Keithley 610 User manual

MODEL 610
MULTI-PURPOSE ELECTROMETER
AND ACCESSORIES
KEITHLEY INSTRUMENTS, INC.
CLEVELAND, OHIO
.

CONTENTS
SECTION
INTROCUCTION
. . . . . . . . ..*..*...*...*....*....**...........
SPZCIFICATIONS AND DESCRIPTION
. . . . . . . . . . . . ..*...........
CIRCUIT DISCUSSION......,...............................
A. Voltmeter
B. Ammeter
(1) Normal
(2) Fast
C. Ohmmeter
(1) Normal
(2) Guarded
(3) External Voltage
D. Standard Resistance Check
E. Regulated Supplies
OPERATION....... ..,......**...*....*.................**.
A. Preliminary Steps
B. Voltmeter
C. Ammeter
(1) Normal
(2) Fast
D. Ohmmeter
(1) Normal
(2) Guarded
(3) External Voltage
E. Internal Resistance Check
F. Internal Voltage Check
G. Using External Indicators
H. Miscellaneous Applications
(1) Current Integrator
(2) Current Source
(3) Static Charge Detector
ACCESSORIES
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..a.........
MAINTENANCE
. . . . . . . . . . . ..*..........*........*...........
A. Trouble Shooting
B. Schematic
C. Voltage-Resistance Diagram
D. Replacement Parts List
I
II
III
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V
VI
XEITHLFY INSTRUMEX~TS CLEVELAND, OHIO

SECTION I INTRODUCTION
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The Keithley Model 610 Electrometer is an ultra-high impedance
voltmeter with full-scale ranges of 0.01, 0.03, 0.10, 0.30, 1.0,
3.0, 10, 30, and 100 volts. Accuracy is within 2% of full scale
on all ranges.
The maximum input resistance is greater than lo14 ohms; in addi-
tion, 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 610 is not only appropriate for lreasure-
ment in high-impedance circuits, but also can be used where a high
input impedance would merely introduce unwanted pickup.
The 610 may be used as a direct-reading ammeter from 3 amperes
to lo-13 ampere full scale. This &-decade range is covered in
overlapping 3x and 10x scales.
from 3 amperes to lo-8 alnpere, Accuracy is within 3s of full scale
and 4$ of full scale from 3 x 10-Y
to lo-13 ampere.
Two current measuring methods are available to the user of the 610.
They are selected by a slide switch at the back of the instrument.
Normally, current is determined by measuring the voltage drop across
a resistor shunted from input to ground.
to lo-l3 ampere ranges, Alternately, on the 10e4 negative feedback can be applied to the in-
put of the voltmeter through the current measuring resistor. This
largely eliminates the input drop and increases rceasuring speed,
particularly on the more sensitive ranges.
The 610 measures 0.2 ohm to 1011 ohms with a two-terminal input.
With a guarded input, its range is extended to 1014 ohms.
volt external supply wouId further extend the range to 101% lOOO-
ohms.
Unlike conventional ohmmeters, information is presented on the
same linear scales used for current and voltage readings. Accu-
racy is within 3% of full scale up to 3 x 100 ohms, within 5%
beyond.
As a dc preamplifier, the 61.0 has a maximum gain of 1000, obtainable
in 9 steps of 01, 0.3, 1, 3, 10, 30, 100, 300, and 1000. Gain
accuracy is within l$ on all gain steps. The continuing stability
of the gain is assured by a feedback factor in excess of 100 on any
range.
The output is either 10 volts for driving high impedance devices
such as oscilloscopes or pen recorder amplifiers, or 1 ma for
driving low impedance recorders or similar devices. A calibration
Potentiometer is provided with the I. ma position for calibrating
recorders. A slide switch next to the output connector permits
selecting the desired output.
I -1

SECTION II SFECIFICATION AND DESCRIPTION
1
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SPECIFICATIONS
Ranges:
(a) Voltage: 0.01, 0.03, 0.1, 0.3, 1, 3, 10, 30, and 100
volts full scale.
(b) Current: 3 amperes to lo-13 amperes full scale in
lx and 3x overlapping ranges.
(c) ohms: 10 ohms to 1014 ohms full scale on linear lx
and 3x overlapping ranget3.
Accuracy:
(a) Voltage: 2s of full scale on all ranges.
(b) Current: 376of full scale from 3 amperes to lo-10
ampere s . 4s of full scale from 3 x lo-10 to lo-13
amperes.
(c) Ohms: 376of full. scale from 10 ohms to 101' ohms.
5% of full scale from 3 x 1010 ohms to 1014 ohms.
Resistance Standards:
1, 10, 100, 1000, 104, 105, 106, 107, 108
109, lOlo, and 1011 ohms, 2Yjlaccuracy. ohms, 1% accuracy;
The 109 and 101' ohm and 10 resistors may be expected to
change slightly in value with age.
Input Impedance:
On the VOLTS position the input impedance is greater than .
1014 ohms reeistive, shunted by approximately 30 micromicrofarads. '
Drift:
Less than 2 millivolts per hour after a 30 minute warm-up.
Recorder Output:
1 milliampere or 10 volts for full scale meter deflection,
selected by a rear panel switch.
Amplifier:
Frequency response is DC to 500 cycles on the most sensitive
range, rising to 1Okc on the least sensitive range. Maximum
gain is 1000. Noise ie less than 3% (peak to peak) of full
male.
Line Regulation:
A ten percent change in line voltage in the range of 100 to
130 or 200 to 263 volt6 will cause a change of less than 200
micro-volts equivalent input.
II - 1
c .

TuboE:
TWO 5806, two EF86, OIB 6BH8, two 12AX7, on@lZB&A, one OG3,
one OA2, one OB2.
Cabinet:
7$ wide by 11-l/8 high by 13$ deep. Weight 17 lbs.
Power Supply:
loo to 130 (or 200 to 260) Volta, 50 to 60 cycles at
approximately 50 watts.
II - 2

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DESCRIPTION
The Keithley Model 610 is a line operated multipurpose dc measure-
ing instrument of extremely wide range. The measuring ranges are
summarized below:
VOLTAGE: 10 millivolts to 100 volts full scale. The input im-
pedance is greater than lOl!+ ohms shunted by approximntely 30
micromicrofarads on the VOLTS position of the function switch.
The input resistance may be varied from 1011 ohms to 1 ohm in
decade steps by rotating the function switch in the AMPERESrange
marking.
HIGH VOLTAGEWITH ACCESSORIES: The Model 6102 1O:l divider probe
extends the measuring range to 1000 volts. The divider resistance
is lOlo ohms and its division accuracy is 1s.
The Model 6103 1OOO:l divider probe extends the measuring range to
30 Kv. Its input resistance is 101' ohms and its division accuracy
is 34’0.
CURRENT:
3 amperes to lo-13 amperes full scale. From 3 amperes
to 3 x 10-3 amperes the current is measured by measuring the drop
across a resistor shunted across the input. From 10-k to lo-13
amperes, the method above may be used or, by placing the FAST-NORMAL
switch on the back panel in the FAST position, negative feedback
is applied around the shunt resistor. This makes the input drop
negligible and improves speed of response considerably on the low
current ranges.
owls : 10 ohms to 1014 ohms full scale.
The linear ohms scale is achieved by measuring the unknown resistor
with a known, constant current flowing through it. The voltage drop
across the sample is then proportional to the resistance. Resistance
from 10 ohms to 1011 ohms full scale is measured by a two terminal
method. From 1011 to 1014 ohms, use of the GIJA'AWterminal available
at the rear of the instrument is recommended. An auxiliary 100 volt
supply at the re.ar of the instrument is provided when measuring ob-
jects with appreciable capacitance or when it is desired to extend
the measuring range. With the 100 volt potential, the leakage cur-
rent is read on AMPERESand the resistance calculated.
DC AMPLIFIER: The frequency response of the Model 610 as an amplifier
is from dc to 500 cycles on the 10 millivolt range rising to 1Okc on
the 100 volt range. The output is either 10 volts or 1 milliampere
for full scale meter deflection. In the NORMALmicro-microammeter
position, one side of the output is grounded; in the FAST micro-
microammeter position the output is not grounded. For directions
pertaining to the use of recorders see Section IV-G.
II - 3

CONTROLSAND TERMINALS: The input connector is Amphenol 83-798. The
mating connector is supplied as well a* an accessory binding post
which plugs into the center of the connector. A ground binding post
is mounted on the panel above the input connector.
Front Panel controls are:
FUNCTION switch, located in the center of the front panel under
the meter. This control selects VOLTS, OHMS, or AMPERES. On the
AMPERESposition, a shunt resistor whose value is the reciprocal
of the designated range may be used to decrease the input re-
sistance *s well as to measure current.
VOLT FULL SCALE switch, located at the left under the meter,
determines the voltage sensitivity of the dc amplifier, and sets
the voltage range when the FUNCTION is set on VOLTS. On OHMSor
AMPERES, the setting of this knob multiplied by the OHMSor
AMPERESsetting gives the meter scale factor.
The ZERO control, located in the center of the front panel directly
under the meter, is used to set the meter to zero.
The METERswitch, at the right under the meter, turns the instrument
on, determines meter polarity, and tests the potentials used in
measuring ohms.
The OPERATEswitch, located at the bottom right, selects normal
operation or one of the two check positions.
Rear Panel controls are:
In the ZERO CHECKposition, the Input terminals are shorted through
1 megohm, while the amplifier input is shorted. In the RES CHECK
position, the internal high megohm resistance standards are measured.
FUSE, at the upper right. With 117 volt AC power use 1.5 ampere
G; with 230 volt power use 1 amp fuse.
POWERINPUT. Unless indicated, instrument is wired for 117 volts
PO-60 cps. For 230 volt operation, consult the circuit schematic
diagram.
SET 1OOV. Used to
if meter indicates adjust the 100 volt internal test potential
correction is needed.
SET 225V. Same as
for Set 1OOV.
RECORDERCAL. Used to calibrate 1 ma. recorders, so their scale
corresponds with the panel meter.
1 MA - 1ov. In the 1 MA position, OUTPUTwill drive 1 milliampere
recorders. In the 1OV position, the output is 10 volts for full
scale panel meter deflection.
II - 4

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OLTPUT connector for external recorders.
--
NORMAL-FACT. This control is locked in NORMALposition.
In FkST position, current measurements are made with feed-
back around the shunt resistor. On OHMS, the FAST position
is used when the INPUT GUARDterminal is used.
INPUT GUARD. With the NORMAL-FASTswitch 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
sample.
l.oov * This test potential is used when it is desired to test
leakage resistances with constant relatively high, potential
applied across the unknown.
COARSEZERO. If the amplifier is quite badly unbalanced, the
COARSEZERO switch is used to bring the front panel ZERO control
in range.
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II - 5

SECTION III CIRCUIT DISCUSSION
The basic element of the Model 610 is a highly accurate, stable dc volt-
meter with a full SC
"Ee sensitivity of 10 millivolts and an input imped-
ance greater than Id- ohms shunted by 30 micro-microfarads. Amperes
and ohms are measured by the use of resistance standards. The various
connections necessary for amperes and ohms measurements will be discussed
following the detailed description of the amplifier.
A. VOLTMETER
Refer to DR 11861 D at the rear of the manual.
The amplifier proper consists
of Vl through V5,-A. Vg-B is
a Cathode follower which drives
--O
INPUT
0
the amplifier at the same in-
stantaneous potential as the
- input signal. In other words
the neutral or ground termi-
nal of the amplifier is not
grounded to the chassis but
is attached either directly
I or through divider Fi165
) through Rl71 to the output
cathode follower. Fig. 61.0-l
OUTPUT QROUND
shows this dia@'amatically.
The amplifier A is driven by
FIGURL 610-I the cathode follower. If it
is desired to have unity gain,
the amplifier ie connected directly to the cathode. To increase the voltage
gain, a fraction of the output voltage rather than all of it is fed back. '
The purpose of this arrangement is to allow the input to accept relatively
large input voltages without use of input dividers, which are neither stable
nor accurate at high impedance. Consequently, the Model 610 will accept
100 volts without the use of input dividers, preserving the high input impe-
dance and accuracy of the amplifier. Accessory probes are available for ex-
tending the voltage range at reduced input resistance and accuracy.
Since the amplifier proper is driven by the cathode follower, the plus and
minus 220 volt supplies for the cathode follower are referred to input
pound while the t225 volt and the -85 and -150 volt supplies for the amp-
lifer 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 through a dropping resistor from the
regulated B-plus supply. The control grid of Vl, the active electrometer
tube, is protected by Rl23, a one megobm resistor, bypassed for high fre-
quencies by ClOl. The control grid of V2, the "dummy" tube, is returned
III - 1

,B
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to fleeting ground, The input switch, SW3, connects the grid of Vl
to the input terminal on the OPERPJ'Eposition and connects it to
ground, through the 1 megohm protective resistor, on ZERO CHECK.
The screen grids of Vl and V2 are returned, in effect, to the cathodes
of V3 and V4 through SW4 (COARSEBALANCE) and Rl80 (ZERO). The bal-
ance controls function by adjusting the dc voltages of the electrometer
tube screens. Since the cathode of V3 and V4 are free to move, the
result is that a negative feedback loop for signals in phase at the
electrometer tubes exists through the cathode circuit of V3 and V4 back
to the screens of Vl and V2. This connection stabilizes the plate po-
tential of the input tubes, and causes the first stage gain to be much
greater for signals arriving at the active tube control grid than
spurious signals at both electrometer tubes, such as variation in the
plate supply and changes in transconductance due to filament tempera-
ture changes. Also due to this stabilization, electrometer tube oper-
ating points are maintained even though 10 meg plate load resistors
are used to assure a large voltage gain in this stage. This obviates
the need for regulation of the filaments of subsequent stages.
V3 and V4 form an ordinary differential amplifier and their output is
taken single ended into V5-A. V6-A drives the output cathode follower.
The voltmeter sensitivity ia determined by the fraction of the cathode
follower voltage fed back via the divider, ~165 through R171. 10 volts
appears at the V5-B cathode for full scale meter deflection for the
ranges from 10 millivolts through 10 volts. On the 30 and 100 volt
ranges, 30 and 100 volts respectively are fed directly back to floating
ground. Sl61 is the meter multiplier resistor from 10 millivolts to
LO volts. On the 30 and 190 volt ranges, x162 and ~163 are used. .
The OUTPUTis derived directly from the 6BB8 cathode except on the 30 I
and 100 volt ranges, where x158 and Rl59 are interposed. If the out-
put switch is set at 10 V, ~158 and R159 form e divider with Rl77 to
attenuate the output to 10 volts. If the output switch is set at 1 ma,
these resistors in combination with ~164 and ~160 are used to provide
enough series resistance ao that 1 milliampere flows into the recorder
terminals. ~164 and I~60 calibrate the recorder on all ranges.
The feedback loop is stabilized against oscillation by Cl02 and Cl03
together with Rl.72 through R176. Insertion of R172 through ~176 in
the cathode of V5-A, or the omission of a resistor by the range switch,
determines the loop gain. The gain is kept high enough so that there
is a feedback factor of at least 100 on all ranges, but the gain is not
allowed to become high enough to ceuae oscillation. Cl02 and Cl03
provide a 6 db per octave dominant lag cut-off characteristic.
B. AMMEER
Grid current of the input electrometer tube fixes the minimum current
that may be measured.
than 2 x lo-l4 amperes. The Model 610 grid current will usually be less On low current ranges, the grid current will
be apparent and may be balanced out with the ZERO control or subtracted
from the final reading.
III - 2

(1) Shunt Resistor Method (NORMAL)
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FIBURE 610-2A
(2) Feedback Method (FAST)
FIGURE 610-20
In the normal operating connec-
tion as shown in Fig. 61041,
current is measured by placing
a resistor across the input
terminals and measuring the
voltage drop. currents from
3 amperes to 10-13 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 VOLTS switch; the set-
ting is the input voltage
drop for full-scale meter
deflection,
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
connector. In the FAST con-
nection, shown in Fig. 610-2~~
the amplifier ground is con-
nected to the low impede&e
side of the input; the cath-
ode follower ground floats,
and negative feedback is ap-
plied through the shunt
resistor.
In the Model 61.0, it is possible to use this connection with currents of
100 microamperes or less. To change the connection, remove the lock from
the NORMAL-FASTswitch 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 compared to the NOF34AL
connection, corresponding to a loo-fold increase in response speed.
(b) The input drop will be reduced at least 100 times.
If Fig. 610-a is again consulted, it will be seen that this connection con-
verts the 61.0 into an operational amplifier with a resistor from the output
to the input. Therefore the following cautions apply:
III - 3

(a) The input cannot be shorted since this will remove the feedback.
(b) The internal impedance of the current source being measured should
not be less than about one-tenth of the value of the feedback resistor
used for measurement.
(c) This connection should not be used for measuring the leakage cur-
rent of capacitors since the connection of a capacitor to the input
causes the circuit to be transformed into a differentiator with the
resultant extreme sensitivity to very small voltage transients. For
this measurement the NOHMALshould be used.
(d) Do not attempt to use the FAST connection for currents exceeding
100 microamperes.
C. OBMMETER
(1) Two Terminal Method.
The Model 610 employs a lin-
ear scale to provide a megohm-
meter of high accuracy. The
linear ohms scale is achieved
by supplying a constant cur-
rent to the sample and measur-
ing the voltage drop across it.
One method is shown in Fig.
610-3.
The constant current sourcs
FIGURE 610-3
can consist of a high voltage
and a large resistor of kn'own
value. As long as the drop across the unknown resistor is of the order of 1%
of the total voltage, the current can be considered constant. In the Model
610 on the Id and 104 ranges, the current is supplied in this manner from a
100 volt supply with the appropriate dropping resistor as illustrated in
Fig. 610-3. For example, with a current of one milliampere, the voltage
drop
across a one ohm resistor will be one millivolt. Thus this value can be read
on the 10 millivolt range of the 610.
On the 105 range and higher, a
second method is used to ob-
tain a constant current. This
- is illustrated in Fig. 610-k.
The ground connections are in
the NOHMALposition, that is,
RX the amplifier ground is driven
and the cathode-follower ground
is attached to the input ground.
F The voltage source is only one
volt. However, it is attached
FIOURE n10--4
between floating ground and the
grid of the voltmeter while, as before, the test sample is attached between in-
put ground and the voltmeter grid. Since feedback to the amplifier ground
keeps it at virtually the same potential as the input grid regardless of the
input voltage, the voltage across the current source resistor cannot change.
III - 4 *

1
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1,
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1
Therefore this arrangement provides a true current 6ouzce regardless of the
input voltage. Thus, resistances may be measured using any voltmeter range
on the 106 to lOl.2 ohmmeter ranges as opposed to the limit of 1 volt maxi-
mum on the 103 to 105 ohmmeter ranges.
(2) Ohms measurement using GUARDterminal.
There are two disadvantages with the method just outlined:
(a) When measuring resistances greater than 1011 ohms, input capacity
came6 the meter reading to be annoyingly slow.
(b) If it is desired to use large voltages acro88 the sample, this
same voltage will appear acro88 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.
For these reasons a second connection for measuring ohms is provided.
Rx The switch at the rear of the
instrument le moved from
NORMALto FAST and the low im-
pedance end of the resistance
sample is connected to the
GUARDterminal. Fig. 610-5
shows the arrangement. NOW,
a~ with measuring amperes with
the FAST method, the amplifier
ground is attached to the in-
put ground and the cathode-
follower ground is floating.
The result is that feedback is
applied through the mown
resistance to reduce the slow-
FIOURE EIO- 5
ing effect of instrument input
capacity. Also, since the po-
tential across the input terminal ie small, the leakage error is reduced.
(3) Use of External Voltage Supply.
With the constant current method of measuring resistance, the voltage acro89
the unknown may not be arbitrarily selected, and the time of measuring ca
pacitor 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 external voltage supply
and measure the leakage current on the AMPERESocale (NORMALoperation).
III - 5

+--+=j---;--
The unknown 18 connected between the
input terminal of the electrometer
~~~~:;6%~;<Tl::d
voltage is large compared to the
voltage drop acro88 the electrometer
EXTERNAL
sample is substantially the applied
VOLTAOE F
voltage) the resistance is simply
equal to the voltage applied divided
by the current measured. If the
FIQURE 010-6
voltage drop is an appreciable frac-
tion of the applied voltage, the re-
sistance equals the voltage applied minus the input drop divided by the cur-
rent measured. It will be rarely necessary to correct for the input drop of
the electrometer due to the excellent voltage sensitivity of the Model 610.
It is advisable to use the NORMALmicro-microammeter connection for the
measurement of leakage resistance of capacitors in this manner, since insta-
bility is likely to occur using the FAST connection. However, in cases
where the capacity shunted acro88 the sample is small, it will be possible
to realize a considerable increase in speed of response by utilizing the
FAST connection.
Some precautions are recommended when testing capacitors. Be 8ure that ca-
pacitors have discharged before removing from test circuit. With the 610
input switch on ZEROCHECK, the input is shorted to ground through 1 megohm,
providing a discharge path for the capacitor. Simultaneously the 100 volt
test potential at the rear of the instrument is disconnected. The reading
time may be shortened if the capacitor is allowed to charge through a low
impedance position on the AMPEREswitch before the appropriate measuring .
resistor is inserted In the circuit.
It should be further noted that capacitor measurement is likely to be a
elow 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 8ome cases to
achieve a stable reading.
D. STANDARDRESISTOR CHECK
The resistance standards used in the Model 610 have been describe
specification section. 8 in the
In general the resistors from 1 ohm to 10 ohms
can be expected to retain a 1% accuracy throughout the life of the instru-
ment . The high megohm resistors are correct to 2% when installed, and
will usually be between 1% and 2% above the nominal value. Since they
always decrease in value with time, they are likely to remain within spe-
cifications for three to six years after the instrument is delivered.
Bowever, to determine the accuracy of these resistors, a resistance check
position 18 provided on the input switch. Thus corrections can be made
in the readings of small current and high resistance.
III - 6

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The method used in checking the re-
sistors is outlined in Fig. 610-7.
The ohmmeter is used in the stand-
ard manner except that the input
switch is turned to KZS CHECK. In
this position a L,$ 108 ohm resistor
is placed across the Input. In turn,
109, 1010 and 1011 ohm resistors are
used to supply current through this
resistor from 10 volts. Thus If the
1011 position on the OENS segment of
the function switch is used, the
meter should read full scale on the
.Ol position of the OHMS-AMPSMULTI-
PLIER. Correspondingly, the reading
is full scale on the 0.1 position
for the 101' ohm resistor and the 1.0 position for the 109 ohm resistor.
If the reading is not correct, a correction factor can be applied to the
ohms and amperes reading,
Due to the fact that the current through the resistor is the reciprocal
of the resistance value, if the reading is low, the correction is sub-
tracted on AMPERESand added on OFIMS. If the reading is high, the op-
posite is done.
E. THE REGULATD POWERSUPPLIES
The negative regulator consists of cascaded voltage regulator tubes Vll .
and VlO. This combination provides a well-regulated supply for the
negative return of the second ampltiier stage and reference for the
positive supply. The maximum current supplied by this regulator com-
bination is about 2.5 milliamperes so that the regulator tubes are able
to operate satisfactorily over a 100 to 130 volt range of line voltage.
Vll, type OA2, supplies a minus 150 volt potential for the amplifier
interstage dividers.
The positive 225 volt regulator is a three tube regular circuit con-
sisting of V8, the series tube, and V6 and V7 which form the feedback
amplifier. This circuit operates satisfactorily from 100 to 130 volts
and is largely responsible for the extreme freedom from line transients
which the Model 610 exhibits.
III - 7

SECTION IV OPERATION
A. PREPARINGTRE INSTRUMENTFOR OPERATION
(1) Connect to power line of proper voltage and frequency. Due to
the extreme sensitivity of the Model 610, the appearance of 60 cps
noise at the output terminals is sometimes encountered. IF THIS
NOISE IS FOUNDTO BE HIGHER THAN 2% OF FULL SCALE, THE POWERPLUG
MAY BE Pi3VERSEDTO REDUCETHE NOISE. It may also help to ground
the case of the instrument to a water pipe or similar earth ground.
Unless otherwise indicated at rear of instrument, the Model 610 is
wired for 100 to 130 volts 50 to 60 cps. If it is desired to oper-
ate on 200 to 260 volts 50 to 60 cps, consult DR 11861 D at rear of
the manual for instructions.
(2) set controls as follows:
VOLTS SWITCH: 100 volts.
FUNCTION SWITCH: VOLTS
OPERATESWITCH: ZERO CHECK
INPUT TERMINAL: Shield with cap.
(3) Turn the Power switch to meter c. The instrument should come to
zero in approximately 30 seconds.
(4) Rotate the VOLTS switch toward the high sensitivity end, adjust-
ing ZERO as required. If it is impossible to zero the meter with the
front panel ZERO control, use COARSEBAI. control on rear panel to
bring the instrment within range of the ZERO control. . <~.
(5) 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 610 may be
used.
If the impedance is low and leads can be kept short, the binding
post adapter furnished with the instrument may be used.
The Keithley Model 6101 Shielded Test Probe will suffice for most
measurements.
B. MEASURING VOLTAGE
Place FUNCTION switch at VOLTS. Turn VOLTS switch to expected sensi-
tivity and check meter zero. Turn OPERATEswitch to OPERATEand read.
If the sensitivity of the instrument is increased, rocheck the zero
reading.
For voltages greater than 100 volts, use the Model 6102~10~1 Divider
Probe, or the Model 6103~1ooo:i Divider Probe and measure as above.
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C. mASURIX'- ZGYX
(1) NOFJGL;_ _neres to 10-13 amperes full scale).
Turn FUN:== .z-: desired AMPERX range. Make sure the switch
at the TEL- 5 2 z?xnent is on the NORMALposition. Connect
current 5:--Y x zz7. The product of the reading on the FUNCTION
switch ef< -2 X25 MlJLTIPLl3R gives the meter scale factor.
Check zex 5~ = :X'RATE switch and then read unknown current.
The voltis zz =r the instrument is the meter reading multi-
plied by -3 -c :1 the OHMS-AWS MULTIPLIER.
(2) FAST Y-Z --~ :o lo-l3 amperes full scale).
Proceed ZE = m-z move the FAST-NOFXAL switch at the rear of
the instrz 7 z ?.iST position. The input drop is now negli-
gible an< -2 --1 = response is increased approximately 100 times.
However c‘:= T ~-Lowing cautions:
(a) -2 c-x zput switch to check zero; DO NOT SHORTINPUT.
(b) & 5 z :Z the output is no longer grounded.
There:: ;z Jstrument is being used with an output record-
er t&c zzzzczt not be grounded to the case of the 610.
(c) :t zz fx.z position for the measurement of capacitor
1eak=;s.
D. MEASURINGz>
(1) NORM!; ---_ 13x8 to 1011 ohms full scale).
Tlu'r, func:'z =_-I desired OHMSrange. Make sure that NORMAL-
FAST switc? - r1-Z?UL position.
Connect resin %Ie to be measured only after OPERATEswitch
has been _-=_ -1 CHECK.
__- Do not open-circuit instrument when
onomls, s--'z=* will develop a large voltage due to its
constant zI=-=r -erietic. However, if the sample is first
connected z5~z~Z'EXATF. switch is turned to OPERnTEthe
input volt= I=:;13 value read on the meter scale multiplied
by the se: L z 3i-AMPS MULTIPLIER.
Before ~5%: 75 xxx FUNCTION switch to the approximate range
of the I~-:-T- ~523. By manipulating the OHMS-AWS MULTIPLIER
and the -:._ z. the sample can be tested at a number of
test potezti : zired.
The full-srG = -4 is the FUNCTION switch setting multiplied
by the se:---, = x~ :34S-AMPS WTIPLIER.
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This two terminal method is the simplest and will work quite sat-
isfactorily up to about 1011 ohms. At resistances greater than
1011 ohms, it is desirable to employ a GUARDconnection both to
speed up the response of the instrument and to nullify the error
of leakage across the electrometer input insulation.
(2) GUARDEDmethod (10" to 1014 ohms full scale).
Proceed as with the two terminal method with the exception that the
sample is connected between the INPUT terminal and the GUARDtermi-
nal on the rear panel, the FAST-NORMALswitch must be set at FAST.
(3) EXTERNALVOLTAGEmethod.
Any external voltage may be used, or the 100 VOLT terminal on the
back panel.
The unknown is connected between the test potential and the INPUT
terminal of the electrometer. The current is then measured, using
the NORMALor FAST method, and the resistance calculated.
Proceed as follows:
(a) Turn input switch to ZERO CHECK.
(b) Connect unknown between INPUT terminal and source of po-
tsntial. A switch should be connected in the high voltage
line so that when the sample is disconnected from the potential,
the low impedance end of the sample is grounded. If the 100
volt tap at the rear of the 61.0 is used, the potential is turned
off when input switch is in either ZERO CHECKor RESISTANCE
CHECKposition. *
(c) FAST-NORMALswitch should be at NORMAL,
(d) Apply potential to sample before switching to OPERATE. Start
the function 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 meter reading times the setting of the VOLTSFULL SCALE
switch), the resistance is equal to:
POTENTIAL APPLIED
CURRENTREADING
If the potential applied is not large compared to the ammeter
drop, the resistance is equal to:
POTENTIAL APPLIED - INPUT DROP (VOLTS)
CURRENTREADING
(e) If it is possible to operate on FAST micro-microammeter,
the input drop need not be considered in the calculation.
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E. INTERNAL RESISTOR CREW
(1) To check 109:
to OHMSx 109. Turn input switch to ZERO CRECK, function switch
Turn VOLTS FULL SCALE to 1.0 or 3.0. Turn input
switch to RES CEECK.
1.00 x 109. If reading is exactly one volt, resistor is
If reading is low, subtract the percent correction
when measuring AMPERESand add the percent correction when measur-
ing ORMS.
(2) To check 101': Turn VOLTS FULL SCALK to .l or .3. Reading
should be .1 volt.
(3) To check 1011: Turn VOLTS FULL SCALE to .Ol or .03. Reading
should be .Ol volts.
F. INTERNAL VOLTAGRCHECK
The Internal 225-volt and lOO-volt supplies are used to test re-
sistance samples and therefore should be checked periodically and.
always befors the high megohm standards are checked. To check,
turn meter switch to CRECK225~. The meter should point to 2.25
on the 3.0 scale.
Then turn meter to 100~. The meter should read exactly full scale.
If either potential is not correct, set with the appropriate con-
trol at the back of the instrument.
G. USING EXTERNAL INDICATORS
The output of the Model 610 will drive one milliampere recorders and
servo rebalance recorders, as well as higher impedance instruments such
as pen recorder amplifiers and oscilloscopes.
(1) For use with one milliampere instruments such as Esterline
Angus, General Electric, and Texas Instrument Rectiriter: Connect
to output connector at rear of instrument, pin 1 is the positive
terminal. Place output switch at 1 MA position. Output is approx-
imately 1 ma for full scale meter deflection on any range and can
be made exactly 1.00 ma. Turn to a voltage rangs such as 100 milli-
volts full scale, where zero control has enough latitude, and adjust
ZERO until panel meter reads full scale. Then adjust mCORDRRCAL
at the rear until the recorder also reads full scale. Next check
the zero of the recorder and the panel meter and repeat full scale
calibration. The meter polarity switch does not reverse the re-
corder output.
(2) For use with servo rebalance recorders: On the 1 MA position,
there is enough latitude in the RECORDERCAL pot so that even if
the recorder terminals are short circuited, exactly one milliampere
can be made to flow at full scale deflection of the panel meter.
Therefore for servo rebalance recorders, place a resistor across
the output terminals equal to 1 ohm per millivolt of span and ad-
just RRCORDEXCAL to make sensitivity equal to full scale meter
deflection. For example, with a 50 millivolt recorder place 50
ohms across output terminals before connecting recorder.
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(3) For use with oscilloscopes and pen recorder amplifiers, set
output switch at the 10~ position. output is now 10 volts for
full scale meter deflection on any range.
The frequency response is dc to 500 cycles on the 10 millivolt
range rising to 10 kc on the 10, 30 and 100 volt ranges. The
maximum amplitude which can he delivered by the amplifier is
approximately 10 volts peak to peak. Maximum permissible load
across the output terminals in this mode
megohm. ~& a- e$&t itit g I ?'d of operation is one
With the FAST-NORMALswitch at the rear of the instrument in the
NORMALposition, the negative side of the output is grounded to
the case of the instrument. However in the FAST position neither
side is grounded. Therefore, no difficulty will be experienced
using oscilloscopes and pen amplifiers with the 610 in NORMAL
operation. However if it is desired to use the FAST position,
care must be taken that there is no common ground between the pen
writer or the oscilloscope and. the Model 610 case.
H. MISCELLANEOUSAPPLICATIONS
CURRFJITINTEGRATOR: The Model 610 may be used as an integrator
for small currents such as cyclotron and mass spectrometer beam
currents, since it is basically an operational amplifier with
electrometer input when the FAST-NORMALswitch at the rear is
placed in the FAST position.
To integrate current connect a polystyrene capacitor of suitable
value between the GUARDterminal and the input. The FUNCTION
switch is set at VOLTS so that there is no resistance placed
across the capacity. Then if Fig. 610-2B is consulted, it can
be seen that the standard resistor has been replaced by a cap-
acitor and the 610 is now an integrator. The charge on the cap-
acitor in coulombs is simply the product of the capacitor value
chosen (in farads) and the setting of the VOLTS FULL SCALE switch
(in volts). If it is desired that a time constant 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
grounded can. The connection to the GUARDterminal may be made
by a simple unshielded lead. The connection to the input terminal
should be made by means of a coaxial connection to one side of a
"tee" adapter. The current input is made to the other side of the
"tee" .
The following procedure is suggested: Turn input switch to ZERO
CHECK, thus removing the charge from the capacitor and shorting the
input. Zero if necessary. Turn 'Lo OPERATE. If the integration
is to take place over a long period of time it is suggested that
the instrument be used on the one volt range or higher so that
zero drift and grid current will not be fac.tors.
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