulation. Air dry the cables or connections after washing with alcohol or use dn/ nitrogen or Freon.

Circuit

Input High Center

Input Low

Case Outer Shield

NOTE

JIOI Terminal

Inner

2-1

2-2

Figure 2-l. Model 602 Front Panel Controls

Figure 2.2. Model 602 Rear Panel Terminals

2-3

batteries checked by position. If the reading for any battery other than 8203 is below two-thirds, replace all batteries except for 8203. If the reading for B203 is less than two-thirds

full scale, replace it. Note, that, new batteries may cause the

Model 602 to drift more than normal for at least 72 hours due

to change in battery terminal voltage.

Set the controls as follows:

ZERO CHECK Button LOCK

Range Switch VOLTS Multiplier Switch FEEDBACK Switch METER Switch

NORMAL POWER OFF

Figure 2-3. Triaxial Input

For low impedance measurements (below 1080 or above lO*RA) unshielded leads may be used. When the Model 602

is used on the most sensitive current ranae with the FEED-

BACK switch at FAST, some insulators kuch as Teflon” ) may produce random signals which show up as erratic meter deflections. Insulation used in the Model 602 is carefully selected to minimize these spurious signals.

If a well shielded chamber and a well made high impedance transfer switch is available, it is advantageous to connect the Model 602 to the circuit only when a reading is being made. In some cases, the offset current can charge the external test circuitry. One example of this occurs when measuring a capacitor’s leakage resistance by observing the decay of ;he terminal voltage. If the leakage current is less than the offset current (less than 5 X 10.‘5A there may be no decay of the terminal voltage when the Model 602 is left connected across the capacitor’s terminals.

NOTE

Keep the shield cap on the INPUT connector

when the Model 602 is not in use.

The Model 6012 Triaxial-to-Coaxial Adapter permits use of cables and accessories with the Model 602 by adapting the triaxial INPUT connector to the UHF coaxial type.

CAUTION

The Model 6012 connects low to case

ground. The Modal 602 cannot be used offground when using the Model 6012. The instrument’s cabinet will be at the same

potential as the input low.

2.5 PRELIMINARY PROCEDURES Check battery condition by holding the METER switch in the

BATTERY CHECK position. Rotate the multiplier switch through the ,001 to 0.1 positions and observe the meter readings. The meter should read at least two-thirds of full scale in each multiplier switch position. Table 2-2 shows the

Table 2-2. Multiplier Switch Positions for Checking

Conditions of Batteries

Multiplier Position

,001

1 tc

1. Turn the METER switch

I CENTER ZERO. Within ten seconds, the mater needle should con?,.? ‘to the center position. If not, adjust the mater zero with the MEDIUM and FINE ZERO controls. Normally, there is no need to use the COARSEZERO

‘.

NOTE

Using the center zero scales decreases accuracy

0.5% because the scale span is reduced.

2. After a few moments increase the voltage sensitivity by advancing the multiplier switch. Continue zeroing with the

FINE ZERO control.

3. After long periods of storage or after an overload, the Model 602 may drift excessively. The input transistors are

insensitive to mechanical shock; however, a severe input overload may cause a zero offset. This is corrected with the ZERO controls. Drifting can occur for several hours.

NOTE

If the Model 602 has been stored for some time, the offset current will exceed the specification when first used, then decrease to below the specified amount after one or two hours of use. This is an inherent characteristic of the input transistors; the instrument is not faulty.

4. Although the offset current of the Model 602 is below that found in conventional voltmeters, it can be observed on the meter. The current charges the input capacitance, and the Model 602 appears to drift when the input is open. Use the ZERO CHECK button to discharge the charge build-up.

Depressing the ZERO CHECK button removes all signal

from the amplifier and reduces the input impedance

between HI and LO terminals of the INPUT connector to 10MR.

2-l

5. Follow the procedures in paragraphs 2.6 to 2.10 for measuring voltage, current, resistance and charge.

NOTE When using multiplier switch settings of 10, 3 and 1 in the voltage, current, resistance and charge measuring modes, make sure the OUT-

PUT switch is set to 1V if the output is connected to a load of more than 2kR. Otherwise, the meter will not read full scale signals correct-

ly. When the output is loaded, this effect is not

present.

2.6 VOLTAGE MEASUREMENTS

Set the controls as follows:

ZERO CHECK Button LOCK

Range Switch VOLTS Multiplier Switch

10 FEEDBACK Switch FAST METER Switch CENTER ZERO

Connect the unknown voltage to the high (center) terminal of

the INPUT connector and to the OHMS GUARD terminal on the rear panel. Use the LO terminal as a guard between circuit

high and low. Unlock the ZERO CHECK button. Set the METER switch to + or -, as necessary. Recheck zero setting after increasing sensitivity. To make off-ground voltage measurements, see paragraph 2.7.

The Model 602 can be used to measure voltages. In the normal method (FEEDBACK switch at NORMAL) the unknown voltage is connected to the INPUT connector. Input impedance with the range switch in the VOLTS position is 10%. 2OpF.

To reduce the effects of input cable capacity, use the fast

method to measure the voltage. Set the FEEDBACK switch

at FAST and drive the inner shield of the cable with the Xl

OUTPUT which is connected to the LO terminal in the FAST position, A guarded circuit is possible this way. To reduce stray pick-up when making routine measurements fix. measuring from low impedance sources1 the range resistors or capacitors may be used to shunt the input. Accessory probes extend the Model 602’s range to 1OkV.

NOTE

Locking the ZERO CHECK switch places 1OMB between input high and low, which may temporarily cause instability in e.ome types of high impedance sources.

2.6.1 Normal Method Voltage Measurements Set the controls as follows:

ZERO CHECK Button LOCK Range Switch VOLTS

Multiplier Switch 10 FEEDBACK Switch NORMAL METER Switch CENTER ZERO

Connect the unknown voltage to the high (center) terminal of the INPUT connector and to the OHMS GUARD terminal on the rear panel. Use the LO terminal as a guard between circuit high and low. Unlock the ZERO CHECK button. Set the mater switch to + or -, as necessary. Increase sensitivity with the multiplier switch. Recheck zero setting after increasing sensitivity. To make off-ground voltage measurements, see paragraph 2.7.

2.6.3 Low Impedance Sources To decrease input resistance, set the FEEDBACK switch to

NORMAL and the range switch to one of the AMPERES ranges. The input resistance is now the reciprocal of the current range. For instance, to obtain an input resistance of

lo%, set the range switch to the 10.rA range Set the full scale voltage range with the multiplier switch. Operating procedures are the same as paragraph 2.6.1. With reduced input resistance, the Model 602 will not be deflected off scale by stray fields when the input is left open.

2.7 OFF-GROUND VOLTAGE MEASUREMENTS The Model 602 can measure an unknown voltage whose low

impedance terminal is up to 1500V off-ground. Safe opera-

tion of the Model 602 is ensured by grounding the case (see

paragraph 2.6).

CAUTION Operating the Model 602 more than 16OOV off-ground may permanently damage the instrument. Isolation between circuit low and ground may break down somewhere in the instrument. Since these breakdowns are very difficult to locate, it might not be

possible to float the instrument safely

again.

2.7.1 FEEDBACK Switch Set To NORMAL Disconnect the shorting link between LO and CASE

GROUND terminals on the rear panel. Make sure the Model

602 case is securely connected to an earth ground, and that the low of the unknown voltage is less than 1500V off-

ground. Connect the unknown voltage directly to the INPUT connector. Operate the Model 602 as described for normal method voltage measurements.

2.6.2 Guard Method Voltage Measurement This method reduces the effects of input cable capacity with

very high impedance source.s and allows guarded voltage measurements.

2.7.2 FEEDBACK Switch Set To FAST

Disconnect the shorting link between the LO and CASE GROUND terminals on the rear panel. Make sure the Model 602 case is securely connected to an earth ground, and that

2-5

the low of the unknown voltage is less than 1500V offground. Connect the high of the unknown voltage to the

center terminal of the INPUT connector. Connect the low to

the OHMS GUARD terminal. Use the LO terminal or inner

shield of the INPUT connector as a guard. Operate the Model

602 as described for fast method voltage measurements.

WARNING If the output is used for recording when the Model 602 is off-ground in the normal or fast mode, make sure the shell of a mating plug to the OUTPUT connector is not connected to either pin in the connector. Also. the recorder output will be off-ground.

WARNING Use only an insulated blade screwdriver to adjust the COARSE ZERO switch and 1 MA CAL control when floating the Model 602. An ordinary screwdriver could short the circuit low to case ground, creating a shock hazard and damaging the external circuitry.

2.8 CURRENT MEASUREMENTS The Model 602 can measure current three ways.

1. In the normal method luseable on any range) the current is determined by measuring the voltage drop across a resistor

shunting the amplifier input. This method is useful when low noise is more important than fast response speed or if some damping is needed.

2. In the fast method (for use only below the lC-‘5A range) the shunt resistor is between the amplifier output and input in the feedback loop. This circuit largely neutralizes the effect of input capacity and greatly increases the response speed. Also, the input voltage drop is reduced to a maximum of 1mV on any range.

3. For galvanometric current measurements, the Model 602 acts as a null indicator between a known current and the

unknown current source.

Rise time varies primarily with the current range, the input capacity and the method used. Wifh the FEEDBACK switch in the FAST position, the rise time on the most sensitive range is less than 2sec and on the l@‘A range, less than 3msec. Given a choice, it is better to place the Model 602 nearer to the current source than fo the data reading instrument. Transmining the input signal through long cables slightly decreases the response speed and greatly increases noise due to cable capacitance.

To measure from a source with both terminals off-ground in either method, remove the link between the LO and CASE

GROUND terminals on the rear panel. Connect the unknown current fo the INPUT connector. The source must be less than & 15OOV off-ground (see paragraph 2.7 and Figure 2-4).

Is = Es/R*

ERROR = 1%. 1.

?&ERROR = E,,/E, Y Km IF E,N< <Es. THEN IM = Is.

NOTE: CURRENT SDURCES MAY SE CONSIDERED A VOLTAGE ,E, IN SERIES WITH A RESISTANCE ii?). THE CURRENT WlTH THE AMMETER SHORT CIRCUITED IS

I=E/R. WITH THE SHORT REMOVED, THE EFFECTIVE

INPUT RESISTANCE OF THE AMMETER WITH THE SOURCE RESfSTANCE (RI.

Lz-

IR,,l IS IN SERIES

Figure 2-4. Error Due to Ammeter Resistance

2.8.1 Normal Mode (0.3 to 10’4A Ranges1 Set the controls as follows:

ZERO CHECK Button LOCK

Range Switch lo-’ AMPERE Multiplier Switch

1 FEEDBACK Switch NORMAL METER Switch CENTER ZERO

Connect the unknown current to the high terminal (center

terminal) of the INPUT connector and use the low terminal

(inner shield) for the return path. Unlock the ZERO CHECK button. Set the METER switch to + or -, as necessary. Increase the sensitivity with the range switch and the multiplier switch. Do not set the multiplier switch higher than 3 for range switch settings 103 and above. Check zero with the

ZERO CHECK button.

The full scale current range is mulriplier switch setting times range switch setting. Use the smallest multiplier switch setting possible to minimize input voltage drop and thus obtain the best accuracy. The input resistor varies with the range switch setting, from 100, to l@‘A to 101% for 1011A. The full scale input voltage drop is equal to the multiplier switch setting.

2.8.2 Fast Method (Current Below 10’6A) Set the controls as follows:

ZERO CHECK Button LOCK

Range Switch 106 AMPERES Multiplier Switch 1 FEEDBACK Switch FAST METER Switch

CENTER ZERO

Connect the unknown source to the INPUT connector and lock the ZERO CHECK button. Set the METER switch to t or -, as necessary. Increase the sensitivity with the range

switch and the multiplier switch. Check zero only with the ZERO CHECK button. Do not short the input, because this will remove the feedback from the circuit.

2-6

The full scale current range is the multiplier switch setting times the range switch sening. When selecting the multiplier switch setting, remember smaller settings permit lower source resistances, and larger senings improve instrument zero stability.

With the fast method, the input drop is reduced and the

response speed is increased at least 100 times. However, the

following safety precautions should be observed.

1. The internal impedance of the unknown current source should not be less than 0.1 of the value of the feedback

resistor being used. Otherwise, adequate feedback voltage cannot be developed at the input and zero instability results. The feedback resistor value is the reciprocal of the AMPERES range of the range switch.

2. The low side (pin No. 2) of the OUTPUT connector is no longer connected to the low side of the INPUT connector. Therefore, do not use a grounded recorder. As an alternative use the unity-gain output. (See paragraph 2.12).

3. Use, with caution, the fast method to measure capacitor leakage. A very stable voltage supply must be used. Connecting a capacitor to the input changes the circuit to a differentiator, resulting in extreme sensitivity to very small voltage transients and an increase in meter noise.

2.8.3 Galvanometric Method

Operate the Model 802 as a picoammeter in the fast method.

Use an accurate reference current source such as the Keithley Model 261 to buck out the unknown current source. Connect as shown in Figure 2-5.

Set the METER switch to CENTER ZERO and use the higher

current ranges. Adjust the buck out current to indicate null on the Model 602. Increase the Model 602 sensitivity as needed. When the Model 602 is as close to null as possible, the

unknown current is equal to the algebraic sum of the Model 261 sening and the Model 602 current reading.

NULL

DETECTOR

2.9 RESISTANCE MEASUREMENTS The Model 802 can measure resistance by two methods.

In the constant current method, the Model 602 measures the voltage drop across the unknown sample as a known, constant current flows through it. The voltage drop is proportional to the resistance of the sample. In this method the Model 602 can be used in one of two different modes:

normal or fast. The normal mode is recommended for use from 100 to 101’0. Above 101%, the fast method is preferred. It results in faster response speed and also nullifies

leakage across the Model 602 input, since the potential across the input terminal is small.

In the preceding method, the voltage across the sample

cannot be arbitrarily set. In some cases, as in measuring

capacitor leakage, this results in excessively long testing time. In the voltmeter ammeter method, the Model 602 is

used as a picoammeter. The unknown resistance sample is

connected to an external known voltage source and the

current through the sample is measured. Either the normal

or fast method may be used. The resistance is calculated from the reading.

NOTE Discharge any capacitor completely before removina it from the circuit. Depressing the ZERO CHECK bunon shorts the input through a 1OMQ resistor, providing a discharge path.

2.9.1 Normal Constant Currant Method Set the controls as follows:

ZERO CHECK Button LOCK

Range Switch 10’2 OHMS Multiplier Switch FEEDBACK Switch NORMAL METER Switch

Connect the high impedance side of the resistance sample to the high terminal (center terminal) of the INPUT connector and the low impedance side to the low terminal (inner shield) of the INPUT connector. Unlock the ZERO CHECK button. Check zero only with the ZERO CHECK button.

I--- - -----w

CURRENT

NOTE: “SE AN ACCURATE REFERENCE CURRENT SOURCE TO SUCK OUT THE UNKNOWN CURRENT SOURCE. THE MODEL 602. ON ITS CVRRENT RANGES, SERVES AS A NULL DETECTOR. USE A UHF-TEE FITTING AND MODEL 6012 ADAPTER AT THE MODEL 602 INPUT. CONNECT THE MODEL 60.2 TO THE TWO SOURCES WITH COAXIAL CABLE. SELECT CABLE CAREFULLY FOR VERY LOW CURRENTS.

Figure 2-5. Measuring Current by the Galvanometric

Method

CURRENT

SOURCE

NOTE Do not open circuit Model 602 on the OHMS ranges; the input will increase up to 1OV due to its constant current characteristic. Keep the input shorted or the ZERO CHECK button locked.

The full scale ohms range is the multiplier switch times the

range switch sening. Use the smallest range switch setting possible to obtain the best accuracy.

Before making a final reading, manipulate the multiplier and range switches so the sample is tested at a number of teat potentials. The applied test voltage is the percentage of full scale that the meter reads times the multiplier switch setting.

2-7

When the test current is applied, the high terminal of the

INPUT connector is positive. The test current is the reciprocal

of the OHMS range setting.

NOTE

Shield the input if the resistance sample exceeds

10%.

2.9:2 Fast Constant Currant Method Follow the instructions of paragraph 2.5. Set the controls as

follows: ZERO CHECK Button LOCK

Range Switch 10” OHMS Multiplier Switch 1 FEEDBACK Switch FAST METER Switch

Connect the high impedance side of the resistance sample to

the center terminal of the INPUT connector and the low im-

pedance side to the OHMS GUARD terminal. Unlock the

ZERO CHECK button. Read the resistance.

NOTE

Shield the input if the resistance sample exceeds

10%

NOTE: A POTENTIAL FROM A KNOWN SOURCE, V. IS APPLIED TO THE KNOWN RESISTANCE SAMPLE, R,. THE MODEL SO2 MEASURES THE CURRENT THROUGH, A,, FROM WHICH THE RESISTANCE IS CALCULATED. SWITCH S CONNECTS THE LOW END OF R, TO INPUT LOW WHEN NO POTENTIAL IS APPLIED.

Figure 2-6. Measuring Resistance By The External

Voltage Method

To remove the sample, set the ZERO CHECK button to LOCK and set switch S back to the position shown in Figure 2-6.

The low terminal of the INPUT connector is now a driven guard. It may be used to minimize the effects of capacity between high and low and errors due to leakage resistance between high and low.

The Model 6011 Input Cable, supplied with the Model 602,

provides a convenient means of making guarded resistance measurements. Connect the shorting link between the CASE GROUND and OHMS GUARD terminals on the rear panel.

This allows the CASE GROUND or green test lead terminal to

be connected to the low impedance side of the unknown resistance. The inner shield or the black test clip is the OHMS GUARD terminal.

2.9.3 Voltmeter-Ammeter Method ITo 10%)

Turn the ZERO CHECK switch to LOCK. Connect sample

between high terminal of the INPUT connector and power supply (See Figure 2-6). Put a switch in the high voltage line to connect the low impedance end of sample to input low when it is disconnected from the potential.

If the power supply must be floating, remove the link between the CASE GROUND and LO terminals and connect the CASE GROUND terminal to an earth ground.

Set the FEEDBACK switch to NORMAL. Usually this method

is best, since instabilities can arise for resistance samples less than 0.1 the value of the feedback resistor.

To make a measurement, start with switch S as shown in

Figure 2-6 and make sure the ZERO CHECK button is set to

LOCK. Set switch S to apply a potential across the sample for a known period of time. Then unlock the ZERO CHECK button and take the reading. Set the range switch to l&trA and increase sensitivity until a reading is obtained.

If the potential applied is at least 100 times the full scale input drop (multiplier switch setting), the resistance is equal to the applied potential divided by the current reading. The high voltage sensitivity of the Model 602, therefore, permits external voltages of O.lV or more to be used.

If the potential applied is less than 100 times the input drop, the resistance is equal to the difference between the applied

potential and the input drop all divided by the current reading.

If the current is read by the fast method, the input drop is so slight that it need not be included in the calculation. If the

capacity shunted across the sample is large, such as en-

countered in capacitor leakage measurements, the faster

method increases response speed and this connection is

recommended. Note, however, that power supply transients will be magnified.

2.10 CHARGE MEASUREMENTS

Follow the instructions of paragraph 2.5. Set the controls as

follows:

ZERO CHECK Button LOCK

Ranae Switch 10’ COULOMBS Multiplier Switch .Ol FEEDBACK Switch FAST METER Switch CENTER ZERO

Unlock the ZERO CHECK button and then connect the unknown source to the INPUT connector. If the Model 60.2

reads off scale, increase the multiplier switch setting. If the sensitivity is not enough, decrease the multiplier switch sening until the reading is on scale. Changing the multiplier switch setting does not affect the transfer of charge from the

unknown source to the instrument. If increasing sensitivity with the multiplier switch does not bring the reading on scale,

2-8

increase sensitivity with the range switch and repeat the preceding steps.

The full scale charge range is the range switch setting times the multiplier switch sening. Input offset contributes a charge

of 5 X lo-‘SC per second maximum. Use the ZERO CHECK button to discharge the integrating

capacitor. Discharge for at least 20sec on the 1OrC range

before making another measurement. On the 10-8C range,

discharge for at least two seconds.

2.11 RECORDER OUTPUTS Recorders, oscilloscopes and similar instruments can be used

with the Model 602. The Model 602 has two outputs, k 1V and * lmA, to amplify signals within % % for recorders, oscilloscopes and similar instruments. These can be used on all ranges of the Model 602.

WARNING

The Model 602 may be used with the FEED-

BACK switch in FAST position with other instruments. However, make sure there is no common ground connection between low terminals of the Model 602 and the other instrument.

1V Output-Connect osciiloscopes and pen recorder amplifiers to the OUTPUT connector. Pin 1 is the output ter-

minal and pin 2 is grounded when the FEEDBACK switch is sat to NORMAL. Set the OUTPUT switch to 1V. The Model 602 output is now + 1V for full scale meter deflection on any

range, Internal resistance is 910R. The frequency response (+3db) is DC to 1OOHz at a gain of 1000, rising to 4OHz at gains of 1 .O and below. Noise is less than 3% rms of full scale

at a gain of 1000, decreasing to less than 0.5% at gains of 10. The METER switch does not reverse the output polarity. Out-

put polarity is opposite input signal polarity.

For servo rebalance recorders, use a divider of not greater

than a total of 2kO across the Model 602 OUTPUT connector

ISee Figure 2-71. Set the OUTPUT switch to 1 MA. Use the 1 MA CAL control to trim the output for full scale recorder

deflection. Operation is the same as for current outputs.

J103

OUTPUT 1

NOTE: USE 5% RESISTORS IN THE DIVIDERS. THE VALVE OF RESISTOR R IS 10 FOR EVERY Im” OF OUTPUT.

Figure 2-7. Divider Circuits Across Model 602 Output

for Driving 50 and 1OOmV Recorders

When the FEEDBACK switch is in the NORMAL position, the

negative side of the output terminal is connected to the LO terminal. Therefore, no difficulty will be experienced using oscilloscopes and recorders with the Model 602 set for normal operation. In FAST position, however, neither output

terminal is common to the LO terminal. If this is used, make

sure there is no common connection between the recorder or oscilloscope and the Model 602 LO terminal, or use the unity gain output (See Figure 2-B).

WARNING Neither terminal of the OUTPUT conneotor will be at case ground potential if the Modal 602 is used off-ground. Make sure the shall of any mating plug is not connected to either terminal in the connector. Use a recorder with an isolated input when making off-ground measurements.

1mA Output-Connect 1mA instruments to the OUTPUT

connector pin 1 is the negative terminal (for positive inputs).

Set the OUTPUT switch to 1 MA. The output is approximately 1 milliampere for full scale meter deflection on any range.

For exact output, adjust the meter on the .003V range with the FINE ZERO control for full scale deflection., Then adjust the 1 MA CAL control until the recorder reads full scale.

Check the recorder and meter zero and repeat adjustment if

necessary. The METER switch does not reverse the output

polarity. Use only insulated screwdriver to adjust the 1 MA CAL control.

NOTE:

THE MODEL SO2 IS USED BETWEEN A HlGH

RESlSTANCE SOURCE, Vx, AND A 0.01% VOLTMETER TO OSTAlN HlGH ACCURACY WITHOUT CAUSING CIRCUIT

LOADING. THE DMM CONNECTS UNIN-GAIN TERMINALS.

THE

MODEL 602

Figure 2-8. Measuring Potential of High Resistance

Source with 0.025% Accuracy

2.12 UNITY-GAIN OUTPUT The unity-gain amplifier can be used as an impedance

matching device to minimize circuit loading errors or for convenient connections to a recorder when the FEEDBACK switch is in FAST position.

The unity-gain output is equal to the input within 1Oppm when the load resistance is 1OOkO or greater. By placing the

Model 602 between a lOrOn source, for example, and a

2-9

0.01% voltmeter with 1MQ input resistance, overall accuracy better than 0.025% can be achieved.

1. Connect the voltmeter to the Xl OUTPUT and GUARD

terminals as shown in Figure 2-8. The GUARD terminal is connected to LO terminal with the FEEDBACK switch in NORMAL. Maximum output amplitude is f 1OV.

2. Adjust the Model 602 zero controls to obtain a zero voltage reading on the external voltmeter. Make sure the latter’s sensitivity is high enough for a precise zero ad-

justment. This adjustment is necessary because a slight

zero shift may cxxur when the Model 602 is changed from the O.lV range or lower to a range above O.lV. The shift,

caused by a gain-reducing network switched in by the amplifier on the 1V and higher ranges, is too slight to be read on the meter, but it can cause an error in accurate measurments using the unity-gain output.

3. To avoid the shift use the Model 602 with the multiplier switch set to 10.

When the FEEDBACK switch is in FAST position, the unitygain terminals permit more convenient connections to oscilloscopes with a load resistance of greater than 1OOkQ without special precautions. In this mode, the Xl OUTPUT terminal is common to the input low and the OHMS GUARD terminal delivers an output equal to the input signal.

2-10

SECTION 3

THEORY OF OPERATION

3.1 INTRODUCTION The Keithley Model 602 is an extremely stable and linear DC

voltmeter with a full scale sensitivity of 1mV and an input impedance of 1014R shunted by 2OpF. By using the front panel controls, shunt resistors and capacitors are selected to make

measurements over a total of 75 voltage, current resistance, and coulomb ranges. Current and resistance are measured using precision resistance standards, from 100 wirewound

resistors to 101’0 glass sealed, deposited carbon resistors. Coulombs are measured using close tolerance polystyrene film capacitor standards. Batteries furnish the necessary amplifier power.

3.2 VOLTMETER OPERATION The Model 602 uses matched insulated gate, field-effect tran-

sistors followed by a transistor differential amplifier with a

high voltage complementary output stage. Figure 3-l shows the block diagram for the voltmeter mode of operation. Voltmeter operation of the Model 602 is as follows.

1. The amplifier is always in a unity-gain, input voltage to output current converter configuration. The internal circuitry is arranged such that a full scale input voltage (e,l results in exactly a 1mA output current, through the divider string composed of R,, R167 and the meter. Voltage gain of the circuit is determned by the ratio of R167 to R,. Output is taken across R167.

2. The voltage drop across the amplifier is: ei

e =K+1

where K is the amplifier loop gain, greater than 10s on all ranges.

The complementary output stage, Q114 and Q115, drives the amplifier ground at the same potential as the input signal. Thus the impedance is maintained for any value input voltage and the need for input dividers is eliminated. The amplifier ground is not chassis ground, but is connected directly to J105, the unity-gain output.

NOTE

Refer to schematic diagram 21174E for circuit

designations.

3.3 VOLTMETER CIRCUIT

1. The amplifier input stage is a pair of insulated gate, fieldeffect transistors, 0101 and Q102, in a differential configuration. The gate of Q102 is returned to amplifier common, the unity-gain output.

NOTE:

CIRCUIT DESIGNATIONS AEFER TO SCHEMATlC DIAGRAM. S106 IS THE MULTIPLIER SWITCH, R, IS THE RESISTOR FOR A GIVEN SElTING. R, IS THE RESlSTOR

SELECTED BY THE RANGE SWITCH, S102. SIOS IS THE FEEDBACK SWITCH.

Figure 3-1. Block Diagram of Model 602 in Voltmeter

Mode.

2. Depressing the ZERO CHECK button, S103, places the gate of the active insulated gate devices at zero potential.

3. The input stage is followed by a transistor differential amplifier, composed of 0103X11 10. Q108 and Q109 makeup the output gain stage, which is utilized in a gain multiplier configuration. This stage provides the remainder of the high gain required by the amplifier. Also, this stage prevents fold-over and lock-up with positive input overloads. Diode DlOl, between base and emitter of QllO. prevents fold-over and lock-up under negative input overloads.

4. Frequency compensation is provided by capacitors Cl 14, C115, resistors R145, R148 and capacitor C116. The com-

pensation networks provide a controlled frequency characteristic to ensure stability under all conditions of capacitive loading on input and output while on any range.

5. The recorder output is derived from the current flow from Q114 and (1115 through the divider, R,, R167 and the meter. With the lV-1MA switch, S108 on 1V f 1V for full

scale deflection is obtained at output connector, J103, by

f l.lmA flowing through the divider. With S108 at 1MA. R187 and R188 are connected across J103, allowing * 1mA f 556, to pass through an external load.

3.4 AMMETER OPERATION

3.4.1 Normal Method In the normal method of current measurements (FEEDBACK

switch in NORMAL position), one of the range switch

resistors, R102 through R112, shunts the input (See Figure

3-2). The Model 602 then measures the voltage drop across the resistor. The meter is calibrated to read the current in amperes for the appropriate range.

3-l

L r

NOTE: CIRCUIT DESIGNATIONS REFER TO SCHEMATIC DIAGRAM. S106 IS THE MULTIPLIER SWITCH; R, IS THE RESISTOR FOR A GIVEN SETTING. R, IS THE UNKNOWN RESISTANCE BEING MEASURED; E IS THE VOLTAGE SOURCE; R, IS THE RANGE RESISTOR SELECTED WlTH

THE RANGE SWITCH.

Figure 3-2. Block Diagram of Model 602 as a Picoam-

meter.

3.4.2 Fast Method In the fast method of current measurements (FEEDBACK

switch in FAST position), the Model 602 functions as an ammeter with negative feedback. The differential amplifier output is divided by the multiplier switch resistors, R156 to

R164. and fed back to the amplifier input through a feedback

resistor selected with the range switch (See Figure 3-2).

Floating ground is connected to the low impedance side of

the input, and the output ground is floating. This method increases the response speed by minimizing the effects of input capacity; it also rsduces the input drop to less than 1mV.

3.5 OHMMETER OPERATION

3.5.1 Normal Method

In the normal method of resistance measurements BACK switch in NORMAL position) the Model 602 uses a constant-current, voltage drop circuit. Refer to Figure 3-3. Rx is the unknown resistor. A voltage source, E, applies a po-

tential across Rx. The source is obtained from the batteries,

8201 and 8202, through the resistor divider network, R184, R142 and R143. E varies depending upon the OHMS range

used. The voltage source is connected between floating ground and the input gate of QlOl through R,, the range

resistor. R equal to E voltage drop across Rx does not exceed the multiplier switch

is one of the resistors, R102 through R112. I is

R,, regardless of the value of Rx, as long es the

(FEED-

setting. This circuit provides a true source regardless of the

input. The Model 602 can then measure the voltage drop

acmss Rx and indicate the resistance value on its calibrated

meter.

35.2 Guarded Method In the guarded method of resistance measurements (FEED-

BACK switch in FAST position and the sample resistance

connected between the INPUT terminal, J108, and the

GUARD terminal, J107) feedback is applied through the

sample. Refer to Figure 3-2. The circuit is similar to the nor-

mal method, except for the feedback. This reduces slowing

effect of the instrument’s input capacity. Leakage error is also reduced since the potential acmss the input terminal is small. In this mode, floating ground is connected to the low impedance side of the input and the output ground is floating.

The GUARD terminal is at output ground potential.

NOTE: CIRCUIT DESIGNATIONS REFER TO SCHEMATIC DIAGRAM. SlO6 IS THE MULTIPLIER SWITCH; RM IS THE RESISTOR FOR A GIVEN SETTING. R, IS THE UNKNOWN RESISTANCE BEING MEASURED; E IS THE VOLTAGE SOURCE: Rs IS THE RANGE RESISTOR SELECTED WITH THE RANGE SWITCH.

Figure 3-3. Block Diagram of Modal 602 for Normal

Method Measuring Resistance

3.6 COULOMBMETER OPERATION The Model 602 circuit for measuring charge is similar to that

used for an ammeter with the fast method. A negative feedback is applied around a shunt capacitor, Cl08 to Clll, selected with the range switch. The shunt capacitor replaces

R, in Figure 3-2. The stored charge is proportional to the voltage acmss the capacitor, which is measured by the Model 602 voltmeter circuits,

3-2

SECTION 4

SERVICING INFORMATION

4.1 INTRODUCTION This section contains information necessary to maintain,

calibrate and troubleshoot the Model 602 Electrometer.

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 individual to potentially lethal voltages that could result in personal injury or death if

normal safety precautions are not ob-

served.

4.2 CALIBRATION

The calibration information provided is a method of checking the Model 602 to make sure it operates properly and within specification. See the specifications that precede Section 1.

4.2.1 Recommended Equipment Recommeded calibration equipment is listed in Table 4-l.

Alternate test equipment may be used as long as equipment accuracy is et least as good as the specifications listed in Table 4-1.

NOTE Unless otherwise stated, all the following calibration procedures will be made with the

FEEDBACK switch set to NORMAL and the IV-1MA switch set to 1V.

4.2.2 Calibration Schedule

1. Check offset current (paragraph 4.7) at regular intervals to make sure the input transistors are functioning correctly.

2. Verify the value of the high megohm resistors (paragraph

4.9) approximately every six months.

3. Calibrate the meter zero (paragraph 4.4) about once a year or when components are replaced.

4. Check the Model 602 accuracy (paragraph 4.10) once a year, after adjustment, suspected.

4.3 PRELIMINARY PROCEDURES Battery Check-Check the condition of the batteries as

outlined in paragraph 2.5 and Table 2-2. Zero Balance-Set the Model 602 to the 1OV range and turn the instrument on. Set the ZERO CHECK button to lock.

1. If the unit is operative, the meter should be on scale + or -.

Zero the meter with the COARSE, MEDIUM, and FINE controls. Increase the voltage sensitivity in steps to the

1mV range by advancing the multiplier switch. Zero the

instrument on each range.

2. If the instrument is inoperative (meter pinned, etc.) check error in setup end obvious problems before troubleshooting.

Isolation Check-Set up the test circuit in Figure 4-1.

Disconnect the shorting link from CASE to LO. Set the Model 480 to the 1OnA range and zero check. Program the Model 230 to output 1OOV. Take the Model 480 out of zero check.

The Reading on the Model 480 should be less than WA

IlOnA). Usina Ohms law calculate the isolation resistance.

For example:-R = E/I = lOOV/lO-aA= 1O”‘D.

or if improper operation is

Table 4-l. Recommended Test Equipment

Item Description

B Voltage Source 1oov Keithley C Picoammeter 0 RMS Voltmeter

E Chart Recorder

F Null Detector 1OOpV Null Resolution Keithley G Current Source H 10-W Resistor 1O”D +2% Keithley

I Signal Generator J AC Voltmeter K 1OW Resistor low +2%

M 1WD Resistor l@D *2% Keithley

DMM

109R Resistor low *29/o Keithley

Specification lpV-1ooov Keithley

10.9A sensitivity

lo-5A to 10.‘A f0.2%

Mfg.

Keithley H-P H-P 70358

Keithley H-P

H-P Keithley R-289-10”’

Model

195 230 480 3400A

165 220

R-289-10” 200CD 400F

R-289-109

R-289-108

4-l

MODEL so2

“EAR PANEL,

0 XIOUTPUT 0 OHMS OUARD

-0 CASE p LO

MODELaO

PlCOAMMETER

Figure 4-l. Model 602 Case To LO Isolation Check

4.4 MECHANICAL METER SET AND METER ZERO CALIBRATION

Zero the Model 802 whenever adjustments are made. To set

the mechanical zero meter, turn the METER switch to METER OFF and set the mechanical zero meter adjustment for zero meter reading (top-scale zero). Refer to Table 4-2 for Model 602 internal controls. To calibrate meter zero do the following:

1. Turn the Model 602 on. Zero the meter on the ,001 multiplier switch setting. Set the multiplier switch to 1; apply 1V -+0.06% with the Model 230 to the Model 280 INPUT connector. Monitor the output with the Model 195. Adjust the FINE ZERO control for l.OOOV at the output. Adjust the meter cal potentiometer, R177, for full scale meter reading.

2. Set the center zero by first zeroing the meter on the ,001 multiplier switch sening. The switch to the 1 position. Set the METER switch to CENTER ZERO and adjust the CENTER ZERO CAL potentiometer, R179, for exact center-scale meter zero.

Table 4-2. Model 602 Internal Controls

Circuit Refer to

Control Meter Calibration

Center Zero Calibration

Desig.

R177

Paragraph

4-2

R179 4-2

4.5 TRACKING CHECK AND 1MA OUTPUT

CALIBRATION

Tracking-Set the METER switch to +, the multiplier switch to 1 and apply 1V with the Model 230 to the INPUT connector.

1. If the 1V range has good accuracy, the meter should indicate full scale. If not, use the .l or 10 multiplier switch settings, whichever has the beet full scale accuracy.

2. Check the meter O-10 scale for no more than ‘A% (‘A division) tracking error going from zero to full scale in l/10 of full scale voltage steps.

1MA Output-Load output of the Model 602 with a 14OOQ resistor.

1. Set the lV-1MA switch to 1MA. the multiplier switch to 1 and apply 1V to INPUT connector with the Model 230.

2. Adjusting the 1MA CAL control (R187) should vary the output voltage from 1.33V to 1.47V. indicating a current

variation from 0.95 to 1.05mA.

3. Depending on the exact value of the 14003 load, the

voltage range may be slightly higher or lower then 1.33 to

1.47V (for example: 1.34 to 1.48V or 1.32 to 1/46V). This is at least 140mV and the maximum voltage is near 1.47V.

4. Remove the 14003 load end set the lV-1MA switch to 1V

when completed.

4.6 NOISE CHECK

1. Zero check the unit and connect the output to a Model 3400A rms voltmeter.

A. Set the METER switch to CENTER ZERO and zero the

Model 802 on the 1mV range.

B. The meter noise must be less than 5OwV peak-to-peak.

C The output noise must be less than 30+ rms.

2. Switch the Model 802 to the 300mV range. Output noise must be less than 6mV rms.

3. Typical rms output noise is approximately 20mV on the 1mV range and 1 to 2mV on the 300mV range.

4.7 OFFSET CURRENT CHECK Check offset current whenever excessive noise or drift is

suspected. To reed the offset current of the Model 602, set the front panel controls as follows:

ZERO CHECK Button LOCK

Multiplier Switch

.KG Range Switch 10” AMPERES FEEDBACK Switch FAST METER Switch +

Cap the INPUT connector and unlock the ZERO CHECK button. The offset current indicated on the meter should be less than 5 X lO’sA. (This is less than 20% of full scale). If

this is exceeded, check the battery condition and the input transistor QlOl. If the instrument has not been used for a

long time, allow it to run seven hours before checking the offset current.

4.6 DRIFT CHECK Set the front panel controls as follows:

ZERO Check Button LOCK

Multiplier Switch

.Ol Range Switch VOLTS FEEDBACK Switch NORMAL METER Switch

Set the OUTPUT switch on the back panel to 1V.

1. Connect Model 602 to the Model 70358 chart recorder.

Adjust recorder sensitivity control for full scale deflection

of + 1V. Make sure Model 602 chassis cover is attached

with at least two screws.

2. Make two drift runs with the Model 602 to determine time and temperature stability individually. For each run allow

the Model 602 to warm up for half hour. A zero drift of less than 2mV after the first half hour is indicative of a satis-

factory temperature coefficient. Atier the first half hour the time stability should be less than 1mV per 24 hours. The offset due to temperature should be less than 150rV per DC.

3. If the instrument does not meet the zero drift specification,

check the batteries. If the batteries are satisfacton/ and the instrument still does not meet the zero drift specification, the input transistors are faulty.

NOTE NOTE

If new batteries have been installed, the Model If new batteries have been installed, the Model

602 zero drift will be exceeded for at least 24 602 zero drift will be exceeded for at least 24

hours. Age the unit for 24 hours to enable the hours. Age the unit for 24 hours to enable the battery terminal voltages to stabilize. battery terminal voltages to stabilize.

4.9 HIGH-MEGOHM RESISTOR VERIFICATION

About every six months it is necessaw to check the value of the high-megohm resistors, RI10 to R112, on the range switch. The instrument should be within its rated accuracy for two or three years from the time it leaves the factory. After this, some of the resistors should be replaced. Faulty high-megohm resistors will the accuracy of measurements for the

may

drift out of tolerance and

l&9

to 10.“AMPERES

affect

and the 108 to lO’*Q settings of the range switch. To check these resistors, it is necessary

use a bridge capable of better than 1% accuracy up to lOlQ2. If such equipment is not available, either return the instrument to the factory for resistor calibration; or replace the high-megohm

resistors periodically with a certified set from Keithley Instruments to assure absolute calibration accuracy.

4.10 ACCURACY CHECK

Checking the accuracy of the Model 602 is the quickest way to spot faulty operation. Pet-form a check of the unit about once a year, if components are replaced or if other adjustments are made. If accuracy is verified over all ranges, the

Model 602 should be able to meet all specifications. If the accuracy must be checked often, check the stability.

4.10.1 Voltage Accuracy Check Connect the Model 602 input to the Model 230 and monitor

the output with the Model 195. First, set the Modal 602 for the 1OV range. Increase the input voltage in 1V steps from 0 to 1OV. The Model 602 should indicate the input voltage to

* 1% of full scale. Make sure the OUTPUT switch is in the

1V position for the 1,3 and 1OV ranges lsee note in paragraph

2.5 step 5).

4.102 Current Accuracy Check Connect the Model 602 to the Model 261 and monitor the

output with the Model 195. Check the full scale accuracy of all the current positions on the range switch. For the 10s to

l@“A ranges, set the FEEDBACK switch to FAST and the

multiplier switch to 1. Check the output for lVk2%. For the

ranges above 10-5A, use the Model 220. Set the Model 602 FEEDBACK switch to NORMAL and the multiplier switch to .Ol when calibrating these ranges. Check the output for

lVi2%.

NOTE

For 10.‘A through 10-5A ranges. a larger multiplier switch setting will result in inaccuracies due to loading of the current source; hence the .Ol multiplier switch setting must be used. The appropriate current source is two decades lew than range setting; that is, on the l@‘A ranges use lo-sA source.

4.10.3 Resistance Accuracy Check Zero check the Model 602 and connect the input to a

resistance source and the output to the Model 195. The cable between resistance source and the input must be as short as possible in order to obtain accurate readings. Set NORMAL/FAST switch to NORMAL.

1. Check the 1OQ range as follows: A. Set Model 602 aid resistance source to 105fi.

B. Zero Model 602 with multiplier set at ,001. C. Switch multiplier to 1. A zero shift will be seen. Do not

rezero.

D. Release ZERO CHECK and check for lV+ 3% at Model

602 output.

2. With multiplier at 1, do the following: A. Check 106 through 108Q ranges for 1V &3% at Model

602 output. Use an appropriate resistance source for

each range.

8. Check the 109 through lO”Q ranges for 1V *3% at

Model 602 output. Use appropriate resistance source (Items K, L and M Table 4-l) for each range.

NOTE

When working with high resistance (z 108X

always use a shielded enclosure for the resistors.

3. With multiplier set at .l, check 101Q range for lV* 5% at Model 602 output. Resistance source is 1OlQ.

4. If difficulty is experienced in obtaining accurate readings

4-3

on the 101’ and 10’s ranges, use the FAST position and connect the shielded enclosure that contains the resistors to the Model 602 GUARD. The cable between the resistors and the input must be short as possible; a solid triex to

BNC adapter is recommended (Keithley Model 6147).

5. If all or most ranges are at or out of tolerance on the high side, the probable cause is that 6203 battery voltage is too high. The battery terminal voltage should be 1.34V

f0.02V. Age battery for 15 minutes if needed.

Table 4-3. Coulomb Ranges Accuracy Check

Multiplier

Switch

Setting

.Ol

.l 10s

10 lo-‘0

Coulombs

Range

10-7

lo-9

Rise Time, Zero

to Full Scale

(seconds)

10 10

4.10.4 Charge Accuracy Check To check the Model 602 as a charge amplifier, set the FEED-

BACK switch to FAST. Apply 1OV from the Model 230 voltage supply through a 10llD resistor IR-20-10m to the Modal 602 input. Set the multiplier switch to the settings given in Table 43. Use a stop watch or an oscilloscope to time the rise to full scale deflection. Check each range to

f5%.

4.11 UNITY-GAIN CHECK

1. Zero check the Model 602 and set the instrument to the

1OV range. Set up the circuit shown in Figure 4-2.

2. Set the Model 155 to the 3OOAV range. Zero the Model 155 with the Model 602 fine zero control.

NOTE A transient of up to 1OmV may be generated when the Model 230 is oroarammed from standby to output. To prevent jalse indication, program the Model 230 to output and program the voltage as indicated.

3. With the Model 230 output at zero (output LED is on). Release the zero check on the Model 602. Notice the

Model 155 reading remains the same.

4. Program the Model 230 to output + 1OV. The Model 155 reading should not vary by more than 1OOpV.

6. Program the Model 230 to output zero volts. The Model 155 should return to the original reading in step 3 t *50@

zero offset).

6. Repeat steps 2 through 5 using -lOV.

4.12 FREQUENCY RESPONSE CHECK

1. Zero check the unit. Connect a HP Model 200CD signal

generator through a 1OOO:l divider to the Model 602 input

and connect the Model 602 output to a Model 400F AC VTVM. Set the Model 602 FEEDBACK switch to

NORMAL.

MODEL 802

ELECTROMETER

- CASE

CASE

MODEL 230

VOLTAGE

SOURCE

INPUT

t HI

HI LO

MODEL 155

pVOLTMETER

NULL

DETECTOR

Figure 4-2. Model 602 Unity-Gain Test Set-Up

NOTE If other than a constant amplitude signal generator is used, it will be necessary to monitor

the output of the signal generator with another VTVM in order to maintain the same signal level at various frequencies specified.

2. Zero the Model 602 on the 1mV range. A. Set the signal generator to 20Hz at minimum output.

Release the Model 602 ZERO CHECK button and increase the generator output to obtain 2V rms at the Model 602 output.

B. Set the generator to 100Hz. The Model 602 output

voltage must be within f3dB of the 20Hz 2V rms output.

3. Zero the Model 602 on the 1V range and change the divider to 1OO:l.

A. Set the generator to 1OOHz for minimum output.

Release the Model 602 ZERO CHECK button and increase the generator output to obtain O.lV rms at the Model 602 output.

B. Set the generator to 40kHz. The Model 602 output

must be within f3%dB of the 1OOHz O.lV mw output.

4. Zero the Model 602 on the 1V range and change the divider to l&l.

A. Set the generator to 1OOHz and for minimum output.

Release the ZERO CHECK button and increase the generator output to obtain 2V rms at the Model 602 output.

B. Set the generator to 3kHz. The Model 602 output must

be within f3dB of the 1OOHz 2V rms output.

4.13 COMMON MODE REJECTION CHECK Cap the INPUT connector and set the Model 602 front panel

controls as follows: ZERO CHECK Button LOCK

Multiplier Switch Range Switch FEEDBACK Switch

1 l@‘o AMPERES NORMAL

METER Switch OFF

1. Connect the Model 2OOCD generator between the Model 602 LO and CASE GND terminals and connect an oscilloscope to the Model 602 OUTPUT connector.

2. Apply a 35V peak-to-peak, 60Hz signal to the Model 602 input. The output should be less than 35mV peak-to-peak.

4.14 TROUBLESHOOTING

The procedures which follow give instructions for repairing troubles which might occur in the Model 602. Use the procedures outlined and use only specified replacement parts. Table 4-l lists equipment recommended for troubleshooting.

If the trouble cannot be readily located or repaired, contact a Keithley representative.

Table 4-4 lists the more common troubles which might occur.

If the repairs indicated in the table do not clear up the trouble, find the difficulty through a circuit by circuit check, such as given in paragraph 4.15. Refer to Section 3 to find the more critical components and to determine their function in the circuit.

4.14.1 Servicing Schedule

Periodically check the condition of the batteries ISee

paragraph 2.5 and Table 2-21. Except for batten, replacement, the Model 602 requires no periodic maintenance beyond the

normal care required of high quality electronic equipment. Then value of the high-megohm resistors, RllO, Rlll and

R112 should be checked every six months for specified accu-

,tXy.

4.14.2 Parts Replacement The replaceable parts list in Section 5 describes the electrical

components of the Model 602. Replace components only as necessary. Use only reliable replacements which meet the specifications. The MOSFET input transistors, QlOl and Q102, are specially selected and matched: order only as a plug-in unit (PIN 23733A) from Keithley Instruments.

4.15 PROCEDURES TO GUIDE TROUBLESHOOTING If the instrument will not operate, check the condition of the

batteries and OUTPUT switch. This switch should be in the

1V position with no load. If these are found satisfactory, use

the following procedures to isolate the trouble. The schematic diagram indicates all transistor terminal

voltages referenced to either floating ground or output ground; a properly operating Model 602 will have these values k lo%, if operating from fresh batteries. The control settings for these values are: range switch at VOLTS, multiplier switch at 1, and the meter zeroed. Measurements are with the Model 195.

1. To check the amplifier, disconnect the feedback loop by

removing batteries 8204, 8205, 8206 and 8207. This allows each stage of the amplifier to be individually checked. It also eliminates the possibility of applying excessive voltage to the input transistors, causing serious damage.

2. Connect the Model 195 between the drains of (1101 and

Q102. Adiust the COARSE and MEDIUM ZERO controls for null. If’null cannot be reached, check the COARSE and MEDIUM ZERO control circuits (resistors R114 to R135). and transistors Q103 an Q104. Check Q103 and Q104 by removing them and adjusting for null again. If null is now reached, replace the transistor pair with a new pair.

3. Check the next stage by connecting the Model 195 across

the emitters of Q103 and Q104 and adjusting the COARSE

Difficulty Excesssive zero offset.

Excessive offset current.

Cannot zero meter on any range. Unable to zero meter on most

sensitive range. Meter will not zero on one

multiplier switch setting. lo-‘0 to 10.‘4A current ranges are

out of specification.

Table 4-4. Model 602 Troubleshooting

Probable Cause Input transistors may be defective.

Batteries failina.

Excessive temperature fluctuation

or defective input transistors.

Instrument not used. See paragraph 4.15. Incorrect gate voltages on input

transistors.

Faulty resistor for setting of multiplier switch.

Defective high megohm resistors.

Solution Check QlOl and Q102; replace

if faulty.

Replace batteries (paragraph

Check QlOl and Q102; replace if faulty.

Run for seven hours. See paragraph 4.15, step 6. Check per paragraph 4.15.

Check resistors; replace if

faulty.

Check per paragraph 4.9.

4-5

and MEDIUM ZERO controls for null. If null is not reached, check this stage and the base circuit of the next stage. Check the base circuit by removing transitors 0105 and Q106 and again adjusting for null. If null is now reached, replace the transistor pair with a new pair.

4. Check the next stage bY connecting Model 195 across the collectors of QlO5 and 0106 and adjusting the COARSE

and MEDIUM ZERO controls for null. If null is not reached. check this stage and check for shorts in the base circuit of Q107 and Q108.

5. Connect Model 195 to the collector of Q109. Adjust the FINE ZERO control for null. If null is reached, the DC

amplifier is operating correctly. If null is not reached, check transistors Q107 through QllO and diode DlOl.

6. The feedback loop includes the multiplier resistors, R156 through R164, the recorder output resistors, R167 on 1V position or R187 and R188 on 1 MA position and the meter. An opening of any of these components prevents zeroing for only that particular multiplier setting.

7. Replace batteries 8204 through 8207 and troubleshoot

the output stages, transistors 0114 and Q115, by making

measurements with Model 195 to within 510% of the specified schematic value.

4.16 SERVICING HIGH IMPEDANCE CIRCUITRY High impedance circuitry is sensitive and must be kept clean

of oil, dirt, dust and contaminants. Replacing a component or components within a high impedance circuit requires special cleaning and handling to maintain the high impedance level of the circuit. After replacing any component in the high im-

pedance circuitry or if the high impedance circuitry IlOe to

10.ItA range resistors) is contaminated, use the following procedure to clean the circuit:

1. Clean the entire high impedance circuit with methanol and

a clean

2. Blow dty the circuit with dry nitrogen gas. Ordinary compressed air may contain contaminans such as oil or water.

3. Inspect the circuit for any residue (contamination) and repeat steps 1 and 2 if any residue is found.

4. Reassemble the circuit or instrument taking care not, to

touch the clean components.

cotton

swab.

4-6

SECTION 5

REPLACEABLE PARTS

5.1 INTRODUCTION

This section contains an illustration of the chassis, Figure 5-l.

replacement parts information, component location drawings and a schematic diagram of the Model 602.

5.2 PARTS LIST Parts are listed alphabetically in order of their circuit desig-

nations. Table 5-2 contains the replaceable parts of the Model

602.

5.3 ORDERING INFORMATION

To place an order or to obtain information concerning replacement parts, contact a Keithley representative or the factory. See the inside front cover for addresses. When ordering include the following information:

*Instrument Model Number *Instrument Serial Number *Part Description *Circuit Description (if applicable)

Keiihley Part Number

5.4 FACTORY SERVICE If the instrument is to be returned to the factory for service,

photocopy and complete the service form which follows this

section and return it with the instrument.

5.5 SPECIAL HANDLING OF STATIC SENSITIVE

DEVICES

5-l lists all the static sensitive devices of the Model 602. Steps 1 through 7 provide instruction on how to avoid damaging these devices.

Table 5-l. Model 602 Static Sensitive Devices

1. Devices should be handled and transported in protective containers, antistatic tubes or conductive foam.

2. Use a properly grounded work bench and a grounding wrist strap.

3. Handle device by the body only.

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

5. Use antistatic solder removers.

6. Use gounded tip soldering irons.

7. After devices are soldered or inserted into the socket they are protected and normal handling can resume.

5.6 COMPONENT LOCATION DRAWINGS Figure 5-2 contains a drawing of the components for the

RANGE switch, S102, while Figure 5-3 shows the component layout of the MULTIPLIER switch, S106. Figure 54 contains

a component layout of PC186, while Figure 5-5 shows component locations for PClZJ.

5.7 SCHEMATIC DIAGRAM

MOS devices are designed to function at high impedance

levels. Normal static charge can destroy these devices. Table

A schematic diagram of the Model 602 is presented in Figure 5-6.

5-l

BZOl. B202, 8204 THRU

BATTERIES

8207

Jm(J k SWITCH sioi

”

R114THRU R125 I&

PC127

” I

zii

:H S106

NOT SHOWN

PC186

I I

“CONTAINED IN SHIELDED COMPARTMENT NOT SHOWN.

R136, R138. R139, R154 THRU R164 R169, R170 C112, Cl17

Figure 5-l. Model 602 Chassis Side View

T \

SWITCH SlO2

r-l

Ill-l

l-l LJ

uuuuuLlLlLluuLlu uLluuuuuuuuuu

I I

Figure 5-2. RANGE Switch, S102, Component Location Drawing

Figure 53. MULTIPLIER Switch, S106, Component Location Drawing

Table 5-2. Model 5502 Replaceable Parts List

Circuit Desig. Description

B201 8202 Battery, 9V. Zinc Carbon BA-17 8203 Battery, 1.35V 8204 Battaty, 9V. Zinc Carbon BA-17 8205 Battery, 9V. Zinc Carbon BA-17 8205 Battery, 9V. Zinc Carbon BA-17 8207 Batten/, 9V, Zinc Carbon BA-17 Cl01 Capacitor, 15OpF, 5OOV, Ceramic Disc C-22-150~ Cl02 Capacitor, 5pF, 2OOV, Polystyrene c-31-5p Cl03 Capacitor, lOpF, 5OOV. Polystyrene c-135-1OD Cl04 Capacitor, 22pF. 5OOV, Polystyrene C-1382ip Cl05 Cl05 Capacitor, lOOpF, 2OOV. Polystyrene c-108100p Cl07 Capacitor, 1OOOpF. ZOOV, Polystyrene c-10&1000p Cl08 Capacitor, .lpF, 2OOV, Polystyrene C-2517.1 Cl09 Capacitor, .OlpF, 2OOV. Polystyrene Cl10 Capacitor, .OOlpF, 2OOV, Polystyrene

Cl11 Capacitor, 1OOpF. 2OOV, Polystyrene c-10&100p Cl12 Capacitor, .0047~F, 5OOV. Ceramic Disc Cl13 Capacitor, IOOpF, IW, Electrolytic c-3-100

Cl14 Capacitor, .033wF, ZOOV, Mylar c-143-.033

Cl15 Capacitor, .033sF, 2OOV. Mylar

Cl15 Capacitor, 15OpF, 5OOV. Ceramic Disc C-22-150~

Cl17 Capacitor, .OOlpF, lOOOV, Ceramic Disc c-54.001

DlOl Diode, Silicon, 1 N545

D102

D103 Diode, Silicon, 1 N914 RF-28

D104 JIOZ Binding Post, LO (Black) BP-116

J103 Receptacle, Microphone, Output CS-32

J104

J105

J105 Binding Post, LO (Black) BP-IIB

J107 Binding Post, Guard IBlue

J108

Ml01 Meter ME-81

QlOl’

Q102”

a103

a104

Q105

0105 Transistor, NPN, Silicon, 2N3903

0107 Transistor, NPN, Silicon, 2N3903

Q108 Transistor, NPN, Silicon, 2N3903 TG49 a109 Transistor, PNP, Silicon, 2N3905 TG-53 a110 a111 Transistor, PNP, Silicon, 2N3538A TG-33 Q112 a113 a1 14 cl115

*QlOl and Q102 are matched and mounted on a specially built plug-in card with built-in overload pro-

tection.

Battery, 9V, Zinc Carbon BA-17

Capacitor, 47pF, 5OOV. Polystyrene

Selected Low Leakage Transistor 24746A Diode, Silicon, IN914 RF-28

Binding Post, Case Ground (Green) BP-11GRN Binding Post, Xl Output (Red) BP-l 1 R

Receptacle, Triaxial, INPUT Plug, Triaxial, Mate of J108 cs-141 Cap, Input Receptacle CAP-18

Transistor, NPN, Silicon, 2N3903

Transistor, NPN, Silicon, 2N3903 Transistor, NPN, Silicon, 2N3903

Transistor, NPN, Silicon, 2N3903

Transistor, PNP, Silicon, 2N3638A Transistor, PNP, Silicon, 2N3538A Transistor, PNP, Silicon, 2N3905 Transistor, NPN, Silicon, 2N3903

Keithley Part No.

BA-24

c-13a47p

c-108.01 c-108.001

C-22-.0047

c-143-.033

RF-14

BP-l 1 BLU cs-44+ I61

TG49 TG49 TG49 TG49 TG-49.

TG-49

TG-33 TG-33 TG-53 TG49

Table 52. Model 602 Replaceable Parts List Wmt.1

Circuit Desig.

RlOl R102 R103 R104 R105 R106

R107 R106 RlOS RllO Rlll R112 R113 R114

R115

R116

Rl17 R116 RllS R120 R121 R122 R123 R124 R125 R126 R127 R126 R129 R130 R131 R132 R133 R134 R135 R136 R137 R136 R139 R140 R141 R142 R143 R144 R145 R146 R147 R146 R149 R150 Rl51 17152 R153 R154 R155

Description Resistor, lM, 10%. %W, Composition

Resistor, 100, 1%. lOW, Wire Wound

Resistor, lOOR, l%, 1OW. Wire Wound

Resistor, lk, 1%. ‘hW, Carbon

Resistor, lOk, 1%. %W, Carbon

Resistor, lOOk, 1%, %W, Carbon Resistor, 1M. 1%. KW. Carbon Resistor, 10M. 1%. %W, Carbon Resistor, 100M. SppmiV, Glass Epoxy Resistor, 1G. 5ppm/V, Glass Epoxy Resistor, 10G. 5ppm/V, Glass Epoxy Resistor, 100G. 5ppm/V, Glass Epoxy Resistor, 135k. .5%, 116W. Metal Film Resistor, 66.lk. 1%. %W, Carbon Resistor, 606R. 1%. %W, Carbon Resistor, 606Q, 1%. %W. Carbon Resistor, 606Q, 1%. HW, Carbon Resistor, 60652, 1%. YzW, Carbon Resistor, 6060, 1%. ‘hW, Carbon Resistor, 606R. l%, KW, Carbon Resistor, 6060, 1%. %W, Carbon Resistor, 806fL 1%. !hW, Carbon Resistor, 606Q. 1%. KW, Carbon Resistor, 6060, 1%. %W, Carbon Resistor, 66.lk. 1%. YzW, Carbon Resistor, 2490, 1%. %W, Carbon Resistor, 2490, l%, KW, Carbon Resistor, 2490, 1%, KW, Carbon Resistor, 2490, 1%. ‘hW, Carbon Resistor, 2490. 1%. %W, Carbon Resistor, 249R. 1%. %W, Carbon Resistor, 249Q, 1%. %W, Carbon Resistor, 2490, 1%. %W, Carbon Resistor, 2493, 1%. HW, Carbon Resistor, 249Q, 1%. %W, Carbon Resistor, 40.2k, 1%. (/W, Carbon

Resistor, 39k. 10%. %W, Composition

Resistor, 20k. 1%. %W, Carbon

Resistor, 20k, 1%. 1/W, Carbon Resistor, 34.6k, 1%. KW, Metal Film Resistor, 200k. 1%. %W, Metal Film Resistor. 9k. .5%, %W, Metal Film Resistor, 3.46k. 1%. 116W. Metal Film Resistor, 200k. 1%. KW, Metal Film Resistor, 2.2k, lo%, % W, Composition Resistor, 36.5k, 1%. %W, Metal Film Resistor, 36.5k. 1%. %W, Metal Film Resistor, 2.2k. 10%. %W, Composition Resistor, 21.5k, 1%. %W, Metal Film Resistor, 7.15k, 1%. %W, Metal Film Resistor, 270k, lo%, %W, Composition Resistor, 2.7k. lo%, %W, Composition Resistor, lOOk, 10%. %W, Composition Resistor, lOk, 1%. HW, Carbon Resistor, 1.5k, 1%. XW, Carbon

Keithley Part No.

R-1-1M R-34-10 R-34-100 R-12-lk R-12.10k R-12-100k R-12.1M R-12.10M R-269.100M R-269-1 G R-269.10G R-269.100G R-234.135k R-12-66.lk R-12-606 R-12-606 R-12-606 R-12-606 R-12-606 R-12-606 R-12-606 R-12-606 R-12-606

R-12-606

R-12.66.lk

R-12-249 R-12-249 R-12-249 R-12-249 R-12-249 R-12-249 R-12-249 R-12-249 R-12-249 R-12-249 R-12-40.2k R-l-39k R-12-20k R-12.20k R-94-34.6k R-94-200k

R-61.Sk

R-66-3.46k

R-94200k R-1.2.2k R-94-36.5k R-94.36.5k R-1.2.2k R-94-21.5k R-947.15k

R-1-270k

R-1-2.7k

R-l-look

R-12-10k

R-12.1.5k

5-5

Table 52. Model 602 Replaceable Parts List ICont.1

Circuit. Desig.

R156 R157 R156 R159 R160 R161 R162 R163 R164 R165 R166 R167 R166 R169 R170 R171 R172 R173 R174 R175 R176 R177 R176 R179 R160 R161 R162 R163 R164 R165 R166 RI67 R166 R169 R190 R191 R192 SlOl

5102

5103 5104

s105 S106

3107 5106

216508

Description

Resistor, 9.lk, ,596, ‘/iW, Metal Film Resistor, 2.73k. .5%, %W, Metal Film Resistor, 9100, ,536, %W, Metal Film Resistor, 27322, .5%, %W, Metal Film Resistor, 910, .6%, %W, Metal Film Resistor, 27.3Q, .5%. %W, Metal Film Resistor, 9.10, .5%, %W. Wire Wound Resistor, 2.73R. ,536, %W. Wire Wound Resistor, O.SlQ, .5%, ‘/W, Wire Wound Not Used Resistor, lOQ, 5%. YiW, Composition Resistor, 9100, .5%, %W, Metal Film Resistor, 10k. 10%. %W, Composition Pot, 10k Resistor, 10k Resistor, 6.6k, 10%. HW, Composition Resistor, 6.6k, 10%. (/W, Composition Resistor, 160k, 10%. %W, Composition Resistor, 160k. 10%. ‘/IW, Composition Resistor, 62k; 10%. 1/2W. Composition Resistor, 120k. lo%, %W, Composition Pot, 2k Resistor, 1200, lo%, %W, Composition Resistor, 6.06k. 1%. %W, Metal Film Pot, 15k Resistor, 1200, lo%, ‘hW, Composition Resistor, lOk, 10%. %W, Composition Resistor, 120k. 10%. ‘/W, Composition Resistor, lk, .5%, %W, Metal Film

Resistor, 26.7k. 1%. %W, Metal Film

Resistor, 11.6k. 156, %W, Metal Film Pot, 20k

Resistor, 6.66k. 1%. %W, Carbon Resistor, 5OOQ, 196, %W, Carbon Resistor, 6.6k. lo%, ‘/iW, Composition

Resistor, 6.6k, 1056, ‘/iW. Composition Resistor, 6.6k, 10%. %W. Composition

Rotary Switch less components, Coarse Zero Rotary Switch with components Rotary Switch less components, Range Rotary Switch with components Dial assembly, Range Switch

Push button switch, Zero Check

Rotary Switch less components, Medium

Zero

Rotary Switch with components

Knob assembly Slide Switch, Feedback Rotary Switch less components, Multiplier Rotary Switch with components Dial assembly, Multiplier Switch Rotary Switch less components, Meter Rotary Switch with components Slide Switch, Output

MOS FET Input Plug-in card Battery Snap, 6 required Battery Holder

Keithley Part No.

R-61-9.lk R-El-2.73k R-61-910 R-61-273 R-61-91 R-61-27.3 R-123-9.1 R-123-2.73 R-123-91

R-76-10 R-61-910 R-1-1Ok RP-42-10k R-12-10k

R-1.6.6k R-1.6.6k R-1.160k R-1.160k R-1.62k R-1.120k RP-34-2k R-1-120 R-94-6.06k RP-3-15k R-1-120 R-1-1Ok R-1-120 R-61-lk R-94-26.7k R-94-1 1.6k RP-34.20k R-12.6.66k R-12-500

R-1-6.6k A-l-6.6k R-l-6.6k

SW-166 209248 SW-204 209228

16039A

14376A SW-209

209268

16039A 19069 SW-205

209296

19223A SW-320

242766

SW-45

23733A

BH-6 20944A

6-6

R147 R166

BOARD11 -; R:44 R146 1 1 1~1 I

n Ol

’ R146

Figure 6-4. Model 602, PC186, Component Location Drawing

Rl77

mu A

TT L.I

PC166

RI66 R140

R153 0

R169

ZERO

R176

R143

---hid-

Figure 55. Model 602, PC127, Component Location Drawing

DP,,,

5-7/5-a

----~--

tti I III

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.

Intermittent

EEE failure

aFront panel operational q All ranges or functions are bad

Display or output (circle one)

Drifts

]Unstable

mOverload

Calibration only

Data required

(attach any additional sheets as necessary.) Show a block diagram of your measurement system including all instruments connected (whether power is turned

Also, describe signal source.

aAnalog output follows display q Particular range OT function bad; specify aObvious problem on power-up

Unable to zero

Will not read applied input

IJC of C required

Batteries and fuses are OK

Checked all cables

on or

not).

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

What power line voltage is used? ~

Relative humidity?

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

Be sure 10 include your name and phone number an this xrvice form.

Other?

Ambient Temperature?

Model 602 Solid-State Electrometer Addendum

INTRODUCTION

This addendum to the Model 602 Solid-State Electrometer Instn~ction Manual is being provided in order to supply you with the latest information in the least possible time. Please incorporate this information into the manual immediately.

Page 2-2; Figure 2-l. Model 602 Front Panel Conk&.

The circuit designations for the RANGE switch and ZERO CHECK switch on the front panel of the Model 602 are incorrectly stated. The correct designation for the RANGE switch is 5102 and 5103 for the ZERO CHECK switch.

Page 5-6; Replace Table 5-2 with the following:

29111-c-1 /7-90

Table 5-2. Model 602 Replaceable Parts List (Cont.)

Circuit Deeig.

A156 PI157 R158 R159 R160 R161 R162 R163 R164 A165 R166 R167 R166 R169

R170 R171 R172 R173 R174 R175 R176 R177 ,

R178 R179 R180 R181 R182 R183 R184 R185 R186 R187 R188 R189 R190 R191 R192

Description

Resistor, 9.1 k, .5%, 1/2W, Metal Film Resistor, 2.73k, .5%, 1/2W, Metal Film Resistor, 910R, .5%, 1/2W, Metal Film Resistor, 273Q .5%, 1/2W, Metal Film Resistor, 9X2, .5%, 1/2W, Metal Film Resistor, 27.3R, .5%, 1/2W, Metal Film Resistor, 9.1R, .5%. 1/2W, Wire Wound Resistor, 2.73Q .5%. 1/4W, Wire Wound Resistor, 0.91R, .5%, 1/4W, Wire Wound Not Used Resistor, iOR, 5%, 1/4W, Composition Resistor, 91OQ .5%, 1/2W, Metal Film

i+$i;too IOk, 10%. 1/2W, Composition Re&tor, 1 Ok

Resistor, 6.6k. 1 O%, 1/2W, Composition Resistor, 6.8k, lo%, 1/2W, Composition Resistor, 180k, IO%, 1/2W, Composition Resistor, 180k, 10%. 1/2W, Composition Resistor, 82k. lo%, 1/2W, Composition Rz;i;t$, 120k, lo%, 1/2W, Composition

Resistor, 120R. 10%. 1/2W, Composition Resistor, 8.06k, l%, 1/2W, Metal Film Pot, 15k

Resistor, 12OQ lo%, 1/2W. Composition Resistor, lOk, lo%, 1/2W, Composition Resistor, 120k, lo%, 1/2W, Composition Resistor, lk, .5%, 1/2W, Metal Film Resistor, 28.7k, l%, 1/2W, Metal Film Resistor, 11.8k. l%, 1/2W, Metal Film Pot, 20k Resistor, 8.66k, l%, 1/2W, Carbon Resistor, 500Q l%, 1/2W, Carbon Resistor, 6.8k, 1 O%, 1/2W, Composition Resistor, 6.8k, lo%, 1/2W, Composition Resistor, 6.8k, lo%, 1/2W, Composition

Keithley Part No.

R-61-9.1 k Fi-61.2.73k R-61-910 R-61 -273 R-61 -91 R-61-27.3 R-123-9.1 R-123-2.73 R-123-.91

R-76-1 0 R-61-910 R-I-1Ok RP-42-10k

R-12-10k R-1-6.8k R-l-6.8k R-1.180k R-l-180k R-l-82k R-l-120k RP-34.2k

R-1-120 R-94-8.06k RP-3.15k R-1-120 R-1-1Ok R-1-120 R-61.lk R-94.28.7k R-94-l 1.6k RP-34-20k R-12-8.66k R-12-500 R-l -6.8k R-l-6.8k

R-l-6.8k 5101 3102

5103 3104

5105 3106

$107

$108 !185OB MOSFET Input Plug-in card

Rotary Switch less components, Coarse Zero Rotary Switch with components Rotary Switch less components, Range

Rotary Switch with components Knob, Range Switch Knob, Zero Check Rotary Switch less components, Medium Zero Fl;Fbry Switch with components

Slide Switch, Feedback Rotary Switch less components, Multiplier Rotary Switch with components Knob, Multiplier Switch Rotary Switch less components, Meter Rotary Switch with components Knob Slide Switch, Output

Battery Snap, 6 required Battery Holder

SW-166 209248 SW-204 209228 KN-51 KN-47 SW-209 209268 KN-45 19089 SW-205 209298 KN-49 SW-320 242788 KN-50 SW-45

23733A BH-6 20944A

29111-c-1/7-90

Keithley 602 Service manual

Specifications and Main Features

Frequently Asked Questions

User Manual