Keithley 502 Service manual [en, fr]
INSTRUCTION MANUAL
MODEL 502
MILLIOHMHETER
Kelthley Instruments. Inc.
29776 Aurora Road/Cleveland, Ohio 44139/(216) 249-0400
INSTRUCTION MANUAL
MODEL 502
MILLIOHMMETER
OCOPYRIGRT 1975, ~ITRLEY INSTRUMENTS, INC.
PRINTED JULY 1977, CLEVELAND, OHIO, U. S. A.
CONTENTS
SECTION
IN'IRODUCTION
SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...*..
OPERATION
A.
B.
C.
D.
CIRCUIT DESCRIPTION
MAINTENANCE
A.
B.
.,,...*.........,.................................
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Connections
(1) Low resistances
(2) Higher resistances
Procedure
Battery Test
Precaution5
..,............,.,.....,...................
,...........................,......................
Batteries
Trouble Shooting
I
II
III
IV
v
0762
Schematic, DR 12189 C
C.
D.
Tube Voltage Diagram, DR
Replacement Parts List
E.
12256
C
MODEL 502
MILLIOHMMlKTHH
INl'FiODUCTION
SECTION I - INTRODUCTION
The Keithley Model 502 is a battery operated, portable milliohmmeter
for measuring resistances from 0.00003 to 1000 ohms. The instrument
employs an AC testing method, eliminating zero drift and permitting
resistance readings in the presence of DC currents.
The reading is
presented on a linear scale panel meter.
Typical applications of the instrument include measurement of
con-
tact resistance, conductivity of semi-conductor samples, fuse and
squib testing, and electrolyte conductivity.
Maximum
power dissipation in the sample is 2 microwatts, permitting
the measurement of detonator fuses without danger of detonation.
In the measurement of contact resistance, the model 502 may be
considered a "dry circuit" tester.
However, the instrument may be
used in the presence of DC biasing currents to measure the change
in resistance caused by these currents.
FIGCFZ 1. Keithley Model
carrying case open.
502
MilJiohmmeter with
l-1
MODEL 502 MILLIOHMMETER
Ye
:: ::
SECTION II - SPECIFICATIONS
SPECIFICATIONS
RANGES: The test current,
the input vpltage drop, and the power dissipation
(Pd = 2&E,,) for full-scale readings on each range are given below:
tinge,
Ohms
Average
Average
Applied Current, Voltage Drop,
Milliamperes Microvolts
Maximum
Dissipation
in Sample,
Microwatts
0.001 10
0.003 10
0.01 10.00
0.03 3.33
0.1 1.00
0.3 0.33
1 0.1
3 0.2
10 0.06
30 0.02
100 0.006
300 0.002
10
30
100
100
100
100
100
600
600
600
600
600
0.2
0.6
2.00
0.66
0.2
0.066
0.02
0.24
0.072
0.024
0.0072
0.0024
1000 0.0006
600
0.00072
ACCURACY: 3% of full scale on all ranges except the O.OOl-ohm range, where
it is 5% of full scale. Less than 2% error is added in measuring samples with
a series reactance of 4% of sample resistance.
OUTPUT: Meter only.
SAFETY AND RELIABILITY: Maximum power dissipation in the sample with improper
range setting is three milliwatts. Maximum dissipation caused by instrument
component failure and improper range setting is six milliwatts.
INPUT ZERO: Lever switch prevents off-scale meter indications while changing
samples.
SPEED OF RESPONSE:
Five seconds to 90% of final reading on all ranges.
ZERO DRIFT: None.
REPEATABILITY:
WARMUP TIME:
Within 30 seconds.
Within 2/,.
D
0963R
2-1
SPECIFICATIONS
:.
::
BATTERY LIFE: 360 hours minimum. :
MODEL 502 MILLIOHMMETER
BATTERY TEST:
An internal resistance standard is measured in the Battery
Test Position to provide a comple<e check of battery condition and proper instrument operation.
BATTERY COMPLEMENT: Two RM 401R, two RM 42R, one 412, one 413.
TUBE COMPLEi%ENT: One 6418, four 6419.
TRANSISTOR COMPLEMENT: Four 2N1381.
ACCESSORIES FURNISHED:
ligator clips;
CONNECTORS:
one set Klipson adapters; mating connectors.
Amphenol 80C and 80-PC2F receptacles.
Model 5021 Current and Voltage Leads; one set of al-
DIMENSIONS:~ 9 inches high x 6 inches wide x 7 inches deep.
NET WEIGHT: 7-l/2 pounds.
'02648
MODEL 502 MILLIOHMMETER
CONNECTIONS
.A.
(1) Lower resistances (less than 3 ohms).
OPERATION
-T
: ::
':sECTION III - o~mm10N
Each test lead has two clips,
a black instilator.
Use both test leads
one with a red insulator and the other with
to
make a connection, making sure
like-color clips are on the same side of the sample (see Figure 2). Connect
the current supply leads to the sample at any point which assures current
flow through the entire sample.
This connection may include the leads
on the sample.
CURRENT
Black
SOURCE
Red
I
RX
Connect the voltmeter leads across only
that part of the sample which is to be
measured, as shown in Figure 2. If the
terminal or test leads of the resistance
Black
I-+
VOLTMETER
Red
being measured are included within the voltmeter clips,
the reading will include the
resistance of these leads.
FIGURE 2.
NOTE
Do not connect the red clips to the black clips.
The clip-to-sample resistance of both voltmeter
clips
are
added in series with the unknown, and
large errors can result.
(2) Higher resistances (3 ohms and greater).
For ranges over 3 ohms full scale,
the clip contact resistance is insignificant compared with the full scale value, so voltage and current
leads may be paired and the standard two-terminal ohmmeter method em-
ployed.
Of course,
the four-terminal method above may be used, but the
two terminal method is faster for repeated testing.
PROCEDURE
B.
Turn the power ON while the READ-SHORT Switch is at SHORT.
The instrument
will stabilize in about 15 seconds.
Connect the leads to the sample as outlined above.
SHORT switch to RF,AD.
Rotate the OHMS FULL SCALE switch until a suitable
Then IIIOW the RRAD-
on-scale reading is obtained.
The READ-SHORT switch shorts the voltage input in the SHORT position.
It keeps the meter pointer on scale while the test leads are being connected
to an unknown.
opening the READ-SHORT switch, no damage will result.
If an overload is applied to the input by inadvertently
However,
approxi-
mately 30 seconds will be required for the amplifier to recover.
0264~
3-l
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