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Model 600A
Instruction Manual

Contains Operating and Servicing Information
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 batter-
ies, 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, vansportation prepaid, to the indicated service facility.
Repairs will be made and the product returned, transportation prepaid. Repaired or replaced products are warranted for the balance
of the original warranty period, or at least 90 days.

This warranty does not apply to defects resulting from product modification without Keithley's express written consent, or misuse
of any product or part. This warranty also does not apply to fuses, software, non-rechargeable batteries, damage from battery leak-
age, or problems arising from normal wear or failure to fallow instructions.


Safety Precautions

The following safety precautions should be observed before using Users of this product must be protected from electric shock at all
this product and any associated instrumentation. Although some in- times. The responsible body must ensue that users are prevented
struments and accessories would normally be used with "on-haz- access and/or insulated from every connection point. In some cases,
ardous voltages, there are situations where hazardous conditions connections must be exposed to potential human contact. Product
may be present. users in these circumstances must be trained to protect themselves
from the risk of electric shock. If the circuit is capable of operating
This product is intended for use by qualified personnel who recog- at or above 1000 volts, no conductive part of the circuit may be
nize shock hazards and are familiar with the safety precautions re- exposed.
quired to avoid possible injury. Read the operating information
carefully before using the product. As described in the International Electrotechnical Commission
(IEC) Standard IEC 664, digital multimeter measuring circuits
The types of product users are:
(e.g., Keithley Models 175A, 199,2000,2001,2002, and 2010) are
Responsible body is the individual or group responsible for the use Installation Category II. All other instruments' signal terminals are
and maintenance of equipment, for ensuring that the equipment is Installation C&gory I and must not be connected to mains.
operated within its specifications and operating limits, and for en-
suring that operators are adequately trained. Do not connect switchjng cards directly to unlimited power circuits.
They are intended to be used with impedance limited sources.
Operators use the product for its intended function. They must be NEVER connect switching cards directly to AC mains. When co"-
trained in electrical safety procedures and proper use of the instm- netting sources to switching cards, install protective devices to lim-
ment. They mut be protected from electric shock and contact with it fault current and voltage to the card.
hazardous Iive circuits.
Before operating an instrument, make sure the line cord is connect-
Maintenance personnel perform routine procedures on the product ed to a properly grounded power receptacle. Inspect the connecting
to keep it operating, for example, setting the line voltage or replac- cables, test leads. and jumpers for possible wear, cracks, or breaks
ing consumable materials. Maintenance procedures are described in before each use.
the manual. The procedures explicitly state if the operator may per-
form them. Otherwise, they should be performed only by service For maximum safety, do not touch the product, test cables, or any
personnel. other instruments while power is applied to the circuit under test.
ALWAYS remove power from the entire test system and discharge
Service personnel are trained to work on live circuits, and perform any capacitors before: connecting or disconnecting cables or jump-
safe installations and repairs of products. Only properly trained ser- ers, installing or removing switching cards, or making internal
vice personnel may perform installation and service procedures. changes, such as installing or removing jumpers.

Exercise extreme caution when a shock hazard is present. Lethal Do not touch any object that could provide a current path to the
voltage may be present on cable connector jacks 01 test fixtures. The common side of the circuit under test or power line (earth) ground.
American National Standards Institute (ANSI) states that a shock Always make measurements with dry hands while standing on a
hazard exists when voltage levels greater than 30V RMS, 42.4V dry. insulated surface capable of withstanding the voltage being
peak, or 60VDC are present. A good safety practice is to expect measured.
that hazardous voltage is present in any ""known circuit before
The instrument and accessories must be used in accordance with its The WARNING heading in a manual explains dangers that might
specifications and operating instructions or the safety of the equip- result in personal injury or death. Always read the associated infor-
ment may be impaired. mation very carefully before performing the indicated procedure.

Do not exceed the maximum signal levels of the instruments and ac- The CAUTION heading in a manual explains hazards that could
cessories, as defined in the specifications and operating informa- damage the instrument. Such damage may invalidate the warranty.
tion, and as shown on the instrument or test fixture panels, or
switching card. Instrumentation and accessories shall not be connected to humans.

When fuses arc used in a product, replace with same type and rating Before performing any maintenance, disconnect the line cord and
for continued protection against fire hazard. all test cables.
To maintain protection from electric shock and fire, replacement
Chassis connections must only be used as shield connections for
components in mains circuits. including the power transformer, test
measuring circuits, NOT as safety earth ground connections.
leads, and input jacks, must be purchased from Keithley Instru-
ments. Standard fuses, with applicable national safety approvals,
IF you are using a test fixture, keep the lid closed while power is ap
may be used if the rating and type are the same. Other components
plied to the device under test. Safe operation requires the use of a
that are not safety related may be purchased From other suppliers as
lid interlock.
long as they are equivalent to the original component. (Note that se-
lected pans should be purchased only through Keithley Instruments
[email protected] screw is present, connect it to safety eanh ground using the
to maintain a.ccuracy and functionality of the product.) IF you are
wire recommended in the user documentation.
unsure about the applicability of a replacement component, call a
Keithley Instruments office for information.
Then symbol on an instrument indicates that the user should re-
fer to the operating instructions located in the manual.
To clean an instrument, use a damp cloth or mild, water based
cleaner. Clean the exterior of the instrument only. Do not apply
Then symbol on an instrument shows that it can source or mea-
cleaner directly to the instrument 01 allow liquids to enter or spill
sure IO00 volts or more, including the combined effect of normal
on the instrument. Products that consist of a circuit board with no
and common mode voltages. Use standard safety precautions to
case or chassis (e.g., data acquisition board For installation into a
avoid personal contact with these voltages.
computer) should never require cleaning if handled according to in-
structions. If the board becomes contaminated and operation is af-
fected, the board should be returned to the factory for proper

Rev. ?.I99


Title Pa3
section I. - Introduction. ........................ 1-l
Section II. - Specifications ....................... 2-1
Section III. - Operation ......................... 3-1
A. Controls andTerminals ....................... 3-l
B. Preparing the Instrment for Operation ............... 3-2
C. Measuring Voltage. ......................... 3-2
D. Measuring Current. ......................... 3-2
E. MeasuringOhms ........................... 3-3
F. BatteryCheck. ........................... 3-4
G. Using Extenal Indicators. ..................... 3-5
R. Misce.Ll.aneous Applications ..................... 3-5
I. Zero Center Operation. ....................... 3-6
Section IV. - Circuit Discussion ..................... 4-l
A. Voltmeter .............................. 4-l
B. Ammeter.. ............................. 4-2
C. Ohmmeter .............................. 4-3
Section V. - Accessories ......................... 5-l
Section VI. -Maintenance. ........................ 6-1
section VII. - Replaceable Parts List. .................. 7-l
Voltage-Resistance Diagram ....................... 7-3
Schematic Diagram. ........................... 7-5
rChangeNot.ice ............................. La&Page

?+l'heyellow Change Notice sheet is included only if the instrument contains mod-
ifications which affect the instruction manual.

0962~ i


The Keithley Model 600A Electrometer is an ultra-high impedance voltmeter
with full-scale ranges of 0.01, 0.03, 0.10, 0.30, 1.0, 3.0 and 10 volts.
The maximum input resistance is greater than 10lh ohms; in addition, the
input resistance may be varied in decade steps from one ohm to 1011 ohms
by means of the shunt resistors built into the instrument. Thus, the
600A is not ,only appropriate for measurement in high-impedance circuits,
but also can be used where a high input impedance would merely introduce
unwanted pickup.
The 6OOAmay be used as a direct-reading ammeter from 3 amperes to lo-l3
ampere full scale. This &decade range is covered in overlapping 3x
and 10x scales. Two current measuring methods are available to the user
of the 6OOA. Normally, current is determined by measuring the voltage
istor shunted from input to ground. Alternately, on
g,"",;"';"t"~ ;,33 ampere ranges, negative feedback can be applied to the
input of the voltmeter through the current measuring resistor. This
largely eliminates the input drop and increases measuring speed, particu-
larly on the,more sensitive ranges.
The 600A measures 10K to 1012 ohms full scale wit a two-terminal input.
With a guarded input, its range is extended to 10P3 ohms. Unlike con-
ventional ohmmeters, information is presented on the linear scales used
for current and voltage readings.
As a dc preamplifier, the 600A has gains of 0.1, 0.3, 1, 3, 10, 30 and
100. The continuing stability of the gain is assured bv a feedback
factor in excess of 100 on any range.
The output is minus 1 volt, open circuit, with an internal resistance
of 17K. Thus, the outputmay be used for driving oscilloscopes or
pen recorder amplifiers, or the output may be shunted down to provide
lo- or SO-mv outputs for servo-rebalance recorders.
When the Model 600A is shipped from the factory, an angle
bracket (Keithley Part No. 13766A) sapports the printed
circuit board (PC-29). The bracket is fastened to the
rear panel with a #I6 x S/16 sheet metal screw. The bracket
and screw may be removed after the Model 600A is received.

D704R 1-l




RANGE: 0.01 volt full scale to 10 volts in seven lx and 3x ranges.

ACCURACY: 'r2% of full scale on all ranges exclusive of drift.

ZERO DRIFT: Less than 2 millivolts per hour after l-hour warm-up.

INPUT IMPEDANCE: Greater than 1014 ohms shunted by 30 picofarads. Input resistance may
be selected in decade steps from 1 ohm to 101~ ohms.

RANGE: LO-l3 ampere full scale to 3 amperes in twenty-eight lx and 3x ranges.

ACCURACY: 23% of full scale on 3-ampere to lo-lo using smallest available
MLJLTIPLIER Switch setting; +5% cf full scale on 3 ampef~lr::g;;~13
x 10 ampere ranges.

GRID CURRENT: Less than ~5 x LO-l4 ampere.


RANGE: LO4 ohms full scale to 1013 ohms in nineteen linear lx and 3x ranges.

ACCURACY: 23% of full scale on lo4 to 1010 ohm ranges, using largest available MULTIPLIER
Switch setting; ?5% of full scale on 3 x 10~' to 1013 ohm ranges.


GAIN: 0.1, 0.3, etc., to 100.

FREQUENCY RESPONSE(Within 3 db): dc to 100 cps at a gain of 100, rising to 1.5 kc at a
gain of 0.1.

NOISE: Less than 3% peak-to-peak of full scale.

INPUT IMPEDANCE: Greater than 1014 ohms shunted by 30 picofarads. Input resistance may
be selected in decade steps from 1 ohm to 1011 ohms.

OUTPUT: +-1 volt for full-scale input. Internal resistance is 17 kilohms. Output polar-
ity is opposite input polarity.

POLARITY: METER Switch selects left-zero (positive or negative) or center-zero scales.
Output polarity is not reversed.

CONNECTORS: Input: uhf type; ground binding post. output: Amphenol 80-PC~F.

0565R 2-1

BATTERIES: Two 413 (30 volts), four El46 (8.4 volts), two RM42R (1.34 volts). 500 hours
minimum battery life.

DIMBNSIONS, WEIGHT: 10-l/4 inches high x 6-l/2 inches wide x 6-l/2 inches deep; net
weight, ?-l/2 pounds.

ACCESSORIESSUPPLIED: Mating input and output connectors; binding post adapter,

2-2 0565R


A. comIs Am -m
Controls and Terminals: The input connector is a UHF type receptacle.
An accessory binding post which plugs into the center of the con-
nector is furnished,. A ground binding post is mounted on the panel
above the input connector.
Front Panel iontrols:
RANGE switch, located in the center of the front panel under
the meter. This control selects VOLTS, OHMS,or AMF'ERES. On
the AMPERES position, a shunt resistor whose value is the re-
ciprocal of the designated range may bs used to decrease the
innut resistance as well as to measure current.
MULTIPLBR switch, located in the center of the front panel
directly under the meter, determines the voltage sensitivity
of the dc amplifier, and sets the voltage range when the
is or the setting of
this knob multiplied by the OHMS AMPERES
or setting gives the
full scale meter reading.
ZEROcontrol, located at the left under the meter, is used to
set the meter to sero.
METER-BATTERY switch, at the right under the meter, turns the
instrument on, determines meter polarity or zero center opera-
tion, and tests the batteries.
ZEROCBECKswitch, located at the bottom right, shorts the
input terminal through one megohm, while the amplifier input
is shorted.
Rear Panel Controls:
connector for external recorders.
NORMAL-FAST. This control is locked in NORMAL position. In
FAST position, current measurements are made with feedback
around the shunt resistor. On OBMS,the FASTposition is used
when the INPUT GUARD terminal is used.
INPUT GUARD. With the NORMAL FAST switch on FAST, the low
impedance end of the test sample is returned to this terminal
when it is desired to measure the resistance of a guarded
COARSE ZERO. If the amplifier is quite badly unbalanced, the
COARSE ZEROswitch is used to bring the front panel ZEROcon-
trol in range.
ZEROCENTER When meter cannot be centered with ZEROcontrol it
may be brought within range with this control.

og6m 3-l

(1) Set controls as follows:
WITCH: Locked
INPUT TERMINAL: Shield with cap
(2) Turn the bigTERswitch to meter +. The instrument should come
to eero in approximately 5 seconds.
(3) Rotate the MULTIPLIER switch toward the high sensitivity end,
adjusting ZEROas required. If it is impossible to eero the meter
with the front panel ZEROcontrol, use COARSE ZEROcontrol on rear
panel to bring the instrument within range of the ZEROcontrol.
(II) Connect leads as required for measurement. If high impedance is
involved, the input should be shielded using a coaxial connection or
shielded enclosure. The various accessories for the Model 600A may
be used.
If the impedance,is [email protected] about lOlo ohms) and leads can be kept
short, the binding post adapter furnished with the instrument may be
The Keithley Model 6101A Shielded Test Lead will suffice for mDst
C. [email protected]
Place RANGE switch at VOLTS. Turn MLTIPLIW. switch to expected
sensitivity and check meter zero. Release ZEROcheck, and read.
If the sensitivity of the instrument is increased, recheck the
zero reading.
method (3 amperes to lo-l3 amperes full scale)
Turn RANGE switch to desired AMPERES range. Make sure the switch at the
rear of the instrument is on the NORMAL position. Connect current source
to the input, Full scale sensitivity is the product of the settings of
the RANGE switch and MULTIPLIEJt. Check aero with the ZEROCHECK switch
and then read the unknown current.~ The full scale voltage drop is the
setting of the MULTIPLIER switch.

3-2 0962R

(2) FASTmethod (low7 to lo-l3 amperes full scale).
Proceed as above except with the FAST-NORMAL switch at FAST. The inout
drop is now negligible and the inout circuit time constant is reduced
at least 100 times. Observe the following cautions:
(a) Use only the ZEROCHECK switch to check zero.
Do not short the input.
(b) The low side of the output is no longer at ground.
Therefore, a recorder attached to the output must
not be grounded to the Model 6COA.
(c) Do not use this method for the measurement of
capacitor leakage.

----- OHMS
method (10K to lo11 ohms full scale).
Turn RANGE switch to desired OHNS range. Make sure that NORMAL-FAST
switch is in the NORMAL position.
Connect resistance sample to be measured only after ZEROCHECK switch
has been locked. The test voltage at full scale is the setting of the
MULTIPLIER switch. Before reading OHMS,turn RANGE switch to the ap-
proximate range of the unknown resistance. By manipulating the NULTI-
PLIER and the RANGE switch, the sample can be tested at a number of test
potentials, if desired.
This two terminal method is the simplest-and will wcrk quite satis.fac-
torily up to about 1011 ohms. At resistances greater than 1011 ohms,
it is desirable to employ a GUARD connection both to speed up the re-
sponse of the instrument and to nullify the error of leakage across
the electrometer input insulation.
method (10" to lo13 ohms full scale).
Proceed as with the two terminal method with the exception that the
sample is connected between the INPUT terminal and the GUARD terminal
on the rear panel. The FAST-NORMAL'switchmust be set at FAST.
Any external voltage may be used. The unknowo is connected between
the test potential and the INPUT terminal of the electrometer. The
current is then measured, using the NORMAL FAST method, and the
resistance calculated.

og62R 3-3

Proceed as follows:
(a) Lock the ZEROCHECKSwitch.
(b) Connect unknown between INPUT terminal and source of po-
tential. A switch should be connected in the hiph voltage line
so that when the sample is disconnected from the potential, the
low impedance end of the sample is grounded.
switch should be at NORMAL.
(d) Apply potential to sample before unlocking ZEROCHECK.
Start the RANGE switch at low current sensitivities and
advance the sensitivity until a reading is obtained.
If the potential applied is at least 100 times the ammeter drop (the
setting of the MULTIPLIER switch), the resistance is equal to:
If the potential applied is not large compared to the ammeter drop,
the resistance is equal to:
le) If it is possible to operate on FAST micro-microanmreter..
the input drop need not be considered in the calculation.
Turn METER-BATTERY switch to Bl, B2, etc. All batteries should read
half scale or higher on the meter.
Bl, B3, Bh, and B5 are tested directly. B2a and B2b are tested in
series on position B2. Since the battery drains are nearly iden-
tical in B2a and B2b, both should be changed when the series arrange-
ment reads low.
B6 and B7 are not tested because they are operated under virtually
shelf-life conditions. They may be replaced yearly as preventive
maintenance or may be tested at any time by removing the case and
measuring with a voltmeter. They should be replaced if.they test
less than eight volts.


The output of the Model 6CGAmay be used to drive servo rebalance
recorders as well as hish impedance devices such as oscilloscopes
and pen drive amplifiers.
(1) For use with servo rebalance recorders;
The output circuit consists of a 16.67K resistor through
which 60 microamperes flow for full scale deflection of
the .panel meter, Shorting the output does not affect the
meter reading of the Model 6OOA,but low impedances placed
across the output terminals lower the terminal voltage
for full scale deflection. Thus, if it is desired that
the output voltage for full scale be 10 millivolts, a
168 ohm resistor should be connected across the output
terminals. If a full scale of 50 millivolts is.required,
878 ohms should be used.
(2) For use with oscilloscopes and pen recorder amplifiers,
the output is minus one volt for full scale meter deflection
on any range.
The frequency response is dc to 100 cycles on the 10 milli-
volt range rising to 1 kc on the 10 volt range. The maximum
amolitude which can be
. delivered bv the amplifier is approxi-
mately 2 volts peak to peak. "
The Model 6OOAmay be used
as an integrator for small
currents such as cyclotron
and mass spectrometer beam
currents, since it is basic-
ally an operational ampli-
fier with electrometer input
when the FAST-NORMAL switch
at the rear is placed in the
To integrate current, con-
nect a polystyrene capacitor
of suitable value between
the GUARD terminal and the
input. The RANGE switch
is set at VOLTSso that there is no resistance placed across the,capacity.
Then if Fig. 600-l is consulted, it can be seen that the standard resis-
tor has been replaced by a capacitor and the 600A is now an integrator.
The full scale charge on the capacitor in coulombs is simply the product
of the capacitor value chosen (in farads) and the setting of the MULTIPLIER

Cg62R 3-5
switch (in volts). If it is desired that a time ccnstant be introduced
into the integrating circuit the appropriate shunt resistor may be
selected by the function switch.
Practically, it is suggested that the capacitor be enclosed in a ground-
ed can. The connection to the GUARD terminal may be made by a simple un-
shielded lead. The connection to the input terminal should be made by
means of a coaxial connection to one side of a Wee" adapter. The cur-
rent input is made to.the other side of the %eeu.
The following procedure is suggested: Depress the ZEROCHECK switch,
thus removing the charge from the capacitor and shorting the input.
Zero if necessary. Release the ZEROCHECK switch. If the integration
is to take place over a long period of time it is suggested that the
instrument be used cx the one volt range or higher so that zero drift
and grid current will not be factors.
CURRENT SOURCE: When measuring ohms, the instrument is designed to supply
a constant current to any device placed across its input terminals. The
magnitude of the current is equal to the reciprocal of the designation on
the OHMS segment of the RANGE switch. Therefore the instrument may be
used as a current source for calibration of other instruments if desired.
Depress ZEROCHECK and turn RANGE switch to OHMS. The current that is
supplied on each range is the reciprocal,of the OHMSsetting, and is not
affected by the setting of the MULTIPLIER switch. However, for the cur-
,rent to be accurate, the amplifier should be in balance. It will be
sufficient to balance the amplifier on the .l volt range of the MJLTI-
PLIER Switch.
STATIC CHARGE MEASUREMKNTS: instrument is zeroed and the RANGE
switch ulaced on VOLTS. The voltage sensitivity is perhaps placed at
3 or lO*volts full scale. The charged object is then brought near the
uncovered, unshielded input connector of the 600A. Depending on the dis-
tance between the charge and the instrument a voltage will be induced on
the input terminal and can be read on the panel meter. The instrument
zero should be checked frequently since accumulation of charge due to the
electrometer tube grid current will cause a slow drift of input voltage.
Connecting a capacitor across the input reduces the drift due to grid
current and also the sensitivity to charge. An electrode connected to
the INPUT terminal which increases the capacitance between the INPUT
terminal and the charged object will increase the sensitivity to charges.
In some applications, such as null indication or in measuring volt-
ages of either polarity near zero, it may be desirable to use the ZERO
CENTER position on the bWl'ER-BATTERY switch. Onthis position, opera-
tion is just the same as for left-zero (normal), except that for zero
input voltage or current, the meter pointer is at center scale.
The ZEROCENTER control On the rear panel is used to set the meter
pointer to zero for zero center operation. It should require only
infrequent attention.

3-6 0962R


The basic element of the Model 6OOAis a highly accurate, stable dc
voltmeter with a full scale se sitivity of 10 millivolts and an in-
put impedance greater than 101C ohms shunted by 30 micro-microfarads.
Amperes and ohms are measured by the use of resistance standards.
The various connections necessary for ampere and ohms measurements
will be discussed following the detailed description of the amplifier.
Refer to DR1201hCat the rear of the manual.
The amplifier proper con-
sists of Vl, V2, and V3.
VL is a cathode follower
which drives the amplifier
at the same instantaneous
potential as the input
signal. In other words the
neutral or ground terminal
of the amplifier is not
grounded to the chassis out
is attached to the output
cathode follower. Fig.
600-2 shows this diagram-
atically. The amplifier A
FIOURE BOO- 2 is driven by the cathode
Input dividers are neither stable nor accurate at high impedance. Con-
sequently the Model 600A will accept 10 volts without the use of input
dividers, preserving the high input impedance and accuracy of the ampli-
fier. Accessory probes are available for extending the voltage range at
reduced input resistance and accuracy.
Since the amplifier proper is driven by the cathode follower, the plus
and minus 30 volt batteries for the cathode follower are referred to
input ground while the battery supplies for the amplifier are referred
to amplifier ground which is "floating". In subsequent discussion,
reference will be made to the amplifier ground as "floating ground" and
to cathode follower ground as "output ground".
The amplifier input consists of two balanced 5886 electrometer tubes.
The filaments are operated in parallel from battery Bl. The control
grid of Vl, the active electrometer tube, is protected by R2, a 109 ohm
resistor, bypassed for high frequencies by C2. The control grid cf 712,
the 'tdummy" tube, is returned through a variable voltage to floating
ground. This variable supply is made up from B2a, B2b, R15 (ZEROon the
front panel) and Rll, ~28, R29;R30, R31, R32 on SW-& (COARSE ZEROon
rear panel).

og62R 4-1

The ZEROccntrcls function by adjusting the dc voltage of the dummy
electrometer tube grid.
The voltmeter sensitivity is determined by the resistor placed in
series with the meter, R33 through R39. Meter current passing
through Rh2 develops the constant one volt output for any ranse.
C3 and R6 serve to stabilize the feedback loop against oscillation.
Grid current of the input
electrometer tube fixes the
minimum current that may be
measured. The Model 600A
grid current will us~&lly
be less than 2 x lo-
OUTPUT amperes. On low current
ranges, the grid current
will be apuarent and may be
balanced out with ZEROcon-
trol or subtracted from the
CHASSIS GROUND final reading.

PIQURE' 600- 3

(1) Shunt Resistor Method (NORMAL)
In the normal operating connection as shown in Fig. 600-3, current is
measured by placing a resistor across the input terminals and measuring
the voltage drop. Currents from 3 amperes to lo-13 amperes may be
measured by this method since the range switch selects resistors ranging
from one ohm to 1011 ohms in decade steps. The voltage drop is selected
by the MULTIPLW switch; the setting is the input voltage drop for full-
scale meter deflection.
(2) Feedback Method (FAST)
In the voltmeter discussion above, floating ground has been driven by
the cathode follower and output ground has been connected to the low
impedance side of the input conne&or. In the FAST connection, shown
in Fig. 600-1, the amplifier ground is connected to the low impedance
side of the input; the cathode follower ground floats, and negative
feedback is applied through the shunt resistor.
In the Model 6OOA, it is possible to use this connection with currents
of 0.1 microamperes or less. To change the connection, remove the lock
from NORMAL-FAST switch at the bottom of the rear panel and change it to
the FAST position. The advantages of this connection are:
(a) The effect of input capacity is largely neutralized, that
is, the time constant of the input and cable capacity and the
shunt resistor used will be decreased at least 100 times as

4-2 0962R

compared to the NORMAL connection, correspcnding to a loo-fold
increase in response speed.
(b) The input drop will be reduced~ about 100 times.
If Fig. 600-l is again consulted, it will be seen that this connecticn
converts the 600A into an operational amplifier with a resistor from
the output to the input. Therefore, the following cautions apply:
(a) The input cannot be shorted since this will remove the feed-
(b) The internal impedance of the current source being measured
should not be less than about one-tenth of the value of the feed-
back resistor used for measurement.
(c) This connection should not be used for measuring the leakage
current of capacitors since the connection of the capacitor to the
input causes the circuit to be transformed into a differentiator
with the resultant extreme sensitivity to very small voltage tran-
sients. For this measurement the NORMAL should be used.
(d) Do not attempt to use the FAST connection for currents exceed-
ing 0.1 microamperes.
(1) Two Terminal Xethod
The Model:600A employs a
linear scale to provide a
megohmmeterof high accur-
acy. The linear ohms scale
is achieved by supplying a
constant current to the
sample and measuring the
voltage drop across it.
The method is shown in
Fig. 600-h.
(2) Ohmsmeasurement using
CIOURE 600-4 GUARDterminal:
There are two disadvantages
with the method just out-
(a) When measuring resistanoes greater than 1011 ohms, input capa-
city causes the meter reading to be annoyingly slow.
(b) If it is desired to use large voltages across the sample, this
same voltage will appear across the input insulation of the electro-
meter and the input insulation will contribute error to the reading
because of the current also flowing in it.

Og62R 4-3

For these reasons a second connection for measuring ohms is provided.
The switch at the rear of
RX the instrument is moved
from N0FW.L to FAST and
the resistance sample is
connected to the GUARD
terminal. Fig. 600-5
shows the arrangement.
Now, as with measuring
amperes with the FAST
method, the amplifier
ground is attached to the
input ground and the ca-
thode-follower ground is
floating. The result is
FIQURE 600-8 that feedback is applied
through the unknown re-
sistance to reduce the
slowing effect of instrument input capacity. Also, since the potential
across the input terminal is small, the leakage error is reduced. .
(3) Use of External Voltage Supply
With the constant current
t method of measuring resist-
ante, the voltage across the
unknown may not be arbit-
rarily selected, and the
time of measuring capacitor
leakage tends to be long,
since constant-current
charging is slower than the
exponential charge available
with an RC circuit.
Due to these facts, it may
be desirable to use an ex-
ternal voltage supply and
FIQURE 600-6 measure the leakage current
on the AHPERES scale (NORMAL
The unknown is connected between the input terminal of the electrometer
and the source of voltage. This is shosn in Fig. 600-6. If the applied
voltage is large compared to the voltage drop across the electrometer
(so that the voltage across the sample is substantially the applied volt-
age) the resistance is simply equal to the voltage applied divided by the
current measured. If the voltage drop is an appreciable fraction of the
applied voltage, the resistance equals the voltage applied minus the input

4-4 0962R

drop divided by the current measured. It will be rarely necessary
to correct for the input drop of the electrometer due to the excel-
lent voltaRe sensitivity of the Model 600~.
It is advisable to use the NOW micro-microammeter connection
for the measurement of leakage resistance of capacitors in this
manner, since instability is likely to occur using the FAST con-
nection. However, in cases where the capacity shunted across the
sample is small, it will be possible to realize a considerable
increase in speed of response by utilizing the FAST connection.
Someprecautions are recommendedwhen testing capacitors. Be sure
that capacitors have discharged before removing from test circuit.
With the ZEROCHECK switch depressed,the input is shorted to
ground through 1 megohm, providing a discharge path for the cana-
citor. The reading: time may be shortened if the capacitor is al-
lowed to charge through a low impedance position on the AMPERES
switch before the appropriate measuring resistor is inserted in
the circuit.
It should be further noted that capacitor measurement is likely
to be a slow process in any case due to the fact that it may take
considerable time for the molecular orientation of the dielectric
to take place at the testing potential. It may take minutes or
even hours in some cases to achieve a stable reading.



The Model 6101A Lead consists of an input connector, 3 feet of
low noise cable and a shielded probe head. Its purpose is to
allow convenient connection to the electrometer input.
The Model 6102A divider probe is intended for general purpose
measurements where an extension of the upper voltage range of
the 600A is desired. The division ratio is 1O:l correct to 1%
and the probe input resistance is lOlo ohms. The probe is
supplied with a mating connector and 3 feet of cable.
The Model 6103A probe is intended for very high voltage measure-
ments at high impedance. The division rat& is 1OOO:l correct
to 3% and the probe input resistance is 10 ohms. The probe
is supplied with a mating connector and 3 feet of cable.
The Model 61Oh Test Shield is intended for use in making measure-
ments wherein complete shielding of the component under test is
required. External terminals are provided for either grounded
tests, or a test requiring an external voltage source.



No periodic maintenance is required other than checking the batteries
as provided for by the front panel control. The method of performing
these checks is outlined in Section III-E.
The calibration of the voltmeter is set by R41 located on the horison-
tal chassis carrying Bl, B3 Bh and B5. This is set at the factory
and should not require adjustment. If recalibration is performed, an
accurate voltage source should be used.
A. Trouble Shooting
The circuit is completely described in Section IV. Study of that
section will facilitate any trouble shooting.
The most usual trouble encountered is that on the most sensitive volt-
age range, with the input shorted, it is not possible to bring the
meter pointer to zero. However before assuming that the instrument is
at fault make sure that resetting the COARSE ZEROcontrol at the rear
of the instrument will not oring the instrument back into balance.
If this does not work it will be necessary to remove the instrument
cover to gain access to all circuitry. The instrument cover is re-
moved by unscrewing the three screws on both sides of the instrument
and lifting the cover upward. With the cover removed, follow this
Short floating ground to output ground to remove the negative feed-
back. This is most conveniently accomplished by shorting the two
ends of the FAST-NORMAL switch on the rear panel. In this condi-
tion the instrument will become very sensitive and, in operating
the zero control, the meter will be very difficult to hold on
scale. However, t&indication that the circuit is operating
satisfactorily is that it is possible to swing the voltage through
the'correct operating point as indiczited on the voltage-resistance

Now with the MULTIPLIER switch at .Ol volts, proceed to check the
operating points of the tube electrodes.
Regardless of the condition of the amplifier balance, the filament
or cathode, and screen potentials should be reasonably close to
the values on the circuit diagram. The plate and grid potentials
will depend on the settine of the ZEROcontrol, However if it is
possible to swing the voltage through the correct value it may be
assumed that the stage is working. Proceed in this manner until
the point is found where the voltage cannot be swung through the
value marked on the diagram. At this point it will be relatively
easy to find the fault. First check the tube involved and then
check the components.

og6m 6-1

Miscellaneous troubles:

-- Cause Remedy
Excessive erid Defective electrometer Replace Vl and V2
current tube with matched set
Excessive drift Battery failing Replace batterv
Excessive micro- Defective electrcmeter Reulace Vl and V2
phonics tube with matched set
Tnstrument does See section above See section above
not zero.

The proper method of inserting electrometer tubes is shown in the volt-
age-resistance diagram. When inserting do not touch the glass base,
where the leads emerge, with the fingers.

6-2 0962R


7-1. REPLACEABLEPARTS LIST. The Replaceable Parts List describes the components of the
Model 600A. The List gives the circuit designation, the part description, a suggested
manufacturer, the manufacturer's part number and the Keithley Part Number. The name and
address of the manufacturers listed in the "Mfg. Code" column are contained in Table 2.


a. For parts orders, include the instrument's model and serial number, the Keithley
Part Number, the circuit designation and a description of the part. All structural parts
and those parts coded for Keithley manufacture (80164) must be ordered from Keithley
Instruments, Inc. In ordering a part not listed in the Replaceable Parts List, completely
describe the part, its function and its location.

b. Order parts through your nearest Keithley distributor or the Sales Service Department,
Keithley Instruments, Inc.

amp ampere Mil No. Military Type Number
CbVar Carbon Variable n ohm
CerD Ceramic, Disc
Comp Composition P pica (lo-12)

DCb Deposited Carbon v micro (10-6)
f farad v volt
Var Variable
k kilo (103)
w watt
M or meg mega (106) or megohms ww Wirewound
m milli (10-3) WWVar Wirewound Variable
Mfg. Manufacturer

TABLE 1. Abbreviations and Symbols.

1164R 7-l

(Refer to Schematic Diagram DR12014C for circuit designations.)

Circuit Mfg. Mfg. Keithley
Desig. Description Code Part No. Part No.
Bl 1.34 v mercury 37942 RM42R BA-10
B2a 8.4 v mercury 61637 E146X BA-9
B2b 0.4 v mercury 61637 E146X BA-9
B3 1.34 v mercury 37942 FM42R BA-10
B4 30 v dry cell 61637 413 BA-5
B5 30 v dry cell 61637 413 BA-5
B6 8.4 v mercury 61637 EL46X BA-9
B7 0.4 v mercury 61637 EL46X BA-9

Circuit Mfg. Mfg. Keithley
Desig. Value Rating Type Code Part No. Part No.

Cl01 100 pf 1000 " CerD 72982 831XSRlOlK c22-LOOP
Cl02 100 pf 1000 " CerD 72982 831XSRlOLK c22-LOOP
Cl03 0.02 uf 1000 " CerD 72982 84125V203P C22-.02M
Cl04 0.02 uf 1000 " CerD 72982 84125V203P C22-.02M

Circuit Mfg. Keithley
Desig. Description Code Part No.
JlOL Receptacle, uhf, Input, Mil. No. SO-239A (Mfg.
No. 6804) 91737 CS-64
--- Dust Cap for 5101, n, Mil. No. MX-913/U (Mfg.
No. 7901) 91737 CAP-4
Plug, uhf, Mate for Input, Mil. No. 49190 (Mfg.
No. 83-822) 02660 cs-49
Reducing Adapter, uhf, for CS-64 and CS-49, Mil.
No. UG-175/U (Mfg. No. 83-185) 02660 CS-36
5102 Binding Post, Black, G (Mfg. No. DF2LBC) 58474 BP-11B

5103 Receptacle, Microphone, Output (Mfg. No. 80-PC2F) 02660 CS-32
-_- Plug, Microphone, Mate for Output (Mfg. No. 80-MC%) 02660 cs-33
5104 Binding Post, Red, INPUT GUARD (Mfg. No. DF21RC) 58474 BP-11R
Ml01 Meter 80164 ME-16
SlOl Rotary Switch less components, Range 80164 SW-63
--- Rotary Switch with components, Range 80164 L2326B
--- Knob Assembly, Range Switch 80164 153678

7-2 0765R

Circuit Mfg. Keithley
Desig. Description Code Part No.
s102 Push Button, ZERO CEFXK 80164 14376A
s103 Slide Switch, NORMAL-FAST (Mfg. No. G326) 79727 SW-45
s104 Rotary Switch less components, COARSEZERO 80164 SW-51
--- Rotary Switch with components, Coarse Zero 80164 12094B
SLOS Rotary Switch less components, MULTIPLIER 80164 SW-47
--- Rotary Switch with components, Multiplier 80164 12093B
--- Knob Assembly, Multiplier Switch 80164 L5384A
S106 Rotary Switch Less components, METER-BATTERY 80164 SW-62
--- Rotary Switch with components, Meter-Battery 80164 12092B
--- Knob Assembly, Meter-Battery Switch 80164 148388
--- Knob Assembly, ZERO Control 80164 15110A

Circuit Mfg. Mfg. Keithley
Desig. Value Rating Type Code Part No. Part No.
RlOl 18-l lO%, l/2 w Comp 01121 EB Rl-1M
R102 LO9 R 20%, l/2 w Comp 75042 BTS R37-109
R103 Not Used
R104 Not Used
RL05 LO Ml l%, 1 w DCb 91637 DC-1 R13-10M
RL06 a33 !ul lO%, l/2 w Comp 01121 EB Rl-33K
R107 10 m l%, 1 w DCb 91637 DC-1 R13-10M
R108 312 kn L%, l/2 w DCb 79727 CFE-15 R12-312K
R109 Not Used
RllO 220 kG l%, l/2 w DCb 79727 CFE-15 R12-220K
RLll 450 kG l%, L/2 w DCb 79727 CFE-15 R12-450K
R112 3.4 kG l%, 1 w DCb 91637 DC-l R13-3.4K
Rl13 9 'm l%, l/2 w DCI, 79727 CFE-15 R12-9K
RL14 lkn l%, L/2 w DCb 79727 CFE-15 R12-LK
Rll5 10 kG 3%, 5 w WWVar 73138 A RP4-10K
R116 1% DCb 63060 Rx-1 R20-loll
R117 ;,":i n
n 1% DCb 63060 Rx-1 R20-1010
R118 109 n 1% DCb 63060 Rx-1 R20-10g
R119 100 m l%, 2 w DCb 91637 DC-2 R14-100M
R120 10 N-l l%, 1 w DCb 91637 DC-1 R13-10M
R121 1M l%, l/2 w DCb 79727 CFE-15 R12-LM
R122 LOO kQ l%, l/2 w DCb 79727 CFE-15 R12-100K
R123 10 kn l%, l/2 w DCb 79727 CFE-15 R12-10K
* Nominal value, factory set.
0765R 7-3


Circuit Mfg. Mfg. Keithley
Desig. Value Rating 'We Code Part No. Part No.

R124 1 kn l%, l/2 w 79727 CFE-15 R12-LK
R125 100 n l%, LO w ww 91637 RSE-10 R34-100

R126 10 R l%, 10 w ww 91637 RSE-LO R34-10
R127 ln l%, 10 w ww 91637 RSE-10 R34-1
(1) *20 n .l%, 2 w ww 01686 7070 R92-20
R128 450 kc? L%, l/2 w DCb 79727 CFE-15 RL2-450K
RL29 8.6 kn L%, L/2 w DCb 79727 CFE-15 R12-8.6K
R130 8.6 kn l%, l/2 w DCb 79727 CFE-15 R12-8.6K

R131 8.6 krl l%, l/2