Tektronix 601 Instruction Manual
MODEL 601 ELECTROMETER
CONTENTS
TABLE OF CONTENTS
Section
1. GENERAL DESCRIPTION .
l-l. General . . .
1-2.
1-3.
Features .
Specifications ,
l-4. Applications . .
1-5.
1-6.
2. OPERATION . . . . .
2-l.
Accessories . .
Equipment Shipped
. . .
Front Panel Controls
and Terminals . . . .
2-2.
Rear Panel Controls
and Terminals . . .
2-3.
2-4.
2-5.
2-6.
Input Connections . . .
Preliminary Procedures
Voltage Measurements .
Off Ground Voltage
Measurements . . . .
2-7.
2-8.
2-9.
2-10.
2-11.
Current Measurements .
Resistance Measurements
Charge Measurements . .
Recorder Outputs . . . . . . 17
Unity Gain Output . . .
3. APPLICATIONS . . . . . . . . . .
3-l.
General . . . : . . . . , .
3-2. current source , . . . . .
3-3. Static Charge Measurements
3-4.
3-5.
Capacitance Measurements .
current Integrator . . . .
3-6. Potentiometric Voltage
Measurements . . . . , .
3-7.
Measuring Diode
Characteristics . . . . ,
3-8.
4.
CIRCUIT DESCRIPTION . . . , .
Peak-Reading Voltmeter . .
4-l. General . . . . . . .
4-2.
4-3.
4-4.
4-5.
4-6.
5.
SERVICING . . . . . . . . .
Voltmeter Opiration , .
Voltmeter Circuit . . .
Ammeter Operation . . .
Ohmmeter Operation . .
Coulombmeter Operation
5-l. General . . . . . . . .
5-2. Servicing Schedule .
5-3.
Parts Replacement , . ,
Page
1
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1
2
2
4
5
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5
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. . 7
. . 8
. . 9
. . 11
. . 12
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. . 17
. . 18
* 21
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. 21
. 21
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25
25
25
26
27
28
29
31
31
31
31
Section
5-4. Troubleshooting . . . .
5-5.
Procedures to Guide
Troubleshooting . . . .
6. CALIBRATION . . . . . . .
6-l.
6-2.
6-3.
6-4.
General . . , . . . . . . .
Calibration Schedule . . .
Grid Current Check . . . . .
DC Amplifier Balance
Adjustment . . . . . . . .
6-5. High-Megohm Resistor
Verification . . . . . . .
6-6. Meter Zero Calibration . .
6-J.
6-8.
7.
ACCESSORIES . . . . . . . .
J-l.
J-2.
J-3.
Accuracy Check . . . , , . .
Drift Check . . . . . . . .
Model 6011 Input Cable . .
Model 1531 Gripping Probe .
Model 6301 Guarded Probe . .
7-4. Model 6012 Triaxial-to-
Coaxial Adapter . . .
7-5. Model 6102A Voltage Divider
Probe , , . . , . , . . .
7-6. Model 6103A Voltage Divider
Probe , . . . . . , . .
J-7.
Model 6104 Test Shield . .
7-8. Model 6105 Resistivity
Adapter . . . . . . . . .~
7-9.
Models 2501 and 2503 Static
Detector Probes , . . . .
J-10.
Rack Mounting . . . , . . .
J-11. Model 6013 pH Electrode
Adapter . . . . . . . .
J-12.
MQdel
370
Recorder . . . . .
\
8.
REPLACEABLE PARTS . . . . . . .
8-1.
8-2.
Replaceable Parts List . . .
How to Order Parts . . . .
Model 601 Replaceable
parts List . . . . . . . ,
Schematic Diagram 194283 .
,*
Change Notice . . . . . . . . .last page
* Yellow Change Notice sheet is included
only for instrument modifications
affecting the instruction manual.
Page
31
31
35
35
35
35
36
36
36
37
38
43
43
43
43
43
44
44
44
45
46
46
47
4,8
51
51
51
52
58
0667R
i
GENERAL DESCRIPTION
MODEL 601 ELECTROMETER
-
XGURE 1.
ii
Keithley Instruments Model 601 Electrometer.
9666
MODEL 601 ELECTROMETER
GENERAL DESCRIPTION
SBCTION 1.
l-l. GENEXAL.
a. The Keithley Model 601 Electrometer is a versatile battery operated instrument which
measures wide ranges of dc voltages, currents, resistances and charges.
refined dc vacuum tube voltmeter that uses an electrometer tube input to provide greater
than 1014 ohm input resistance.
VTVMs, but Lt can also make many more measurements without loading circuits.
The Electrometer has nine volta e ranges from 0.001 volt full scale to 10 volts,
b.
twenty-eight current ranges from 10'
resistance ranges from 100 ohms full scale to 1013 ohms,
10-12 coulomb full scare to 10-6 coulomb.
The Model 601 offers complete line isolation and excellent off-ground measuring capa-
bi;ity. Up to 1500 volts may be applied between the input low terminal and the case, and
safe operation is
guarding of the high terminal.
The Model 601 employs matched electrometer input tubes followed by three differen-
d.
tial transistor amplifier stages and a transistor output stage.
tive feedback is used for stability and accuracy.
assured
with the case grounded. A three-terminal input allows complete
The Model 601 has all the capabilities of conventional
GENERAL DESCRIPTION
It is a highly
l$
ampere full scale to 0.3 ampere, twenty-three linear
and thirteen charge ranges from
A large amount of nega-
l-2.
hour period after warm-up. During the 2-hour warm-up, zero drift is no more than 2 millivolts after the first hour.
+l volt or fl milliampere for full-scale meter deflection.
25% with 1.4-kilohm recorders. The unity-gain amplifier output is equal to the input
voltage within 50 ppm or 100 inicrovolts, exclusive of zero drift.
&he current is determined by measuring the voltage drop across a resistor shunting the
oxput, or the fast method in which negative feedback is applied through the shunt resis-
tor.
greatly increases the response speed on the low-current ranges.
interruptions for-recharging.
corder output is used.
the panel meter,
FEATURES.
Voltmeter accuracy is *l% of full scale, exclusive of noise and drift.
a.
Zero drift of the Model 601 is 200 microvolts per hour maximum averaged over any 24-
b.
Two amplifier outputs are available. A switch on the rear panel allows either
c.
The-current output is variable
Current measurements can be made by one of two methods: the normal method in which
d.
The former method minimizes noise. The latter method reduces the input drop and
e. The lOOO-hour life of the batteries enables "sage in Long-term experiments without
Battery life is maintained even when the l-milliampere re-
For further convenience, battery condition is readily checked on
056JR
1
GENERAL DESCRIPTION
1-3. SPECIFICATIONS.
AS A VOLTMETER:
MODEL 601 ELECTROMETER
RANGE:
ACCURACY:
ZERO DRIFT:
any subsequent 24-hour period,
METER NOISE:
INPUT IMPEDANCE:
.OOl volt full scale to 10 volts in nine lx and 3x ranges.
~1% of full scale on all ranges exclusive of noise and drift.
After l-hour warm-up no more than 2 millivolts in the second hour, and in
the average drift will not exceed 200 microvolts per hour.
Cl0 microvolts maximum with input shorted on most sensitive range.
Greater than 1014 ohms shunted by 20 picofarads. Input resistance may
also be selected in decade steps from 10
AS AN AMMETER:
RANGE:
ACCURACY:
Multiplier Switch setting;
METER NOISE:
GRID CURRENT:
LO-14 ampere full scale to 0.3 ampere in twenty-eight lx and 3x ranges.
*z% of full scale on 0.3 to lo-11 ampere ranges using the smallest available
24% of full scale on 3 x lo-12 to lo-14 ampere ranges.
Less
than i3 x 10'15 ampere.
Less than 2 x LO-l4 ampere.
AS AN OHMMETER:
to
1011 ohms.
RANGE:
ACCUR4CY:
plier Switch setting:
100 ohms full scale to 1013 ohms in twenty-three linear lx and 3x ranges.
23% of full scale on 100 to 108 ohm ran 8 es using the largest available Multi-
;t5% of full scale on 3 x 10 to 1013 ohm ranges.
AS A COULOMBMETER:
RANGE:
ACCURACY:
LO-12 coulomb full scale to lo-6 coulomb in thirteen lx and 3x ranges.
i5% of full scale on all ranges. Drift due to grid current does not exceed
2 x lo-14 coulomb per second.
AS AN AMPLIFIER:
INPUT IMPEDANCE: Greater than 1014 ohms shunted by 20 picofarads. Input resistance may
also be selected in decade steps from 10 to 1011 ohms.
OUTPUTS: Unity-gain output and either voltage or current recorder output.
UNITY-GAIN OUTPUT:
clusive of zero drift.
At dc, output is equal to input within 50 ppm or 100 microvolts, ex-
Up to 0.1 milliampere may be drawn. Output polarity is same as
input polarity
0366R
MODEL 601 ELECTROMETER
GENERAL DESCRIPTION
VOLTAGE RECORDER. OUTPUT:
+l volt for full-scale input. Internal resistance is 910 ohms.
Output polarity is opposite input polarity.
Gain:
0.1, 0.33,
Frequency Response (Within 3 db):
etc.
to 1000.
dc to 100 cps at a gain of 1000, rising to 50 kc st
a gain of 3.3, decreasing to 1 kc at a gain of 0.1.
Noise:
Less than 2% rms of full scale at a gain of 1000, decreasing to less than 0.5%
at gains below 10.
CURRENT RECORDER OUTPUT:
il milliampere for full-scale input, variable +5% with 1400-ohm
recorders.
GENERAL:
ISOLATION:
Input low to case: greater than 1010 ohms shunted by 0.0015 microfarad. I*-
put low may be floated up to k1500 volts with respect to case.
POLARITY:
Meter switch selects left-zero (positive or negative) or center-zero scales.
Meter switch does not reverse polarity of outputs.
CONNECTORS: Input:
Teflon-insulated triaxial Dage 33050-l. Lo: binding post. Voltage
or current output: Amphenol 80-PC2F. Unity gain output, case ground: binding posts.
BATTERY CHECK:
BATTERIES:
E42N or HG42R).
DIMENSIONS, WEIGHT:
Condition of all batteries may be checked with front panel controls.
Four 2N6 (or 246, VS305 or NEDA 1602); three TR286 (or E286); two RM42R (or
1000 hours battery life.
10-l/2 inches high x 6-5/b inches wide x 10 inches deep; net weight,
14 pounds.
ACCESSORIES SUPPLIED:
Model 6011 Input Cable; mating output connector.
l-4. APPLICATIONS.
Voltmeter applications include directly measuring potentials across pH electrodes,
a.
piezoelectric crystals, capacitors,
electro-chemical cells and biological membranes.
The Model 601 is also useful as a null detector with potentiometers or bridges in high im-
pedance applications.
As a picoammeter the Model 601 can br used with photomultiplier tubes, flame and
b.
beta ray ionization detectors,
lithium ion drift detectors and gas chromatographs.
It is
also useful in nuclear studies , plasma physics and vacuum research.
c. As an ohmmeter the Electrometer is ideal for measuring insulation resistance and
resistor voltage coefficients.
since the Model 601 low terminal can be isolated from case ground.
It is useful for measuring "in circuit" resistances,
Volume and surface re-
sistivities can be measured with the Model 601 and the Model 6105 Resistivity Adapter.
d.
0366R
In addition to measuring charge directly
other coulombmeter uses are measuring
3
GENERAL DESCRIPTION
MODEL 601 ELECTROMETER
charge current over a period and obtaining integral curves of time varying currents. The
Electrometer can also be used as a charge amplifier to measure piezoelectric crystal outputs.
l-5.
ACCESSORIES.
(Also see Section 7).
a. Model 6011 Input Cable has 30 inches of low noise triaxFa1 cable with mating triax-
ial input connector and three alligator clips.
Model 6013 pH Electrode Adapter has a Z-foot cable and triaxial connector and accepts
b.
Leed
& Northrop and Beckman pH electrode connectors.
The Adapter allows accurate and con-
venient pH potential measurements with the Model 601.
c. Model 6301 is a high impedance guarded probe with a 3-foot connecting triaxial
cable that allows measurements to be made more conveniently.
lation resistance of over 1014 ohms.
Using the Probe does not effect any Model 601
The Model 6301 has an insu-
specifications.
Model 1531 is a gripping probe with a 3-foot connecting triaxial cable. The Model
d.
1531 has an insulation resistance of over lOlo ohms.
e. Model 4005 Rack Mounting Kit adapts the Model 601 to rack mounting 10-l/2 inches
high x 19 inches wide.
The Kit can accommodate two Model 601's side-by-side by using an
additional cover.
Model 6012 Triaxial-to-Coaxial Adapter permits using the Model 601 with all Keithley
f.
electrometer accessories having uhf type coaxial connectors. These include the Models
6102A, 6103A, 6104, 6105, 2501 and 2503:
using the Adapter,
the Model 601 should not be floated.
Since circuit low and case ground are connected
Models 6102A and 6103A voltage divider probes, described in Section 7, facilitate
g.
measurements and extend the voltage range to 10 kilovolts.
Model 6104 Test Shield is suitable for resistance measurements with either 2 or
h.
3-terminal guarded connections,
as well as voltage and current tests.
i. Model 6105 Resistivity Adapter is a guarded test fixture for measuring volume and
surface resistivities of materials when used with the Model 601 and the Keithley Model
240A High Voltage Supply.
Models 2501 and 2503 Static Detector Probes are capacitive voltage dividers with a
j.
10,OOO:l ratio, when used with the Probe 3/8 inch from the charged surface.
k. Model 370 Recorder is uniquely compatible with the Model 601 as well as other
Keithley microvoltmeters, electrometers and picoammeters.
The recorder is a high quality
economical instrument that maximizes the performance of the Model 601, and many other
Keithley instruments, even in the most critical applications.
l-6.
with all components in place.
EQUIPMENT SHIPPED. The Model 601 Electrometer is factory calibrated and shipped
The shipping carton also contains the Instruction Manual,
'Model 6011 Input Cable and mating output plug.
4
0667R
MODEL 601 ELECTROMETER
OPERATION
SECTION 2.
2-l. FRONT PANEL CONTROLS AND TERMINALS (See Figure 2)
Range Switch.
a.
divided into a VOLTS position, 11 AMPERES ranges,
ranges.
for all ranges is the Range Switch setting times the Multiplier Switch setting. The 10 or
3 of the top meter scale corresponds to the full-scale deflection for the range selected;
for example,
b.
dc amplifier and sets the full-scale voltage range when the Range Switch is set to VOLTS.
The Multiplier Switch may also be used to multiply the AMPERES (3x maximum setting above
10a3), OHMS and COULOMBS ranges on the Range Switch.
the range used.
c.
position allows checking of the battery condition with the Multiplier Switch. POWER OFF
shuts off the instrument. OFF disconnects only the meter during recorder operation.
+ and - positions determine the polarity of the meter.
for center zero operation (lower meter scale).
A line above the dial skirt indicates the range used. Full-scale sensitivity
on the l-volt range, the needle is at 10 for a l-volt input.
Multiplier Switch.
METER Switch.
The Range Switch selects the measuring mode and the range. It is
The Multiplier Switch determines the voltage sensitivity of the
The Switch has six positions:
OPERATION
eight OHMS ranges and four COULOMBS
A line above the dial skirt indicates
the spring-returned BATTERY CHECK
The
CENTER ZERO sets the instrument
ZERO Controls. Two ZERO Controls are
d.
on the front panel:
knob) and a lo-turn FINE potentiometer
(center knob). These allow precise meter
zeroing.
ZERO CHECK Button. Depressing the
e.
Button effectively removes all input signal
from the instrument by shunting the input
and amplifier through 10 megohms. This
allows meter zeroing on any range. The
Button is locked in the zero check position
when the line is horizontal.
FEEDBACK Switch, The FAST and NORMAL
f.
positions of the Switch determine the feedback connections within the instrument.
With the Switch at FAST, current measure-
ments are made with the range resistors in
the feedback network;
input voltage drops and faster response
speeds. The FAST position is also used for
coulomb measurements, and~to increase re-
sponse speed.
the range resistors shunt the input.
INPUT Receptacle. The INPUT Recepta-
g.
cle is a Teflon-insulated triaxial type
connector.
When the Switch is in NORMAL,
Its center terminal is the cir-
a MEDIUM Switch (outer
this results in lower
FIGURE 2. Model 601 Front Panel Controls
and Terminals.
to Replaceable Parts List and the Schematic
Diagram.
Circuit designations refer
0666R
5
OPERATION MODEL 601 ELECTROMETER
cuit high; the inner shield is circuit low
(circuit ground);
ground.
provided.
Receptacle,
(See Figure 4.) A shield cap is
The LO Terminal, below the
is connected to circuit low;
the outer shield is case
it is connected to case ground only if the
shorting link on the rear panel is connected.
2-2.
REAR PANEL CONTROLS AND TERMINALS
(See Figure 3).
COARSE ZERO SWITCH. The COARSE ZERO
a.
Switch has 11 positions to extend the zeroing capability of the front panel ZERO Controls.
OUTPUT Switch.
d.
The Switch is a twoposition slide switch for the output. In
the 1 MA position,
the instrument will
drive l-milliampere recorders. In the 1 V
position, the output is 1 volt for fullscale meter deflection. Source resistance
is approximately 1090 ohms.
C. 1 MA CAL Control. The Control varies
the output from 0.95 to 1.05 milliampere
for 1400-ohm recorders, so the recorder
scale will correspond with the Electrometer
meter.
OUTPUT Receptacle. A 2-terminal microphone-type receptacle provides 1 volt or 1 mil-
d.
liampere for full-scale meter deflection.
Switch is at NORMAL.
Neither terminal is at ground when the FEEDBACK Switch is at FAST.
Pin No. 2 is at circuit low when the FEEDBACK
Both terminals.are isolated from case ground.
‘LtiUKli 3.
Model
and Terminals.
bUL Kear hnel COntrols
Xl OUTPUT and OHMS GUARD Terminals. The potential between the Xl OUTPUT Terminal
e.
and the OHMS GUARD Terminal (circuit low when the FEEDBACK Switch is in NORMAL) is equal
to the input voltage with 0.005% linearity or 100 microvolts.
When the FEEDBACK Switch
is at FAST, the Xl OUTPUT Terminal is at circuit low and the OHMS GUARD Terminal is floating.
LO Terminal.
f.
A black terminal allows connection to the input low connection. Con-
necting the LO and CASE GROUND Terminals puts both at case ground.
CASE GROUND Terminal.
g.
of the Model 601 and the outside shell of the input connector.
A blue termitial is connected directly to the outside cabinet
It is connected to nothing
else within the instrument.
NOTE
If the Model 601 will be stored for a long period, remove batteries.
Also, make
sure the METER Switch is at POWER OFF when the instrument is not being used.
6
0666R
MODEL 601 ELECTROMETER
OPERATION
7
heavy wire with red clip cover
TABLE 1.
Lead
Input (circuit) high center
thin wire with black clip cover
thin wire with blue clip cover
Input (circuit) low Inner shield
Case Ground Outer shield
Color Coding of Alligator Clips for Model 6011 Input Cable.
Circuit JlOl Terminal
2-3. INPUT CONNECTIONS.
The accessories described in Section 7 are designed to increase the accuracy and
a.
convenience of input connections.
Use them to gain the maximum capability of the Model
601.
b.
tions.
The Mo4el 6011 Input Cable,
Table 1 contains the color coding of the alligator clips.
supplied with the instrument, facilitates input connec-
The high terminal is
shielded by the inner braid of the triaxial cable up to the miniature alligator clip. If
the unshielded clip causes pick up from near-by electric fields, remove it and connect
the shielded lead directly to the source.
NOTE
Techniques and applications are thoroughly discussed in the brochure, Electrometer Measurements, by Joseph F. Keithley.
ments, Inc.,
or its representatives.
It is available from Keithley Instru-
Carefully shield the input connection and the source being measured, since power
C.
line frequencies are well within the pass band of the Electrometer.
is thorough,
any alteration in the electrostatic field near the input circuitry will cause
Unless the shiefding
definite meter disturbances.
Use high resistance, low-loss materials - such as Teflon (recommended), polyethy-
d.
lene or polystyrene - for insulation.
The insulation leakage resistance of test fixtures
and leads should be several orders magnitude higher than the internal resistance of the
SOlL?ZCe.
Excessive leakage reduces the accuracy of readings from high impedance sources.
Triaxial or coaxial cables used should be a low-noise type which employ a graphite or
other conductive coating between the dielectric and the surrounding shield braid.
Amphenol-Borg Electronics Corporation, Microdot, Inc., and Simplex Wire and Cable Company make
satisfactory types. Using the supplied Model 6011 Input Cable is j simple way to insure
good input connections,
NOTE
Clean, dry connections and cables are very important to maintain the value of all
insulation materials. Even the best insulation can be compromised by dust, dirt,
solder flux, films of oil or water vapor. A good cleaning agent is methyl alcohol,
which dissolves most common dirt without chemically attacking the insulation. Wash
salt solutions with distilled water before using the cleaning agent.
Any change in the capacitance of the measuring circuit to low will cause extraneous
e.
disturbances.
cables to prevent their movement.
sinusoidal signal,
Make the measuring setup as rigid as possible, and tie down connecting
A continuous vibration may appear at the output as a
and other precautions may be necessary to isolate the instrument and
0666R
7
OPERATION MODEL 601 ELECTROMETER
the connecting cable from the vibration.
For low impedance measurements -
f.
below 108 ohms or above 10m8 ampere - un-
shielded leads may be used.
the leads short.
However, keep
When measuring currents LO-l4
g.
or less with the FEEDBACK Switch at FAST,
sOme insulators
produce random signals which show up as
erratic meter deflections. Insulation
used in the Model 601 is carefully selected
to minimize these signals.
h.
It is usual,ly better to connect the
Model 601 to the circuit only when a reading
is being made.
rent can charge the external test circuitry.
One example of this occurs when measuring a
capacitor's
the decay of the terminal voltage. If the leakage current is less than the grid current,
there may be no decay.of the terminal voltage when the Electrometer is left connected
across the capacitor's terminals.
Keep the shielded cap on the INPUT Receptacle when the Electrometer is not in
a circuit.
The Model 6012 Triaxial to Coaxial Adapter enables using coaxial cables and acces-
i.
sories with the Model 601 by adapting the triaxial INPUT connector to the uhf coaxial type.
- such as Teflon - may
In some cases, the grid cur-
leakage
resistance
ampere
by observing
L
FIGURE 4. Model 601 Triaxial Incut Receo
tac1e.
input high;
or input low;
ground.
NOTE
The center terminal is circuit 0;
the inner shield is circuit
the outer shield is case
NOTE
The Adapter connects circuit low to case ground.
when using the Adapter.
as the input low.
2-4.
the METER Switch to the BATTERY CHECK position.
through the .OOl to 0.1 positions, and observe the meter readings.
read one-half of full scale or mwre for each
Multiplier Switch position. Table 2 shows
the batteries checked by position.
reading for any battery is below half
scale,
teries may cause the Model 601 to drift more
than normal for at least 72 hours due to
change in battery terminal voltage.
8
PRELIMINARY PROCEDURES.
Check battery condition by setting
a.
Rotate the Multiplier Switch
replace all batt'eries.
The instrument chassis will be at the same potential
The meter should
If the
Note new bat-
Do not float the Model 601
Multiplier position
I
.OOl
.003
.Ol
.03
0.1 R208 h 732n9
TABLE 2. Multiplier Switch Positions for
Checking Condition of Batteries
Battery Checked
B201 & B202
B203
B204 & B205
B206 & B207
0766R
I
MODEL 601 ELECTROMETER
Set the controls as follows:
b.
OPERATION
METER Switch
Range Switch
Multiplier Switch
FEEDBACK Switch NORMAL
ZERO CHECK Button
Turn the METER Switch to CENTER ZERO.
c.
come to the center zero position.
ZERO Controls.
After a few moments increase the voltage sensitivity by advancing the Multiplier
d.
Normally,
Switch to .3, .l, etc.
After long periods of storage or after a" overload,
e.
sively.
The electrometer tubes are shock mounted; however,
there is no need to use the COARSE ZERO Switch.
Continue zeroing with the FINE ZERO Control.
meter may cause a zero offset.
though,
can occur for several hours.
If the Model 601 has been stored for some time, the grid current will exceed the
specification when first used
---I
one or two hours of use.
tube; the instrument is not faulty.
POWER OFF
VOLTS
1
LOCK
the
meter needle should
If not,
Within ten seconds,
adjust to meter zero with the MEDIUM and FINE
the Model 601 may drift exces-
a severe jolt to the Electro-
This is corrected with the Zero Controls.
Drifting,
NUTE
then decrease to below the specified amount after
This is a" inherent characteristic of the electrometer
Although the grid current of the Electrometer is much below that found in conven-
f.
tional voltmeters,
grid current charging the input capacitance,
the input is open.
Follow the particular procedures in paragraph 2-5 to 2-9 for measuring voltage, cur-
g.
rent,
resistance and charge.
voltage, current,
set to IV if the output is notconnected
----effect.
When the output is connected to a load,
it can be observed on the meter.
A small voltage results from the
and the Electrometer appears to drift when
Use the ZERO CHECK Button to discharge the build-up.
When using Multiplier Switch settings of 10, 3 and 1 in the
resistance and charge measuring modes,
---
to a load.
this effect is not present.
make sure the Output Switch is
---
Otherwise,
the meter shows a loading
--
-----
NOTE
Using the center zero scales decreases accuracy 0.5% because Lhe scale spa" is
shorter.
2-5. VOLTAGE MEASUREMENTS.
The Model 601 can be used to measure voltages several ways.
a.
1. In the normal method - FEEDBACK Switch at NORMAL - the unknown voltage is co"-
netted to the INPUT Receptacle.
To reduce the slowing effects of input capacity, use the fast method to measure
2.
Input impedance is iO-l4 ohms, 20 pf.
the voltage. A guarded circuit is possible this way.
3.
if desired.
0667R
To measure Low impedance sources,
the Model 601 input resistance can be decreased
9
OPERATION
Accessory probes extend the Model 601's range to 10 kilovolts.
4, .
NOTE
Locking the ZERO CHECK Switch places 10 megohms acro.ss input high and low, which
may temporarily cause instability in some types of high impedance sources.
Normal Method Voltage Measurements.
b.
MODEL 601 ELECTROMETER
Follow the instructions of paragraph Z-4..
1.
METER Switch
Range Switch VOLTS
Multiplier Switch
FEEDBACK Switch
ZERO CHECK Button
Connect the unknown voltage to the INPUT Receptacle; unlock the ZERO CHECK Button.
2.
Set the METER Switch to + or -, as necessary.
Switch.
3.
C. Fast Method Voltage Measurements.
capacity and allows guarded voltage measurements.
1.
Recheck zero setting after increasing sensitivity.
For off-ground measurements, see paragraph 2-6.
This method reduces the slowing effects of input
Follow the instructions of paragraph Z-4,.
METER Switch
Range Switch
Multiplier Switch 10
FEEDBACK Switch
ZERO CHECK LOCK
CENTER ZERO
10
NORMAL
LOCK
CENTER ZERO
VOLTS
FAST
Set the controls as follows:
Increase sensitivity with the Multiplier
Set the controls as follows:
2. Connect CASE GROUND Terminal to OHMS GUARD Terminal, using the shorting link.
Connect the unknown voltage t.o the high (center) terminal of the INPUT Receptacle
3.
and to the CASE GROUND Terminal on the rear panel. Use the LO Terminal as a guard be-
tween circuit high and low.
or -, as necessary.
ting after increasing sensitivity.
To make off ground voltage measurements, see paragraph 2-6.
4..
d. Low Impedance Measurements.
one of the AMPERES ranges. The input resistance is now the reciprocal of the current
range.
the 10s7 AMPERES range.
Operating procedures are the same as subparagraph b.
Model 601 will not run off scale as easily in the presence of excessive ac fields. This
occurs only when the input is left open.
10
For instance,
Increase sensitivity with the Multiplier Switch. Recheck zero set-
to obtain a" input resistance of 107 ohms, set the Range Switch to
Set the full-scale voltage range with the Multiplier Switch.
Unlock the ZERO CHECK Button. Set the METER Switch to +
To decrease input resistance, set the Range Switch to
At lower input resistances, the
0567R
MODEL 601 ELECTROMETER
OPERATION
To measure sources more than 10 volts, use one of two divider probes.
e.
The Model
6102A 1O:l Divider Probe extends the Model 601's range to 100 volts; overall accuracy is
?3% and input resistance is lOLo ohms.
The Model 6103A 1OOO:l Divider Probe extends the
Model 601's range to 10 kilovolts; overall accuracy is f5% and input resistance is 1012
ohms.
Follow the same operating procedures with the dividers as in subparagraph b. The
Model 6012 Triaxial-to-Coaxial Adapter must be used with the Models 6102A and 6103A
Divider Probes. Note, however, using the Adapter connects circuit low to case ground; do
not float the Electrometer. The full-scale voltage range is the divider ratio times the
Multiplier Switch setting.
Operating the Model 601 nwre than 1500 volts off ground may permanently damage
the instrument. Isolation between circuit low and ground may break down somewhere Fn the circuit, putting the case at an off-ground potential. Since these
breakdowns are very difficult to locate, it might not be possible to float the
instrument safely again.
2-6. OFF GROUND VOLTAGE MEASUREMENTS.
a. The Model 601 can measure an unknown voltage whose low is up to 1500 volts off
ground while its own case is at ground. This allows safe operation of the Electrometer.
Its operation is the same as given in paragraph 2-5, except for input connections and
some added cautions.
These differ, depending upon the FEEDBACK Switch setting.
FEEDBACK Switch set to NORMAL. Disconnect the shorting link between the LO and
1.
CASE GROUND Terminals on the rear panel. Make sure the Model 601 case is securely con-
nected to an earth ground,
volts dff ground.
Connect the unknown voltage directly to the INPUT Receptacle.
and that the low of the unknown voltage is less than 1500
Opel-~
ate the Model 601 as described for normal method voltage measurements.
FEEDBACK Switch set to FAST. Do not use the shorting link.
2.
601 case is securely connected to an earth ground,
tage is less than 1500 volts off ground.
Ground the outer shield of the INPUT Receptacle.
and that the low of the unknown vol-
Make sure the Model
Connect the high of the unknown voltage to the canter terminal of the INPUT Receptacle.
Connect the low to the GUARD Terminal. Use the inner shield of the INPUT Receptacle as
a guard. Operate the Model 601 as described for fast method voltage measurements.
NOTE
When the Model 601 is off ground, make sure the shell of a mating plug to the
OUTPUT Receptacle is not connected to either pin in the Receptacle.
If the Model 6012 Adapter is used, do not float the Model 601. The Adapter connects
b.
the input low to the case ground,
so that the Model 601 chassis and controls are at the
same potential as the Low of the unknown source.
NOTE
Use only an insulated blade screwdriver to adjust the COARSE ZERO Switch and 1 MA
CAL Cdntrol when floating the Model 601.
circuit low to case ground,
creating a shock hazard and damaging the external cir-
An ordinary screwdriver could short the
cuitry.
06668
II
OPERATION
MODEL 601 ELECTROMETER
-------------
r
1
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R
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FIGURE 5.
sarias with a resistance (R).
ammeter is attached to measure the current,
Annneter Circuit Loading. Current sources may be considered a voltage (E) in
The current with no annneter attached is I=E/R. When an
the effective input resistance of the ammeter
Rin is in series with the source resistance (R).
less and Imeter = E/(R + Rtn).
pared to R, Imeter+
2-7.
CURRENT MEASUREMENTS.
- I and the error introduced by circuit loading is negligible.
If the effective ammeter input resistance is small com-
a. The Model 601 can measure currants three ways.
Rin
I meter
The current in the complete circuit is
In the normal method - used on any range - the currant is determined by measur-
1.
ing the voltage drop across a resistor shunting the amplifier input.
This method is
useful when lower noise is more important than faster response speeds or if some damp-
ing is needed.
In the fast method
2.
tor is between the amplifier output and input in the feedback loop.
- for use only below the 10V5
ampere range
- the shunt resis-
This circuit
largely neutralizes the effect of input capacity and greatly increases the response
speed.
Also, the input voltage drop is reduced to a maximum of one millivolt on any
range.
For galvanometric current measurements, the Model 601 acts as a null indicator
3.
between a very accurate current source and the unknown current source.
Its off ground
operating capability makes it ideal for this application since the reference source and
unknown may both have a common grounded terminal.
b. Rise tima varies primarily with the current range, the input capacity and the method
used.
On most ranges, the rise time in the fast mode is less than one second with 50
picofarads across the input. Even with much larger shunt capacities, the negative feedback maintains a short rise time. Given a choice, it is better to placg the Electrometer
nearer to the current source than to the data reading instrument.
Transmitting the input
signal through long cables greatly decreases the response speed and increases noise due
to the cable capacitance.
To measure from a source with both terminals off ground in either method, remove
C.
the link between the LO and CASE GROUND Terminals on the rear panel.
Connect the unknown
current to the INPUT .Receptacle. The source must be less than *1500 volts off ground
(see paragraph 2-6).
12
0766R
MODEL 601 ELECTROMETER
Normal Method (0.3 to lo-l4 ampere ranges).
d.
OPERATION
Follow the instructions of paragraph 2-4.
1.
METER Switch
Range Switch
Multiplier Switch
FEEDBACK Switch
ZERO CHECK Button
Connect the unknown current to the INPUT Receptacle and unlock the ZERO CHECK Button.
Set the METER Switch to + or -, as necessary.
Switch and the Multiplier Switch.
Range Switch settings 10m3 and above.
Full-scale current range is the settings of the Range Switch times the Multiplier
2.
Switch.
drop and obtain the best accuracy.
ting, from 10 ohms at 10-l AMPERES to loll ohms for lo-11 AMPERES.
is the percentage of full scale that the meter reads times the Multiplier Switch setting.
On the low current ranges, balance cut the grid current with the Zero Controls
or subtract the value from the reading.
cap the INPUT Receptacle and read the meter.
Use the smallest Multiplier Switch setting possible to minimize input voltage
Do not set the Multiplier Switch higher than 3 for
Check zero with the ZERO CHECK Button.
The input Fesistor varies with the Range Switch set-
NOTE
To find the aawunt of grid current,
Set the controls as follows:
CENTER ZERO
10-l AMPERES
1
NORMAL
LOCK
Increase the sensitivity with the Range
Input voltage drop
Fast Method (ranges below lOa ampere).
e.
Follow the instructions of paragraph 2-4.
1.
METER Switch CENTER ZERO
Range Switch
Multiplier Switch
FEEDBACK Switch
ZERO CHECK Button
Connect the unknown source to the INPUT Receptacle and unlock the ZERO CHECK Button.
Set the METER Switch to + or -, as necessary.
Range Switch and the Multiplier Switch. Do not set the Range Switch to 10e5 AMPERES or
higher. Check zero with the ZERO CHECK Button.
NOTE
Use only the ZERO CHECK Button to check zero for the fast method.
the input, because this will remove the feedback from the circuit.
The full-scale current range is the Range Switch setting times the Multiplier
2.
Switch setting. When selecting the Multiplier Switch setting, remember small settings
permit lower current source resistance, and larger settings improve instrument zero
stability. Check the caution in subparagraph 3a below.
Set the controls as follows:
10-6
AMPERES
1
FAST
LOCK
Increase the sensitivity with the
Do not short
066711
13
OPERATION
With the fast method, the input drop is reduced and the response speed is in-
3.
creased at least 100 times.
The
4
internal impedance of the unknown current scnxce should not be less than
However, follow these precautions:
MODEL 601 ELECTROMETER
0.1 of the value of the feedback resistor being used. otherwise, adequate feedback
voltage cannot be developed at the input,
and zero instability results. The feedback
resistor value is the reciprocal of the AMPERES range of the Range Switch.
voltage drop across the current source should be at least 100 times the voltage drop
acrOsS the Model 601.
b) The low side (Pin No. 2) of the OUTPUT Receptacle is no longer connected to the
low side of the INPUT Receptacle.
to be electrically connected,
low side of the current source.
Therefore, do not allow the low side of a recorder
such as through the ground lead of a power cord, to the
Another alternative is “sing the unity-gain output.
(See paragraph Z-11.)
c) Do not use the fast method to measure capacitance unless “sing a very stable vol-
tage supply.
to;,
.
resulting in extreme sensitivity to very small voltage transients.
Connecting a capacitor to the input changes the circuit to a differentia-
I
Galvanometric Method.
f.
Also, the
Operate the Model 601 as a pico-
1.
ammeter in the fast method of operation.
Use an accurate reference current source
to buck out the unknown current source.
Connect as shown in Figure 6.
2. Set the METER Switch to CENTER
ZERO and “se the higher current ranges.
Adjust the buckout current to indicate
null on the Model 601. Increase the
Electrometer’s sensitivity as needed.
When the Model 601 is as close to null
as possible, the known reference current source equals the unknown source
* the Model 601 current readings.
FIGURE 6. Measuring Current by the Galvanometric Method. Use an accurate reference
current source to buck Out the unknown current source, I,.
current ranges,
The Model 601, on its
serves as a null detector.
Use a uhf-tee fitting and Model 6012 Adapter
at the Model 601 input.
Connect the Electrometer to the two sources with coaxial
cable. Select cable carefully for very low
2-S. RESISTANCE MEASUREMENTS.
a. The Model 601 can measure resistan-
currents (see paragraph Z-3). For off
ground measurements,
“se triaxial cable and
connectors, grounding the outer shield.
ces by three methods.
1. In the normal or two-terminal method (ammeter-voltmeter), the Electrometer measures
the voltage drop across the unknown sample as a known, constant current flows through
it.
The voltage drop is proportional to the resistance of the sample.
This method is
the simplest for the 100 to loLL ohm ranges.
2. Above 10L1 ohms or to prevent leakage,
the guarded method is better.
It results
in faster response speeds and also nullifies leakage errors acress the Electrometer in-
Put I
since the potential acress the input terminal is small.
In the preceding methods,
3.
set. In some cases,
as in measuring capacitor leakage,
the voltage across the sample cannot be arbitrarily
these methods involve much more
,a
14
06678
MODEL 601 ELECTROMETER
OPERATION
time than if a larger voltage could be applied.
Model 601 is used as a fast picoammeter.
The unknown resistance sample is connected to
In the external voltage method the
an external known voltage source and the current through the sample is measured.
the normal or fast method may be used.
The resistance is calculated from the readings.
NOTE
Discharge any capacitor before removing it from the circuit.
Depressing the
ZERO CHECK Button shorts the input through a lo-megohm resistor, providing a
discharge path.
Normal Method (100 to 10" ohm ranges).
b.
Follow the instructions of paragraph 2-4.
1.
METER Switch
Range Switch
Multiplier Switch
FEEDBACK Switch
ZERO CHECK Button
Connect the resistance sample to the INPUT Receptacle.
Set the controls as follows:
+
105 OHMS
1
NORMAL
LOCK
Unlock the ZERO CHECK Button.
Check zero with only the ZERO CHECK Button.
Either
NOTE
Do not open circuit the Electrometer on the OHMS ranges; the input will develop
up to 10 volts due to its constant current characteristic.
Keep the input
shorted or the ZERO CHECK Button locked.
The full-scale ohms range is the Range Switch setting times the Multiplier Switch
2.
setting. Use the largest Multiplier Switch setting possible to obtain the best accuracy.
Before making a final reading, manipulate the Multiplier and Range Switches, so
3.
the sample is tested at a number of test potentials.
The applied test voltage is the
percentage of full scale that the meter reads times the Multiplier Switch setting.
4. When the test current is applied, high termipal of the INPUT Receptacle is negative.
NOTE
Shield the input if the resistance sample exceeds LO8 ohms.
c. Guarded Method (to 1014 ohm ranges).
1. Follow the instructions of paragraph 2-4. Set the controls as follows:
METER Switch
Range Switch
Multiplier Switch
FEEDBACK Switch
ZERO CHECK Button
loll
1
FAST
LOCK
OHMS
0667R
15
OPERATION MODEL 601 ELECTROMETER
Connect the low impedance side of the resistance sample to the Model 601 GUARD Terminal,
and the high impedance side to the center terminal of the INPUT Receptacle.
ZERO CHECK Button.
Read the resistance as outlined for the normal method, subparagraph b.
2.
Unlock the
The low terminal of the INPUT Receptacle is now a driven guard.
3.
to minimize the slowing effects of capacity between high and low and errors due to leak-
age resistance between high and low.
The Model 6011 Input Cable,
4.
means of making guarded resistance measurements.
CASE GROUND and GUARD Terminals on the rear panel. This allows the CASE GROUND or blue
test lead terminal to be connected to the low impedance side ‘of the unknown resistance.
The inner shield or the black test clip is the GUARD Terminal.
d. External Voltage Method (to 1017 ohms).
1. Turn the ZERO CHECK Switch to LOCK.
of the INPUT Receptacle and the power supply.
high voltage line to ground the low impedance end of the sample when it is disconneCtad
from the potential.
the Power Supply must be floating,
minals and connect the CASE GROUND Terminal to an earth ground.
2. Set the FEEDBACK Switch to NORMAL.
ies can arise for resistance samples less than 0.1 the value of the feedback resistor.
3.
Apply a potential to the sample before releasing the ZERO CHECK Button.
Range Switch to .3 AMPERES and increase sensitivity until a reading is obtained.
Before disconnecting,
supplied with the Model 601, provides a convenient
Connect the shorting link between the
Connect the sample between the High Terminal
(See Figure 7,.) Put a switch in the
make sure to lock the ZERO CHECK Button. If
remove the link between the CASE GROUND and LO Ter-
Usually this method is best, since instabilit-
It may be used
Set the
4. If the potential applied is at
least 100 times the full-scale input
drop (Multiplier Switch setting), the
resistance is equal to the applied poten-
tial divided by the current reading.
high voltage sensitivity of the Model 601,
therefore, permits external.voltages of
0.1 volt or more to be used.
If the potential applied is less
5.
&han 100 times the input drop, the resis-
tance is equal to the difference between
the applied potential and the input drop,
all divided by the current reading.
6. If.the current is read by the fast
method,
it need not be included in the calculation.
sample is large,
capacitor leakage measurements, the fast
method increases response speed and this
connection is recommended.
the input drop is so slight that
If the capacity shunted across the
such as encountered in
The
I
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FIGURE 7. Measuring Resistance by the Ex-
ternal Voltage Method.
known source, V, is applied to the unknown
resistance sample, R,.
sures the current through s, from which
the resistance is calculated.
grounds R when no potential is applied.
Note in a eve i2 figure the power supply is
floating.
I -
A potential from a
The Model 601 mea-
601
Switch S
I
1
16
MODEL 601 ELECTROMETER
2-9. CHARGE MEASUREMENTS.
OPERATION
a. Follow the instructions of paragraph 2-4,.
Set the controls as follows:
METER Switch CENTER ZERO
Range Switch 10-7 COULOMBS
Multiplier Switch .Ol
FEEDBACK Switch FAST
ZERO CHECK Button LOCK
Unlock the ZERO CHECK Button and then connect the unknown source to the INPUT Receptacle.
If the Electrometer reads off scale, increase the Multiplier Switch setting.
If the sen-
sitivity is not enough, decrease the Multiplier Switch setting until the reading is on
scale.
Changing the Multiplier Switch setting does not affect the transfer of charge
from the unknown source to the instrument. If increasing sensitivity with the Multiplier
Switch does not bring the reading on scale, increase sensitivity with the Range Switch
and repeat the above steps.
The full-scale charge range is the Range Switch setting times the Multiplier Switch
b.
setting.
Grid current contributes 2 x 10-14. coulomb per second maximum.
NOTE
Because of the instrument's RC time constant,
internal capacitance on the LOS7
coulomb
wait 20 seconds after discharginlg
range before making another measurement.
On the 10-S coulomb range, wait at least two seconds.
2-10.
omy, versatility and performance.
1% linearity. It can float up to l 500 volts off ground.
RECORDER OUTPUTS.
a. For recording
with
the Model 601, "se the Keithley Model 370 Recorder for ease, econ-
The Model 370 is a pen recorder with 10 chart speeds and
The Model 370's input cable has a
connector which mates directly with the OUTPUT Connector on the Model 601; this avoids
interface problems often encountered between a measuring instrument and a recorder. The
Model 601 OUTPUT, when set to IMA Position,
will drive the 370; no preamplifier is needed.
b. Other recorders, oscilloscopes and similar instruments can be used with the Model
601.
The Model 601 has two variable outputs, fl volt and *l milliampere, to amplify signals within l/2% for recorders, oscilloscopes and similar instruments. These can be used
on all ranges of the Model 601.
NOTE
.
The Model 601 may be used with the FEEDBACK Switch in FAST position with other
instruments. However, make sure there is no common ground between low terminals
of the Electrometer and the other instrument.
c. l-Volt output.
Receptacle. Pin no.
Connect oscilloscopes and pen recorder amplifiers to the OUTPUT
1 is the negative terminal and pin no. 2 is grounded when the FEEDBACK Switch is set to NORMAL. Set the OUTPUT Switch to 1 V. The Model 601 output is now
*l volt for full-scale meter deflection on any range. Internal resistance is 910 ohms.
The frequency response (*3 db) is dc to 200 cps at a gain of 1000, rising to 50 kc at a
gain of 3.3, and decreasing to 1 kc at a gain of 0.1.
scale at a gain of 1000,
decreasing to 0.5% at gains below 10. The METER Switch does not
Noise is less than 2% rms of full
reverse the output polarity.
0667R
17
OPERATION
NOTE
Neither terminal of the OUTPUT
Receptacle should be at case
ground potential if the instru-
ment is used off ground.
sure the shell of any mating
plug is not connected to either
terminal in the Receptacle. The
shorting link should not be connected between LO and CASE GROUND.
Use a recorder with an input iso-
lated from ground when making off
ground measurements.
Make
MODEL 601 ELECTROMETER
L
M^rl.c.l
Lx”UrL
601
output
(Tlcl?I z
1 kR
>
t
Recorder
l-Milliampere Output. Connect 1-mil- b
d.
liampere instruments to the OUTPUT Recept- FIGURE 8.
acle. Pin no. 1 Fs the negative terminal.
Set the OUTPUT Switch to 1 MA. The output
is approximately 1 milliampere for full-
scale meter deflection on any range. For
exact output, adjust the meter on the .003volt range with the FINE ZERO Control for
full-scale deflection.
scale.
Switch does not reverse the output polarity.
the COARSE ZERO Switch and the 1 MA CAL Control.
e.
See Figure 8. Set the OUTPUT Switch to 1 MA.
for full-scale recorder deflection. Operation is the same as for current outputs.
f. When the FEEDBACK Switch is in the NORMAL position,
terminal is grounded to the LO Terminal.
using oscilloscopes and recorders with the Model 601 set for normal operation.
position, however,
common ground between the recorder or.oscilloscops and the Model 601 LO Terminal, or use
the unity-gain output.
2-11.
device to minimize circuit loading errors or for convenient connections to a recorder
when the FEEDBACK Switch is in FAST position.
Check the recorder and meter zero and repeat adjustment if necessary.
For servo rebalance recorders, use a divider across the Model 601 OUTPUT Receptacle.
neither side is grounded. If this is used,
UNITY GAIN OUTPUT. The unity-gain amplifier can be used as an impedance matching
Then adjust the 1 MA CAL Control until the recorder reads full
Therefore,
601 Output for Driving 50 and lOO-Millivolt
Recorders. Use 1% resistors in the divid-
ers for 50-millivolt recorders, resistor R
is 5Ofi; for 100-millivolt, R is 1OOQ.
Use only an insulated screwdriver to adjust
Use the 1 MA CAL Control to trim the output
no difficulty will be experienced
Divider Circuits Across Model
The METER
the negative side of the output
In FAST
make sure there is no
.
a. The unity-gain output is equal to the input within 50 ppm or 100 microvolts when
the load resistance is 100 kilohms or better below 10 volts.
between a lOlo ohm source, for example,
tance,
overall accuracy better than 0.025% can be achieved.
1. Connect the voltmeter to the Xl OUTPUT and GUARD Terminals as shown in Figure 6,
The GUARD Terminal is connected to LO Terminal with the FEEDBACK Switch in NORMAL.
imum output amplitude is 10 volts peak-to-peak.
2. Adjust the Model 601 Zero Controls to obtain a zero-voltage reading on the in-
strument using the unity-gain output.
and a 0.01% voltmeter with a 1-megohm input resls-
Make sure the latter's sensitivity is high enuugh
By placing the Model 601
Max-
MODEL 601 ELECTROMETER
OPERATION
FIGURE 9.
601 is used between a high-resistance source, V,,
accuracy without causing circuit loading.
Measuring Potential of High Resistance Source with 0.025% Accuracy. The Model
and a 0.01% voltmeter to obtain high
The digital voltmeter or, as above, the
Keithley Model 662 Differential Voltmeter connects to the Model 601 unity-gain terminals.
for a precise zero adjustment.
This adjustment is necessary because a slight zero shift
may occur when the Model 601 is changed from the O.l-volt range or lower to a range
above 0.1 volt.
The shift, caused by a gain-reducing network switched in by the ampli-
fier on the l-volt and higher ranges, is too slight to be read on the meter, but it can
cause an error in accurate measurements using the unity-gain output.
When the FEEDBACK Switch is in FAST position,
b.
the unity-gain terminals permit more
convenient connections to recorders without special precautions. In this mode, the Xl
OUTPUT Terminal is grounded and the GUARD Terminal delivers a full-scale output equal to
the Multiplier Switch setting times the input signal.
0866R
19
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