Keithley 510 Service manual
/
MODEL 510
MEGOHMMETER
AND ACCESSORIES
KEITHLEY INSTRUMENTS, INC.
CLEVELAND, OHIO
CONTENTS
SECTION
INTRODUCTORY *,.,...,,*......****.I.*..,..........*...*
"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
..,.,.,...............
. . . . . . . . . ..*.......*.*......
. ..* . . . . .
ii
Rear Cover
510
If58
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
is
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,
5,
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
I
SECTION II
MODEL 510 SPKIE'ICATIONS
L_
_
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
CMCUIT DESCRIPTION
The Model 510 Megohmmeter consists of a regulated voltage supply which
provides
/
ammeter which meters the sample current.
T
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
~6
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
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
a.
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.
f.
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.
3.
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
SO
is long enough; greater capacitance
III - 1
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
1.
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
60
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
General
A.
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
TO
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
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