lNSTRUCT,lON MANUAL
MODEL 610A, 610R
MULTI-PURPOSE ELECTROMETER
AND ACCESSORIES
MODEL 610A
TAHLI. 01: CfIKTEh’TS
Section I.
Section II.
Specifications . . . . . , , . . , . , . . . . ,
Description. . . . . . . . . . . . . . . . . . . 1 1 1
Section III.
Voltmeter. . . . . . . . . . . . . . .
Ammeter. . . . . , . . . . . . . . . . 1 1 1 1 1 1 1 ,
Ohmmeter . . . , . . . . . . . . . . . . . . . . . . . .3-4
Standard Resistance Check,,, , . , . . . , . . , .
The Hegulated power Supplies , . , . . . . , . . , : :
Section IV.
Preparing the Instrument for Operation . . , , , . , . .4-l
Measuring Vo’ltage. . , , . . , . . , . . . . . ,
MeasuringCurrent......
>!easuring Resistance . , , , 1 , , . , , , ,
Internal Resistor Check, , , , , , . . . . , : : : : : .4-4
Internal Voltage Check , , , . , . . . . , . . , . . . .4-4
Using External Indicators. . . . . , . . . . . . . a . -4-4
Miscellaneous Applications , , , . . , . . . . . . , . .4-S
Zero Center Operation. . . . , , . . , . . . . , . . . .4-6
‘Title
Introduction. . . , . . . . . . . . . . . . . . .1-l
Specifications and Description . , . , . , , . .2-l
Circuit Description . . , , , , , . , , . . , .3-l
Operation. . . , , . . . . , , , , . , . . . , .4-l
. . . . . . . . . . . .
m
.2-l
.?-2
. .3-l
.3-3
.3-7
.3-7
.4-2
Section V.
Section VI.
Trouble Shooting , , , , , , , , , , , , , , , , , . . .6-l
Recalibrating power Supplies , . ,
Replaceable Parts List . . , , , , : : : : : : : : : :
Voltage and Resistance Chart . . , , , . , , , . . . . .6-9
Schematic Diagram. . . , , , , , . . . . . . . , , , . .6-11
*Change Notice. , . , . , . , , , , , , , , , , , , , , .Last
*If a change in the instrument affects the instructions, the correction is printed on a yellow sheet at the back of the manual,
0862R
Accessories , . , , , , , , . . . , . , . . . , -5-l
Xaintenance. . . , . . . . . . . . . . . . . .
.6-l
.6-2
.6-S
Page
i
MODEL 610A
INTRODUCTION
SECTION I
The Keithley Model 610A 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,
on all ranges,
The maximum input resistance is greater than 1014 ohms; in addi-
tion
ohm io
instrument, Thus, ~the 610A is not only appropriate for measure-
ment in high-impedance circuits, but also can be used where a high
input impedance would merely introduce unwanted pickup,
The 610A may be used as a direct-reading ammeter from 3 amperes
to lo-l3 ampere full scale, This 14-decade range is covered in
overlapping 3x and l?poscales. Accuracy is within 3% of ful’l
~;“~031y~;;~;e~o lo
Two current measuring methods are available to the user of the 610A.
They are selected by a slide switch at the back of the instrument,
Normally, current is determined by measuring the voltage drop acr ss
;,‘$I5
put of the voltmeter through the current measuring resistor,
largely eliminates the input drop and increases measuring speed,
particularly on the more sensitive ranges,
the ‘nput resistance may be varied in decade steps from one
10lf
ohms by means of the shunt resistors built into the
ampere, and 4% of full scale from 3 x lo-
or shunted from input to ground, Alternately, on the 10
ampere ranges,
negative feedback can be applied to the in-
- INTRODUCTION
Accuracy is within 2% of full scale
sea e
4
4
This
The 610A measures 0.2 ohm to 1011 ohms with a two-
With a guarded input, its range is extended to 10
volt external supply would further extend the range to 1016 ohms,
Unlike conventional ohmmeters, information is presented on the
same linear scales used for current and volt ge
racy is within 3% of full scale up to 3 x
beyond,
As a dc preamplifier, the 610A has a maximum gain of 1000, obtainable in 9 steps of 0.1,
accuracy is within 1% on all gain steps,
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.
potentiometer is provided with the 1 ma position for calibrating
recorders. A slide switch next to the output connector permits
selecting the desired output,
0,3, 1, 3, 10, 30, 100, 300, and 1000.
8
10
ohms, within 5%
The continuing stability
erminal
li
ohms,
readings.
A calibration
input,
A lOOO-
Accu-
Gain
0762R
l-1
INTRODUCTION
Red meter scales and a ZERO CENTER position on the METER switch
permit all of the above operations with the zero reference at the
center of the meter dial rather than at the left,
The Model 610A (left) and the
Model 610R (below) have ident-
ical electrical specifications
and performances, The two
models differ only in phys-
ical appearance; the 610A is
for bench use while the 610R
is for rack mounting.
MODEL 610A
0762R
MODEL 610A
SPECIFICATIONS AND DESCRIPTION
SECTION II
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-l3
3x overlapping ran es,
C.
Ohms :
10 ohms to 10 f 4 ohms full scale on linear lx and
3x overlapping ranges,
d,
Meter scales: Black -
Accuracy:
a.
b,
Voltage:
Current: 3% of full scale from
4% of full scale from 3 x 10-l
C.
Ohms : 3% of full scale from 10 ohms to
of full scale from 3 x 1010 ohms to 10
Resistance Standards:
- SPECIFICATIONS & DESCRIPTION
amperes full scale in lx and
Left zero, 0 to 3 and 0 to 10
- Center zero, -1.5 to 0 to +1,5 and
Red
-5 to 0 to +5.
2% of full scale on all ranges,
to lo-10 amperes,
change slightly in value with age,
Input Impedance:
On the VOLTS position the input impedance is
ohms resistive, shunted by approximately 30 micromicrofarads.
Drift:
Less than 2 millivolts per hour after a 1 hour 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 10 kc on the least sensitive range.
gain is 1000, Noise is less than 3% (peak to peak) of full
scale,
Line Regulation:
A ten
percent
130 or 200 to 260 volts will cause a change of less than
2 mllllvolts equivalent input,
resistors
may
be expected to
greater
than 1014
Maximum
change in line voltage in the range of 100 to
0563~
2-l
SPECIFICATIONS AND DESCRIPTION
MODEL 610A
Tubes :
Two 5886, two EF86, one 6BH8, two 12AX7, one 12B4A, one OG3,
one OA2, one OB2.
Cabinet:
7-l/4 wide by 11-l/2 high by 13-3/4 deep, Weight 21-114 lbs.
Power Supply:
100 to 130 (or 200
to 260) v,olts, 50 to
60 cycles at approx-
imately 50 watts.
DESCRIPTION
The Keithley Model 610A is a line operated multipurpose dc measur-
ing instrument of extremely wide range, The measuring ranges are
summari,zed below:
VOLTAGE :
10 millivolts to 100 volts full scale, The input imped-
ance is greater than 1014 ohms shunted by approximately 30 micro-
microfarads on the VOLTS position of the RANGE SWITCH,
resistance may be varied from 1011 h
o ms to 1 ohm in decade steps
The input
by rotating the RANGE switch in the AMPERES range marking.
HIGH VOLTAGE WITH ACCESSORIES:
The Model 61024 10~1 divider probe.
extends the measuring range to 1000 volts. The divider resistance
is 1010 ohms and its division accuracy is 1%.
The Model 6103A lOOO:l.divide~ pro& extends the measuring .range to
30 KV.
Its input resistance is 10 ohms and its dzvision accuracy
is 3%.
CURRENT :
to 3 x 10-3
3 amperes to 10’13
amperes
full scale.
amperes the current is measured by measur’ngthe
across a resistor shunted across the input,
From 10
From 3 amperes
-4
amperes, the method above may be used or, by placing the FAST-NOR-
MAL switch on the back panel in the FAST position, negative feed-
back is applied around the shunt resistor, This makes the input
drop negligible and improves speed of response considerably on the
low current ranges.
OHMS :
10 ohms to 1014 ohms full scale,
The linear ohms scale is achieved by measuring the unknown resistor
with a known,
across the sample is thff proportional to the resistance.
ance from 10 ohms to 10
minal method.
constant current flowing through it, The voltage drop
Resist-
ohms full scale is measured by a two ter-
From 1011 to 1014 ohms., use of the GUARD terminal
available at the rear of the instrument is recommended,
DC AMPLIFIER:
The frequency response of the Model 610A as an amplifier is from dc to’ 500 cycles on the 100 millivolt range rising to
10 kc on the 100 volt range.
2-2
The output is either 10 volts or 1
0762R
MODEL 610A
SPECIFICATIONS AND DESCRIPTION
milliampere for fu .ll sea
microammeter position,
,le meter deflection, In the NORMAL micro-
one side of the output is grounded, For
directions pertaining to the use of recorders see Section IV-G.
CURRENT SOURCE: When measuring ohms,
the instrument is designed
to supply a constant current to any device placed across its in-
put
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.
CONTROLS AND TERMINALS:
The input connector is Gremar Type #6804.
The mating connector is supplied as well as an accessory binding
post
which plugs into the center of the connector, A ground bind-
ing post is mounted on the panel above the input connector.
Front Panel controls are:
RANGE switch,
themeter,
the AMPERES position,
located in the center of the front panel under
This control selects VOLTS, OHMS, or AMPERES. On
a shunt resistor whose value is the reciprocal of the designated range may be used to decrease the
input resistance as well as to measure current.
MULTIPLIER switch, located in the center directly under the
meter, determines the voltage.sensitivity of the dc amplifier,
and sets the voltage range when the RANGE is set on VOLTS. On
OHMS or AMPERES, the setting of this knob multiplied by the
OHMS or AMPERES setting gives the full scale meter range,
ZERO control,
sr the meter,
located to the left of the MULTIPLIER switch
is used to set the meter to zero.
METER switch, at the right under the meter, turns the instru-
menton, determines meter polarity, and permits zero center
operation,
OPERATE switch, located at the bottom right, selects normal
operation or one of the two check positions.
In the ZERO CHECK position, the input terminals are shorted
through 1 megohm,
the RES CHECK position,
standards are measured,
Rear Panel controls are:
FUSE, at the upper right,
ZiijGre fuse;
with 230 volt power use 1 amp fuse,
POWER INPUT, Unless indicated,
volts 50-66 cps.
cuit schematic diagram,
while the amplifier input is shorted. In
the internal high megohm resistance
With 117 volt AC power use 1.5
instrument is wired for 117
For 230 volt operation, consult the cir-
076211
2-3
SPECIFICATIONS AND DESCRIPTION
>lODEL 610A
RECORDER CAL.
Used to calibrate 1 ma. recorders, so their
scale corresponds with the panel meter.
1 >{A - 1OV.
ampere recorders,
In the 1 MA position, OUTPUT will drive 1 milli-
In the 1OV position, the output is 10
volts for full scale panel meter deflection.
OUTPUT connector for external recorders,
NORMAL- FAST,
FAST position,
around the shunt resistor,
This control is locked
in
NORMAL position, In
current measurements are made with feedback
On OfWS, the FAST position is
used when the INPUT GUARD terminal is used,
INPUT
GUARD.
With the NORMAL-FAST switch on FAST, the low
rmpednnce end of the test sample is returned to this terminal
when it is desired to measure the resistance of a guarded
sample.
COARSE ZERO,
If the amplifier is quite badly unbalanced, the
-switch is used to bring the front panel ZERO control
in range.
I
2-4
0762R
MODEL 610A
CIRCUIT DISCUSSION
SECTION III
- CIRCUIT DISCUSSION
The basic element of the Model 610A is a highly accurate, stable
dc voltmeter with a full scale sensitivity of 10 millivolts and
an input impedance greater than 1014 ohms shunted by 30 micro-
microfarads,
ance standards,
Amperes and ohms are measured by the
use
of resist-
The various connections necessary for amperes and
ohms measurements will be discussed following the detailed descrip-
tion of
A.
Refer to DR 11861 D at the rear of the
the
amplifier,
VOLTMETER
manual,
The amplifier proper consists of Vl through V5-A.
VS-B 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
-9
INPUT
0
-
1 ~_ L
A
-- -
* I
AHR
SND.
-
grounded to the chassis
but is attached either directly or through divider
R165 through R171 to then
+
OUTPUT ‘ROVND
output cathode folliower.
Fig,
610-l shows this dia-
gramatically. The ampli-
FIGURE 610-l
is desired to have unity gain,
to the cathode,
To increase the voltage gain, a fraction of the
the amplifier is connected directly
output voltage rather than all of
it
fier
A
is driven by the
cathode follower,
is fed back,
If it
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.
Conse-
quently, the Model 610A will accept 100 volts without the use of
input dividers, preserving the high input impedance and accuracy
of the amplifier,
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 220 volt supplies for the cathode follower are re-
ferred to input ground while the +225 volt and the -85 and -150
volt 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”.
0762R
3-1
CIRCUIT DISCUSSION
MODEL 610A
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 R123, a ten megohm resistor,
bypassed for high frequencies by ClOl. The control grid of V2,
the “dummy” tube, is returned to floating ground,
The input switch,
SW3, connects the grid of Vl to the input terminal on the OPERATE
position and connects it to ground,
resistor,
on ZERO CHECK,
through the 1 megohm protective
The screen grids of Vl and V2 are returned, in effect, to the cathodes
of V3 and V4 through SW4 (COARSE BALANCE) and R180 (ZERO), The
balance controls function by adjusting the dc voltages of the electro-
meter 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 potential 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,
conductance due to filament temperature changes,
stabilization,
such as variation in the plate supply and changes in trans-
Also due to this
electrometer tube operating 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 VS-A,
V6-A drives the output cathode
follower,
The,.voltmeter sensitivity is determined by the fraction of the cathode
follower voltage fed back via the divider, R165 through R171. 10
volts appears at the VS-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. R161 is the meter multiplier resistor
from 10 millivolts to 10 volts,
R162 and R163
are
used.
On the 30 and 100 volt ranges,
The OUTPUT is derived directly from the 6BH8 cathode except on the
30 and 100 volt ranges,
the output switch is set at 10
with R177 to attenuate the output to 10 volts.
is set at 1 ma,
these resistors in combination with R164 and R160
where R158 and R159 are interposed, If
V, R158 and R159 form~a divider
If the output switch
are used to provide enough series resistance so that 1 milliampere
flows into the recorder terminals. R164 and R160 calibrate the
recorder on all
ranges.
The feedbacks loop is stabilized against oscillation by Cl02 and
Cl03 together with R172 through R176.
Insertion of R172 through
R176 in the cathode of VS-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 cause oscilla-
3-2
076213
MODEL 610A
CIRCUIT DISCUSSION
tion.
Cl02 and Cl03 provide a 6 db per octave dominant lag cut-
off characteristic,
B.
AMMETER
Grid current of the input electrometer tube fixes the minimum cur-
The Model 610A grid current will usually
~?:e::a~h~~Y2b~ ~~“sYr~~~eres On low current ranges the grid
current will be apparent and rniy be balanced out with Ihe ZERO control or subtracted from the final reading,
(1) Shunt Resistor Method (NOWIAL)
In the normal operating
connection as shown in
Fig, 610-2A, current is
measured by placing a
resistor across the input
terminals and measuring
the voltage drop, Cur-
;;“I? ;;;;&a;;;r;; lco
measured by this method
since the range switch
selects resistors r nging
from one ohm to 1Ola ohms
in decade steps,
The volt
age drop is selected by
the MULTIPLIER switch; the
setting is the input voltage drop for full-scale
FIGURE 610-2A
meter deflection.
(2) Feedback Method (FAST)
In
the voltmeter discus-
sion above, floating grounc
has been driven by the
cathode follower and out-
put ground has been
con-
nected to the low impedance side of the input
connector,
connect ion,
In the FAST
shown in Fig.
610-2B, the amplifier
ground is connected to
the low impedance side
of the input; the cathode
follower ground floats,
z
FIGURE 610-2B
and negative feedback
is applied through the
shunt resistor,
In the Model 610A, it is possible to use this connection with currents
of 100 microamperes or less,
To change the connection, remove the
lock from the NORMAL-FAST switch at the bottom of the rear panel and
change it to the FAST position, The advantages of this connection
are :
0762R
3-3
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