Keithley 602 User manual

MODEL 602
INSTRUCTION MANUAL
Instruction Manual
Model 602
Solid-State Electrometer
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 aperiod of 1year 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 origi-
nal 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, INDI-
RECT, 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. - 28775Aurora Road* Cleveland, OH 44139 * 216-248-0400 *Fax: [phone] * http://www.keithley.com

SPECIFICATIONS
AS A VOLTMETER:
RANGE: .OOlV full scale to 1OVin 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 109to 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 15OOVwith 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 Title Page
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
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 l-GENERAL DESCRIPTION
Introduction ...........................
Model 602 Features. ....................
Warranty Information ...................
ManualAddenda .......................
Safety Symbols and Terms. ..............
Safety Precautions .....................
Specifications .........................
Optional Accessories. ...................
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 ......
SECTION Z-OPERATION
Introduction ..........................
Front Panel Controls ...................
Rear Panel Terminals. ..................
Input Connections .....................
Preliminary Procedures. ................
Voltage Measurements. ................
Normal Method Voltage Measurements
Guard Method Voltage Measurements
Low Impedance Source ..............
Off-Ground Voltage Measurements .......
FEEDBACK Switch Set To NORMAL ...
FEEDBACK Switch Set To FAST ......
Current Measurements .................
Normal Mode IO.3to lO~‘4ARanges) ....
Fast Method (Current Below lo-=A) ....
Galvanometric Method ...............
Resistance Measurements ..............
Normal Constant Current Method ......
Fast Constant Current Method. ........
Voltmeter-Ammeter Method (To 10%)
Charge Measurements .................
Recorder Outputs .....................
Unity-Gain Output .....................
SECTION 3-THEORY OF OPERATION
Introduction ..........................
Voltmeter Operation ...................
Voltmeter Circuit ......................
Ammeter Operation. ...................
Normal Method .....................
Fast Method. .......................
Ohmmeter Operation ..................
Normal Method .....................
Guarded Method ....................
Coulombmeter Opration ................
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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-l
3-1
3-l
3-1
3-l
3-2
3-2
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
5.1
5.2
5.3
5.4
5.5
5.6
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 ................................................................
SECTION S-REPLACEABLE PARTS
Introduction ...................................................................................
PartsList .....................................................................................
OrderingInformation ............................................................................
FactoryService ................................................................................
Special Handling of Static Sensitive Devices ........................................................
ComponentLocationDrawing ....................................................................
41
4-l
4-l
4-l
4-l
4-2
4-2
4-2
z
4-3
4-3
43
2
4-4
zl
4.4
45
z
4.2
4-6
5-l
5-l
51
5-l
51
51
r*
5.7 SchematicDiagram.........................,.,.............,,..,............................... o-1
ii

LIST OF FIGURES
Figure Title Page
2-1 Model 602 Front Panel Controls .......................................... ................
2-2 Model 602 Rear Panel Terminals .......................................... ................
2-3 Triaxiallnput .......................................................... ................
2-4 Error Due to Ammeter Resistance. ........................................ ................
2-5 Measuring Current by the Galvanometric Method, ........................... ................
2-6 Measuring Resistance by the External Voltage Method ....................... ................
2-7 Divider Curcuits ccross Model 602 Output for Driving 50 and 10OmV Recorders ... ................
2-8 Measuring Potential of Hich Resistance Source with 0.025% Accuracy. ......... ................
3-1 Block Diagram of Model 602 in Voltmeter Mode ............................. ................
3-2 Block Diagram of Model 602as a Picoammeter .............................. ................
3-3 Block Diagram of Model 602for Normal Method Measuring Resistance ......... ................
4-l Model 602 Caseto LO Isolation Check ..................................... ................
4-2 Model 602 Unity-Gain Test Set-Up. ....................................... ................
5-1 Model 602 Chassis, Side View. ........................................... ................
5-2 RANGE Switch, S102, Component Location Drawing ........................ ................
5-3 MULTIPLIER Switch, S106, Component Location Drawing ................... ................
5-4 Model 602, PC186, Component Location Drawing ........................... ................
5-5 Model 602, PC127, Component Location Drawing ........................... ................
5-6 Model 602, Schematic Diagram, Dwg. No. 21174E .......................... ................
LIST OF TABLES
Table Title
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 ........................
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......... 2-9
......... 2-9
......... 3-l
......... 3-2
......... 3-2
......... 4-2
......... 4-4
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57
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......... 5-9
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.OOlVfull 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.
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 loca-
tions. Check the inside front cover of this manual for ad-
dresses.
1.4 MANUAL ADDENDA
The Model 602 offers complete line isolation and excellent Information concerning improvements or changes to the
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. 1.5 SAFETY SYMBOLS AND TERMS
The Model 602 employs matched insulated-gate field-effect
transistors followed by transistor differential amplifier stages The following safety symbols and terms are used in this
and a compliritentary-output stage. A large amount of manual or found on the Model 602.
negative feedback is used for stability and accuracy.
1.2 MODEL 602 FEATURES The symbol A on the instrument indicates that the user
should refer to the operating instructions in this ;nanual.
1. The Model 602 has excellent zero stability which permits The symbol # on the instrument indicates that a po-
accurate measurements with minimal adjustment. Short tential of 1OOOVor more may be present on the terminaltsl.
term zero drift is less than 50& per hour. Zero offset due Standard safety precautions should be observed when such
to temperature change is less than 15O/rVper OCafter 30 dangerous voltages are encountered.
minute warm-up period. This offset, however, can easily
be compensated for with the front panel zero controls. The WARNING heading in this manual explains dangers that
2. Fast warm-up is an inherent characteristic of the Model could result in personal injury or death.
602. It can be operated 30 minutes after warm-up on the
most sensitive range and almost immediately on less sensi- The CAUTION heading in this manual explains hazards that
tive ranaes. could damage the instrument.
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 per-
formance is obtained by use of a unique input circuit. The
Model 602 Electrometer will withstand damage and has
good recovery.
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.
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 sup-
plied 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.
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:lvoltage 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.
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 Electri-
cal 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.
1.8.5 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 re-
quire 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

SECTION 2
OPERATION
2.1 INTRODUCTION
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 instru-
ment 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 con-
nections 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
connected to case ground, only if the shorting link on the rear
panel is connected.
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 unshield-
ed 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.
Circuit JIOI Terminal
Input High Center
Input Low Inner
Case Outer Shield
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 dis-
turbances 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. NOTE
Clean, dry connections and cables are very im-
portant 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.
2-1

Figure 2-l. Model 602 Front Panel Controls
2-2

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 ex-
cept 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 1
FEEDBACK Switch NORMAL
METER Switch POWER OFF
Figure 2-3. Triaxial Input Table 2-2. Multiplier Switch Positions for Checking
Conditions of Batteries
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-
Multiplier Position
,001
BACK switch at FAST, some insulators kuch as Teflon” ) 1
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. 1. Turn the METER switch
1 tc
If a well shielded chamber and a well made high impedance I CENTER ZERO. Within ten
transfer switch is available, it is advantageous to connect the seconds, the mater needle should con?,.?‘tothe center posi-
Model 602 to the circuit only when a reading is being made. tion. If not, adjust the mater zero with the MEDIUM and
In some cases, the offset current can charge the external test FINE ZERO controls. Normally, there is no need to use the
COARSEZERO ‘.
circuitry. One example of this occurs when measuring a
capacitor’s leakage resistance by observing the decay of ;he NOTE
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 Using the center zero scales decreases accuracy
terminal voltage when the Model 602 is left connected across 0.5% because the scale span is reduced.
the capacitor’s terminals. 2. After a few moments increase the voltage sensitivity by
NOTE
Keep the shield cap on the INPUT connector
when the Model 602 is not in use.
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
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.
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
CAUTION
The Model 6012 connects low to case
ground. The Modal 602 cannot be used off-
ground when using the Model 6012. The in-
strument’s cabinet will be at the same
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.
potential as the input low. 4. Although the offset current of the Model 602 is below that
2.5 PRELIMINARY PROCEDURES found in conventional voltmeters, it can be observed on
the meter. The current charges the input capacitance, and
Check battery condition by holding the METER switch in the the Model 602 appears to drift when the input is open. Use
BATTERY CHECK position. Rotate the multiplier switch the ZERO CHECK button to discharge the charge build-up.
through the ,001 to 0.1 positions and observe the meter Depressing the ZERO CHECK button removes all signal
readings. The meter should read at least two-thirds of full from the amplifier and reduces the input impedance
scale in each multiplier switch position. Table 2-2 shows the 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 con-
nected 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
The Model 602 can be used to measure voltages. In the nor-
mal method (FEEDBACK switch at NORMAL) the unknown
voltage is connected to the INPUT connector. Input im-
pedance 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 tem-
porarily 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.
2.6.2 Guard Method Voltage Measurement
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.
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 cur-
rent 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 pro-
cedures 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.
2.7.2 FEEDBACK Switch Set To FAST
This method reduces the effects of input cable capacity with Disconnect the shorting link between the LO and CASE
very high impedance source.s and allows guarded voltage GROUND terminals on the rear panel. Make sure the Model
measurements. 602 case is securely connected to an earth ground, and that
2-5

the low of the unknown voltage is less than 1500V off-
ground. 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 con-
nected 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 cir-
cuit 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 ef-
fect of input capacity and greatly increases the response
speed. Also, the input voltage drop is reduced to a maxi-
mum 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 instru-
ment. 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 & 15OOVoff-ground (see paragraph 2.7 and Figure 2-4).
I Lz- 11 I
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 IR,,l IS IN SERIES
WITH THE SOURCE RESfSTANCE (RI.
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. In-
crease 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 set-
ting 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 set-
ting.
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 alter-
native 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. Con-
necting 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
I--- ------w
CURRENT CURRENT
SOURCE
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 60.2TO THE TWO SOURCES WITH COAXIAL CABLE.
SELECT CABLE CAREFULLY FOR VERY LOW CURRENTS.
Figure 2-5. Measuring Current by the Galvanometric
Method
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 pro-
portional 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 pre-
ferred. 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
1OMQresistor, 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.
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 lock-
ed.
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.
The low terminal of the INPUT connector is now a driven
guard. It may be used to minimize the effects of capacity be-
tween high and low and errors due to leakage resistance be-
tween 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 be-
tween 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.
NOTE
Shield the input if the resistance sample exceeds
10%
NOTE: A POTENTIAL FROM A KNOWN SOURCE, V. IS AP-
PLIED 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.
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 ex-
ternal 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 1OOHzat a gain of 1000, rising to 4OHz at
gains of 1.Oand 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.
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 mak-
ing 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 approximate-
ly 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.
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).
I I
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 TO THE MODEL602
UNIN-GAIN TERMINALS.
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 con-
venient 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 1OOkOor 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 unity-
gain 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