Keithley 510 Service manual

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Page 1

MODEL 510

MEGOHMMETER

AND ACCESSORIES

KEITHLEY INSTRUMENTS, INC.

CLEVELAND, OHIO

Page 2

CONTENTS

SECTION

INTRODUCTORY *,.,...,,*......****.I.*..,..........*...*

SPECIFICATIONS AND DESCRIPTION........................ II

OPERATION....,.....'..................,................

MAINTENANCE' ~,......,,................,.................

III

Iv General Circuit schematic

voltage and resistance diagram

Replaceable parts list

APPENDIX

Accessories..................,...,...,....,...,.,. i

Model

51.036

Test Leads

Model

5101

Model 5102 Volume Reoistivity Adapter Models 51024 and

Measuring technique

Introduction Speed of indication Component measurements

Volume resistivity

Special shielded enclosures Use of other than standard test potentids

ASTM Reprint

*.*....*.*...

Component Adapter

51060

Cables

..,.,.,...............

. . . . . . . . . ..*.......*.*......

. ..* . . . . .

Rear Cover

510

If58

Page 3

SECTION I INTRODUCTION

The Keithley Model 510 Megohmmeter utilizes a unique logarithmic circuit to present six decades of resistance on a

meter.

With so great a dynamic range,

six-inch mirror-scale panel

range switching is not necessary,

and the speed and ease of measurement are greatly increased.

Because of the logarithmic ocale,

a conventiona, ohmmeter is eliminated. length is maintained at every point on the scale; this

accuracy of about lO$ of the reGiotance being measured.

the usual high-end scale compression of

An accuracy within l$ of the scale

equivalent to an

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 measuring voltage coefficients,

50 and 500 volts are furniohed. They are useful in

and offer freedom in selecting a safe

potential for all test samples.

5’0

1158

-1

Page 4

SECTION II

MODEL 510 SPKIE'ICATIONS

Range and Test Potentials:

Test Potential.

_--

5 volts

50 volts

500 volts

ACCURACY:

within 15 of scale length, uniform over the entire scale.

After a 15-minute warmup,

calibration drift is negligible over an

Resistance Span

107 to 1013 ohms 108 to 1Ol't ohms 10'3 to 1015 ohms

eight-hour period. REGULATED TEST VOLTAGES:

Regulation within 0.01s for line voltage

changes from 100 to 130 volts. OPERATING CONTROLS are the Test Potential-Calibrate Switch and a'three-

position lever switch, Test-Charge-Discharge. The lever switch

discharge of capucitors, quick charge,

and pro-electrification when

allOW

desired.

PR0TECTIVE FEATURNS:

switch is in the discharge position.

All test potentials are removed when the operating

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.

ACCESSORIES SUPPLIED:

Hi and ground leads terminated in alligator clips. The leads are useful

bout

;yv"dl;zy z; gift

Model 51036 Test Leads, 36 inches long, separate

1012 ohms with a 5-volt potential, 1013 ohms with

ohms with 500 volts. For higher readings, the 5101 or

5102 adapters should be used.

ACCESSORIES AVAILABLE:

Models 5101 and 5102 Test Adapters; Models 51024

and 51060 Cables. CABINNT is aluminum, 6,-5/o" x lO$' high x 12$' deep. Net weight, 164 pounds.

II - 1

510

11'58

Page 5

CMCUIT DESCRIPTION

The Model 510 Megohmmeter consists of a regulated voltage supply which

provides

ammeter which meters the sample current.

shield around all high impedance input leads to the micro-microammeter assures negligible error due to leakage across the input terminal insulation. method is called guarding and the negative terminal of the supply is referred to as the guard potential.

5, 50

FIGURE IlO-!

and 500 volt test potentials,

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 applied to the unknown specimen through the micro-microammeter. The voltage drop across the input of the micro-microammeter is small

oompared to the test potential. Using the negative terminal of the voltage supply as a

and a logarithmic micro-micro-

The panel meter reads ohms directly.

The

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 rectifierfilter system and a two-stage electronic regulator. Selenium rectifiers SR5 through SR9 provide a half wave rectified output which is filtered by R401,

c402

series capacitors.

tube and V7 and Vg as a two stage amplifier. The output of the 500 volt supply, divided dolm by R415, R411, and R410, is

compared to voltage reference tube ~8.

tial at 500 volts.

divider consisting of R415, R414, X413 and R412.

amplifier which measures the potential across diode Vl. 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

and

C403.

Following the filter is an electronic regulator employing

The micro-microammeter consists of shunt diode, Vl, and an electrometer

R&Q and X403 are used to equalize the voltage across the

as a series

Vg acts as the error detector.

R411 is used to set the test poten-

50 and 5 volt test potentials are obtained from the

This potential is

II - 2

Page 6

tubes. to the electrometer tube filaments stabilizes the

Overall negative feedback from the 6C4 output cathode follower, V5,

aNplifier

gain. The power supply for the micro-microammeter is derived from the Sola tranoformer through transformer T2 and utilizes conventional rectifier-filter

systems.

The megohmmeter is calibrated by means of

~1.28

and Rl2g on

SW3.

With 107 ohms in the circuit (R127), the meter is set to 107 ohms by adjusting diode bias with R106.

ing amplifier gain with

Subsequently the meter is Bet to 1011 ohms by adjust-

H124.

Occasionally amplifier balance should be

checked by turning SW3 to 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.

SECTION III OPERATION

The Model 510 Megohmmeter is 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.

Turn the Calibrate-Test Potential switch to Calibrate, 107 ohms.

c!.

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,

BO the meter reads exactly 10-f.

Turn the Calibrate-Test Potential switch to Calibrate 1011 ohms.

Adjust the Cal 1011 potentiometer 80 that the meter reads exactly

10ILg*

h. Connect the test leads to the Megohmmeter by fastening the connector end to the input connector on the front panel. unknown resistance.

The small, flexible wire ie at ground potential. The

Clip the free ends to the

larger coaxial cable is the guarded HI lead.~

Turn the Calibrate-Test Potential switch to apply the desired po-

i. tential to the unknown resistance.

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. the unknown resistance, a second or

If there is little capacitance (0.1 mfd or less) acroBB

is long enough; greater capacitance

III - 1

Page 7

will require a longer wait. The Model

to reduce the effects of when measuring reaiBtance8 above about 1Ol-l ohms. Some rcsitance specifi-

cations require an applying the test potential and reading the resistance. The ASTM pamphlet, 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.

After meaaming, return the Test-Charge-Discharge switch to Discharge.

k. 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 chcanged without danger of shock to the operator.

After the instrument has been connected, turned on, warmed up, calibrated, 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.

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,

eight hour period.

"electrification time",

no more calibrations should be necessary during the following

cps pickup, which slows the response appreciably

51036

Test Leads employ a capacitor

which is the interval between

m. To rebalance the amplifier, to 5 volts, the Amp. Bal. potentiometer, reads 107.

The operating procedure is the same for test leads, fixtures, or the Keithley 5101 or 5102 Adapters. A wide variety of specialized setups is

discussed in the Appendix.

When designing special testing fixtures, leads, or electrodes, provision

must be made for operating the relay in the Model 510 to remove the short circuit at the input of the micro-microammeter. carrying the cable from the unknown to the Model

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.

end the Test-Charge-Discharge switch to Discharge.

on the left side of the cabinet, 80 that

This adjustment is required only every month or 80.

Reading the Meter: 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.

eet the Calibrate-Test Potential switch

Then adjust

meter

Pins 2 and 3 of the connector

510

input can be jumpered

Fig.

510-3

is an en1 rged

510 l/58

III - 2

Page 8

General

The Keithley Model 510 Megohmmeter has been designed to give long,

trouble-free service.

SECTION IV MAINTENANCE

-,-.--_--

High quality components have been used throughout.

DR 115044, page IV-2,

the Model 510.

The circuit operation W&B discussed in Section II,

is the detailed circuit schematic diagram of

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.

the test potential with R411, ohms per volt) from Guard to Ground,

connect a high impedance voltmeter (20,000

set the Calibrate-Test Potential

readjust

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.

When inspecting or replacing the electrometer tubes, the glass base

should not be touched with the hands, because the dirt and moisture will

cauu8e leakage 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-

moved by brushing with a camel's hair brush.

Servicing. DR 11698-C, page IV-3, shows the tube layout. Included

are the voltage and resistance measurements which may be made at each

tube element under specified conditions.

IV - 1

Page 9

-. Y

Page 10

--T

VOLTAGE AND RESISTANCE WART

Page 11

REX'LACEP&E PARTS LIST - MODEL 510

---rcircuit

Desig.

--.Cl01

Cl02

c401

c402

c403 c404 c405 ~406

c407

C408

c409

-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

Same as C402 same as Cl02 Capacitor, Capacitor, tubular, electrolytic, 40 mfd, 250V Same as cho6 Same as ~406 Capacitor, tubular, electrolytic, 150 mfd, 15OV.

molded paper, 0.1 mfd, 600~

-Part

.-.-.-A”.

Cll-1000 c22-.02

c8-30

c2-0.1 C27-40

C23-1.50

C42.a:

c411

C412 Fl

M RlOl R102

B103

RlO4 R105 R106 R107

Same as ~406 Same as 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%

c35-4

FU 8 ME9

Rl-22K

R12-50

R12-150 R12-2K

~12-300 RI'13

-1K

Rl-22M R108 RlOg RllO

Resistor, deposited carbon, 250 ohm, l$, &J Resistor, deposited carbon, lOM, l$, 1W Resistor, wirewound, l2.5K, 3'$, '7W

Iv-4

R12-250 R13-10M ~7-12.5~

Page 12

--r----7--

Circuit Des!.g.

_-._--.

lU?PLACEABLI? PARTS LIST - MODEL

Description

510

r*rt

Iio.

-__

Rlll R112 R113 R114 R115 R116 Resistor, deposited carbon, 4,3K, l$,

Same as RllO Same as R109 Resistor, deposited carbon, 200 ohm, l$, $J

Same as RI.13

Potentiometer, composition, 200 ohm

$QJ

R117 Same as X104

~1.18

Rll9 R120

R121

Resistor, deposited carbon, 60K, I$, &

Same as R11.8

Resistor, clepositerl

carbon, 1.5M, l$, $W

Resistor, deposited carbon, 4.45M l$, &

R122 Resistor, deposited carbon, 200K, l$, 31

--t--

R12-200

RP13-200 R12-4.3K

~1.2-609

R12-1.5M R12-4..45>

R12-200K R123 ~124 R125

~126 R127

R128 Rl29

R130

R131

Resistor, deposited carbon, 70K, l$, $J

Same as RlO6

Resistor,

deposited carbon, 5K, l$, $J Resistor, deposited carbon, 250 ohm, J+$, 4W Resistor, deposited carbon, 1:.7X, l$, $J Same as Rl.09

Resistor, Resistor,

hi-meg, 1011 ohms

deposited carbon, lK, 1%) $+J Resistor, deposited carbon, )

X132 Same as Xl15 x401

R402

Resistor, composition, 680 ohm, lO$, +W Resistor, composition, 22OK, lO$, 1W

"OK, l$, 1W

X12-70K

R12-5K

~12-250

R12-47K

R20-1011 R12-1K Rl3..50K

Rl-680

R2-220K

R403 Same as ~402 __--___--_---____-l___

510

l/58

-___

IV - 5

Page 13

RXPLACYXBLE PARTS LIST - MODEL 510

Circuit

Desig.

-R404

p405 R406

R407 Rho8

R’k09

R4LO R4ll R412 R413

Description

Resistor, deposited carbon, 200K, l%, $I

Same a8 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

part

No.

-.__ R12-200K

R30-80K RI2 -470X

R12-6OK X12-390X

RP12-100 R13-1K Rl.3-9K

R414.

R415 ~416

RUT

R418 R419 R420

R421 R422 la1

SRl SR2-SR9

Resistor, deposited carbon, 1OK, I.$, 1W Same s.s R406 Resistor, composition, 470 ohm, lO$, & same .a8 RJ+16 Real&or, composition, I.00 ohm, lO$, $W Resistor, wirewound, 1250 ohm, 5$, 5W same as ~416

Same as X419 Resistor, composition, l.OOK; lO$, 2W Relay, special Rectifier,

selenium bridge

Rectifier, selenium, 130~, 65 ma printed circuit style

R13-10K

m-470

RI-LOO X4-1250

R3-100K

RLLM m6 RF10

SRlO SRll

SW1

Rectifier, selenium, 13Ov, 65 ma

Silicon alloy diode, Pacific Semiconductor #~~695 SPST Bat Randle toggle switch

m'8 RF13

SW-l.4

Page 14

PJ@LACJZABLE PARTS LIST - MODEL 510

---.-

SW2

’

SW3

Tl T2 Vl v2

v3 v4 v5

v6 W

DPDT

Power transformer, Sola

Power transformer Stancor ~~841.6

VWUUDI

vacuum tube, type

vacuum tube, type Vacuum tube, type 12AV7

vacuum tube, type vacuum tube, type 12~4.1'. Vacuum tube, type 12AX7

Rs.t Handle toggle switch (center off)

pole, 5 position rotsxy switch, special

tube, type 5886

Description

71354

sold

5886

6~4

(includes CJ+Ol)

8,s

matched pair

w-5886..

~~-5886..

EV-12AU7

~-6~4

EV-l'B4A EV-12AX7

V8 v9

---

Vacuum tube, type OG3

same as v7 Input connector, 5 conductor, Cannon RSK-U4-3lSL

Pilot lamp, #51 (two per instrument)

EV-OG3

IV - 7

Page 15

Section i Accessories

__ _-.--_

APPENDIX

ModeI

a input connector.

Use of the Model.

merits.

Model. 5101. Component Adapter is a shielded enclosure to be used with

-Y-M the Model. 510 when tosti~esis-tars,

parts. meter,

Model 3102 Volume Hesistivity Adapter is a shielded enclosure, exter-

nally similar to Model tate making volume resistivity measurements <and is fully described

in Section ii, Volume Resistivity.

Models

_-A-

adaptors when it ie desiraa‘d to separate the adapter from the

Model

51036

inch ground lead and a connector which mates with the Model. >lO

510.

Test Leads consist of a

--__ The leads are terminated with alli.gator clips.

51036

It is designed to attach directly to the Model. 310 Megohm-

See Sectiou ii, Component Measurements.

_- ._.-. . . _

51024

and 51060 Cables are used with either of the above

The cnbles are

is described in

5101.

-I_ It has a set of electrodes which facili-

and 36 inches long, respectively.

inch double shielded cable,

Section ii, Component Measure-

capacitors and other small

Page 16

Section ii Measuring Technique

INTRODUCTION

-----

The American Society for Testing Materials has prepared a booklet, D257-5&T,

Insulating Materials," the important parameters of insulating materials.

"Tentative Methods of Test for Electrical Resistance of

which describes the procedures for measuring

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 material, 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

ampere for.several hours after it has been flexed moderately.

Electrification time,

coaxial cable, for example, can lose charges at the

voltage and temperature coefficients, and moisture

or solvent content are also important consiclerations when measuring insu-

lation resistance. SPEED OF INDICATION

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

Page 17

Faster response can be obtained by using a battery to furnish the test

potential, and Keithley Models

leakage current.

Using the 2OOB on the 0.008 volt range permits the

200B and 2008 combination to read 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 mmf capacitor 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

volt supply will read

within 10% of final current in about 12 seconds. COWOWNT MJZRSUiXMENTS

Measuring with Modal

the Model

51036

_~-_

51036

Teat Lea&s: The Mod01

510

is shipped. with

%st Leads for general purpose use. Tnsse leads are intended for measuring unshielded objects such as resistors, insulating terminals, and <.he coil-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 alligator clips. ThiJ is particularly dangerous when testing capacitors at

500

volts.

When measuring 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

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. of tho amplifier and meter are slowed.

value in

2.5

secon3.8, one may measure lo*--- ohms using 5 volts ted pot-,;,.-

tial, ,1012 ohms with 50 volts, and lo12 ohms with 500 volts.

ings require proportionately longer times.

Because of the capacitor, however, the response

$.or instance, to read gO$ of f!!;ial.

jIi &--;a r 1‘6; 0.d _

For fast measurement of high

resistances, the object being measured must be shielded from 60 cps pickup, 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 Component Adapter: The Keithlcy Model 5101

-.---Component Adapterisaenient shielded enclosure for holdin,g electronic

components,

such as resistors or capacitors,

maasured. It connects directly to the Model 510.

-.while their. resistance is being

The circuit schematic

diagram is given on DR 11504-C, the main diagram for the F<odel 510.

For most components, the most convenient connections are two spring clips

on banana plugs (Grayhill@-l), one plugged into GND and the other into HI.

The component leads slip easily into the springs which hold the component from touching the box or the relatively low resistance insulation. Two clips are furnished with each 5101 Adapter.

a .-

Page 18

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 ASTM Specification 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 electrode patterns should be painted or stencilled on the surfaces, as described

in the ASTM Snecification. The electrode dimensions of the Model 5102 are given below.

The conversion of the resistance

ing of a sample into resistivity

readunits

is given by

where P 5

resistivity in ohm-centimeters

center electrode diameter in

inches sample thickness in inches

t 5

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,

8 R ohm-centimeters

a-3

Page 19

While the diameter of the specimen is set by elec-trade structure, any

thiCkncS8 of

sample up to i$ inch may be tested.

Fig. not suited to the Model

A spring in used on the end of a rod to make the connections. Note that the hi&h impedance

prevent 60 cps pickup by the HI conductor The Keithley Model 5101 Component Adapter 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.

510-6

large rigid ~lpecimeno which are

showo a holder for

51.02.

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

Fig. 510-T 18 a dia-

gram of the Model 5101 used in this

fashion.

Measuring Volume Resistlvity using the Model 5101 Component Adapter.

If temperature coefficients of resistance or the high temperatLn?e performance of insulating material are of interest, 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.

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.

Fig.

51.0-8

shows such a fixture in

the specimen and holder are

510 1158

a-4

Page 20

The Guard and HI electrodes must be mounted 80 that at operating temperatures they are in the same plane.

Fig. 510-8 shows the connecting cables passing directly through holeo in the

oven walls. 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 electrically from the oven wall which should be at Ground.

provided for the operator, because the exposed parts of the plug can be

500

volts below ground.

If it io desired to mount connector8 in the oven walls, Fig.

Some protection must be

The metal housing of an oven generally makes a good shield against

pickup, and should be connected to ground. pickup of the from door hinges which are not conducting and tend to insulate the door from the cabinet. 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.

or n%ar heating elements.

and, with materials which are known to have good surface properties, Che

surface resistance is much higher than the volume resistance.

is chosen large enough and heavy enough to give consistent measurements. The Model 5101 Component Adapter &es a convenient shielded enclosure for

these meaourements. the GND jack is a convenient measuring table.

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.

CPR voltages from exposed conductors or heating coils and

In most c&see, no shielding in addition to the grounded

Great care should be taken when using teflon cables in ovens

A metal plate fastened to a banana plug slipped into

Difficulties may arise through

Figure 510-10 illustrates a

variation of the guarded elec-

trode connection for measuring

volume resistivity of these sheets, or for quick comparisions of resistances between sheets. leakage path is very long,

The weight is connected by

Here, the surface

cps

The weight

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

megohnrmeter input. This provides a current p&h in addition to the micro-

microammeter of the megohmmeter,

low resistance.

For example using the 5 volt test potential, the desired current when read-

ing

d-3

the undesired current from gue+rd to input falls through a'field of 1.5

volts.

ohms falls through a potential field of about 6.5 volts, lrhereas

Thus, with equal currents, desired and undesired, the leskage

causing the meter to read an erroneously

a-5

Page 21

resistance from guard to high could be

x lo13

For the undesired current to cause less than lC$ error would require a

leakage resistance higher than 2.3 x 1013 ohms between high and guard. On the

and the leakage current 8ource 1s still about 12 volte, 80 that now the leakage resistance may be 2.lt x 1012 ohms for less than lC$ error.

Similarly,

2.4

In short, then, if surface leakage is a problem, the best results will be obtained at the highest teot potential. This 'is because with virtually constant undesired current, the relative error is less with higher values of actual test current.

This error may occur particularly in the ca8e of a glass plate on which

electrodes are applied by vacuum depositing metal films. sistance of the plate is very high, but the narrow surface between the electrode is easily contaminated by the water vapor from the air, or by

water films, oil films and salts resulting from fingerprints,

volt test potential, the test current source is about 51 volts

x 1011.

on the 500 volt test potential, the leakage resistance may be

2.3

x 10

ohms.

The volume re-

Similes problems can arise if the graphite used in making an electrode on a sample is streaked acro88 the gap to the Guard, or if the sample is put on the rings of the volume resistivity holder 80 that it is poorly centered, and the HI and Guard are nearly short circuited by the central electrode.

MEASURING WITHTEST LEADS TO A SHIXLDED ENCLOSURE

When resistance greater than those practical with the Model

Leads are to be measured, test connections without the added capacitance acro88 the micro-microammete~ section must be used. test object must then be thoroughly shielded against

Keithley Model 5101 Cbmponent Adapter

r----i

r----

is a convenient completely shielded

accessory for holding small objects.

-For larger objects, specially build shielded enclosures iS neceanary, and

the connection to the Megohrmneter must

be made with guarded cable. Fig. 510-11

shows an enclosure made with copper screening, a.nd connections made to the

Megohmmeter with double shielded cable.

The cable and connector can be obtained

fromKeithley Inotrument%, Inc., on

special order.

But the leads and the

51036

CPB pickup, The

Test

a-6

Page 22

USE OF OTHER-THAJ STANDARD TEST POTJQWXLS

The occar;ion may arise when it 18 necessary to measure resistance with a volt-

/ age other than 5, 50 or 500.

tions involved such measurements can be made. Aa indicated in Section II - DESCRIF'TION, the Model 510 comprioen e. voltage

ROU'CB and micro-microammfiter in series. If additional voltage is used, then, it must be connected in serieo with the test sample and a suitable factor applied to the resistance reading obtained. Fig. 510-12 shows the

connection to be used.

Although not recommended becauoe of the precau-

True resistance is found by multiplying the reading by E2 + El.

Thus, in testing with an external 4500 volt BOWce with the Model 510 on itti 500 volt test potential, the actual resistance is ten times the value indi-

When using this arrangement the following points should be noted:

Guard potential is available and useful &8 indicated previounly for

1. guarding the HI lead and for driving any guard rings which may be employed.

The sample is above ground by the potentialE2.and care must be exer-

cised In handling samples.

The discharge switch cannot diecharge the

sample except for the contribution of El.

All previous commento regarding shielding against stray 60 cpps pickup

apply.

E2 must be a very stable source if the reading is to be valid.

battery is preferable in most cases especially if the teat sample

capacitative.

Measurement speed, discussed in Section IV B, is calculated a8 indicated

with the "E" in the equation being El + E2. Do not u8e the 5 volt range on the 510 for this test. At low test poten-

tials inaccuracies occur which have been compenoated on the 5 volt range. To uee a large voltage externally but to compensate,aa if 8. low voltage were being used will give erroneous results.

If there is danger of the sample's breaking down and applying external

teRt voltage to the Model 510, eeparate means should be employed to

limit the input current to about one milliampere. Thus, with an ternal 5000 volt supply, a 5 megohm reoiotor should be used in series with the HI lead. withstanding 5000 volts or it,

Necdle~s to say, the resistor muot be capable of

too, would break down and afford no

protection to the Model 510.

a-7

ex-

Page 23

Page 24

' CHANGE NOTICE

fiY 29,

Page 23.

1968 MODEL 605 NEGATIVE CAPACITANCE ELECTROMETER

_ Change to the following:

Circuit

Desig. R117

Rl18 R119

Rl20 R121

R122

Value

499 n 499 n 499 0. 499 n 499 n

499 n

Rating

l%, l/2 w

l%,

l/2

w l%, l/2 w l%, l/2 w

l%, l/2 w

change to the following: page 24.

Circuit De&g.

R123 499 cl

R124 499 0.

R125 499 n

Value ,Rating

l%, l/2 w l%, l/2 w l%, l/2 w

R126 499 n l%, l/2 w

TYPO DCb

DCb DCb DCb DCb

DCb

TYPO DCb

DCb

DCb DCb

Mfg.

code

91637 91637 91637 91637 91637

91637

Mfg.

Code 91637

91637 91637

91637

Mfg.

Keithley

Part No. Part No. DCF-l/2

DCF-l/2 DCF-l/2 DCF-l/2 DCF-l/2

DCF-l/2

Mfg.

Part No.

Rl2-499 R12-499 R12-499 Rl2-499 Rl2-499

R12-499

Keithley

Part No.

DCF-l/2 R12-499 DCF-l/2 R12-499 DCF-l/2 Rl2-499 DCF-l/2 R12-499

Fig. Rf!f.

Fig. Ref.

7 7 7 7