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INSTRUCTION MANUAL
MODELS 200,200A
ELECTROMETER VOLTMETERS
WARRANTY
We warrant each of our products to be free
from defects in material and workmanship. Our
obligation under this warranty is to repair or
replace any instrument or part thereof (except
tubes and batteries) which, within a year after
shipment, proves defective upon examination.
We will pay domestic surface freight costs.
To exercise this warranty, call your local field
representative or the plant directly, DDD 216.
795.2666. You will be given assistance and
shipping instructions.
REPAIRS AND RECALIBRATION
Keithley Instruments maintains a complete re-
pair service and standards laboratory in Cleve-
land, and has authorized field repair facilities
in Los Angeles and Albuquerque.
To insure prompt repair or recalibration serv.
ice, please contact your local field represent-
ative, or the plant directly, before returning
the instrument.
Estimates for repairs, normal recalibrations,
and calibrations traceable to the National Bu-
reau of Standards are available upon request.
MODEL
200, 2OOAELFLYl'ROMEXl'ER
TARLEOF COl4TEN'B
Title EeE!
Section I. General .................. L-1
Table of Specificationa ................ l-2
section II. Description ............... 2-l
Section III. Operation ................ 3-l
Connections ...................... 3-1
Range ......................... 3-l
Zero .......................... 3-l
Measurement ...................... 3-1
Increasing Voltage Sensitivity ............ 3-3
Alternative Methods of Recording ........... 3-3
Uses ......................... 3-3
Section IV. Maintenance ............... 4-l
Battery Replacements ................. 4-l
Tube Replacement ................... 4-l
Recalibration Instructions .............. 4-l
Insulation Resistance ................. 4-2
Schematic Diagrams
Appendix - Uses
0762~
MODEL
200, 200A EI.,EX!TRoMETER GENERAL
SECTION1 -GENERAL
The Keithley Vacuum Tube Electrometers provide rapid and accurate measurements
of dc voltage in circuits having extremely high internal resistance, and for dc
applications where no current can be drawn from the voltage source. They are also
widely used as micromicroammeters, megohmmeters, and static detectors. The in-
struments contain a subminiature electrometer tube which operates from batteries
within the case. Highly stable circuits insure long battery life, very low drift,
instantaneous warmup, and accurate calibration over long periods of time. Prin-
cipal characteristics are:
A. Ranges, Model 200: The two ranges are 2 volts and 20 volts full scale;
the pointer can be electrically zeroed at any point on the scale to read posi-
tive or negative inputs.
Ranges, Model 2oOA: The two ranges are 2 volts and 8 volts full scale;
the pointer can be electrically zeroed at any point on the scale to read posi-
tive or negative inputs.
B. Input Impedance: The input circuit has a resistance higher than 1014 ohms
in parallel with a capacitance of 8 micro-microfarads.
C. Grid Drift Current,
Model 200: The open grid drift current is less than
5 x 10eL* ampere on the 2-volt range, and 5 x 10-l-3 ampere on the 20-volt range.
This means that with the RI input terminal floating, the meter pointer will
drift across the scale on either range in approximately three minutes. The
drift rate is reduced when capacitance is connected across the input
and no drift or zero displacement is observable if a resistance of 10
or less is connected across the input terminals.
Grid Drift Current, Model ZOOA: The open grid drift current on the 2..volt
range is less than 5 x 10-l" ampere, just as in the Model 200. On the 8-volt
range the current is less than 2 x lo-13 ampere.
05633 l-l
MODEL
200, 200A ELECTROMETER
TABLEOF SPEKIFICATIONS
RANGES: Model 200: Zero to 2 Volts; Zero to 20 Volts.
Model 2OCA: zero to 2 Volts; Zero to 8 Volts.
AccuRAcy: 2% of full scale.
ZERODRIFT: Less than 1% per hour after a 2-hour warmup.
INPUT IMPEDANCB:More than 1014 ohms, 8 micro-microfarads.
GRID CURRENT: 5 X lo-l4 ampere maximum.
OUTPUT
RANDWIDTH:DC to 20 kc.
MAXIMCM
NOISE LZVRL: 0.5% of full scale.
INPUT PROTECTION:1 megohm.
OUTFUTGAIN: About .65 on each range.
OUTHJTIMPEDANCE: 50K (Loads under 5 megohmsaffect meter reading).
POWER
REQUIREMENTS:
Batteries: One D cell, two type 4l.l, seven penlight cells.
D cell life, 200 hours; others, 800 hours.
"IWE COMPLEMENT: 5886.
one
DIMENSIONS: 8 in. high X 5* in. wide X 4 in. deep.
WZIGRT: 5 pounds.
1-2 0563~
MODEL
200, 200A ELEXXROMEX!FB DFixxtpmON
SECTION - DESCRII'TION
II
The equipment layout and circuit schematic diagrams are enclosed at the back of
the bulletin.
A. Meter: The large meter on the face of the instrument indicates the dc poten-
tial inlts across the input terminals.
B. Selector switch, Model 200 (OFF-20-2): The right hand knob on the panel turns
the instrument off or to the 20-or 2-volt r-es.
Selector switch, Model 2OOA(OFF-8-2): The right hsnd knob on the panel turns
the instrument off or to the &or a-volt ranges.
C. zero: The knob at the left is the electrical zero adjustment; with it, the
meterpointer can be set to any point on the scale with the input terminals con-
nected together. The scale is marked for zero at the left and for zero at the
center.
D. Input Terminals: The input terminals are RI and ground.
E. Output Terminals: The output terminals of the Models 200 and 2OOAelectro-
meters are located on the panel to the right of the range switch. The white ter-
minal is connected to the cathode (F-) of the electrometer tube; the black terminal
is marked I.0 and is connected to ground. Thus, the terminals permit the use of
the electrometer tube as a cathode follower. 10 megohmsis the minimwn permiss-
able load resistance for less than 2% change in the panel meter sensitivity. Table
I, below, gives the voltage gain and zero offset (the voltage between the two out-
put terminals with the electrometer input short-circuited and the panel meter set
to zero) for the three ranges of the battery electrometers.
Table I
Range Voltage Gain Zero Offset
0.54 2.6 volts
i:: vo1ts 0.68 4.6
20.0 0.66 7.6
F. Input Switch: The input switch 52, is depressed while setting the instru-
ment zero. It connects the tube grid to the low side of the circuit. The one-
megohmresistor, Rl, prevents short-circuiting the circuit under test.
G. Calibration Controls: The two range calibration controls, R7 and R8, are
accessible through holes in the back of the case. CAUTTON W NOTAJNUST
-- THFSE
CONTROLS hITROUT-G 'x) THE RFCALIBRATIONINSTRUCTIONS PAGE4-l.
ON
H. Batteries and Tube: The batteries and tube are readily accessible by re-
moving the panel from the case.
0762R 2-l
MODEL
200, 2OOAEL?3CTROIWl'EX OPEmON
SECTIONIII - OPERATION
The Model 200 and Model 2OOA VIXUUII Tube Electrometers arc shipped complete with
a fresh set of batteries, and are accurately calibrated at the factory. NWIIWOUS
applications and circuit possibilities for use of these instruments are discussed
in the appendix.
A. Connections: The HI terminal should be connected to the high resistance,
or hi-insulated terminal, of the circuit under test. Ground is the other
input terminal.
B. Range, Model 200: Set the range switch at the Z-volt or 20-volt position
as required to read the voltage across the input terminals. In measuring potent-
ials ,over 20 volts, the ground terminal can be raised in potential to approximate
the source voltage and the difference rea on the Electrometer, as discussed on
$2
paQ;eU. Or, if a shunt resistance of 10 ohms across the source is permissible,
1OC:l and 1OOO:l Voltage Divi.ders,'Models 2006 and 2007 respectiveq may be used
to extend the'maxiium voltage to 20,000 volts.
Range,Model ZOOA: Set the range switch at the 2-volt or O-volt position as
required to read the voltage across the input terminals. In measuring~otentials
over 8 volts the methods discussed on page IA nay be used, or, if a 10 ohm load
is permissible, 1OO:l and 1OOO:l Voltage Dividers, Models 2006 and 2007 respectively,
may be used to extend the maximumvoltage to 8000 volts.
Be certain that the range switch is in the OFPposition after using the instrument
to avoid unnecessary discharge of the batteries.
C. zero: The instrument should be zeroed b;r depre oning the input switch and
rotatzthe ZEROlmob to bring the meter pointer to the desired zero. If the
voltage to be measured is positive, use the zero point at the left of the scale
to take advantage of the full scale range; if the voltage changes sign or is
negative, use the mid-scale zero; or zero at the right for large negative potent-
ials. Depressing the input switch connects a one-megohmresistance across the
input terminals. If charged capacitors are in the circuit under test, they will
be discharged or brought to the proper initial state of charge, as the case may
be,when the input switch is closed. In any case, the one-megohmresistor pre-
vents high surge currents from flowing.
D. Measurement: Read the voltage directly on the appropriate scale, keeping
in mind the full-scale voltage corresponding to the position of the range switch
At this point, several precautions should be mentioned.
1. Shielding;:. Circuits with internal resistance less than lOlo ohms can
usually be shielded adequately against stray electrostatic and power frequency
fields by keeping the HI lead short - no more than a few inches long.
It is sometimes necessary to enclose the highly insulated portion of the cir-
cuit and lead to the HI terminal in an electrostatic shield. Support insu-
lators may be fashioned from polystyrene or polyethylene stock. The impor-
tance of rigid supports cannot be overemphasized, especially if the shield
is at a high potential with respect to the HI terminal. Small relative motions
0762~ 3-l
OPEWION MODEL
200, 200A ?&ECTROMETXR
of these parts cause .the capacitance ofthe system to change, and as the charge
remains constant, large changes in potentials result from the motion, as in
the fsmiliar condenser microphone. Frictions.1 electricity which results from
the HI leads moving over the surface of an insulating support can also cause
annoying disturbances.
2. Time Constant: The RC time constant of the measurement circuit begins
to approach one second when the resistance across the input terminals of
the Electrometer gets above 1011 ohms, for the input capacitance is about
6 mmf. To get accurate readings, it is necessary to wait until the pointer
stops moving. The inherent circuit drift of the Electrometer is very low,
so that any drift that is apparent can usually be attributed to drift in
the circuit under test or to slow recovery in circu.its having extremely
long time constants.
The most significant exception is that upscale drift will occur if there
is no resistor across the input terminals of the Electrometer and the cap-
acitance between these terminals is low or virtually only the internal cap-
acity of the instrument. Here, the reverse grid current of the tube charges
the circuit'being measured and the pointer drifts slowly upscale.
3. Correction for Grid Current: The grid current of the Electrometer
may be measured by timing the open-grid drift upscale.
I = C$ = 6 x l~-~~-$-smpere
In making this ,test the HI terminal should be shielded, preferably by a
metal tube large enough to slip over the guard ring. The following table
illustrates the grid current computations for the different ranges:
RANGE "0 Et At
2 volt 0 0.2 volt 24 sec. 5.0 X 10"14 ampere
8 volt 0 0.8 24 2.0 x 10-13
20 volt 0 2.0 24 5.0 X lo-l3
Alternatively, the g&d current may be measured by observFng the voltage
across a known high resistance connected between the input terminals.
R must be at least 1012 ohms, giving a long time constant, and steady state
conditions must be reached before reading E. The grid current is approx-
imately constant over the Z-volt range, but on the 20-volt range, it is
greatest near zero volts and decreases considerably as HI is made more posi-
tive .
The grid current may be abnormally high if the tube has not been in use
for a long period. After an hour's operation the grid current should fall
to within the normal limits.
3-2 0762~
WDEL 200, 200A EIECTIiCMETER OPTXWCION
In low current circuits, the grid current must be subtracted (algebraically)
from the total current read to give the correct current in the circuit be-
ing measured.
4. Correction for Input Capacity: It must be remembered that the inter-
nal capacitance of the Electrometer shunts any external capacitance co%cted
to the input terminals. The internal capacity is approximately 6 x 10~
farad, and corrections must be made if this is appreciable compared to an
external capacitor whose voltage is being measured.
E. Increasing Voltage Sensitivity: The panel meter on the Models 200 and 200A
has a O-50 microampere movement. If a more sensitive galvanometer were connected
in series with the panel meter, the voltage sensitivity of the electrometer, as
read on the galvanometer, would be proportional to the increase in sensitivity
afforded by the galvanometer. The limitation of the increase in most cases comes
when the zero control of the electrometer becomes too coarse.
F. Alternative Methods of Recordi%: An alternative way to record is to con-
nect a galvsnometer in series with the panel meter, whose movement is O-50 micro-
amperes. Photographic recording is most commonwith the mirror gal-meters.
The General Electric Photoelectric recorder, however, has also found use; here,
the mirror galvanometer actuates a photoelectric servo system, and a pen recorder
is made to follow the galvanometer deflections. The meter connections are made
accessible by removing the cabinet, then removing the battery tray.
G. Uses: Typical applications of the Electrometer are described in the Appendix.
The s=sted circuits are indicative of the many uses of the instrument in measur-
ing voltage, current, charge, capacitance, resistance, and various capacitor par-
ameters more quickly and accurately than was previously possible.
In many cases the circuit arrsngement is greatly simplified through the use of
the various Keithley Electrometer accessories. These include shunts, voltage
dividers, a test voltage supply, and a static detector, listed in the descrip-
tive literature included with the instruction manual.
0762~ 3-3
MODEL
200, 2OCAELECTROMETER MAINTENANCE
SECTIONIV - MAINTENANCE
The Keithley Model 200 and Model 200A VacuumTube Electrometers have been de-
signed to give long, trouble free service; the only regular attention necessary
is the occasional replacement of batteries. The tube should give severalthou-
send hours service in normal use. The sensitivity adjustments at the rear of
the instruments do not require attention throughout the life of the batteries.
The calibration, nevertheless, should be rechecked occasionally, and particularly
after replacing the tube.
A. Battery Replacement: To check the batteries, remove the panel from the case
by removing the six No. 4 sheet metal screws around the edge of the panel. Then
remove the battery co;er plate by removing the two screws holding it.
Low batteries may cause the zero to shift beyond the range of the zero control;
they may cause rapid drift, or high forward grid current. Since the D cell (flash-
light cell) has the shortest rated life, it should be checked first; it should
be replaced if it measures below 1.1 volts, using a lOOO-ohms-per-volt meter.
The miniature B batteries should be replaced if they measure less than 12 volts.
If they are too low, the zero control cannot be advanced far enough clockwise
to zero the instrument at full scale on either scale. Low B batteries also cause
high forward grid current on the high end of the 20-volt scale. This is evident
if the zero is set at full scale and the meter drift observed with the input ter-
minals open. The pointer moves quickly downscale, and stops at about 3/4 full
scale. This behaviour indicates that the B batteries should be replaced. Low
penlight cells cause the same effect on the a-volt range. These cells should
be replaced if the series voltage of the 10.5-volt group goes below 7 volts.
Low batteries have very little effect on the calibration of either range, down
to the point where the instrument cannot be zeroed to full scale. When replac-
ing batteries, it is essential that the indicated polarities be observed.
B. Tube Repticement: The tube should give thousands of hours of service in
this application, but it can easily be replaced with a Keithley Instruments
Part ~~-5886-3 (Model 200) or w-5886-4 (Model ZOOA)if it becomes damaged.
Observe caution when replacing the tube: DIRT or MOISTURE from the RAND2 will
cause leakage from the base of the tube to the grid lead, which impairs the oper-
ation of the instrument in measuring low currents. Connect the leads as shown
in DR 10299 or 10446, Figure 3.
New tubes sometimes exhibit large reverse grid current, which falls to normal
value after an hour's operation.
C. Recalibration Instructions, Model 200: To reset the sensitivity, a voltmeter
to read 1.5 volts end 15 volts to 2% is required for comparison. Calibration
at these two points on the 2-volt and 20-volt scales gives the best overall ac-
curacy . The 20-volt scale is calibrated by applying 15 volts, zeroing the meter
by closing the input switch, and adjusting the pointer to 15 volts with the cali-
bration control at the back of the~instrsment. This adjustment has a small ef-
fect on the zero setting, so the process should be repeated several times to ob-
tain an accurate setting. The s&meprocedure is followed with the Z-volt scale,
except 1.5 volts are applied to the input terminal.
4-l
MUNTEWANCE MODEL
200, 200A ELRCTROMETJ?,R
Recalibration Instructions, Model 200A: The procedure is the same as above,
except 6 volts are applied to calibrate the a-volt range.
Adjustments of the calibration control for one range do not affect the other
range in either instrument.
D. Insulation Resistance: Clean insulation is essential for a high input re-
sistance. The resistance should always be sufficiently high to permit reading
grid current by observing the open circuit meter drift (Section 111-D-3). To
clean the insulation supporting the RI terminal and supporting the input resistor
inside the case, dust it with a small brush, or if necessary wash it lightly
with carbon tetrachloride. Spurious static charges may accumulate on the insul-
ation after cleaning, necessitating a wait of several minutes after cleaning
before operation can be resumed.
The insulation resistance will be lowered by extremely high humidity, but the
excellent high resistance properties return when the humidity decreases.
E. Severe Damage: If the instrument cannot be calibrated by following the
procedure outlined above, factory repairs are recommended.
4-2 0762~
,."._
- EOUIPYENT
1
:
DIAGRAM
R4 275K
RED DO
FIG. 3
TUBE
(R9250K o$* E B4 CONNECTIONS
ZERO AOJ.
MODEL 200 VACUUM TUBE ELECTROMETER
FIG.1 CIRCUIT SCHEMATIC DIAGRAM
1 DR 10446 -A
CONFIDENTIAL
KEITHLEY INSTRUMENTS
CLEVELAND, OHIO
Typical applications are included on the next few pages to indicate the many
measurements which the Electrometer and its accessories can make accurately
end quickly. Full operating instructions for the various accessories are in-
cluded in the last section of this book.
High resistance source within scale range. The high resist-
ance or highlyinsulated terminal of the source is connected
to the HI terminal of the Electrometer. The voltane is read
directly, as described previously under OPKRATIOK. I
High resistance source, less than 2o,oclo volts. The
Keithley Models 2006 end 2007 volta ,ge dividers, (1OO:l and.
1OOO:l ratios), convert the Electrometer into an extremely
sensitive kilovoltmeter. 1012 obms input resistance.
High resistance source, buckout method. An additional
voltage source, such as the Keitbley Model 2004A, is
used to buck out most of the voltage, and the differ-
ence is read on the Electrometer. To avoid having ex-
cessive grid current flow through the unlau~n voltage
source, the bucking voltage should be made more posi-
tive then the unknown voltage initially, then reduced
until the difference can be reed on the Electrometer. In this appllcatian the G
terminal potential should not be made greater then about 50 volts from ground.
Surfaoe contact potentials in semi-conductors or thermionic
devices. The vmasurement is made by direct connection to the
Electrometer.
Piezo-electric potentials. The electrode which provides the
best shielding is connected to the G terminal. The other
electrode is connected to the HI terminal. The electrometer
reads the instantaneous voltage at the terminals of the crys-
tal at low frequencies. The KI lead should be connected so
that it does not move appreciably, particularly with crystals
which have low internal capacitance.
KEITHLEY ?zrw!.x~S CKWIXAND, OHIO
XEITHLEYELECTROMXTERS APPENDIX- USES
Potentials of charged capacitors. Connect HI to the high im-
pedance terminal end G to the low impedance terminal, being
careful not to discharge the capacitor through low resistance
paths while making the connections. The
directly.
Vacuum Tube electrode potentials. The Electrometer is well
suited to measuring electrode potentials in vacuum tube cir-
cuits, for only a very slight disturbance is caused by its
connection, even in high resistance circuits. This is par-
ticularly desirable in dc amplifier work where small varia-
tions in potential can be greatly amplified, upsetting the
normal operating conditions. The HI terminal is connected
to the electrode, and G to ground or an auxiliary potential
source depending on the magnitude of the voltage to be msas-
ured. As shown, a voltage divider is being used to permit measurement of the screen
potential. An alternative method would be the buckout method described above.
The presence of a large ac signal at the electrode being measured can cause an er-
roneous reading, because of rectification in the electrometer tube grid circuit,
The peak value of the ac signal should be heldwithin the voltage of the scale
range used, or a simple sigaal filter which passes only the dc component can be
used.
Static charge detection. The Electrometer is extremely sen-
sitive to static charges, and can be used to make both quali-
tative and qusntitive measurements. Addition of the Model 2005
Static Detector accessory, shown here , permits varying the sen-
sitivity of the Electrometer, and confines the sensitivity to a
small cone along the axis of the detector, permitting quick
location of charged objects.
Equipotential contour plotting in an electrolytic aaslogy
tank. The Electrometer is a particularly useful instrument
for electrolytic field plotting. Conventional techniques
are ,employed, dc potential is applied, and a high resistance
electrolyte is used. In addition to the usual following of
preset equipotential lines, the potential of any point can
be read directly.
KEITHLEY INSTRCMENTS 2A cLEvEm, OHIO
KEITHL?XY
ELFCTSOMETEPS APPEWDIX USES
-
TfFIcALcuRRKNT MFJASDREMENTs
The Electrometer is converted quickly to a micromicroammeter by use of the Keithley
Decade Shunt, Model 2008, which permits accurate measurements
ampere.
Photoelectric cell current. With very high shunt resist-
ances, small currents which represent very low levels of
illumination can be measured. It is important to keep the
leakage across the photocell and its connector low, for the
measured current should be predominantly emission current.
The G terminal should always be kept at ground potential.
Mass spectrometer currents and inverse currents in semi-
conductors can easily be measured by the ssme direct method.
Ion Chamber currenq by accumulaticm of charge, or meas-
llated charge. Current from sources such
as photoelectric cells or ion chambers can be measured by
the rate of accumulation of charge on a known capacitance.
Discharge C, and observe the increase of E2 with time;
The current, derived from the relationship in the diagram, is the magnitude of a
constant current or the average value of a varying current. The value of C de-
termines the rate of rise, and should be chosen so that the time can be read ac-
curately. A low leakage capacitor should be used. The electrometer can bs re-
moved from the circuit during the accumulation to prevent its grid current from
charging the capacitor.
The total accumulated charge resulting from an instantaneous exposure of a photo-
cell to light or sn ion chamber to radiation can also be measured with this cir-
cult. E2, the capacitor potential, is made zero initially, and the accumulated
charge is CE2, as indicated.
It is essential that the charge originate in an infinite impedance source such
as a photocell or an ion chamber.
The charge Q is a measure of the total radiation dose when an ion chamber is
the current source. When a photocell is the current source, the charge is a
measure of the total light falling on the cell and corresponds to photographic
exposure.
ICZITHLK'Y
INSTPUMglFI'S 3A CLEVELAND,
OHIO
KRITRLEYELECTROMETERS APPENDIX- USES, V-C
TYPICAL RESISTANCE
MEASJRRKFJiTS
The Keithley Electrometer can be used for accurate msasure-
msnt of resistances up to approximately 1016 ohms. Here are
three suggested methods:
Insulation leakage~resistance. Make the connections as shown,
and allow the circuit to come to equilibrium after releasing
the input switch.
It should be noted that high resistances often do not follow Ohm's law, but exhibit
appreciable voltage coefficients of resistance, This effect is observed by trying
various values of El. The voltage across Rs must be kept within the manufacturer's
rating, or the voltage coefficient of the standard will introduce some error.
High Resistance by the Charge leakage method.
High resistances may be nksasured with the Elec-
trometer, a good capacitor (leakage resistance
high compared with the unknown), and a stop
watch. In the illustration a Keithley Regulated
Voltage Supply is used as a convenient charging
source. Once the capacitor is charged, the switch
is released, the decay of ES with time is observed,
and the unknown resistance la computed,
The leakage resistance of the capacitor may be determined by omitting R, from the
circuit.
This measurement method can also be used to determine the deviation of the capaci-
itor and leakage resistance from the ideal relationship. By plotting the decay of
voltage with time on semi-log graph paper (time-linear, voltage-logarithmic), de-
parture from a straight line indicates the presence of factors other than R and C.
Such a capacitor probably cannot be used for accurate integrating over long periods
oftime. If C has little capacitance, correction should be made for the internal
capacitance of the Electrometer, Section III. In extreme cases it may also be
necessary to correct for grid current, Section III.
High Resistance by Wheatstone Bridge Method. Accurate
measurements of high resietances can be made by using
the familiar Wheatstone Bridge. The Ratio Arms, RA
and Rg, of relatively low resistance, are adjusted until
the Electrometer reads zero. The voltage coefficients
of the standard end the unknown can affect the balance
point; thie can be checked by varying the battery volt-
age.
KEITHLEY INSTRUMENTS 4A CLEVEIAND,OHIO
ICEITElLEYELJXTROMETKRS APPENDIX- USES
TYPICAL CAPACITANCE
MEASUREMENTS
Measurement of Capacity by Charge leakage method.
This uses the same circuit as measuring resistance
by the charge leakage m&hod except a Keithley
Shunt is used as & standard resistance and the
equation is solved by capacitance. Thus, a
standard high resistance can be used to measure
the capacity of a low leakage capacitor.
Measurement of capacity, parallel capacitors. Switch
and C&,-, in parallel, and discharge the system. Switch
ix to El, charging it. Finally, switch Cx across CsTb and
&e Electrometer. The charge is conserved and the unknown
capacitance is computed.
Measurement of capacity, series capacitors. Switch Cx to
ground, discharging both capacitors. Switch Cxto connect El
across the capacitors in series. The charges will be equal
on both capacitors, and the relationship under the diagram
gives the unknown.
In both the series and parallel methods of measuring capacity, Cx and CST~
can be interchanged to increase the range of measurement.
The Keithley Regulated Voltage Supply, Model POO~A, is a convenient source for
El in each of the above set-ups.
KiZITEfXX INSTXJMWPS 5A cmLAND, aI0
APPENDIX- ACCESSORIES
DIVIDERS -- MODELS
VOLTAGE 2006, 2007
Two resistive voltage dividers are made by Keithley Instruments. The Model 2007
is taller than the Model 2006 Divider illustrated; both may be used with all
Keithley 200~series Electrometers.
No special techniques are required in using the dividers. Each plugs over the
HI terminal of the Electrometer, extending its range by the ratio indicated on
the nameplate.
Principal characteristics are as followe:
INPUT MAX. VOLTAGE TEMP. RESISTOR
MODEL RATIO RATIO ACCURACY RES. OHMS INFU'I V. COEFF. COEFF. MANUFACTURER
2006 1OO:l lOI.2 2000 -0.2$p RPC
2007 100O:l 1012 20000 -0.2$/% RPC
RPC Resistance Products Company, Harrisburg, Pennsylvania
XEITHGEYINSTRUMENTS 6~ CLEVEDiVD,OHIO
KEITHLEYELECTROMETERS APPENDIX- ACCESSORIES
MODEL
2005 STATIC DETECTOR
Description. The Model 2005 Static Detector is au
accessory for Keithley Electrometers which increases
their usefulness in locating static charges.
The Electrometers are extremely sensitive to static
charges--so much so as to be almost useless for
locating a charged object, especially in an area
where other electrostatic fields are present. The
Static Detector controls the sensitivity of the
Electrometer and also gives a directional character-
istic to the instrument. Maximumsensitivity is
along the cylinder axis.
Operation The Static Detector is clipped onto the
Electrometer RI terminal. The meter is then set to
zero electrically by depressing the Input Switch and turning the zero knob, If
the charges being investigated are of unlcaown polarity, as is usually the case,
the meter should be set to the center zero. This zero setting must be done away
from the charged object. If the meter zero is set while in the static field the
meter will deflect in a direction opposite from normal when the instrument is re-
moved from the field.
The sensitivity of the instrument is determined by the meter range and by the pos-
ition of the inner tube of the Static Detector. Least sensitivity results when the
meter is set on the highest voltage range and the inner tube is fully extended.
Closing the tube completely will increase the sensitivity about 200 times. Switch-
ing to the most sensitive voltage range of the Electrometer will, of course, give
maximan sensitivity.
Normally the instrument will be held in the operator's hands and readings will be
made as outlined. If the stray fields are strong enough, a charge may be induced
in the operator's body, which will cause erroneous readings. In such ca6es it may
be necessary to run a metallic conductor from the earth to the G terminal of the
Electrometer.
KJmEmY INsTRuMEN!rs 7A CLEVELAND,
OHIO
KEITRUYELECTROMNTRRS APPENDIX- ACCESSORIES
MODEL
2008 DECADE
SRDNT
DESCRIPTION This shunt clips onto a Keithley
Electrometer to make a very sensitive micro-
micro.mmeter. Current ranges on the panel are
reciprocals of resistor values in the circuit.
The current being measured is simply the
Electrometer reading times the current range.
Thus, 1.5 volts on the lo-l2 range is 1.5 x
lo-12 ampere.
Both the Short position of the selector switch,
and the button on top short-circuit the input,
to permit zeroing the Electrometer pointer.
The Open position disconnects all resistors,
permitting voltage measurements with minimum
current drain.
The low terminal Is connected internally to
the cabinet, and should be on the low.impe-
dance side of the test circuit.
OPERATIONTurn on the Electrometer, zero the
pointer, and turn the Shunt switch to the
right until the Electrometer needle indicates.
Overlapping voltage ranges of the 200A and 210
Electrometers permit upper-scale readings of
most currents.-
Keep test leads short, and shield high-impedance circuits to prevent disturbances
from stray electrostatic and power-frequency fields.
MAINTENANCE Occasionally clean the insulation at the high terminal and switch
with a lint-free cloth. Do not touch the glass resistor envelopes with the hands.
PZSISTORSPECIFICATIONS
Nominal Amps Full Scale on Typical
Current Ohms Resistor Electrometer Ranges
Range Resistance Tolerance 30 mv Range 0.8 v Range
Short 0
10-3 103 1% x 10-5 8 x 10-4
10-4 104 1% 3 x 10-G
10-5 105 1% x 10-7 : :: :::z
10-G 1.06 1% 3 x 10-8 8 x 10-7
3
10-7
10-8 107
108 1%
1% 3 x
x 10-9
10-10 ; x g:;
10-9 109 + @* 3 x 10-11 8 :: 10-10
10-10 1010 + 3x 10-12 8 x 10-11.
10-11 1011.+ 3 x 10-13 8 x 10-Q
10-12 1012 + 3: 8 x 10-13
open --__--. *Listed at back of Shunt within 1%
+Temperature coefficient is 0.1 - 0.1% per degree; resistors are measured
at 25Oc. A drift of about l/2$ per year is to be expected.
KEITHLEY INSTRUMENTS 8~ CLEVELAND,
OHIO
November 6, 1964 I.SJDELS
200, 2006 EL-RCTROMEi'RRS
mdel 200 Sc&gmtlc Drewin&Q&10299:
Change the value of R2 to 50 IC ohm nominal value.
&lcdel 200A schematic s - :
Change the value of R& to 275 13;
Chenge the vcrlue of R5 to 60 ILL;
Chanse the value of RlO to 333 Pi.