Keithley 510 User manual

/
MODEL510
MEGOHMMETER
AND ACCESSORIES
KEITHLEY INSTRUMENTS, INC.
CLEVELAND, OHIO

CONTENTS
SECTION
INTRODUCTORY*,.,...,,*......****.I.*..,..........*...* "I
SPECIFICATIONSANDDESCRIPTION........................ II
OPERATION....,.....'..................,................ III
MAINTENANCE'~,......,,................,................. Iv
General
Circuit schematic
voltage and resistance diagram
Replaceable parts list
APPENDIX
Accessories..................,...,...,....,...,.,. i
Model 51.036 Test Leads
Model 5101 ComponentAdapter
Model 5102 Volume Reoistivity Adapter
Models 51024 and 51060 Cables
Measuring technique ..,.,.,............... . ..* . . . . . ii
Introduction
Speed of indication
Component measurements
Volume resistivity
Special shielded enclosures
Use of other than standard test potentids
ASTMReprint *.*....*.*... . . . . . . . . . ..*.......*.*...... Rear Cover
510
If58

SECTIONI INTRODUCTION
The Keithley Model 510 Megohmmeterutilizes a unique logarithmic circuit
to present six decades of resistance on a six-inch mirror-scale panel
meter. With so great a dynamic range, range switching is not necessary,
and the speed and ease of measurement are greatly increased.
Because of the logarithmic ocale, the usual high-end scale compression of
a conventiona, ohmmeter is eliminated. An accuracy within l$ of the scale
length is maintained at every point on the scale; this is equivalent to an
accuracy of about lO$ of the reGiotance being measured. It is limited only
by the meter accuracy, and is about as good a6 conventional megohmmeter
circuits at mid-scale, but superior to conventional circuits at other than
mid-scale meter readings.
Test potentials of 5, 50 and 500 volts are furniohed. They are useful in
measuring voltage coefficients, and offer freedom in selecting a safe
potential for all test samples.
I -1
5’0
1158

SECTIONII
MODEL510 SPKIE'ICATIONS
L_ _
Range and Test Potentials:
Test Potential.
_--
5 volts
50 volts
500 volts
Resistance Span
107 to 1013 ohms
108 to 1Ol't ohms
10'3 to 1015 ohms
ACCURACY:within 15 of scale length, uniform over the entire scale.
After a 15-minute warmup, calibration drift is negligible over an
eight-hour period.
REGULATEDTESTVOLTAGES: Regulation within 0.01s for line voltage
changes from 100 to 130 volts.
OPERATINGCONTROLSare the Test Potential-Calibrate Switch and a'three-
position lever switch, Test-Charge-Discharge. The lever switch allOW
discharge of capucitors, quick charge, and pro-electrification when
desired.
PR0TECTIVEFEATURNS: All test potentials are removed when the operating
switch is in the discharge position. Similarly, a switch is included in
the test fixtures (Models 5101 and 5102) that automatically grounds al.1
electrodes when the cover is raised. The instrument cannot be damaged
by short circuits.
ACCESSORIESSUPPLIED: Model 51036 Test Leads, 36 inches long, separate
, Hi and ground leads terminated in alligator clips. The leads are useful
bout
;yv"dl;zy z; gift 1012 ohmswith a 5-volt potential, 1013 ohmswith
ohmswith 500 volts. For higher readings, the 5101 or
5102 adapters should be used.
ACCESSORIESAVAILABLE: Models 5101 and 5102 Test Adapters; Models 51024
and 51060 Cables.
CABINNTis aluminum, 6,-5/o" x lO$' high x 12$' deep. Net weight, 164 pounds.
II - 1
510
11'58

CMCUIT DESCRIPTION
The Model 510 Megohmmeterconsists of a regulated voltage supply which
provides 5, 50 and 500 volt test potentials, and a logarithmic micro-micro-
/ ammeter which meters the sample current. The panel meter reads ohmsdirectly.
Figure 510-l shows a simplified diagram
of a resistance measurement using the 510.
The positive terminal of the test potential
is grounded and the negative terminal is ap-
plied to the unknown specimen through the
micro-microammeter. The voltage drop across
the input of the micro-microammeter is small
T FIGUREIlO-! oompared to the test potential. Using the
negative terminal of the voltage supply as a
shield around all high impedance input leads to the micro-microammeter assures
negligible error due to leakage across the input terminal insulation. The
method is called guarding and the negative terminal of the supply is referred
to as the guard potential.
Figure 510-2 is a simplified diagram of the micro-microammeter used in
the Model 510.
The following circuit description refers to DR 11504-C in MAINTENANCE,
Section IV.
The power supply comprises a Sola regulating transformer, a rectifier-
filter system and a two-stage electronic regulator. Selenium rectifiers SR5
through SR9provide a half wave rectified output which is filtered by R401,
c402 and C403.
R&Q and X403 are used to equalize the voltage across the
series capacitors.
Following the filter is an electronic regulator employing ~6 as a series
tube and V7 and Vg as a two stage amplifier. Vg acts as the error detector.
The output of the 500 volt supply, divided dolm by R415, R411, and R410, is
compared to voltage reference tube ~8. R411 is used to set the test poten-
tial at 500 volts. 50 and 5 volt test potentials are obtained from the
divider consisting of R415, R414, X413 and R412.
The micro-microammeter consists of shunt diode, Vl, and an electrometer
amplifier which measures the potential across diode Vl. This potential is
proportionalto the logarithm of the current through the diode. The grid
and filament of Vl act as the diode. The electrometer amplifier consists of
two 5886 tubes, V2 and V3, operated as pentodes followed by V4, a l2AU7
twin triode differential amplifier. Local feedback from the triode cathodes
to the pentode screens stabilizes the operating point of the electrometer
II - 2

tubes. Overall negative feedback from the 6C4 output cathode follower, V5,
to the electrometer tube filaments stabilizes the aNplifier gain. The
power supply for the micro-microammeter is derived from the Sola trano-
former through transformer T2 and utilizes conventional rectifier-filter
systems.
The megohmmeteris calibrated by means of ~1.28 and Rl2g on SW3. With
107 ohms in the circuit (R127), the meter is set to 107 ohmsby adjusting
diode bias with R106. Subsequently the meter is Bet to 1011 ohmsby adjust-
ing amplifier gain with H124.
Occasionally amplifier balance should be
checked by turning SW3to lx, 10x or 100x position with the lever switch
in DISCHARGE. Under these conditions the panel meter should read 107 ohms.
If adjustment is necessary, R115 is used.
SECTIONIII OPERATION
The Model 510 Megohmmeteris shipped with the Model 51036 Test Leads. To
use this combination for measuring resistances, the following procedure
should be followed:
a. Plug the power cord into 110 volts 60 cps ac. A Sola constant volt-
age power transformer is used in the Model 510, and ite proper functioning
depends upon a constant power line frequency of 60 cps. A 50 cps model is
available.
b, Turn the Test-Charge-Discharge switch to Discharge.
c!. Turn the Calibrate-Test Potential switch to Calibrate, 107 ohms.
a. Turn the power switch to ON, and wait a minute or two for the tubes
to reach operating temperature.
e. Set the Cal 107 potentiometer located on the panel under the meter,
BOthe meter reads exactly 10-f.
f. Turn the Calibrate-Test Potential switch to Calibrate 1011 ohms.
10ILg* Adjust the Cal 1011 potentiometer 80 that the meter reads exactly
h. Connect the test leads to the Megohmmeterby fastening the connector
end to the input connector on the front panel. Clip the free ends to the
unknown resistance. The small, flexible wire ie at ground potential. The
larger coaxial cable is the guarded HI lead.~
i. Turn the Calibrate-Test Potential switch to apply the desired po-
tential to the unknown resistance.
3. Switch the Test-Charge-Discharge switch to Charge, and then to Test.
The nature of the unknown determines the length of time to remain in the
Charge pooition. If there is little capacitance (0.1 mfd or less) acroBB
the unknown resistance, a second or SO is long enough; greater capacitance
III - 1

/
will require a longer wait. The Model 51036 Test Leads employ a capacitor
to reduce the effects of 60 cps pickup, which slows the response appreciably
when measuring reaiBtance8 above about 1Ol-l ohms. Somercsitance specifi-
cations require an "electrification time", which is the interval between
applying the test potential and reading the resistance. The ASTMpamphlet,
included in this Manual, discusseo this in detail. The electrification time
is measured from the time the Test-Charge-Discharge switch is moved from
Discharge to Charge.
k. After meaaming, return the Test-Charge-Discharge switch to Discharge.
The instrument is now ready for the next test specimen. With the switch in
the Discharge position, all testing conductor8 are at ground potential, 80
that specimens can be chcangedwithout danger of shock to the operator.
After the instrument has been connected, turned on, warmed up, cali-
brated, and the test voltage selected, the operating procedure for measur-
ing a number of resistances is very simple. Just connect the unknown to the
test clip8; turn the Test-Charge-Discharge switch to TEST; read the meter;
return the switch to DISCRARGE:and then change to a new unknown resistor.
1.
After the instrument ha8 been operating for about five minutes, it
should be realigned to eliminate the effects of warmup drift. After this
ha8 been done, no more calibrations should be necessary during the following
eight hour period.
m. To rebalance the amplifier, eet the Calibrate-Test Potential switch
to 5 volts, end the Test-Charge-Discharge switch to Discharge. Then adjust
the Amp. Bal. potentiometer,
reads 107. on the left side of the cabinet, 80 that
meter
This adjustment is required only every month or 80.
The operating procedure is the samefor test leads, fixtures, or the
Keithley 5101 or 5102 Adapters. A wide variety of specialized setups is
discussed in the Appendix.
Whendesigning special testing fixtures, leads, or electrodes, provision
must be madefor operating the relay in the Model 510 to remove the short
circuit at the input of the micro-microammeter. Pins 2 and 3 of the connector
carrying the cable from the unknown to the Model 510 input can be jumpered
in the connector, or a switch to connect them can be made a part of the
special fixture, following the design of the switch in the Modela 5101 and
5102 adapters.
Reading the Meter: Fig.
510-3 is an en1 rged
sketch of one decade of the meter scale. 8 10 end
109 are the major division marks. The integer8
between them are also marked, with the 5 line made
longer and heavier for quick identification. The
other decade8 are read in a similar manner.
III - 2
510
l/58

SECTIONIV MAINTENANCE
-,-.--_--
A. General
The Keithley Model 510 Megohmmeterhas been designed to give long,
trouble-free service. High quality components have been used throughout.
DR115044, page IV-2, is the detailed circuit schematic diagram of
the Model 510. The circuit operation W&Bdiscussed in Section II,
DESCRIPTION.
Maintenance Adjustment is R&11, which sets the 500 volt test potential.
As disxssed in GfiE?c small variations from.500 volts do not affect
the calibration of the Model 510; but for proper functioning of the power
eupply, it should be set within about 5%of 500 volts. TO readjust
the test potential with R411, connect a high impedance voltmeter (20,000
ohmsper volt) from Guard to Ground, set the Calibrate-Test Potential
switch to 500 volts and the Test switch to TEST. Adjust Rkll for 500 volts
test potential.
Resetting R411 i8 not necessary under normal circumstances, even though
the tubes in the regulator have been changed, but it should be checked after
a tube change.
The tubes used in the,V2 and V3,positions are selected, matched and
labelled ~~-5886-5 and ~~-5886-6 respectively. Replacements are sold in
pairs only. The tube used at Vl is not selected.
Wheninspecting or replacing the electrometer tubes, the glass base
should not be touched with the hands, because the dirt and moisture will
cauu8eleakage from the grid to the other electrodes. Also, when soldering
high impedance conductors to the teflon standoffs, care should be taken to
keep the teflan clean,
All vacuum tubes, other than the 5886'~ are conventional, and selection
of replacements is not necessary.
Calibrate - Test Potential Switch and RN1 should be inspected period-
ically, and any dust which has accumulated on the insulation should be re-
movedby brushing with a camel's hair brush.
Servicing. DR11698-C, page IV-3, shows the tube layout. Included
are the voltage and resistance measurements which maybe made at each
tube element under specified conditions.
IV - 1

i
-.Y
5

c
--T
VOLTAGE AND RESISTANCE WART

---r-
circuit
Desig.
--.-
Cl01
Cl02
c401
c402
c403
c404
c405
~406
c407
C408
c409
C42.a:
c411
C412
Fl
M
RlOl
R102
B103
RlO4
R105
R106
R107
R108
RlOg
RllO
REX'LACEP&EPARTSLIST - MODEL510
-- Description -
Capacitor, electrolytic, tubular, 1000 nffd, 12V.
Capacitor, ceramic disc, .02 ma., 600~.
Capacitor, oil., 1.0 tid. (supplied with Tl)
Capacitor, tubular, electrolytic, 30 mfd, 450V
Sameas C402
same as Cl02
Capacitor, molded paper, 0.1 mfd, 600~
Capacitor, tubular, electrolytic, 40 mfd, 250V
Sameas cho6
Sameas ~406
Capacitor, tubular, electrolytic, 150 mfd, 15OV.
Sameas ~406
Sameas C405
Capacitor, tubular, electrolytic, 4 mf'd, 600~.
Fuse, 1.5 amp. 3AG
Panel meter, O-200 microamp
Resistor, composition, 22K, 16, $7
Resistor, deposited carbon, 50 ohm, lgb, $I
Resistor, deposited carbon, 150 ohm,
Resistor, deposited carbon, 2K, l$, ;W
Resistor, deposited carbon, 300 ohm, l$, -$W
Potentiometer, composition, 1K
Resistor, composition, 22M, 10%
Resistor, deposited carbon, 250 ohm, l$, &J
Resistor, deposited carbon, lOM, l$, 1W
Resistor, wirewound, l2.5K, 3'$, '7W
Iv-4
-- Part
.-.-.-A”.
Cll-1000
c22-.02
.
c8-30
-
-
c2-0.1
C27-40
.
C23-1.50
-
c35-4
FU 8
ME9
Rl-22K
R12-50
R12-150
R12-2K
~12-300
RI'13 -1K
Rl-22M
R12-250
R13-10M
~7-12.5~

lU?PLACEABLI?PARTSLIST - MODEL 510
--r----7--
Circuit
Des!.g. Description
_-._--. -
Rlll Sameas RllO
R112 Sameas R109
R113 Resistor, deposited carbon, 200 ohm, l$, $J
R114 Sameas RI.13
R115 Potentiometer, composition, 200 ohm
R116 Resistor, deposited carbon, 4,3K, l$, $QJ
R117 Sameas X104
~1.18 Resistor, deposited carbon, 60K, I$, &
Rll9 Sameas R11.8
R120 Resistor, clepositerl carbon, 1.5M, l$, $W
R121 Resistor, deposited carbon, 4.45M l$, &
R122 Resistor, deposited carbon, 200K, l$, 31
R123 Resistor, deposited carbon, 70K, l$, $J
~124 Sameas RlO6
R125
Resistor, deposited carbon, 5K, l$, $J
~126
Resistor, deposited carbon, 250 ohm, J+$, 4W
R127
Resistor, deposited carbon, 1:.7X,l$, $J
R128 Sameas Rl.09
Rl29
Resistor, hi-meg, 1011 ohms
R130
Resistor, deposited carbon, lK, 1%) $+J
R131 Resistor, deposited carbon, ) "OK, l$, 1W
X132 Sameas Xl15
x401 Resistor, composition, 680 ohm, lO$, +W
R402
Resistor, composition, 22OK, lO$, 1W
R403 Sameas ~402
__--___--_---____-l___
IV - 5
r*rt
Iio.
-__
--t--
R12-200
RP13-200
R12-4.3K
~1.2-609
R12-1.5M
R12-4..45>
R12-200K
X12-70K
R12-5K
~12-250
R12-47K
R20-1011
R12-1K
Rl3..50K
Rl-680
R2-220K
-___
510
l/58

RXPLACYXBLEPARTSLIST - MODEL510
.
/
i
Circuit
Desig.
--
R404
p405
R406
R407
Rho8
R’k09
R4LO
R4ll
R412
R413
R414.
R415
~416
RUT
R418
R419
R420
R421
R422
la1
SRl
SR2-SR9
SRlO
SRll
SW1
-
-
Description
Resistor, deposited carbon, 200K, l%, $I
Samea8 R404
Resistor, wirewound, WOK,l$, LOW
Resistor, depoa-i.ted carbon, 470K, I.$, SW
Same*a R407
Resistor, dcpositcd carbon, 60K, l$, 31
Resistor, deposited carbon, 390K, l$, $4
Potentiometer, composition, 1OOK
Resistor, deposited carbon, lK, l$, 1W
Resistor, deposited carbon, PK, l$, 1W
Resistor, deposited carbon, 1OK, I.$, 1W
Sames.s R406
Resistor, composition, 470 ohm, lO$, &
same .a8RJ+16
Real&or, composition, I.00 ohm, lO$, $W
Resistor, wirewound, 1250 ohm, 5$, 5W
same as ~416
Sameas X419
Resistor, composition, l.OOK;lO$, 2W
Relay, special
Rectifier, selenium bridge
Rectifier, selenium, 130~, 65 maprinted circuit style
Rectifier, selenium, 13Ov, 65 ma
Silicon alloy diode, Pacific Semiconductor #~~695
SPSTBat Randle toggle switch
part
No.
-.__
R12-200K
R30-80K
RI2 -470X
R12-6OK
X12-390X
RP12-100
R13-1K
Rl.3-9K
R13-10K
m-470
RI-LOO
X4-1250
R3-100K
RLLM
m6
RF10
m'8
RF13
SW-l.4

/ c
i
---.-
SW2
’ SW3
Tl
T2
Vl
v2
v3
v4
v5
v6
W
V8
(, v9
---
PJ@LACJZABLEPARTSLIST - MODEL510
-
Description
-
DPDT Rs.t Handle toggle switch (center off)
3 pole, 5 position rotsxy switch, special
Power transformer, Sola 71354 (includes CJ+Ol)
Power transformer Stancor ~~841.6
VWUUDI tube, type 5886
vacuum tube, type
vacuum tube, type 5886
sold 8,s matched pair
Vacuumtube, type 12AV7
vacuum tube, type 6~4
vacuum tube, type 12~4.1'.
Vacuumtube, type 12AX7
Vacuumtube, type OG3
same as v7
Input connector, 5 conductor, Cannon RSK-U4-3lSL
Pilot lamp, #51 (two per instrument)
-
w-5886..
~~-5886..
EV-12AU7
~-6~4
EV-l'B4A
EV-12AX7
EV-OG3
IV - 7

I
APPENDIX
Section i Accessories
__ _-.--_
ModeI 51036 Test Leads consist of a 36 inch double shielded cable,
--__
a 36 inch ground lead and a connector which mates with the Model. >lO
input connector. The leads are terminated with alli.gator clips.
Use of the Model. 51036 is described in Section ii, ComponentMeasure-
merits.
Model. 5101.ComponentAdapter is a shielded enclosure to be used with
-Y-M
the Model. 510 when tosti~esis-tars, capacitors and other small
parts. It is designed to attach directly to the Model. 310 Megohm-
meter, See Sectiou ii, ComponentMeasurements.
Model 3102 Volume Hesistivity Adapter is a shielded enclosure, exter-
_-._.-... _ -I_
nally similar to Model 5101. It has a set of electrodes which facili-
tate making volume resistivity measurements <andis fully described
in Section ii, Volume Resistivity.
Models 51024 and 51060 Cables are used with either of the above
_-A-
adaptors when it ie desiraa‘d to separate the adapter from the
Model 510. The cnbles are 24 and 36 inches long, respectively.

Section ii Measuring Technique
INTRODUCTION
-----
The American Society for Testing Materials has prepared a booklet,
D257-5&T, "Tentative Methods of Test for Electrical Resistance of
Insulating Materials," which describes the procedures for measuring
the important parameters of insulating materials. A reprint is
included as a part of this instruction book.
The Model 510 with its accessories is an excellent instrument for
making the tests, and the following paragraphs will describe testing
procedures in detail, with special emphasis on the precautions neces-
sary to obtain accurate measurements of the very high resistances
which the extreme sensitivity of the Model 510 permits.
Three major difficulties are encountered in measuring extremely hi.gh
resistances. They are: a) 60 cps pickup by the high impedance con-
ductors; b) spurious current leakages; and c) charges and currents
generated by sliding or deforming the insulating sample. "
60 cps pickup is eliminated by shielding the input, test circuit con-
auctors, and the specimen, as in the Models 5101 and 5102 adapters;
or by using a capacitor across the micro-microammeter as in the special
case of the Model 51036 Test Leads.
Spurious current leakage is avoided by using excellent insulation ma-
terial, such as teflon or polyethylene, in the test leads and fixtures,
and by guarding all leakage paths.
The spurious charges, or "static electricity," can be avoided by handling
the test sample as little as possible before measuring it. A 200 foot
piece of pol ethylene
rate of 10-Y coaxial cable, for example, can lose charges at the
ampere for.several hours after it has been flexed moderately.
Electrification time, voltage and temperature coefficients, and moisture
or solvent content are also important consiclerations when measuring insu-
lation resistance.
SPEEDOFINDICATION
The measurement of the leakage resistance of capacitors with the Model 510
involves long times when the product of the resistance and capacitance is
large. The capacitor is charged quickly to the test potential by the
Test-Charge-Discharge switch, bringing the reading on scale, but reading
equilibrium is often a slow process. The following empirical expression
gives T, the time in seconds for the 510 to read within lO'$ of the final
resistance value:
TX RC
W where R is the leakage resistance in ohms
C is the capacitance in farads
E is the test potential in volts
a-l

Faster response can be obtained by using a battery to furnish the test
potential, and Keithley Models 200B and 2008 combination to read the
leakage current. Using the 2OOBon the 0.008 volt range permits the
lowest practical shuntresistor in the 2008, which is substantially
smaller than the effective diode resistance in the Modal 510 at equi-
librium.
As t-m example, consider the measurement of a 5000 mmfcapacitor with a
leakage resistance of 1013 ohms. The 510 with 50 volts applied to the
sample will read within lO$ of 1013 in about 4 minutes. The 20013,using
the .008 volt range, with a 109 ohm shunt and 50 volt supply will read
within 10%of final current in about 12 seconds.
COWOWNTMJZRSUiXMENTS
- _~-_
Measuring with Modal 51036 Teat Lea&s: The Mod01 510 is shipped. with
the Model 51036 %st Leads for general purpose use. Tnsse leads are
intended for measuring unshielded objects such as resistors, insulating
terminals, and <.hecoil-to-coil and coil-to-frame insulation of motors
of transformcrr: ~
The TestC1iars.e -Dizharge switch should be in the Discharge position when
changing specimen;, otherwise the test potential appears across the alli-
gator clips. ThiJ is particularly dangerous when testing capacitors at
500 volts.
Whenmeasuring capacitors, the twitch should remain in the Charge position
long enough to assure t'nat the capacitor is completely charged before mov-
ing the switch to the Test position.
The effects of 60 cps pickup by the specimen ars eliminated by a 500 mmf
capacitor located in the connector housing and connected across the input
of the micro-microammeter. Because of the capacitor, however, the response
of tho amplifier and meter are slowed. $.or instance, to read gO$ of f!!;ial.
value in 2.5 secon3.8, one may measure lo*--- ohmsusing 5 volts ted pot-,;,.-
tial, ,1012 ohmswith 50 volts, and lo12 ohmswith 500 volts. jIi &--;ar 1‘6;0.d_
ings require proportionately longer times. For fast measurement of high
resistances, the object being measured must be shielded from 60 cps pick-
up, and the micro-microammeter not slowed with a capacitor.
The detailed steps of lining-up and making measurements with the Model 510
were given in Section III, OPERATION.
Measuring with the Model 5101 ComponentAdapter: The Keithlcy Model 5101
-.---- -.-
ComponentAdapterisaenient shielded enclosure for holdin,g electronic
components, such as resistors or capacitors, while their. resistance is being
maasured. It connects directly to the Model 510. The circuit schematic
diagram is given on DR11504-C, the main diagram for the F<odel510.
For most components, the most convenient connections are two spring clips
on banana plugs (Grayhill@-l), one plugged into GNDand the other into
HI. The component leads slip easily into the springs which hold the com-
ponent from touching the box or the relatively low resistance insulation.
Two clips are furnished with each 5101 Adapter.
a .- 2

,
Closing the lid of the box operates switch SWl. One section ungrounds
the Guard circuit, and the other operates relay Rl in the Megohmmeter,
which opens the input to the micro-raicrosuumeter.
Opening and closing the lid performs all the necessary switching when
changing samples.
mi% RXSISTIVITY:
Volume resistivity is determined by measuring the resistance of an insula-
tion sample, as described in the ASTMSpecification Section 4 (b), and
reducing the geometry to an equivalent cube, as shown in Section 9 of the
Specification. Fig. 4 shows the most popular electrode configuration
whose dimensions are usually measured in centimeters, giving the volume
resistivity in ohm-centimeters.
r-i CND r-----l
The Keithley Model 5102 Volume Resistivity Adapter provides the desired
electrode configuration in a shielded box which can be connected directly
to the Model 510. Graphite, or aquadag, or silver conducting paint elect-
rode patterns should be painted or stencilled on the surfaces, as described
in the ASTMSnecification. The electrode dimensions of the Model 5102 are
given below.
-
The conversion of the resistance
ing of a sample into resistivity
is given by
where P 5
DE
t 5
R.
read-
units
resistivity in ohm-centimeters
center electrode diameter in
inches
sample thickness in inches
resistance reading in ohms
The electrode structure in the Model
5102 is designed to be used with a center
electrode diameter of two inches. For
this case,
Pr 8
R ohm-centimeters
t
a-3

While the diameter of the specimen is set by elec-trade structure, any
thiCkncS8 of sample up to i$ inch may be tested.
prevent 60 cps pickup by the HI conductor
Fig. 510-6 showo a holder for
large rigid ~lpecimenowhich are
not suited to the Model 51.02.
A spring in used on the end of
a rod to makethe connections.
Note that the hi&h impedance
oonductor is well guarded.
If the specimen has a resistance
greater than about 109 or lOlo
ohm, the test fixture should be
inside a grounded enclosure to
The Keithley Model 5101 ComponentAdapter makes a convenient encloser for
measuring amal. rigid samples. A table can be plugged into the ground jack,
and springs which contact the HI and Guard electrodes can be connected to
plug8 which are inserted into the HI and Guard jacks.
Fig. 510-T 18 a dia-
gram of the Model
5101 used in this
fashion.
Measuring Volume Resistlvity using the Model 5101 ComponentAdapter.
If temperature coefficients of resistance or the high temperatLn?e perform-
ance of insulating material are of interest, the specimen and holder are
mounted in an oven.
For temperatures up to about l2O'?F, the Model 5101 or 5102 adapters are
suitable. Acceasoryfcables Models 51024 or 51060 are available for con-
necting between the Models 510 and the adapter.
Above l20%, a special fixture is required, deeigned to
tithetand the heat. Fig.
51.0-8 shows such a fixture in
an oven connected to the Model 510. The insulation in
the fixture is ceramic or tefl.on, and the connecting
cable usee teflon insulation, because polyethylene
softens at elevated temperatures.
a-4
510
1158

The Guard and HI electrodes must be mounted 80 that at operating temperatures
they are in the sameplane.
Fig. 510-8 shows the connecting cables passing directly through holeo in the
oven walls. If it io desired to mount connector8 in the oven walls, Fig.
510-g shows the details of a typical installation. Teflon insulated con-
nectors, such ae MIL Type 0-239A should be used. The shell of the HI: lead
connector which ia operated at Guard potential must be insulated electrical-
ly from the oven wall which should be at Ground. Someprotection must be
provided for the operator, because the exposed parts of the plug can be
500 volts below ground.
The metal housing of an oven generally makes a good shield against 60 cps
pickup, and should be connected to ground. Difficulties may arise through
pickup of the 60 CPRvoltages from exposed conductors or heating coils and
from door hinges which are not conducting and tend to insulate the door
from the cabinet. In most c&see, no shielding in addition to the grounded
metal oven and shelves if! necensary.
One of the constituents of teflon is fluorine. At room temperature, teflon
io chermically stable, but when elevated above about 500°F., it gives off
toxic fumes. Great care should be taken when using teflon cables in ovens
or n%ar heating elements. Figure 510-10 illustrates a
variation of the guarded elec-
trode connection for measuring
volume resistivity of these
sheets, or for quick compari-
sions of resistances between
sheets. Here, the surface
leakage path is very long,
and, with materials which are known to have good surface properties, Che
surface resistance is much higher than the volume resistance. The weight
is chosen large enough and heavy enough to give consistent measurements.
The Model 5101 ComponentAdapter &es a convenient shielded enclosure for
these meaourements. A metal plate fastened to a banana plug slipped into
the GNDjack is a convenient measuring table. The weight is connected by
a short pigtail to a banana plug slipped into the HI terminal. There is
no Guard connection, and the pigtail from the high terminal to the weight
must not touch anything.
A source oP serious error in measuring the volume resistivities of the
better insulatoro is conductivity between the HI and Guard conductors,
both on tha ourface of the sample itself and in the connection% to the
megohnrmeterinput. This provides a current p&h in addition to the micro-
microammeter of the megohmmeter, causing the meter to read an erroneously
low resistance. a
For example using the 5 volt test potential, the desired current when read-
ing d-3
ohmsfalls through a potential field of about 6.5 volts, lrhereas
the undesired current from gue+rdto input falls through a'field of 1.5
volts. Thus, with equal currents, desired and undesired, the leskage
a-5