Keithley 610B User manual

Instruction Manual
Models 6106, 610BR
Mul_tl&flqnge. ElecVpeters
Keithley Instruments. Inc.
26775 Aurora Road/Cleveland. Ohio 44139A216) 248-0400

MODELS 61013, 610BR ELECTROMETERS
TABLEOF CONTENTS
Section Page
1. GENERAL DESCRIPTION ........ 1
l-l. General ........... 1
l-2. Features. .......... 1
l-3. Differences Between the Models
6108 and 610BR. ....... 1
l-4. Specifications. ....... 2
l-5. Applications. ........ 3
l-6. Accessories ......... 4
l-7. Equipment Shipped ...... 4
Section ?:I'22
4-6. Calibration Procedures. . . . 31
4-J. Grid Current Check. 33
4-a. DC Amplifier Adjustment 31
4-9. High-Megohm Resistor Veri-
fication. . . 35
4-10. Calibration of Ohms Ranges. 35
4-11. Meter Zero Calibration. . 3j
4-12. Accuracy Check. . . . . . 35
4-13. Drift Check . 36
5. ACCESSORIES . . . . . . 43
2. OPERATION ............. 5
2-1. Front Panel Controls and
Terminals .......... 5
2-2. Rear Panel Controls and
Terminals .......... 6
2-3. Input Connections ...... 6
2~4. Preliminary Procedures. ... 8
2-5. Voltage Measurements ...... 9
2-6. Current Measurements. .... 10
2-7. Resistance Measurements ... 13
2-8. Charge Measurements ..... 15
2-9. Recorder Outputs. ...... 15
Z-10. Unity-Gain Output ...... 17
Z-11. current source. ....... 17
2-12. Static Charge Measurements. . 17
Z-13. Capacitance Measurements. .. 18
2-14. Application Notes ...... 19
5-l. Model 6101A Shielded Test
Lead. . . . . . . . . 43
5-2. Model 61018 Gripping Probe. 43
5-3. Model 6102A Voltage Divider
Probe . . . . . . . . . 43
5-4.. Model 6103A Voltage Divider
Probe . . . . . . . . . 43
5-5. Model 6104 Test Shield. . . 44
5-6. Model 6105 Resistivity
Adapter . . . . . , . . . 44
5-7. Models 2501 and 2503 Static
Detector Heads. . . . . . . . 45
5-8. Model 6106 Electrometer
Connection Kit. . . . . . . . 46
5-9. Model 6107 pH Electrode
Adapter . . . . . . . . . . . 4i
5-10. Model 370 Recorder. . . . . . 48
3. CIRCUIT DESCRIPTION ........ 21
3-l. General ........... 21
3-2. Voltmeter Operation ..... 21
3-3. Voltmeter circuit ...... 22
3-4. Ammeter Operation ...... 24
3-5. Ohmmeter Operation. ..... 24
3-6. Coulombmeter Operation. ... 25
3-7. Power Supply. ........ 26
4. UAINTENANCE ............ 29
4-l. General ........... 29
4-2. Parts Replacement ...... 29
4-3. Troubleshooting ....... 29
4-4. Procedures to Guide Trouble-
shooting. .......... 30
4-5. 234-Volt Ooerarion. ..... 32
6. REPLACEABLE PARTS . . . . . . . 51
6-l. Replaceable Parts List. . . . 51
6-2. How to Order Parts. . . . . . 51
Models 6108, 610BR Replaceable
Parts List. . . . . . . . 52
Model 6108 Schematic Diagram
177953. . . , . . . . . . . 59
Green Repair and
Calibration Forms . . 61
* Change Notice Last Page
* Yellow Change Notice sheet is included
only for instrument modifications affect-
ing the Instruction Xanual.
O268R 1

GENERAL DESCRIPTION MODELS 6lOB, 610BR ELECTROMETERS
FIG
FIGURE 2. Keithley Instruments Model 610BR Electrometer. Model
610BR is the rack version of the Model 6108.
ii i 1064R

MODELS 6108, 610BR ELECTROMFPERS GENERAL DESCRIPTION
SECTION1. GENERALDESCRIPTION
l-l. GENERAL.
a. The Keithley Model 610B Electrometer is a versatile instrument which
measures wide ranges of dc voltages, currente, resistances and charges. It
is a highly improved form of conventional dc vecuum tube voltmeters that
ueee an electrometer tube input to provide greeter than lo14 ohm Fnput re-
sistance. T’he Model 6lOB has all the capabilities of conventional VTVMe,
but it ten also make many more measurements without loading circuits.
b. The Electrometer has 11 voltage ranges from 0.001 volt full scale to
100 volts, 28 ~urm-ie: ranges from Lo-14 ampere full scale to 0.3 ampere,
25 linear resistance ranges from 100 ohms full scale to 1014 ohms, and 15
couLomb ranges from LO-12 coulomb full scale to LO-5 coulomb.
c. The Model 6LOB input stage uses a matched pair of electrometer tubes.
The output stage uses a vacuum tube; othewiee.solid-state devices are
used for all amplifier stages and the power supply. This increases re-
liability end stability and aLlows greater regulation of the power supply.
l-2. FEATURES.
a. Voltmeter accuracy is Cl% of full scale, exclusive of noise and drift.
b. Zero drift of the Model 6108 is 200 microvolts per hour maxirmun averaged
over any 24-hour period after warm-up. During the 2-hour warm-up, zero drift
is no more then 2 millivolts after the first hour.
c. Two amplifier outputs are available. A switch on the rear panel allows
either 23 volts or 21 milliampere for full-scale meter deflection. The current
output is variable 25% with 1.4-kilohm recorders. The unity-gain amplifier
output is equal to the input voltage within 50 ppm or 100 microvolts, exclusive
of zero drift.
d. Current measurements can be made by one of two methods, the normal method
in which the current is determined by measuring the voltage drop across a re-
sistor shunting the input, or the fast method in which negative feedback is
appliedthrough the shunt resistor. The latter method reduces ehe input drop
end greatly increases the response speed on the low-current ranges.
1-3. DIFFERENCES BETWEENTHE MODELS 610B AND 610BR.
a. The Model 610BR
is the rack version of the cabinet configuration,
Model 610B. The circuits, specifications, electrical parts end operating
procedures for the two models are the same. Besides the outside dimensions,
the main difference between them is the Model 6LOBR’s COARSE ZERO Control
is on the front panel, not on the rear panel.
b. The instructions in the Manual are for both models, although only the
Model 610B is mentioned. Any differences are identified for the correct model.
t064R 1

GENERAL DESCRIPTION ?,ODELS 6108, 610BR ELECTROMTERS
1-4. SPECIFICATIONS.
AS A VOLTMETER:
RANGE: ,001 volt full scale to 100 volts in eteven Lx and 3x ranges.
ACCURACY: ?L% of full scale on all ranges exctusive of noise and drift.
ZERO DRIFT: After L-hour warm-up no more than 2 millivolts in the second hour, and in any
subsequent 24-hour period, the average drift wilt not exceed 200 microvolts per hour.
HETER NOISE: +tO microvotes with input shorted.
INPUT IMPEDANCE: Greater than Lot4 ohms shunted by 22 picofarads on the VOLTS position of
the Range Switch. Input resistance may be selected in decade steps from LO to LOLL ohms
with the Range Switch.
AS AN AMMETER:
RANGE: 10-14 ampere full scale to 0.3 ampere in twenty-eight Lx and 3x ranges.
AccuRAcY: ?2% of full scale on 0.3 to 10-11 ampere ranges using smattest available Ilulti-
ptiee Switch setting; 14% of full scale on 3 x tOeL2 to tOdL4 ampere ranges.
METER NOISE: Less than i3 x lO-L5 ampere.
GRID CURRENT: Less than 2 x lO-L4 ampere
AS AN OHMMETER:
RANGE: 100 ohms full scale co 1014 ohms on twenty-five Linear Lx and 3x ranges.
‘KcIJRAcY: ?3% of full scale on 100 to log ohm ran es using highest available Multiplier
Switch setting; ?5% of full scale on 3 x LO9 to to K4 ohm ranges.
AS A COULOMBMETER:
RANGE: LO-L2 coulomb full scale to tom5 coulomb Ln fifteen lx and 3x ranges.
ACCURACY: ?5% of full scale on all ranges.
2 x 10eL4 coulomb per second. Drift due to grid current does not exceed
AS AN AMPLIFIER:
INPUT IHPEDANCE: Greater than tot4 ohms shunted by 22 picofarads on the VOLTS position
of the Range Switch. Input resistance may be selected in decade steps from LO to LOLL
ohms with the Range Switch,
OLTPUTS: Unity-gain output and either voltage or current recorder output.
Unity-Gain Output: At dc, output is equal to input within 50 ppm or 100 microvolts.
exclusive of zero drift, for output currents of LOO microamperes or Less. up to one
milliampere may be drawn for input vottages OE LO votes or Less.
.* * .
t066R .

MODELS 6108, 610BR ELECTROMETERS GEXERAL 3ESCRI?TIO”
Voltage Recorder Output: +3 volts for full-scale
input.
Internal resistance is 3 kil-
ohms. Output polarity is opposite input polarity.
Gain: 0.03, 0.1, etc., to 3000
Frequency Response (Within 3 db): dc to 300 cps at a gain of 3000, rising to 25 kc
at a gain of 30, decreasing to 2.5 kc at a gain of 0.03.
Noise: 3% rms of full scale at a gain of 3000, decreasing to 1% at gains below 100.
Current Recorder Output: tl milliampere for full-scale input, variable T5% with LLiOO-
ohm recorders.
GENERAL:
POLARITY: METER Switch selects left zero (positive or negative) or center-zero scales
Output polarity is not reversed.
LINE STABILITY: A 10% change in line voltage will ca”se less than a LO-microvolt merer
defLection on aLL ranges.
CONNECTORS: Input: uhf type; ground binding post.
output: Voltage or current, AmphenoL 80-PCZF; Unity-gain, binding posts
POWER: 105-125 or 210-250 volts (switch selected): 50 to 1000 cps; IO Watts
DIMENSIONS, WEIGHT: Model 6108: 10-l/2 inches high x 6-S/8 inches wide x 10 inches dee?;
net weight, 12 pounds. Model 610BR: 5-l/4 inches high x 19 inches wide x 10 inches deep;
net weight, 12 pounds.
ACCESSORIES SUPPLIED: Mating input and output plugs; 3:2 power line adapter; binding plug.
l-5. APPLICATIONS.
a. Voltmeter applications include directly measuring potentials of vacuum tube plates
and grids, pH electrodes, piezo-electric crystals, capacitors and electrochemical cells,
and the gate potentials of field effect transistors. With the Model 2501 or 2503 Static
Detector Probe, the Model 610B can measure electrostatic voltages.
b. As a picoammeter, the Electrometer can measure mass spectrograph currents. It can
be used with photo multiplier tubes, flame and beta ray and lithium ion-drift detectors.
Other uses are in gas chromatograph work, nuclear studies, plasma physic studies and
vacuum studies. Also, it can be used as a current null detector with an accurate current
reference source.
c. As an ohmeter, its uses include measuring diode characteristics, insulation resis-
tance, and resistor voitage coefficients. With the Model 6105 Resistivity Adapter and a
power supply, the Node1 610B can measure volume and surface resistivities.
d. In addition to measuring charge directly, other coulombmeter uses are measuring charge
current over a period and obtaining integral curves of time-varying currents. The Model
6108 can measure the total energy output from a pulsed laser on its coulomb ranges when
used with a calibrated photo tube or photo diode. It also can be used as a charge ampli-
fier to measure pieza-electric crystal outputs.
1066R 3

GENERAL DESCRIPTION MODELS 61OB, 610B~ ELECTROMETERS
1-6. ACCESSORIES.
a. Three accessory probes, fully described in Section 5, facilitate measurements end
extend the Electrometer’s voltage range to 30 kilovolts.
b. Model 6104 Test Shield is suitable for resistance measurements with either 2 or 3-
terminal guarded connections, as well as voltage and current tests.
c. Model 6105 Resistivity Adapter ts a guarded test fixture for measuring volume and
surface resistivitirs of materials when used with the Model 6108 and the Keithley Node1
240A High Voltage Supply.
d. Models 2501 and 2503 Static Detector Probes are capacitive voltage dividers with a
10,OOO:l ratio, when used with the probe 3/B inch from the charged surface.
e. Model 6106 Electrometer Connection Kit contains a group of the mwt useful leads
and adapters for electrometer measurements.
f. Model 6107 pH Electrode Adapter has a 2-Eoot cable and coaxial caxxector and accepts
a Beckman and Coleman (B-C) or a Leeds and Northrup (L &N) connector. The Adapter allows
accurate and convenient pH potential measurements with the Model 6lOB.
g. Model 370 Recorder is uniquely compatible with the Model 610B es well es other
Keithley microvoltmeters, electrometers and picoarmneters. The recorder is a high quality
economical instrument that maximizes the performance of the Model 6108 and many other
Keithley instruments, even in the most critical applications.
l-7. EQUIPMENT SHIPPED. The Model 6108 Electrometer is factory-calibrated and is ship-
ped with all components in place. The shipping cartnn contains the Instruction Manual and
mating plugs for the input and output receptacles. The Model 610BR is shipped with the
rgles and screws for rack mounting packed separately within the shipping carton.
FIGURE 3. Model 610ER Front Panel Controls and Terminals. Circuit designations refer to
Replaceable Parts List and the schematic diagram.
I 0667R

MODELS 610B, 610BR ELECTROMETERS OPERATION
SECTION2. OPERATION
2-1. FRONT PANEL CONTROLS AND TERMINALS (See Figures 3 and 4)
a. Range Switch. The Range Switch selects the measuring mode and the
range. It is divided fnto a VOLTS position, 11 AMPERES ranges, eight OHMS
ranges and four COULOMBS ranges. The range used is indicated by an X above
the dial skirt.
b. Multiplier Switch. The Multiplier Switch determines the voltage sen-
sitivity of the 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 maxinolm setting above LO-3), OHMS and COULOMBS
ranges on the Range Switch.
c. METER Switch. The Switch has five positions: POWEROFF shuts off
the instrument. OFF disconnects only the meter during recorder operation.
The + and - positions determine the polarity of the meter. CENTER ZERO
sets the instrument for center zero operation (lower meter scale).
d. ZERO Controls. Two ZERO Controls are on the front panel: a MEDIUM
Switch (outer knob) and a lo-turn FINE potentiometer (center knob). These
allow precise meter zeroing.
Circuit designations refer to Replaceable Parts List and the
schematic diagram.
0764R

OPERATION MODELS 6108, 610BR ELECTROMETERS
e. ZERO CHECK Button. Depressing the 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.
f. FEEDBACK Switch. The FAST and NORMAL positions of the Switch determine
the feedback connections within ehe instrument. Voltage measurements are
made only in NORMAL. With the Switch et FAST, current measurements are made
with lower input voltage drops and faster response speeds. The FAST position
is also used to make guarded resistance measurements, for couLomb measurements,
and to increase response speed.
!z. INPUT Receptacle. The INPUT Receptacle fs a Teflon-insulated uhf-type
connector. A dust cap is provided. The ground post is below the recep-
tacle.
2-2. RFAR PANEL CONTROLS AND TERMINALS (See Figure 5).
a. COARSE ZERO Switch (On front panel of Model 610BR). The COARSE ZERO
Stitch has 11 positions to extend the zeroing capability of the front panel
ZERC Controls.
b. Output Switch. The Switch fs a two-position slide switch for the output.
In the 1 MA position, the instrument will drive l-milliampere recorders. In
the 3 V position, the output is 3 voles for full-scale meter deflection.
Source resistance is 3 kllohms.
c. 1 MA CAL Control. The Control varies the output from 0.95 to 1.05 milli-
ampere for 14CO-ohm recorders , so the recorder scale will correspond with the
Electrometer panel meter.
d. OUTPUT Receptacle. A 2-terminal microphone-type receptacle provides
3 volts or 1 milliampere for full-scale meter deflection. Pin no. 2 is at
case ground potential if the FEEDBACK Switch is at NORMAL.
e. Xl OUTPUT and GUARD Terminals. The potential between the Xl OUTPUT
Terminal and the CUARD Terminal (case ground for the FEEDBACK Switch in NORMAL)
Fs eaual to the input voltage with 0.005% linearity or LOO microvolts. when
the FEEDBACK Switch is at FAST, the Xl OUTPUT Terminal is et case ground end
rhe,GUARD Terminal is floating.
f. FUSE. For 105-125 volt operation, use a l/4 ampere, 3 AG Slow Blow
fuse. For 210-250 volt operation, use a L/8 ampere, 3 AC Slow Blow fuse.
g. 117-234 Switch. The screwdriver-operated,slide switch sets the Model
610B for 117 or 234-volt ac power lines.
h. Power Cord. The 3-wire power cord with the NEMA approved 3-prong plug
provides a ground connection for the cabinet. An adapter for operation from
2- tenninal outlets is provided.
2-3. INPUT CONNECTIONS.
a. The accessories described in Section 5 are designed to increase the
6 1064R _

MODELS 610B, 6108R ELECTROMETERS OPERATION
PJ.wJtu 3. PlOceL OIVH liear Y*“eL m*troLs an* TerminaLs. CLl32U
designations refer to Replaceable Parts List and the schematic
diagram.
accuracy and convenience of input connections.
capability of the Model 6LOB. Use them to gain the maximm
NOTE
Using the accessories and coaxial cables is the best
way to make input connections.
b. Carefully shield the input connection and the source being measured,
since power Line Erequencies are well within the pass band of the Electrometer
Unless the shielding is thorough, any alteration in the electrostatic field
near the Input circuitry will cause definite meter disturbances.
c. Use high resistance, Low-Loss materials - such as Teflon (reconrmended),
polyethylene or polystryene - for insulation. The insulation leakage resis-
tance of test fixtures and Leads should be several orders magnitude higher
than the internal resistance of the source. If it is not, leakage Losses
will cause Lowered readings. 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,
Hicrodot , Inc. , and Simplex Wire and Cable Company make satisfactory types.
1064R

OPERATION MODELS 6108, 610BR ELECTROMETERS
Using the Model 6LOLA Probe is a simple way to insure.good input connections.
NOTE
Clean and dry connections and cables are very important
to maintain the value of all insulation materials.
d. Any change in the capacitance of the measuring circuit to ground will
cause extraneous disturbances. Make the measuring setup as rigid as possible,
and tie down connecting cables to prevent their movement. If a continuous
vibration is present, it may appear at the output as a sinusoidal signal and
other precautions may be necessary t" isolate the instrument and the connecting
cable from the vibration.
e. For Low impedance measurements, unshielded Leads and a binding post
adapter may be used. However, keep the leads short.
f. When measuring currents LO-l4 ampere or less with the FEEDBACK switch
at FAST, some insulators - such as Teflon - may produce random signals which
show up as erratic meter deflections. Insulation used in the Model 6108 is
carefully selected to minimize these signals.
.s. Connect the M"deL 610B to the circuit only when a reading is being made.
I" some cases, the grid current can charge the external test circuitry when
it is connected to the Electrometer input. One example is measuring a
capacitor's Leakage resistance by observing the decay of its terminal voltage.
If the Leakage currant is less than the grid current, there is no decay of
the terminal voltage when the electrometer is Left connected across the
capacitor's terminals. Instead, there is a build-up which seems to indicate
that the capacitor dielectric has a negative resistance.
NOTE
Techniques and applications are thoroughly discussed
in thebrochure, Electrometer Measurements, by Joseph
F. Keithley. It is available by writing to Keithley
I"stnlae"ts, 1°C.
2-4. Preliminary Procedures.
a. Check the 117-234 Switch and the Fuse for the proper ac Line voltage.
NOTE
Make sure MRTRR Switch is sst to POWEROFF before connecting
or disconnecting the power cord.
b. Set the controls as follows:
METER Switch POWEROFF
Range Switch VOLTS
Multiplier Switch 1
FEEDBACK Switch NORMAL
ZERO CHECK Button
LOCK
a 0667R

MODELS 61.0~. 610B~ ELECTROMETERS OPERATION
c. Connect the power cord and turn the XF,TER Switch to CEpiTER ZERO. Within
ten seconds, the meter pointer should come to the center zero position. If
not, adjust to meter zero with the MEDIUM and FINE ZERO Controls. Normally,
there is no need fo use the COARSE ZERO Switch.
d. After a few moments increase the voltage sensitivity by advancing the
Multiplier Switch to .3, .L, etc. Continue zeroing with the FINE ZERO Control.
NOTE
Always turn the Model 6lOB off using the METER Switch. Do not
shut the instrument off by disconnecting the power cord or otherwise
externally shutting off the power supply. If it w be turned off
externally, set the Multiplier Switch to 1 or lower. If these
cautions are not followed, the Electrometer may drift for several
hours when it is used again.
e. After Long periods of storage or after an overload, the Model 610B
may drift excessively. Although the electrometer tubes
are shock mounted, a
severe jolt can also cause a zero offset. This is corrected with the Zero Con-
trols. Drifting, however, can occur for a few hours.
f. Although the grid current of the Electrometer is much below that found
in conventional voltmeters, it can be observed on the meter. A small voltage
results from the grid current charging the input capacity, and the Electro-
meter appears to drift when the input is open. Use the ZERO CHECK Button
to discharge the build-up.
NOTE
Keep the protective cap on the INPDT Receptacle when the
Electrometer is not in a circuit.
g. Follow the particular procedures for measuring voltage, current, re-
sistance and charge in the next four paragraphs.
2-5. Voltugo Measurements.
a. The Model 610B’s high input impedance allows circuit measurements with-
out causing circuit loading. For low resistance in-circuit tests, the input
resistance can be Lowered to avoid pick-up problems,
NOTE
Make all voltage measurements with the FEEDBACK Switch &
in the NORMAL position.
b. High Impedance Measurements (LO14 ohms, 22 picofarads). Follow the
instructions of paragraph 2-4. Set the controls as follows:
METER Switch
Range Switch
Multiplier Switch
FEEDBACK Switch
ZERO CHECK Button
CENTER ZERO
VOLTS
100
NORMAL
LOCK
t064R Y
I

OPERATION 8fom.s 610~) 610~~ ELECTROMETERS
Connect the unknown source to the INPUT Receptacle and unlock the ZERO CHECK
Button. Set the METER Switch to + or -, as necessary. Increase the sensitivity
with the Multiplier Switch, Recheck the zero setting after increasing the sen-
sitivity.
c. Low Impedance Measurements. To decrease the input resistance from 1014 ohms,
set the Range Switch to one of the AMPERES ranges. The input resistance is now
the reciprocal of the current range. For instance, to obtain an input resistance
of 107 ohms - which is normal for conventional VTVMs - set the Range Switch
to the 10-7 AMPERES range. Set the full-scale voltage range with the Multiplier
Switch. Operating procedures are the same as subparagraph b above.
d. To measure sources more than 100 volts, use the Model 6102A 1O:l Divider
Probe or the 6103A 1OOO:l Divider Probe. The Model 6102A extends ths Model
610B’s range to 1000 volts;
1010 ohms. overall accuracy is *3% and input resistance is The Model 6103A extends the Model 610B’s range to 30 kilovolts;
overall accuracy is C5% and inputresistanceis 1012 ohms. Follow the same
operating procedures with the dividers as in subparagraph b. The full-scale
voltage range is the divider ratio times the Wltiplier Switch setting.
Accuracy decreases 0.5% when the center zero scales are used
because the scale span is shorter.
2-6. Currant Mearuremantr.
a. The Model 610B can measure currents three ways.
1. In the normal method - used on any range -. the current is determined
by measuring 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 damping is needed.
2.
In the fast method - for use only below the lO-5 ampere range -
the shunt resistor is between the amplifier output and input in the feedback
loop.
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.
3. For galvanometric current measurements, the Model 610B acts as a null
indicator between a very accurate current source and the unknown current source.
b. Rise time varies primarily with the currant range, theinput capacity
and the method used. On most ranges, the rise time 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
place the Electrometer near to the current source than to the data reading in-
strument. Transmitting the fnput signal through long coaxial cables greatly de-
creases the response speed and increases noise due to the cable capacitance.
c. Normal Method (0.3 to LO-l4 ampere ranges).
1. Follow the instructions of paragraph 2-4. Set the controls as follows:
10 1064R

MODELS 610B, 6lOBR ELECTROMETERS OPERATION
METER Switch CENTER ZERO
Range Switch 10-l AMPERES
Multiplier Switch 1
FEEDBACK Switch NORMAL
ZERO CHECK Button LOCK
Connect the unknown source to the INPUT Receptacle and unlock the ZERO CHECK
Button. Set the METER Switch to + or -, es necessary. Increase the sensitiv-
ity with the Range Switch and the Multiplier Switch. Do not set the Multiplier
Switch higher then 3 for Range Switch settings lo-3 and above. Check zero with
the ZERO CHECK Button.
2. The full-scale current range is the Range Switch setting times the tilti-
plier Switch setting. Use the smallest Multiplier Switch setting possible to
obtain the best accuracy. The input resistor varies with the Range Switch set-
ting, from 10 ohms et 10-l AMPERES to lo11 ohms for lo-l1 AMPERBS. The input
voltage drop is the meter reading times the Multiplier Switch setting.
3. On the 10-S to lo-11 AMPERES settings of the Range Switch, the high-megohm
resistors used have a voltage coefficient of a nominal y.0277 per volt. If the
input voltage drop reaches 100 volts, en error of 100 x .02% or 2% occurs to
lower the specified accuracy. Therefore, use a low filtiplier Switch setting
- best is 0.1 to 1 - so neither voltage coefficient nor zero stability pre-
sents a problem.
On the low current ranges, balance out the grid current
with the Zero Controls or subtract the value from the
reading. To find the amount of grid current, cap the
INPUT Receptacle and read the meter.
d. Fast Method (ranges below 10e5 ampere).
1. Follow the instructions of paragraph 2-4. Set the controls as follows:
METER Switch CENTER ZERO
Range Switch 10-6 AMPERE.5
Wltiplier Switch 1
FEEDBACK Switch FAST
ZERO CHECK Button LOCK
Connect the unknown source to the INPUT Receptacle and unlock the ZERO CHECK
Button. Set the METER Switch to + or -, as necessary. Increase the sensitivity
with the Range Switch end the Multiplier Switch. Do not set the Range Switch
to 10-S AMPERES or higher. Check zero with the ZERO CHECK Button.
NOTE
Use only the ZERO CHECK Button to check zero for the
East method. Do not short the input, because this will
remove the feedback from the circuit.
1264R

OPERATION HOODELS610B, 610BR ELECTROMETERS
2. The full-scale current range is the Range Switch setting times the Multi-
plier Switch setting. When selecting the Multiplier Switch setting, remember
smell settings permit lower current source resistance, and larger settings im-
prove instrument zero stability. Check the caution in subparagraph 3a below.
3. With the fast method, the input drop is reduced and the response speed
is increased at least 100 times,
However, follow these cautions:
a) The internal impedance of the unknown current source should not be less
than .l of the value of the feedback resistor being used. Otherwise, the
full 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.
b) The low side of the OUTPUT Receptacle is no longer grounded. Therefore,
do not ground recorders or oscilloscopes to the Elecerometer’s case, such as
through the ground lead of the power cord. Another alternative is using the
unity-gain output (paragraph Z-10).
C) Do not use the fast method to measure capacitor leakages. Connecting
a capacitor to the input causes the circuit to be transformed into a differ-
entiator, resulting in extreme sensitivity to very smell voltage transients.
e. Galvanometric Method.
1. Operate the Model 610B as a picoarmneter in the fast method of operation.
Use en 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 use the higher current ranges.
Adjust the buckout current to indicate null on the l&de1 610B. Increase the
Electrometer’s sensitivity as needed. When the Model 610B is as close to null
as possible, the known reference current source equals the unknown source f
?hn Mrvi!a1 6,“R c-l,Yv-cxnr r!s,<rl,no
current
Source
>
FIC;URE b. Measuring Current by the Galvanometric Nethod. Use an *ccurs.te
reference current source to buckout the unknown current source, I,. The
Xodel 6LOB, on its current ranges, serves es a null detector. Use a uhf-tee
fitting at the Xodel 6lOB input. Connect the Electrometer to the two sources
with coaxial cable. Select cable carefully for very low currents (see para-
graph Z-3).
12 1064R

MODELS bLOB, 61OBR ELECTROMETERS OPERATION
2-7. Resistance Measurements.
a. The Model 610B can measure resistances by three methods.
1. In the normal or two-terminal method (annneter-voltmeter) , the ELec-
trometer 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.
to LO11 ohm ranges. This method is the simplest for the 100
2. Above LOLL ohms or to prevent leakage, the guarded method is better.
It results in faster response speeds and also nullifies Leakage errors
across the Electrometer input, since the potential across the input ter-
minal is small.
3. In the preceeding methods, the voltage across the sample cannot be
arbitrarily set. In some cases, as in measuring capacitor leakage, these
methods involve much more time than if a Larger voltage could be applied.
In the external voltage method the Model 6LOB Fs used as a fast picoammeter.
The unknown resistance sample is connected to an external known voltage
source and the current through the sample is measured, Either the normal
or fast method may be used. The resistance is calculated from the readings.
NOTE
Discharge any capacitor before removing it from the circuit.
Depressing the ZERO CHECK Button shorts the fnput through a
lo-megohm resistor, providing a discharge path.
b. Normal Method (100 to 10” ohm ranges).
1. Follow the instructions of paragraph 2-4. Set the controls as follows:
METER Switch
Range Switch To5 OHMS
Multiplier Swftch 1
FEEDBACK Switch NORMAL
ZERO CHECK Button LOCK
Connect the resistance sample to the INPUT Receptacle. Unlock the ZERO
CHECK Button. Check zero with only the ZERO CHECK Button,
Do not open-circuit the Electrometer on the OHMS ranges; the
input will develop a Large voltage due to its constant current
characteristic. Keep the input shorted or the ZERO CHECK
Button locked.
2. The full-scale ohms range is the Range Switch setting times the
Multiplier Switch setting. Use the Largest Multiplier Switch setting
possible to obtain the best accuracy.
1064R 13

OPERATION MODELS 6LOB, 6LOBR ELECTROMETERS
3. Before making a final reading, manipulate the Multiplier end Range
Switches, so the sample is tested at a number of test potentials. The
applied test voltage is the meter reading times the Multiplier SwFtch setting.
NOTE
Shield the input if the resistance sample exceeds one megohm.
C. Guarded Method (to 10L4 ohm ranges).
1. Follow the instructions of paragraph 2-4. Set the controls as follows:
METER Switch
Range Switch ;011 OHMS
Multiplier Switch 1
FEEDBACK Switch FAST
ZERO CHECK Button LOCK
Connect the low impedance side of the resistance sample to the Model 610B
GUARD Terminal, and the high impedance side to the INPUT Receptacle. Unlock
the ZERO CHECK Button.
2. Read the resistance as outlined for the normal method, subparagraph b.
d. External Voltage Method (To ~016 ohms).
1. Turn the ZERO CHECK Switch to L,OCK. Connect the sample between the
INPUT Receptacle and the power supply. (See Figure 7.) Put a switch in
the high voltage line to ground the low impedance end of the sample when
it is disconnected from the ootential.
from a known source, V, is applied to the unknown resistance sample, &. The
Model 610B measures the current through &, from which the resistance is calcu-
lated. Switch S grounds s when no potential Fs applied.
2. Set the FEEDBACK Switch to NORMAL. Usually this method is best, since
instabilities can arise if the resistance sample is Less than .L the value
of the feedback resistor.
3. Apply a potential to the sample before releasing the ZERO CHECK Button.
Set the Range Switch to .3 AMPERES and increase sensitivity until a reading
is obtained.
14 1064R

MODELS 6108, 610BR ELECTROMETERS OPERATION
4. If the potential applied is at least 100 times the full-scale input drop (Multi-
plier Switch setting), the resistance is equal to the applied potential divided by the
current reading. The high voltage sensftivity of the Model 61OB, therefore, permits
external voltages of .l volt or more to be used.
5. If the potential applied is less than 100 times the input drop, the resistance is
e~qual 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, the input drop is so slight that it
need not be included in the calculation. If the capacity shunted across the sample is
large, such as encountered in capacitor leakage measurements, the fat method increases
response speed and this connection is reconrmended.
2-&Charge Measurements.
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 sensi-
tivity 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 un-
known 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.
b. The full-scale charge range is the Range Switch setting times the Multiplier Switch
setting. Grid current contributes 2 x LO-l4 coulomb per second maximum.
NOTE
Because of the instrument’s RC time constant,
internal capacitance on the 10.’ wait 20 seconds after discharging coulomb range before making another measurement.
On the 10-B coulomb range, wait at least two seconds.
2-g. Recorder Outputs.
a. For recording with the Model 610B, use the Keithley Model 370 Recorder for ease,
~COUXlly, versatility and performance. The Model 370 is a pen recorder with 10 chart speeds
and 1% Linearity. The Model 370’s input cable has a connector which matee directly with
the OUTPUT Connector on the Model 610B; this avoids interface problems often encountered
between a measuring instrument and a. recorder. No special wiring is needed. No recorder
preamplifier is required. (See paragraph 5-B Eor more on the Model 370.)
b. Other recorders, oscilloscopes and similar instruments can be used with the Model 6108.
The Model 610B has two variable gain outputs, ?3 volts and *l milliampere, to amplify sig-
nals within 112% for recorders, oscilloscopes and similar instruments. These can be used
on all ranges of the Model 610B.
0667R I.5

OPERATION MODELS 6lOB, 610BR ELECTROMETERS
c. 3-Volt output. Connect oscilloscopes and pen recorder amplifiers to the OUTPUT
Receptacle. Pin no. 1 is the negative terminal; pin no. 2 is grounded. Set the Output
Switch to 3 V. The Model 6lOB output is now +3 volts for full-scale meter deflection on
any range. Internal resistance is 3 kilohms. The frequency response ($3 db) is dc to
300 cps at a gain of 3000, rising
to 25 kc at a gain of 30, and decreasing to 2.5 kc at a
gain of 0.03. Noise is 3% rms of full scale at a gain of 3000, decreasing to 1% at gains
below 100. The METER Switch does not reverse the output polarity.
NOTE
The Model 610B may be used with the FEEDBACK Switch fn FAST position with other
instruments. However, make sure there is no common ground between the Electro-
meter us3 end the other instrument.
d. l-Milliampere Output. Connect l-milliampere instruments, such as Esterline Angus,
General Electric or Texas Instrument Rectiriter, to the OUTPUT Receptacle. Pin no. 1 is
the negative terminal. Set the Output Switch to 1 MA. The output is approximately 1 mil-
liampere for full-scale meter deflection on any range. For exact output, adjust the meter
on the .003-volt range with the FINE ZERO Control for full-scale deflection. Then adjust
the 1 MA CAL Control until the recorder reeds full scale. Check the recorder and meter
zero end repeat adjustment if necessary. The METER Switch does not reverse the output
polarity.
e. For servo rebalance recorders, use a divider
across the Model 610B OUTPUT Receptacle.
See Figure 8. Set the Output Switch to 1 MA. Use the 1 MA CAL Control to trim the output
for full-scale recorder deflection. Operation is the same as for current outputs.
A 1-$
Model 1 kn Model
610B 6108
output
(JlO5)
* It 1
1 kn
Output
50-mv (J105) loo-mv
50 0 Recorder 100 n Recorder
50-millivolt output 2) :
100~millivolt output
FIGURE 8. Divider Circuits Across Model 610~ Output. The dividers are for driving 50
and 100-millivolt recorders. Use 1% resistors in the dividers.
f. When the FEEDBACK Switch is in the NORMAL position, the negative side of the output
terminal is grounded to the instrument case. Therefore, no difficulty will be experienced
using oscilloscopes end recorders with the Model 61OB set for normal operation. In FAST
position, however, neither side is grounded. If this is used, make sure there is no com-
mon ground between the recorder or oscilloscope end the Model 6108 case, or use the unity-
gain output.
16
;:
10&R