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CONTENTS MODEL 502A
CONTENTS
section Page
SPECIFICATIONS _______-______---___--------------------------------- iv
1. GENERALDESCRIPTION ---------------_--__------------------------ 1
2. OpE~TION _____----__-------_---------____----______________--- 3
3. CIRCUIT DESCRIPTION ------------------__-------_--------------- ,
4. SERVICING ___------_-------------_---__-----------------------_ 9
5. C&IBuTION ____---___------_-_--------------------------------- 12
6. REPLACEABLEPARTS -___------_-----____I___________________--- 15
$,cHEmT'C ____________________-------------------------------------- 21
PRINTED PEB 75 0275
MODEL 502A ILLUSTRATIONS
ILLUSTRATIONS
Fig. No. Title Page
1 Model 50&j ),filli&met,ar _______------_____----------------- 1
2 Front Panel Controls and Terminals ------------------------- 2
3 Four-Terminal Input Connections --------------------------- 3
4 Circuit For Blocking Capacitors Across Samples ------------- 6
5 Correct Waveform at Grid of Tube V102 (Pin 4) ------------- 10
6 Correct Waveform at Plate of Tube V102 (Pin 1) ------------ 10
7 Correct Waveform at Grid of Tube VlO3 (Pin 4) -------------- 11
0 Correct Waveform at Plate of Tube V103 (Pin 1) ------------- 11
9 Correct Waveform at Grid of Tube V104 (Pin 4) -------------- 11
10 Correct Waveform at Plate of Tube VlO4 (Pin 1) ------------- 11
11 Correct Waveform at Grid of Tube V105 (Pin 4) -------------- 11
12 Correct Waveform at Plate of Tube V105 (Pin 1) ------------- 11
13 Correct Waveform at Junctions of Diodes DlOl and D102 ------ 11
14 Symmetrical Square Wave with Potentiometer R159 Adjusted---- 13
15 Component Layout, Printed Circuit Board ------------------ 14
0275 iii
~._ ,_..
---
SPECIFICATIONS MODEL 502A
SPECIFICATIONS
Applied VOltage Mextmum
C",re"t. D,OD. Dtsstlmtion
RANGE "lllllCWllpA* mlcro;dlta I" sa'nlpte,
Ohms rnls ml8 microwatts
0,001 14 14 0.2
0.003 14 42 0.6
0.01 14 144 2.00
0.03 4.7 144 0.66
0.1 1.4 144 0.2
0.3 47 144 0.066
1.0 0.14 144 0.02
3.0 0.28 850 0.24
10 0.065 850 0.072
30 0.028 850 0.024
100 0.0085 650 0.0072
300 0.0026 850 0.0024
,000 0.00086 850 0.00072
R,BE TME (10% to 90%) 1 second on a,, ranges,
ACCURACY:
Normal Mode: 13% of full scale on lOOO-ohm to 0.003.ohm
ranges: 15% of full scale on 0.001.ohm rangs.
Note: Less than 2% error is added in measuring samples with a
series reactance of 4% 0, sample resistance.
Voltage Limited Mode: Degraded from Normal mode by 2.10%;
atter an on-scale reading is obtained. the unit may be safely
switched to the Normal mode for a more accurate reading.
SAFETY:
Normal Mode: Maximum voltage across sample. 1.4 volts.
Maximum power dissipation due to improper range setting, 3
milliwatts. Maximum power dissipation due to component failure f
and improper range setting, 6 milliwatts.
Voltage Llmlted Mode: Maximum volfage applied across sam-
ple, 25 millivolts peak to peak. Maximum power dissipation due
to improper range setting. 65 microwatts. i
ZERO DRIFT: None.
WARM-UP TIME: 30 seconds.
tNPUT ZERO: Lever switch prevents OH-scale meter indications
white changing samples.
REPEATABILITY: Within 2%.
CONNECTOR& Test Leads: Amphenol SO-PC2F
POWER: Battery Complement: Four Et46 (8.4V): two RM40lR
(1.34 V). two RM42R (1.34V); 360 hour* minimum life.
DIMENSIONS; WEIGHT: 10 in. high x 6% in. wide x 6% in. deep
(265 x 170 x 170 mm,; net Wsight, 9 pounds (3.9 kg).
ACCEBBORlEB SUPPLIED: Model 5022 Current and Voltage
Leads: one set alligator clips: one set Miniprod adapters; mating
COnneCtorS.
iv 0275
UODEL 502A GEXERAL DESCRIPTION
SECTION 1. GENERAL DESCRIPTION
l-l. GDJERAL.
a. The Keithley Model 502A is a battery-operated milliohmmeter with 13 ranges from
0.001 ohm full scale to 1000 ohms. Minimum detectable resistance is 30 micro-ohms.
Accuracy is 23% of full scale on all ranges eqcept the O.OOl-ohm range, where it is ?5%
of full scale.
b. The Miliiohmmeter uses a 4-terminal ammeter-voltmeter technique to eliminate errors
due to lead and contact resistance. A 94-crps square wave current is applied through one
pair of terminals. The resulting voltage drop Eacross the sample is measured through the
other pair. A relatively high-impedance rectifier-type voltmeter measures the voltage.
c. Using a square wave test current eliminates zero drift and minimizes errors caused
by thermal emf's. Also, the Model 51)2A can measure ac*oss a sample upon which a biasing
dc current is superimposed without affecting the accuracy of the reading.
FIGURE 1. Keithley Instruments Model 502A MilLiohmmeter. Furnished acces6orles are
shown inside the carrying case.
GENERALDESCRIPTION MODEL 502A
Mechanical
Meter Zero
CORREITI Power
output
(J102) .&itch
(5103)
Range
' Switch
(5102)
VOLTAGE OPERATE-ZERO
Inout- 'Switch (Slot)
FIGURE 2. Model 502A Front Panel Controls and Terminals. Circuit designations refer
to Replaceable Parts List and schematic diagram.
0275
MODEL 502A OPERATION
SECTION 2. OPERATION
2-l. FRONT PANEL CONTROLSAND TERMINALS (See Figure 2.)
a. Power Switch. The Power Switch has three positions: in OFF, the Model 502A power
supply is disconnected. In VOLTAGE LIMITED, the maximum open-circuit voltage across the
sample never exceeds 25 millivolts. This mode is used to initially determine the magni-
tude of the resistance. In NORMALposition, the Model 502A operates as an accurate milli-
ohmmeter.
b. OPERATE-ZEROSwitch. The OPERATE-ZEROSwitch is a 2-position toggle switch. When
the Switch is in the OPERATEposition, the Millioharneter operates to measure resistances.
Putting the Switch in ZERO position shorts the voltage input and allows connecting a sam-
ple to the input receptacles without overloading the instrument.
C. Range Switch. The Range Switch has 13 overlapping range positions from .OOl ohm
full scale to 1000 ohms. A CAL position is used to check the instrument for a meter de-
flection of 7.
d. CALIBRATE Control. The CALIBRATE Control is a potentiometer immediately beneath the
Range Switch. It adjusts the meter deflection to 7 when the Range Switch is set to CAL.
e. CURRENTand VOLTAGE Receptacles. Two microphone-type receptacles are used for the
~: Model 5022 Test Leads. Either lead may be used in either receptacle. A diagram shows
the lead hookups for measuring a sample.
2-2. INPUT CONNECTIONS.
a. Measuring samples less than 3 ohms.
T 1. Connect the Model 5022 Test Leads Current
to the VOLTAGE and CURRENTReceptacles.
Connect same color alligator clips to the
A same side of the resistance sample. -f%-
Voltage
2. Connect the voltage leads across Leads
that part of the sample which will be mea-
sured. The Model 502A measures the resis-
tance only between the two ooints to which
the voltage leads are connecred. Connect FIGURE 3. Model 502A Four-Terminal Input
the current leads to the sample outside Connections. Make sure current leads are
the voltage leads. Make sure current outside voltage leads and like color clipa
flows through the entire portion of the are on each end of the sample.
sample to be measured.
NOTE
Do not connect the voltage leads to the current leads when measuring resistances
less than 3 ohms. In this connection, the clip resistance and the clip-to-sample
contact resistance are significant enough to increase the reading.
OPERATION MODEL 502A
b. Measuring samples 3 ohms and more: The clip-contact resistance is not significant
when using the 3-ohm and greater ranges. Connect the voltage leads to the current leads.
Then connect the current leads to the sample. The four-terminal methods, given above,
may be used for these ranges, but the two-terminal method is faster for repeated testing.
2-3. OPERATING PROCEDURES.
a. use the voltage limited operating mode, which greatly limits the applied voltage,
to determine the magnitude of the resistance. Then switch to the normal mode for more
accurate measurements without changing the applied voltage or power dissipation.
b. Turn the Power Switch to the VOLTAGELIMITED position. Set the OPERATE-ZEROSwitch
to ZERO. Wait 30 seconds for the Milliohmmeter to warm up.
c. Connect the leads to the sample as described in paragraph 2-Z..
d. Set the OPERATE-ZEROSwitch to ZERO when connecting the leads to the sample. When
the switch is at ZERO, the voltage input is shorted, and the Milliohmmeter can not be
overloaded. An accidental overload will not damage the Model 502A. However, it will take
approximately 30 seconds for the amplifier to recover. Set the OPERATE-ZEROSwitch to
OPERATE. Start at the highest ranges of the Range Switch and turn to the most sensitive
range for an on-scale reading. Turn the Power Switch to NORMAL. Take the readings direct-
ly from the meter.
e. The Model 502A has a convenient calihration~check. Set the Range Switch to CAL and
the OPERATE-ZEROSwitch to OPERATE. The Milliohmmeter should read withu one minor
division of 7. If necessary, adjust the CALIBRATE Control on the front panel to a meter
deflection of 7. If the control will not make the adjustment, check the batteries within
the instrument.
NOTE
Before storing the Milliohmmeter for a long time, remove all batteries.
2-4. ZERO OFFSET.
i
a. The Model 502A has a zero offset. The zero offset is characteristic of any ac volt-
meter that uses rectifying diodes to detect the signal. If there is a zero applied signal
and noise or another unwanted signal is present, the diodes will rectify the unwanted sig-
nal and the meter will see a net ac signal. This is the zero offset.
b. The zero offset will not be added to the signal being measured. If there is more
than one signal present, the Model 502A will read the larger of the two signals. The
smaller signal will be averaged out. That is, if a signal is applied whose peak value is
larger than the peak value of the unwanted signal, the diodes will rectify this signal and
the unwanted component will ride on top of the applied signal and be averaged out. There-
fore, the Model 502A will read within specifications if the value of the signal being
measured is greater than the zero offset being observed.
2-5. 60-CPS INTERFERENCE.
a. On the l-ohm and lower ranges, the Model 502A is sensitive in the microvolt region
and its pass band includes 60 cps. A voltage lead Loop which encloses a 60-cps magnetic
field may cause a meter deflection. Avoid such Loop:;. Also be careful to avoid electro-
static pick-up, although it is not serious at the impedances involved.
4 0275
MODEL 502A OPERATIQW
I Range,
ohms
0.001
Maximum Series
Inductance,
millihenries
.00006
Maximum Shunt
Capacitance,
microfarads
over 1000
0.003 .0002 over 1000
0.01 .0006 over 1000
0.03 .002 over 1000
0.01 .006 700
0.3 .02 225
1.0 .06 70
3.0 .2 22.5
10 .6 7
30 2 2.25
100 6 7
300 20 :225
TABLE 1. Maximum Capacitance and Inductance Allowed by Range. Capacitances and Fnduc-
tances in the sample or input circuit below the Listed amount will not degrade the Model
502A.
b. To test for pick-up, remove the current leads when the voltage Leads are connected
to the sample. If no reading appears, there is.no pick-up. If a reading appears, reduce
pick-up by rotating the instrument for minimum deflection. Even if pick-up is present,
however, the Milliohmmeter will still read within specifications above any residual read-
ing. For example, if-tbe'Mode1 502A reads 0.002 ohm due to stray fields with the voltage
leads shorted, a 0.003-ohm resistance being tested will still read 0.003 ohm. This is
because the dc Level of the rectified signal will be greater than the peek-to-peak value
of the 60-cps signal. In this case, the 60-cps signal will be superimposed on the test
signal and it will not be rectified.
2-6. INDUCTANCEAND CAPACITANCE.
a. The Model 502A measures resistance using 94-cps current through the sample. using
the ac current means inductive end capacitive components in the sample or in the input
circuit will cause some wave form distortion and erroneous readings. The error normally
encountered in a measurement is small and within the Model 502A specifications. For in-
stance, at 94-cps series inductive impedance less than 4% of the resistance of the sampie
causes the reading to be Less than 2% high. Shunt capacitive admittance less than 4%
of the conductance causes the reading to be less than 2% low. Table 1 Lists maximum
capacitance and inductance values to maintain specified accuracy.
2-7. SUPER-IMPOSEDCURRENTSAND VOLTAGES.
a. The Model 502A measures the voltage acroe.s a sample through which a known current
flows. The meter is calibrated to reed the voltage in ohms. Additional currents through
the sample may change the voltage reading and distort the resistance readings.
0275 5
OPERATION MODEL 502A
b. Because the Milliohmeter uses an ac current in its testing, large amounts of dc
current in a sample do not affect the reading. In the milliohm ranges, SO amperes dc
through a sample will not cause error. HOW`3ll?l-, even 0.01~ampere ac current whose freq-
uency is within the Model 502A pass band will cause serious errors.
c. If a voltage greater than 0.05 volt dc is across the sample, use blocking capacitors
in series with the current and voltage leads, Refer to Figure 4. On the voltage leads
use a lOOO-microfarad capacitor which has a voltage rating sufficient to handlcthe dc
sample voltage. Table 2 lists values for the capacitor on the current leads.
.
Range, R, C Added
ohms ohms Microfarads Error
0.1 100 1000 -1%
Model 0.03 47 1000 -3%
502A 0.01 10 4000 -6%
cl 0.003 10 4000 -6%
0.001 10 4000 -6%
urrent
TABLE 2. Component Values For DC Voltage
Across Sample. The values are for the com-
3: 1000 ponents in Figure 4. The added error is
error caused by the additional voltage
across the sample,
Y "
Black
Leads Leads
FIGURE 4. Circuit For Blocking Capacitors
Across Sample. Use this circuit if more
than 0.05 volt dc appears across the sample.
use resistor R to provide a dc return path
for the output transistor, 4104. Refer to
Table 2 for values of R and C.
6 0275
MODEL 502A CIRCUIT DESCRIPTION
SECTION 3. CIRCUIT DESCRIPTION
3-l. GBBBRAL.
a. The Keithley Model 502A Milliohrmseter consists of a 94-cps constant current source
combined with an ultra-sensitive ac vacuum tube voltmeter. Using ac techniques eliminates
. zero drift, and large negative feedback maintains factory calibration. Since both the
current source impedance and the VTVM input impedance are high, connector and lead resis-
tances are insignificant.
b. The current source consists of a pair of transistors connected as a multivibrator.
An output transistor operates as a switch and places the full battery voltage in series
with the resistor which determines the test current for each range.
c. The voltmeter consists of an input transformer with a 6O:l step-up ratio, a 5-stage
subminiature tube amplifier, and an indicating meter in an overall feedback loop.
3-2. CURRENTSOURCE.
a. A multivibrator, made of transistors QlOl and Q102, generates the 94-cps square wave
current. Potentiometer R159 adjusts the square wave syeanetry. Transistors Q103 and Q104
are power amplifiers for the ac current. Transistor QlO4 acts as a 94-cps switch, connect-
ing and disconnecting battery BT107 across the sample and the seri'es resistors, R134 and
R145 through R154, selected with the Range Switch. Because the output peak voltage is
more than 95% of the battery voltage, transistor parameter changes have little affect on
the square wave amplitude.
b. Battery BT108 supplies a negative bias current through resistor R162 to the output
transistor, Ql04, to insure good cut-off characteristics at high ambient temperature.
c. When the Power Switch is in VOLTAGE LIMITBD position, internal resistors R133 and
R135 through R144 are shunted across the sample. The resistor values are chosen so that
the maximum voltage drop due to current from the multivibrator is limited to 25 milli-
volts, even with an improper setting of the Range Switch.
3-3. AC VOLTMETER.
a. The input signal to the ac amplifier is matched to the vacuum tube input by an in-
put transformer, TlOl, on the more sensitive ranges. Above the l-ohm ranges, the trans-
former is not used.
b. The input voltage is compared to the feedback voltage through resistors RlOl and
R102 into the grid of tube VlOl. Tubes VlOl through V105 amplify the signal. The
output voltage is~full-wave rectified by diodes DlOl and D102 to supply indicating
meter current. The current flows through resistors R130 to R132 to supply feedback volt-
age to the first stage.
c. Potentiometer R125 is used to calibrate the ranges which do not use transformer in-
put; potentiometer R129 is used for calibrating the ranges which use the transformer input.
d. When the Range Switch, 5102, is set on CAL, the Model 502A is placed on its lOOO-
ohm range. A 700-ohm, 1% resistor, R163, is connected into the test position and the
0275 7
CIRCUIT DESCRIPTION MODEL 502A
external voltage and current leads are disconnected. The CALIBRATE potentiometer, Rl25,
then can be used to adjust for a reading of 7 on t'le meter. Since the current drain is
essentially the same on all ranges, a reading less than normal usually indicates faulty
batteries.
0275
MODEL 502A SERVICING
SECTION 4. SERVICING
4-1. GENERAL. Section 4 contains the maintenance and troubleshooting procedures for the
Model 502A Milliohmmeter. It is recommended that these procedures be followed as closely
as possible to maintain the accuracy of the instrument.
G-2. SERVICING SCHEDULE.
a. The Model 502A requires no periodic maintenance beyond the normal cars required of
high-quality electronic equipment. No part should need replacement under ordinary use
except batteries and, occasionally, tubes.
b. Recommended recalibration once a year; refer to Section 5.
4-3. PARTS REPLACEMENT. The Replaceable Parts List in Section 6 describes the electrical
components of the Milliohmmeter. Replace components only as necessary. Use only reliable
replacements which meet the specifications.
NOTE
Before replacing any vacuum tube, remove batteries BTlOl and BTl02.
The plate supplies are always on and damage to other tubes can result by shorting
tube leads together.
4-4. BATTERY REPLACEMENT.
a. To reach the batteries, remove the four screws at the rear of the Model 502A. Slide
the instrument out of the case. All batteries are in holders at the top of the instru-
ment.
.. b. Battery BT107, which supplies the current generator, and battery BTl06, which
supplies the vacuum tube filaments, should have a useful life of about 460 hours. If the
Milliohmmeter is used continuously on the three most sensitive ranges, the life of BT107
may shorten to 360 hours.
c. Battery BTlOl, which supplies the plate potential to the output tube, V105, has
about twice the life of batteries BT106 and BT107.
d. Batteries BT102 to BT104, the plate supply for the amplifier, the bias battery
I Instrument use
I
Keithley Instruments Model 153 Microvolt- Check circuit voltages
Ammeter, 100 megohm minimum input resistance,
5% accuracy
Tektronix Type 504 Oscilloscope, 10 megohm Check wave forms
minimum input resistance
TABLE 3. Equipment Recqmmended for Model 502A Troubleshooting. Use these instruments
or their equivalents.
0275 9
sFXJICING MODEL 502A
BTl05,and BTl08, the negative bias for output transistor Q104, should last about two years.
NOTE
To insure good battery operation, it is a good practice to change all batteries
whenever one is replaced. This makes sure all are in peak operating condition.
P
4-5. TROUBLESHOOTING. I,
/
a. The procedures which follow are for repairing troubles which might occur in the
Model 502A. Use these procedures and use only specified replacement parts. Table 3 lists
equipment recommended for troubleshooting. If the trouble cannot be readily located or
repaired, Keithley Instruments, Inc., or its representative can service the instrument.
b. Find the difficulty through a circuit-by-circuit check, such as given in paragraph
4-6. Refer to the circuit desctiption in Section 3 to find the more critical components
and to determine their function in the circuit. The Voltage Chart, 12256C, lists voltages
for the tubes and transistors. The complete circuit schematic diagram, 18346E, is found
at the back of the Manual.
4-6. PROCEDURES GUIDE TROUBLESHOOTING.
TO
a. If the instrument will not operate, check the batteries. If they are all found
satihsctory , continue to check.
b. Check the current wave form at the CURRENTReceptacle, 5102. This should be a 94-
cps square wave with about 1.3-volt amplitude (See Figure 14). Use the 3-ohm range to a-
void oscilloscope loading. If the wave form is not correct, check the generator circuit
stage-by-stage. Refer to the Voltage Chart, 12256C, to check the four transistors.
Check the voltage amplifier. Check operating potentials with those given in the
Voy;age Chart, 12256C. When operating points are all correct, check the amplifier stage
by stage for amplification. Note that tube V105, used to supply meter current, has a
voltage gain of only about one. The voltage required at the junction of capacitor Cl15
and diodes DlOl and DlU2 for full-scale meter deflection is approximately 0.75 volt rms.
d. Figures 5 through 13 show the wave forms found at various points within a properly
functioning Milliohmmeter. Check these points in the order in which they appear in the
figures. Set the Model 502A Power Switch to NORMAL, the Range Switch to CAL, and the
FIGURE 5. Correct Waveform at Grid of FIGURE 6. Correct Waveform at Plate of
Tube V102 (Pin 4). Vertical sensitivity Tube ~102 (Pin 1). Vertical sensitivity
is 1 millivolt/cm; horizontal sweep is is 5 millivolts/cm; horizontal sweep is
5 milliseconds/cm. 5 milliseconds/cm.
10 0275
MODEL 502A
! FIGDRE 7. Correct Waveform at Grid of FIGURE 8. Correct Waveform at Plate of
Tube V103 (Pin 4). Vertical sensitivity Tube V103 (Pin 1). Vertical sensitivity
is 5 millivolts/cm; horizontal sweep is is 50 millivolts/cm; horizontal sweep is
5 milliseconds/cm. 5 milliseconds/cm.
FIGIJRF 9. Correct Waveform at Grid of FIGURE 10. Correct Waveform at Plate of
Tube V104 (Pin 4). Vertical sensitivity Tube V104 (Pin 1). Vertical sensitivity
is 50 millivolts/cm; horizontal sweep is is 1 volt/cm; horizontal sweep is 5 milli-
5 milliseconds/cm. seconds/cm.
FIGURE 11. Correct Waveform at Grid of FIGURE 12. Correct Waveform at Plate of
Tube V105 (Pin 4). Vertical sensitivity
Tube V105 (Pin 1). Vertical sensitivity
is 0.5 volt/cm; horizontal sweep is is 5 volts/cm; horizontal sweep is 5 milli-
5 milliseconds/cm. seconds/cm.
FIGURE 13 (left), Correct Waveform at
Junctions of Diodes DlOl and D102. Verti-
cal sensitivity is 1 volt/cm; horizontal
sweep is 5 milliseconds/cm.
0275 11
.
CALIBRATION MODEL 502A
SECTION 5. CALIBRATION
5-1. GENERAL.
The following procedures are recommended for calibrating and adjusting the Model
50% Use the equipment recommended in Table 4. If proper facilities are not available
or if difficulty is encountered, contact Keithley Instruments, Inc., or its representa-
tive to arrange for factory calibration.
b. Calibration is done in three steps: the ac test current is calibrated, and then
the Model 502A is adjusted on its high and low resistance ranges.
c. If the Model 502A is not within specifications after the calibration, follow the
troubleshooting procedures or contact Keithley Instruments, Inc., or its nearest repre-
sentative.
5-2. CALIBRATION SCHEDULE. Calibrate the Model 502A every 12 months. This is necessary
to compensate for any value changes in the circuit. Use the front panel calibration test,
described in Section 2, as often as desired. If the test shows a discrepancy greater than
one division on the meter scale, perform the complete calibration.
NOTE
Make the calibrations in the order of paragraphs 5-3 and 5-4.
5-3. CURRENTFREQUENCY
AND SYMMETRY
ADJUSTMENTS.
a. Set the Model 502A Range Switch to 3 ohms. Connect the Type 504 Oscilloscope to
the Model 502A CURRENTReceptacle. Connect the Model 200CD Oscillator output to the
horizontal input of the Oscilloscope. Set the Oscillator for a 94-cps output.
b. Set the Model 502A Power Switch to NORMALand the.OPERATE-ZERO Switch to OPERATE.
Monitor the Milliohmmeter frequency and compare it to the Oscillator's. Frequency should
be 94 cps fl cps. To increase the Model 502A frequency, decrease the resistance values
of R158 and R160. To decrease the frequency, increase the resistance values
of R158 and R160.
Instrument use
Hewlett-Packard Model ZOOCDOscillator Comparison for current frequency
ITektronix Type 504 Oscilloscope Check Current Wave Form
IResistance standards, 0.001 to 30 ohms in
lx and 3x steps, absolute accuracy 0.1% Standard to check ranges
Resistance standards, 100 to 1000 ohms in
loo-ohm sews. absolute accuracy. 0.1% I
TABLE 4. Equipment Recommended for Model 502A Calibration. Use these instruments or
their equivalents.
MODEL 502A CALIBRATION
Circuit Fig. Refer to
Control Desig. Ref. Paragraph
Resistance Calibration R125 15 5-4
Low resistance calibration R129 15 5-4
Current symmetry adjustment R159 15 5-3
TABLE 5. Model 502A Calibration Controls. The Table lists internal and front panel
controls used to calibrate the Model 502A, the figure picturing the location anh the para-
graph describing the adjustment.
c. Check the square wave symmetry on the
Oscilloscope. The wave should be approximate-
ly 1.3 volts peak-to-peak. Adjust potentio-
meter Rl59, if necessary, so the
wave form resembles that shown in Figure 14.
NOTE
Use the 3-ohm range to check wave
form symmetry. Using higher ranges FIGURE 14. Symmetrical Square Wave with
will tend to lower the wave ampli- Potentiometer R159 Adjusted. Vertical
tude due to the series resistance sensitivity is 1 volt/cm; horizontal sweep
of the range resistor and the Oscillo- is 5 milliseconds/cm.
scope input impedance.
5-4. RANGE CALIBRATION.
a. Set the Model 502A controls as follows:
Power'Switch NORMAL
OPERATE-ZEROSwitch OPERATE
Range Switch CAL
Let the Milliohnrmeter warm up 30 seconds.
b. Adjust the front panel CALIBRATE Control, RL25, to exactly 7 on the upper meter
scale.
Check meter tracking for the high resistance ranges. Connect the Model 5022 Current
ani*Voltage Leads to the Model 502A. Set the Range Switch to 1K. Use Resistance Standards
100 to 1000 ohms in loo-ohm steps to check meter tracking. The Model 502A should read'the
values within *30 ohms.
d. Check the 1000 to 3-ohm ranges for full-scale readings. Accuracy should be i3% of
full scale.
e. Set the Model 502A Range Switch to 1 ohm. Connect the Model 5022 Leads to l-ohm
resistance standard. Make sure connection is properly made (paragraph 2-2). Model 502A
should read full scale C3%. Adjust LO OHM CAL potentiometer, R129, if nec-
essary, for full-scale deflection
f. Check the 1 through .003-ohm ranges for full-scale readings. Accuracy should be
0275 13
CALIBRATION MODEL 502A
f3% of full scale. Check .OOl-ohm range for accuracy &5% of full scale. If necessary,
adjust potentiometer R129 to split the error on the low ranges.
8. Set the Power Switch to LIMITED. Recheck all the ranges for full-scale readings.
Expect an additional error of from 2 to 10% in this operating mode. The amount of error
varies with test cable resistance.
FIGURE 15. Component Layout, Printed Circuit Board.
MODEL 502A REPLACEABLEPARTS
SECTION 6. REPLACEABLE PARTS
6-1, REPUCFABLE PARTS LIST. The Replaceable Parts List describes the components of the
Model 502A and its accessories. The List gives the circuit designation, the part des-
cription, a suggested manufacturer, the manufacturer's part number and the Keithley Part
Number. The last column lists the figure picturing the part. The name and address of the
manufacturers listed,in the "Mfg. Code" column are contained in Table 7.
6-2. HOWTO ORDERPARTS.
a. For parts orders, include the instrument's model and serial number, the Keithley
Part Number, the circuit designation and a description of the part. All structural
parts and those parts coded for Keithley manufacture (80164) rrmst be ordered from Keithley
Instruments, Inc. 01 its representative. In ordering a part not listed in the Replaceable
parts List, completely describe the part, its function and its location.
b. Order parts through your nearest Keithley distributor or the Sales Service Depart-
ment, Keithley Instruments, Inc.
=mP ampere nil. No. Military Type Number
MY Mylar
Comp Composition
n ohm
Deb Deposited Carbon
PM Paper, metallized
ETB Electrolytic, tubular Poly Polystyrene
P pica (10-12)
f farad
P micro (10m6)
k kilo (103)
V volt
M or meg megs (106) or megohms Var Variable
m milli (10s3)
Mfg. Manufacturer W watt
MtF Metal Film ww Wirewound
War Wirewound Variable
c .
TABLE 6. Abbreviations and Symbols.
0275 15
REPLACEABLE PARTS MODEL 502A
MODEL 502A REPLACFABLEPARTS LIST
(Refer~to Schematic Diagram 18346E for circuit designations.)
BATTERIES
Circuit Mfg. Mfg. Keithley Fig.
Desig. Description Code Pert No. Part No. Ref.
BTlOl a.4 " mercury 10608 El46 aA-9 BH-6
BT102 8.4 v mercury 10608 El46 BA-9 Battery -
BT103 8.4 v mercury 10608 El46 BA-9 Holder -
BT104 8.4 v mercury 10608 El46 BA-9
BT105 1.34 v mercury 10608 E401 BA-8
BT106 1.3 v mercury 37942 RM42R BA-10
BT107 1.3 " mercury 37942 RM42R BA-10
BT108 1.34 v mercury 10608 E401 BA-8
Battery Clip 14749A
CAPACITORS
Circuit Mfg. Mfg. Keithley Fig.
Desig. Value Rating 'BP= Code Part No. Part No. Ref.
Cl01 0.1 pf 50 " MY a4411 601PE C41-.lM 15
Cl02 2.2 uf 50 v ETB 05397 J2R2J50S Cl&g-2.2M 15
Cl03 .22 llf 50 v YT a4411 601PE C41-.22M 15
Cl04 .0082 uf 100 v MY a4411 633lW100 C38-.0082M 15
Cl05 .0022 pf loo " Poly 13934 E3FR-222-1-C Cl52-.0022M 15
Cl06 50 uf 50 v ETB 37942 TC39 C39-50M 15
Cl07 2.2 uf 50 " ETB 05397 J2RZJ50S Cl49-2.2M 15
Cl08 270 pf 500 v Mica 84171 DM15-271J C21-270P 15'.
Cl09 .OOl wf 100 v Mica a4171 DM15-1025 C21-.OOlM 15
Cl10 50 pf 50 " ETB 37942 TC39 C39-50M 15
Cl11 .22 pf 50 v MY a4411 601PE C41-.22M 15
Cl12 2.2 pf 50 v ETB 05397 52R2550S C149-2.2M 15
Cl13 .22 pf 50 v w a4411 601P~ C41-.22M 15
Cl14 820 pf 300 v Mica a4171 DM15-821K c21-82OP 15
Cl15 100 pf 500 " Mica 84171 DM15-1OlJ c21-100P 15
Cl16 2.2 pf 50 v ETB 05397 J2R2J50S Cl49-2.2M 15
Cl17 0.1 nf 50 v MY 84411 601PE C41-.lM 15
Cl18 820 pf 300 " Mica 84171 DM15-821K c21-82OP 15
Cl19 22 pf 500 v Mica a4171 DMl5-220J c21-22P 15
Cl20 1.0 pf 100 " MY 13934 Type 3 c139-IM 15
Cl21 0.1 (If 50 " MY a4411 601PE C41-.lM 15
Cl22 1.0 uf 100 " MY 13934 VP= 3 Cl39-l.M 15
0275
16
MODEL 502A REPLACEABLEPARTS
DIODES
Circuit Mfg. Keithley Fig.
Desig. TYPO Number Code Part No. Ref.
DlOl Silicon lN645 01295 RF-14 15
D102 Silicon lN645 01295 RF-14 15
MISCELLANEOUSPARTS
Circuit Mfg. Keithley Fig.
Desig. Description Code Part NO. Ref.
.I101 Receptacle, Microphone, VOLTAGE (Mfg. NO. 80-PC2F) 02660 CS-32
J102 Receptacle, Microphone, CURRENT(Mfg. No. 80-PC2F) 02660 CS-32 ;
-em Plug, Microphone, Mate of Jl and 52 (Mfg. No. 02660 cs-33
8OMC2M)
Ml01 Meter 80164 ME-59 2
SlOl Toggle switch, OPERATE-ZERO(Mfg. No. 3003-DL) 82389 SW-59 2
5102 Rotary Switch less components, Range 80164 SW-196 2
s103 Rotary Switch less components, Power 80164 SW-195 2
TlOl Transformer 80164 TR-53
RESISTORS
L
Circuit Mfg. Mfg. Keithley Fig.
Desig. Value Rating TYPO Code Part No. Part No. Ref.
RlOl 1l-Q l%, l/2 w MtF 07716 CEC-lM-1% Rll3-1M 15
R102 1MO l%, l/2 w MtF 07716 CEC-lM-1% Rll3-1M 15
R103 2.2 ml l%, l/2 w DCb 79727 CFE-15-2.2M R12-2.2M 15
R104 10 Ia lO%, l/2 w Comp 01121 EB-106-10% Rl-1OM 15
R105 22 wl lO%, l/2 w Comp 01121 EB-226-10% Rl-22M 15
R106 100 kn lO%, l/2 w Comp 01121 EB-104-10% Rl-100K 15
R107 2.2 ml lO%, l/2 w Comp 01121 EB-225-10% Rl-2.2M 15
Rl08 2.2 l-i-l lO%, l/2 w Comp 01121 EB-225-10% Rl-2.2M 15
R109 10 m lo:, l/2 w Comp 01121 EB-106-10% Rl-1OM 15
RllO 47 kn lOk, l/2 w Comp 01121 EB-473-10% Rl-47K 15
Rlll 22 m lO%, l/2 w Comp 01121 EB-226-10% Rl-22M 15
R112 100 kn lO%, l/2 w Comp 01121 EB-104-10% Rl-100K 15
R113 2.2 is lO%, l/2 w Comp 01121 EB-225-10% Rl-2.2M 15
0275 17
REPLACEABLEPARTS MODEL 502A
RESISTORS (Cont'd)
Circuit Mfg. Mfg. Keithley Fig.
Desig. Value Rating TYPO Code Part No. Part No. Ref.
R114 2.2 m lO%, l/2 w camp 01121 EB-225-10% Rl-2.2M 15
R115 10 Ia lO%, l/2 w Comp 01121 EB-106-10% Rl-1OM 15
Rll6 22 I%> lO%, l/2 w Comp 01121 EB-226-10% Rl-22M 15
R117 100 kn lO%, l/2 w Comp 01121 EB-104-10% Rl-100K 15
Rl18 2.2 is lO%, l/2 w camp 01121 EB-225-10% Rl-2.2M 15
R119 2.2 l"n lO%, l/2 w Comp 01121 EB-225-10% Rl-2.2M 15
R120 10 l"n lO%, l/2 w Comp 01121 EB-106-10% Rl-1OM 15
R121 47 kn lO%, l/2 w Comp 01121 EB-473-10% Rl-47K 15
R122 10 w? LO%, l/2 w Comp 01121 EB-106-10% Rl-1OM 15
R123 47 kn lO%, l/Z w Comp 01121 EB-473-10% Rl-47K 15
R124 2.2 m lO%, l/2 w Comp 01121 EB-225-10% Rl-2.2M 15
R125 20 kn lO%, 5 w wwvar 71450 AW-20Kn RP34-20K 15
R126 65 kc] l%, l/2 w DCb 79727 CFE-15-65 Rl2-65K 15
R127 5 kn l%, l/2 w DCb 79727 CFE-15-5K R12-SK 15
R128 5 kn l%, l/2 w DCb 79727 CFE-15-5K R12-5K 15
R129 1 kn lO%, 5 w wwvar 71450 AW-1KO RP3- 1K 15
RI30 95.3 0 l%, 112 w MtF 07716 CEC-95.3-l% R94-95.3 s102
R131 300 '2 l%, l/2 w DCb 79727 CFE-15-300 Rl2-300 5102
R132 1 kn l%, l/2 w DCb 79727 CFE-15-1K RlZ-1K 5102
R133 lfl l%, l/2 w DCb 79727 CFE-15-1 R12-1 s102
R134 60 n l%, l/2 w DCb 79727 CFE-15-60 Rl2-60 5102
R135 3.33 i? l%, l/2 w DCb 79727 CFE-15-3.33 R12-3.33 5102
R136 10 R lO%, l/2 w Comp 01121 EB-lOO-10% Rl-10 s102
R137 33 1 lO%, l/2 w Comp 01121 EB-330-10% Rl-33 5102
R138 100 R lO%, l/2 w Camp 01121 EB-lOl-10% Rl-100 s102
R139 56 r: lo%, 112 w Comp 01121 EB-560-10% Rl-56 5102
R140 180 0. l%, l/2 w DCb 79727 CFE-15-180 R12-180 5102
R141 560 n lO%, l/2 w Comp 01121 EB-561-10% Rl-560 5102
R142 1.8 kn lO%, l/2 w Comp 01121 EB-182-10% Rl-1.8K s102
R143 5. 6 kil lO%, l/2 w Comp 01121 EB-562-10% Rl-5.6K s102
R144 18 kn lO%, l/2 w Comp 01121 EB-180-10% Rl-18K s102
R145 180 n l%, l/2 w DCb 79727 CFE-15-180 R12-180 s102
R146 604 n l%, l/2 w DCb 79727 CFE-15-604 R12-604 s102
R147 1.8 kn l%, 112 w DCb 79727 CFE-15-1.8K RlZ-1.8K 5102
~148 6 kn l%, 112 w DCb 79727 CFE-15-6K Rl2-6K s102
R149 3 kn l%, l/2 w DCb 79727 CFE-15-3K Rl2-3K 5102
R150 10 kn 1%, l/2 w DCb 79727 CFE-15-1OK R12-10K s102
R151 30 kn l%, l/2 w DCb 79727 CFE-15-30K R12-30K s102
R152 100 kn l%, l/2 w DCb 79727 CFE-15-100K Rl2-100K 5102
R153 300 kn l%, l/2 w DCb 79727 CFE-15-300K Rl2-300K s102
18 0577
MODEL 502A WPIACEABLE PARTS
RESISTORS (Cont'd)
Circuit Mfg. Mfg. Keithley Fig.
Desig. Rating Type Code Part No. Part No. Ref.
R154 1MQ l%, l/2 w DCb 79727 CFE-15-1M R12-1M s102
R155 1Mcl l%, l/2 w DCb 79727 CFE-15-l.M R12-1M s102
Rl56 82 R l%, l/2 w DCb 79727 CFE-15-82 R12-82 s102
R157 31u2 l%, l/2 w DCb 79727 CFE-15-3K R12-3K 15
R158 "6.98KR l%, l/2 w DCb 79727 CFE-15-6.98K R12-6.Y8K 15
Rl59 10 kn lO%, 2 w wwvar 71450 WP-1OK RP9-1OK 15
R160 +6.98K0 1%, l/2 w DCb 79727 CFE-15-6.98K Rl2-6.98K 15
Rl61 3m l%, l/2 w DCb 79727 CFE-15-3K R12-3K 15
Rl62 15 kc lO%, l/2 " Comp 01121 EB-153-10% Rl-15K 15
R163 700 Q l%, l/2 w DCb 79727 CFE-15-700 R12-700 5102
R164 2.5 kn l%, l/2 w DCb 79727 CFE-15-2.5K R12-2.5K 15
Rl65 350 n l%, l/2 w DCb 79727 CFE-15-350 R12-350 s102
R166 >'< l%, l/2 w DCb 79727 CFE-15-* Rl2-?: 15
*Value selected at factory
PRANSISTORS
Circuit Mfg. Keithley Fig.
Desig. NllIllber Code Part No. Ref.
QlOl PNP 2N1381 01295 TG-8 15
Q102 PNP 2N1381 01295 TG-8 15
Q103 PNP 2Nl381 01295 TG-8 15
Q104 PNP 2Nl381 01295 TG-8 15
VACUUMTUBES
Circuit Mfg. Keithley Fig.
Desig. Number Code Part No. Ref.
VlOl 6419 81453 EV-CK6419 15
v102 6419 81453 EV-CK6419 15
v103 6419 81453 EV-CK6419 15
v104 6419 81453 EV-CK6419 15
v105 6418 80164 EV-CK6418-1 15
(or CK-592-l)
FURNISHED ACCESSORIES
Mfg. Mfg. Keithley
Description Code Part No. Part No.
Two Alligator Clips, red 83330 304 AC-3R
Two Alligator Clips, black 83330 304 AC-3B
0577 19
REPLACEABLEPARTS MODEL 502A
FURNISHED ACCESSORIES (Cont'd)
Mfg. Mfg. Keithley
Description Code Part No. Part No.
Two Miniprod Adapter Tips, red 08811 33-160 PP-3R
Two Miniprod Adapter Tips, black 08811 33-162 PP-3B
Current and Voltage Lead Assemblies 80164 1848OC
. Plug, Microphone 02660 8OMC2M cs-33
. Phone Tip, Red 83330 237 PP-2R
. Phone Tip, Black 83330 237 PP-2B
30656 Aerovox Corp. 37942 Mallory, P. R., and Co., Inc.
New Bedford, Mass. Indianapolis, Ind.
00686 Film Capacitors, Inc. 71450 CTS Corp.
New York, N. Y. Elkhart, Ind.
31121 Allen-Bradley Corp. 75042 International Resistance Co.
Milwaukee, Wis. Philadelphia, Pa.
31295 Texas Instruments, Inc. 79727 Continental-Wirt Electronics Corp.
Semi-Conductor-Components Division Philadelphia, Pa.
Dallas, Texas
80164 Keithley Instruments, Inc.
32660 Amphenol-Borg Electronics Corp. Cleveland, Ohio
Broadview, Chicag, Illinois
81453 Raytheon Co.
34009 Arrow-Hart and Hegeman Electric ◦ Jabse Service Manual Search 2024 ◦ Jabse Pravopis ◦ onTap.bg ◦ Other service manual resources online : Fixya ◦ eServiceinfo