Service Manuals, User Guides, Schematic Diagrams or docs for : Keithley 503 503A(Model503_252C503C)
<< Back | HomeMost service manuals and schematics are PDF files, so You will need Adobre Acrobat Reader to view : Acrobat Download Some of the files are DjVu format. Readers and resources available here : DjVu Resources
For the compressed files, most common are zip and rar. Please, extract files with Your favorite compression software ( WinZip, WinRAR ... ) before viewing. If a document has multiple parts, You should download all, before extracting.
Good luck. Repair on Your own risk. Make sure You know what You are doing.
Image preview - the first page of the document
>> Download 503A(Model503_252C503C) documenatation <<
Text preview - extract from the document
INSTRUCTION MANUAL
MODELS 503, 503C
MILLIOHMMETERS
0 COPYRIGHT 1976, KEITHLEY INSTRUMENTS, INC.
PRINTED MAY 1977, CLEVELAND, OHIO, U.S.A.
MODEL 503 CONTENTS
CONTENTS
Section Page
SpECIpIC*TIONS ---------------------------------------------------- iv
1. GENERAI,DESCRIPTION ________-___________----------------------- 1
2. OpE&Q-ION ----------------------------------------------------- 2
3. CIRCUIT DESCRIPTION ------------------------------------------- 12
4. SERVICING -_-_------------------------------------------------- 18
5. REpL)&E&LE pm',-- ____-___________________________________----- 24
SCHE&yJIC --------------------------------------------------------- 31
ii 0874
MODEL 503 ILLUSTRATIONS
ILLUSTRATIONS
Pip;. No. Title Page
1 Front Panel. ---------------__---------------------------- 1
2 Pour Terminal Measurement. -------------------------------- 2
3 Model 503 Controls. -_--__________-_-_-___________________ 5
4 lbo-terminal Connection. ------_-_-_________-_____________ 6
5 Modification for &ground Chassis. ------------------------ 7
6 Series Resistance Measurements. ----------_---______------ 9
7 Exploded View for Rack Mounting. ------------------------- 11
a Power Supply Schematic Diagram. ------------_---__________ 12
9 Super Regulated 12 Volt Supply Schematic Diagram. --------- 13
10 Test Current Generator Schematic Diagram. ----------------- 14
11 AC Amplifier Schematic Diagram. _--_________-__--_________ 16
12 Synchronous Demodulator Meter - Output. _-______---_-______ 17
13 Waveform of Synchronous Demodulator. ---------------------- 19
14 Model 503 Internal Components Locations (Top Removed). ---- 21
15 Location of Printed Circuit Board Components. ------------ 22
16 Location of Range Switch Components. --------------------- 23
c
0874 iii
SPECIFICATIONS MODEL 503
SPECIFICATIONS
Applied Voltage ME2tdll"~
C"Wl?"t, Drop. Dissipation
RANGE, milliamperes microvolts in Sample.
oIlIll* rnls rms miorowatts
0.001 100 100 10.0
0.003 33.0 100 3.3
0.01 10.0 100 1.0
0.03 3.30 100 0.33
0.1 1.0 100 0.10
0.3 0.33 100 0.033
1.0 3.0 3000 9.0
3.0 1 .o 3000 3.0
10 0.30 3000 0.9
30 0.10 3000 0.3
100 0.03 3000 0.09
300 0.01 3000 0.03
1000 0.003 3000 0.009
ACCURACY:
Meter: * 1 % of `",I SCSI0 an a,, ranges.
Output Te,lni"al*: +0.5% Of `"II SC& an a,, ranges.
Nom LessU'S" 1% Brmrts addedI" measuring9amp1e.
with B series resctancaOf 2% Of "ample m.i.l."E..
ZERO DRIFT: None.
WARM-UP TIME: 15 minutes.
INPUT ZERO: Lever ~wifch prevenf~ off-scale meter indications while changing samples.
Rl8E TlME 110% to 90%): 0.25 second an a11wmges.
SAFETY: Maximum power dissipation in sample with improper range setting is 80 milli-
wets. Maximum dissipation cawed by instrument component failure and improper range
sating is 160 milliwatts.
REPEATABILITY: Within 0.25% of full-scale range setting.
CALIBRATION: Internal redstance standard for calibration with front panel controls.
RECORDER D"TPwr
Output: + 100 millivolts dc at full scale.
Output Resistance: 800 ohms.
Noise (above IO Hzl: Less than 1 millivolt rms.
CONNECTORS: Test Leads: Cannon XLR-3-32. Output: Amphenol 80.PC2F.
POWER: 105-I 25 or 2 1 O-250 YOltS, 50-1000 HZ. 30 watts.
DIMENSIONS, WEIGHT: 5%" high x 17%" wide by 13%" deep; net weight. 18 Ibs.
ACCE88DRlES 8"PPUED: Model 5031 Current and Voltage Leads; mating o"f,,"t con-
"eCtOr*.
iv 0874
MODEL 503 GENERALDESCRIPTION
SECTION 1. GENERAL DESCRIPTION
The Model 503 Milliohnuwter permits rapid, accurate, low resistance tests. It combines a
ruggedness and ease of operation not possible with bridges. Measurements are read direc-
tly on a mirror scale meter. Balancing is unnecessary, calibration stability is excellent,
and the instrument is not damaged by overload.
Features include: 13 full-scale ranges from 0.001 to 1000 ohms; accuracy of +l% of full-
scale meter indication and ?0.5% of full-scale output voltage; no zero drift; rise time
of 0.25 second to 90% of final value; sample dissipation of less than 10 microwatts; lOO-
millivolt dc output for chart recordings or control functions; and front panel calibration.
The measurement technique involves an ammeter-voltmeter method using an ac test current.
Typical uses include measurements of internal resistance of dry cells, resistivity pro-
files of thermo-electric materials; measurements of temperatures with thermistors; dry-
circuit testing of contacts, and safe measurement of fuses and squibs.
0273
OPERATION MODEL
503
SECTION 2. OPERATION
2-1.APPLICAl'IONS: The Keithley Model 503 Milliohmmeter is especially useful
for accurate measurement of low value resistors; resistances of lead wires,
terminal connector contacts and welds; resistance change in conductors due
to temperature and humidity effects; resistance of ohmic junctions in semi-
conductors; resistivity of semiconductors, contact resistance of vibrators,
relays and choppers and internal resistance of dry cells. Also for resisti-
vity profiles of thermoelectric materials end safe measurement of squibs and
fuses.
2-2.MEAsuRBMERTTECHNIQUE: !CheModel 503 measures resistance by an meter-
Red voltmeter method using an ac test current. Four
0 terminals are employed; two furnish a known
test current to the sample and two measure the
w. 3 resultant voltage drop.(Fig. 1) !Chevoltage is
measured by a synchronous ac voltmeter sensitive
only to the test current frequency.
Most Kelvin resistance methods employ dc current
Current to measure resistance. !l%is method has the ad-
vantage of measuring only the resistive portion
Leads of the sample. However, due to the extremely
low resistance being measured either extremely
high currents must be passed through the sample
or very high sensitivity dc voltmeter techniques
must be used to measure the voltage drop across
* 0 the sample. In the case of-high current operation
(which is the more cosnnon) excessive heating and
damage to the sample msy occur. If high sensi-
0 tivity LX voltage measurement is used, extreme
Black inaccuracy may occur because of thermal EKF's
and other spurious dc disturbances. With the AC
Figure2 method used in the Model 503, there exists some
possibility of error due,to the reactive component
of the sample (Section 2-18) although in most cases at 40 cps testing frequency
this is negligible. However, with an ac exciting test current, thermal E?@'s
are eliminated and very stable high sensititity measurements can be made so that
with this AC method sample dissipation can be held 10 microwatts in measuring
a 1 milliobm sample. A typical dissipation on a
D(: Kelvin Bridge is 1 watt for the ssme measurement.
2-3.ACcuRACY: The accuracy of the measurement can be dependent on several
factors. These are discussed in Section 2-18. The basic accuracy of the 503
is within 1% of full scale for meter indications and 0.5% for full scale output
voltage.
2 0273
MODEL
503 OPERATION
2-4.RRPEATABILSl'Y: Raving once established a reading for a particular sample
measurement, it is possible to repeat within 0.25% of the full scale range set-
ting. This assumes the connections to the sample remain fixed.
2-5.CALIRRATION: The 503 is self calibrating and thus reduces the need for
resistance standards to check its accuracy. It is possible to verify the cali-
bration with or without the sample attached to the test leads. (See Sect. 2-14)
2-6.VOVIMETERSPECIFICATIONS: Since the 503 uses a synchronous demodulator,
the voltmeter is sensitive only to signals of the test current frequency.
The sensitivity and input impedance are listed in Table 2.
TABLE2
Rms Input for Full
Remges Scale Deflection 2 in
Milliohm 100 uv 200 ohms
Ohm 3000 uv 1 x 106 ohms
2-7.TRST CURRENT CRARACTRRISTICS:The testcurrent is a square wave derived
from the transistor inverter. The frequency is about 40 cps, and can be ad-
justed as discussed in Section 3-2. This may be desirable if the power line
frequency is a multiple of 40 cps.
The maximumopen circuit voltage is no more than 20 volts peak to peak. No
more than 80 milliwatts of power can be delivered from this source.
2-8.SPEED OF MEASUREMENT: Fast measurements are possible by virtue of an
overall 0.25 second response (gO$ full scale) of the output voltage. A zero
switch on the front panel shorts the input to the voltage amplifier, thus
preventing off scale indication while changing samples,. Recovery from over-
load is almost instantaneous and normal operation can be immediately resumed.
2-9.wAF@MJP: Operation within the stated specification is-assured if the 503
has a 15 minute period of warm-up. It can be used within one minute, but
measurements may not be within the accuracy specification.
2-lO.RFCORDING: Output terminals are available at the rear of the instrument.
The output is t100 millivolts across approximately 800 ohms. The output noise
level, above 10 cps, is less than 1miUivolt rms. This output is suitable
for driving digital voltmeters and servo-rebalance recorders. The accuracy of
the output is 0.5% of full scale.
2-11.KWER REQUIRBWWI!: The Model 503 can be powered over a range of line
frequencies from 50 cps to 1000 cps. The line voltages can range from either
105 to 125 v0l-h or 210 to 250 v0lts. No special connections or modifications
are required to operate over the range of power line frequencies.
A three prong power line cord is provided, this is to assure proper grounding
of the instrument to the power line.
2-12.CAXNET ORRACKl.KXlNTING: The Model 503 is shipped a8 a bench instrument
unless the order call.6 for rack-sreanting. The Model Koch Rack bunting Kit
adapts the instrument for standard lg-inch rack mounting. Refer to pragraph
2-18 for conversion instructions.
02 3 3
OPERATION MODEL503
2-13.DESCFUFTION OF CONTROIS TERMINALS:
AND
1. RANGE
SELEC!lXX The RANGE SELECTOR six milliohm positions rang-
has
ing from 1 milX.ohm to 300 milJiohms, and seven ohm positions ranging
from lob to lOo0 ohms. A CAL position is provided for Instrument cal-
ibration. (Fig. 3)
2. ON: Toggle switch is the main power switch. Presence of power is
indicated by the il&minated front panel pilot Lamp. (Fig. 3)
3. OPERATE-ZERO:This is a lever switch. With the switch in the up
operate) position the 503 is reaw to take measurements. In the down
1zero) position the 503 is in zero check. (Fie. 3)
4. CALIBMTE: This control is used to calibrate the meter and the out-
put voltage of the 503. It is a recessed slotted control that can be ad-
justed with a screw driver. (Fig. 3)
5. VOLTAGE TERMINAL% A 3-pin male receptacle is used for connection to
the voltmeter circuit. Pin No. 3 is at chassis ground. Either test lead
can be plugged into this receptacle. (Fig. 3)
6. CURRENTTERMINAIS: A 3-pin male receptacle is used for connection,to
the current source. Either test lead can be plugged into this receptacle.
(Fig. 3)
7. OUTHJT: A two terminal receptacle is located at the rear of the chas-
sis. This provides the output voltage for recording. Pin No. 2 is at ckas-
sis ground.
a. RESET(503C ONLY): This unlocks the contact circuit. A g-pin recep-
tacle at the rear of the chassis provides connections for operation with
the contact meter.
9. OUTHJTCti This is a slotted control located inside the instrument
on the chassis behind the front panel. This adjusts the value of the out-
put voltage for a full scale reading.
10. MILIJOHMSCALz This is a slotted control located inside the instru-
ment on the chassis behind the front panel. The milliohm ranges are cal-
ibrated using this control. A low resistance standard is required for its
use. This is a factory adjusted control and should not require attention.
11. KJSE: A fuse extractor post is located on the rear of the instrument.
For 117 volt operation use a 3 AG, $ amp fuse; for 234~volts use a 3 AG, * amp.
12. POWER CORD: The three-wire cord with ,the NEMAapproved three-prong
plug provides a ground connection for the cabinet. An adapter to allow
operation from two prong outlets is provided.
0273
,OPERATION
MODEL 503
FIm 3. 140del 503 Controls.
5
0273
OPERATION MODEL503
2-14.0UTLINE OF PFOCELJJRE:
1. Connect power cord to power source. A three-wire power cord is fur-
nished with the 503. Power line voltage and frequency range are specified
on the rear of the instrument.
2. Set ZERO-OPERATE
lever to the ZEROposition. Set RANGE
SELECTOR
to
lOOC-ohmposition.
3, Turn on the power. Allow 15 minute warm-up.
4. CONNECTIONS: Each test lead set has two clips, one with a red insu-
lator and the other with a black insulator. Whenmaking connections use
both test leads, making sure clips with like color insulators are on the
same side of the sample, (Refer to Figure 2) This is necessary to avoid
meter readings below zero.
a. Four terminal connections: The current leads should be attached
to the sample making sure the test current flows through the entire
sample. This may include leads on the sample. Attach the voltage
leads being sure they are connected only across that portion of the
sample to be measured. If the terminals or the leads of the sample
are included in the voltmeter circuit, their resistance will be
included in the reading. (See Section 2-18)
b. Two terminal connections: This type connection is made by
attaching together voltage and current clips having like color
insulators and measuring across the sample. (Fig, 4) This type
connection is permissible when measuring samples above 3 ohms.
(See Section 2-18)
5. OPERATION: With the sample con-
nected, set the ZERO-OPERATE switch
to OPERATE,rotate the RAWGE SELECTOR
until a deflection is observed.
if the RANGE SELECTOR set at 100
is
milliohms and a reading of 6.3 is
taken, the value of sample resistance Leads Sample Leads
IS 63 milliohms.
?
If the sample is part of a system,
attention should be given to the
grounding of the sample. The voltage
lead with the black insulator is the
E;;; l..d of the 503. (See Sec- FIGURE4. Two-terminal
I connection.
6. FtEMNING `I!m s&m& Place the OPERATE-ZERO
switch in ZEROposition
and remove the sample.
2-15.CALIBRATION: Place the selector switch in CAL position. Set the OPERATE-
ZEROswitch to OPERATE position. Turn the slotted CALIBRATEcontrol for needle
deflection to 7.50 on the meter. The inst-nt can be calibrated independent-
ly of the test leads connected. (See Section 4-2.)
6 0273
MODEL
503 OPERATION
Z-16. OUTPUT. Connect to the output terminals, observing that pin No. 2 is
at ground. The 503 is designed to drive a 100 millivolt recorder. The CALI-
RRATEcontrol on the front panel calibrates the output as well as the meter.
An internal contml R125 OUTPUT CAL is adjusted at the factory to insure track-
ing between the meter and the output voltage. (See Figure 14)
If it is desired to use a recorder other than 100 millivolts, the output ter-
minals may be shunted with the following values:
Recorder Sensitivity Resistance Value
50 m-l 'Z"E
10 mv
lmv 3&Gns
(tap output 7 ohms from ground)
After the divider is added to the output, recalibrate the instrument on the
CAL position. Adjust recorder sensitivity with R125, the internal recorder
CAL control.
2-lT.MEAsuREMENT GROUNDED
OF SAMPLES: It is possible that the test sample may
be independently grounded at some point. Since the voltage test lead with the
black clip insulator is at chassis ground, errors could arise in measurement.
1. TEMPORARY MEAsuRe FOROCCASIONALMEASUREMENTS: Isolate the Model 503
using a two-prong power cord adaptor to remove the ground connection to
the power line. Place the instrument so that the cabinet is not touching
ground. If the tilt bail is not used, the rubber feet can provide the
proper insulation.
2. PgRMANENTSET-up: Should it be necessary to unground the chassis,
(such as in rack use) the followlng modification will facilitate such
measurement. The change allows the instrument to operate only on the
milliohm ranges; the ohm ranges are inoperative.
Removethe chassis ground connection from pin 4 of T-l and pin 3 of J-1.
Then connect pin 3 of J-1 to pin 4 of T-l. In this way both the voltage
and current test Leads will be isolated from ground. (Fig. 5)
c
J-l
FIGlJF?E Modification
5. for unground chassis.
0273 7
OPERATION MCDEL503
2-18.ACCUBACY
CONSIDERATIONS:
1. MEASUFiEkKNT THE PRESENCE Ix: CUBBEETS: The 503 can measure re-
IN OF
sistance with dc currents present in the sample. Aninfluencing factor is
the amount of current that will saturate the voltmeter input transformer.
A 1% error in measurements, using milliohm range settings, will occur if
the dc current causes a 20 millivolt drop across the sample. The dc current
through the sample can be increased if a capacitor is put in series with
a voltmeter lead. The capacitor should be 10,000 ufd with a voltage rat-
ing greater than the dc current source voltage.
With measurements in the range from 1 ohm to 1000 ohms, a 1% error will
~cur if a current greater than 1 milliampere flows through the current
supply circuit. The voltmeter will not be effected unless the source volt-
age of the dc current exceeds 50 volts.
The dc sample current which will cause 1 ma to flow in the current supply
circuit may be computed from the sample resistance and the range resistor
in use.
2. INDUCTIVEANDCAPACITIVEEFFECTS: The Model 503 uses an ac measuring
system and synchronous demodulation to discriminate against 60 cycle pick-
up and to discriminate to a degree against reactive components in the sample.
Therefore, usually, no special precautions or shielding are necessary unless
the ac fields in the neighborhood of the sample are unusually strong. The
usual cause of trouble will be due to electro-magnetic induction. Electro-
static pick-up usually is no problem at the impedance involved. A good way
to test for pick-up is to remove the current leads and leave the voltage
leads attached to the ssmple. If no reading is seen, there is no cause of
concern. If, however, there is a reading, the source of magnetic field must
be removed or the sample oriented in such a way as to minimize the reading.
Because of the ac technique employed, inductive and capacitative components
in the test impedance may cause some wave-form distortion and erroneous
readings. In practice, it has been found that the following method will
enable the user to calculate errors introduced by inductance in series with
the sample or capacitance across it. ExperimentalJy it cm be shown that
the error due to a series inductance or shunting capacitance is equal to
about 50% of what would be calculated, assuming the shunting or series
effect was due to the impedance computed for a 40 cps sine wave.
In the presence of large interfering ac fields, some needle flutter will
be noted. This will be due to a beat between the 40 cps carrier frequency
and the signal. The average value of the pointer indication will be the cor-
rect reading unless the interfering signal is exactly equal in frequency to
the carrier. In this case large errors may be encountered. However,. since
a 40 cps interfering signal is rarely encountered, there will be little
likelihood of trouble.
Coupling between the current and voltage leads can cause significant error
on the 1 milliohm rage. This can be minimized by keeping the voltage and
current leads separated and by twisting the pairs of leads to reduce the
enclosed area.
8 0273
MODEL
503 OPERATION
3. ERRORS M SEFIIESRESISTANCE CUkWEN!T VOLTAGE
IUE IN AND LEADS: Series
resistance may be appreciable in such cases as resistivity profile measure-
ments, or when low resistance connections to the sample cannot be made.
(See Fig. 6)
Current Leads
FIGURE6. Series Resistance Measurements
The tabulated values will give no more thau 1% errc : in metsurement:
T0tsr.l. resistance
in voL~.age leads 2rv
2 1 ohm
Ohmrange settings 33x full scale range 1oK ohms
setting =l
0273 9
OPERATION MODEL
503
2-lV.PREPARATIONFORRACKMOUNTIEG. (See Figure 7.)
1. The Model 503 is shipped for bench use with four feet and a tilt-
bail. The Model 4CCCRack Mounting Kit converts the instrument to rack
mounting to the standard EIA (RETMA)1%Inch width.
Item Keithley
(See Figure 7.) Description Part No. Quantity
1 Cover Assembly M23~ 1
2 Cover Assembly, Bottom (Supplied 1kggOB 1
with Model 503)
Angle, Rack llc624B
z Screw, Phillips Head, lo-32 UEC- -- i
2x4 (Supplied with Model 503)
5 Front Panel (Supplied with Model -- 1
503)
TABLW4. Parts List for Model 4000 Rack Mounting Kit.
2. To convert the Model 503, remove the four Phillips head screws at
the bottom of each side of the instrument case. Lift off the top cover
assembly with the handles; save the four screws. To remove the feet and
tilt bail from the bottom cover assembly, turn the two screws near the back.
The two pawl-type fasteners will release the cover and allow.it to drop
off. Removethe feet and the tilt bail and replace the cover (2).
3. Attach the pairof rack angles (3) to the cabinet with the four
Phillips head screws (4) previously removed. Insert the top cover assembly
(1) in place and fasten to the chassis with.the two pawl-type fasteners
at the rear. Store the top cover with handles, feet and~tilt-bail for
future use.
10 0273
MODEL503 OPFJUl'ION
/o SCREW / "\ /@COVER ASSEMBLY
L
2 COVER ASSEMBLY
FIWJFiE7. Exploded View for Rack Mounting.
0273 11
CIRCUIT DESCRIPTION YODEL503
SECTION 3. CIRCUIT DESCRIPTION
The Model 503 circuit consista of four basic sections; a twelve volt auper-
regulated power supply, a trenaiator dc to ac inverter circuit, e four atege
high gain vecuum tube amplifier and e silicon diode demodulator.
The twelve volt power supply operates from the line voltage and furnishes a
very closely regulated 12 volts. This voltage is used to light the tube fila-
ments and to operate the transistor converter. The converter operates at &C
cpa. The output obtained from the converter transformer via various windings,
operates the demodulator diodes, supplies the 40 cps test current end the B-
plus supply for the ac amplifier via e rectifier-filter system.
The vacumn tube aqlifier operates following an input trensfor?ner on the milli-
ohm ranges and directly emplifiea the signel on the ohm ranges. A high degree
of gain stability is assured by a substantial feed-back factor and by the use
of cloiely reguleted pLate and filaxnent supplies.
The output of the amplifier is synchronously demodulated by a silicon diode
bridge end the resulting dc signal operates the output circuit and the meter.
D20l R 201
m I/vL c-IO.5 v
Ill& - 1 1
i 1
+1 c201 TO Q4
IIIEI- D202
. COLLECTOR
T t -.
0203
Figure 8. Power Supply Schematic Diagram
12 0273
MODEL 503 CIRCUIT DESCRIPTION
3-1. mwFa SUPPLY: (Fig. 8) The power supply consists of three parts:
1. THE AC FOWER TFMSFORMERANDFILTFR-RECTIFIERCIRCUITRY: Thepowertren-
aformer, T-2, may be connected for either 117 or 234 volt operation as indi-
cated in the schemetic. The secondaries of the trenafonner supply 18 volts
at 1 ampere and 117 volts at 5 ma. The output of the 18 volt winding is full-
wave rectified by DZO3end D204 end filtered by C202, C2O3 and A202. The
clc voltage developed across C2O3 is approximately 20 volts. Neither ter-
minal is grounded since the minus terminal of the regnletor is grounded at
the emitter terminal of Ql.
The output from the 117 v winding is half-wave rectified by D201 end filtered
by C201. R201 is a dropping resistor for zener diode D202. This diode is
connected between ground and the supply aide of the load resistor for tran-
sistor Qk. The purpose of this connection will be discussed below.
2. THE SUPRR-RFEULATRD VOLTSUPF'LYz (Fig. 9) The unregulated 20 volts
I.2
dc obtained from rectifiers and the transformer is applied to a solid state
regnletor consisting of QJ.through Q6 and D202, D2O5, end ~206. Q5 and Q6
form e differential amplifier which compares the voltage across the output
of the regnletor (C2O5 is &cross the output) via divider R210 end R2Ogto
the voltage supplied by sener reference diode D2O5. If the voltages at the
bases of Q5 and Q6 are not equal, the collector voltage of Q5 changes. This
change is further amplified by Q4, Q3 and Q2. The signal is finally applied
to the base of the series element in the regulator Ql. The aignel is always
of such megnitude and phase that output voltege is instantaneously brought
beclr to 12 volts. RF-14 is a forward biased diode which sets the emitter
voltage of Qk. The collector load resistor of Q4, R2O5, is returned to minus
10 volts supplied by sener, D202. This extra reguleted voltage permits Q4
ov> 1
R 206 207
1
C 205
3 R203 R204
R206 R209
E
+>
R205 t12v
-10.5>
Figure 9. Super Regulated 12 Volt Supply Schematic Diagram
0273 13
CIRCUIT.DESCRIPTION MODEL
503
to operate at much higher gain than if the collector load were returned
to the unregulated side of the supply and permits linear operation of
Q4 with widely varying input voltages. This connection makes an impor-
tant contribution to the performence of the power supply. Q3 and ~$2are
cascaded emitter followers whose function is to increase the current gain
of the series transistor, Ql. R203 and R204 are added to the circuit to
provide stability at high temperatures since they make available a back-
bias current equal to the leakage current of the series transistors at a
temperature of approxSmately &OC. C204 prevents high frequency oscilla-
tion of the power supply. The twelve volts at the output of the regula-
tor powers the filaments of Vl and V2 and the pilot Lamp E-1.
3. 40 CPS TRANSISMRSTATIC INVERTER CIRCUIT: (Fig. 10) A portion of
the regulated I2 volt power is also used as the supply for a dc converter
consisting of the following parts: Transformer T3, transistors Q7 and
Q8, diodes IX?07 and D208, capacitors ~206 and C207, and resistors R2ll,
Pi212 and R213. The operation is as follows: Transistors Q7 and Q8 are
connected across the 12 volt supply through their emitters and the center-
tap of the 12 volt winding of T3. The bases receive positive feed-back
from another winding on T3. The phasing is such that one transistor is
driven hard on while the other is cut off. This cycle lasts until the
core of T3 reaches saturation. At this point the transformer can no longer
keep the on transistor fully conducting and its collector current decrea-
ses. This causes the polarity of the feed-back winding to change and the
transistor which was cut off now conducts and the conducting transistor is
cut off. The frequency of oscillation is controlled by the transformer
constants. In this case the frequency was picked to be 40 cps. The ten
volts rms secondary winding is used to provide the test signal and pro-
vides a 20 volt peak-to-peak square-wave which is used with series re-
sistors RI28 through Rl39 to provide the proper test current for each
range. Diodes DlOl and D102 limit the output voltage when the current
leads are open circuited.
TEST CURRENT
SVJITCH
R213 +260
I _ Y
> I7
Figure 10. Test Current ,Generator Schematic Dlegrsm
14 0273
MODEL
503 CIRCUIT DESCRIPTION
The 270 volt Winding pmVideS a B+of 260 volts for the vacuum tube ampli-
fier. The signal is rectified by D207 and ~208 and filtered by C207 a and
b'and R213.
Since the stability of the converter circuit depends only on the stability
of the twelve volt power supply, very close regulation is obtained for all
potentials used in the circuit. Consequently line voltage variations from
100 to 130 volts have no effect on the instrument.
3-2.mTcm G-R: (Fig. 10) As mentioned above, the test current is
derived from the 10 volt winding of T-3. Since Q7 and. Q8 bottom on each half
cycle, the amplitude stability of the signal &pen& only on the 12 volt supply,
and is therefore as stable as the well-regulated I2 volt supply. The circuit
is not particularly critical as to frequency or wave-form. However, e nearly
Perfect square-wave is generated and the frequency is stable to better then a
few percent.
The current signal is varied to provide the change in range except between
300 milliohms and 1 ohm where the input transformer is removed from the cir-
cuit . The variation is accomplished by switching resistors ~128 through R139
with each current range. Rlti through ~142 are used in conjunction with RI28
to keep a constant load on the current source winding to insure a high order
of accuracy. Diodes DlOl and DlO2 limit the open-circuit voltage in the cur-
rent leads to plus or minus 0.5 volts.
3-3.!ciaAc VACDUM-mvom: (Fig. 11) On the Milliohm Renges the in-
put signal passes through transformer T-l. This transformer has approximate-
ly a 70:1 step-up ratio and improves the impedance match between the voltage
signal and the input grid by a factor of 5ooO:l. On the ohm ranges, where a
Larger signal is obtainable, the transformer is switched out so that its in-
put impedance will not shunt the resistance being measured. Accordingly, on
the Milliobm ranges, the input resistance is about 200 ohms. On the Ohms
ranges, the input resistance is one megohm.
The input signal is fed into qhe input of the amplifier either through Tl or
around it, depending on range, through Sl, the OPERATE-ZERO switch. This switch
is of the make-before-break variety to prevent switching transients. Follow-
ing the switch is C102, the input blocking capacitor and Rl.01, the input re-
sistor of the feed-back netwdrk. R102 connects the feed-back signal to the
input grid so that the input grid signal is the difference between the input
signal and the feed-back signal or, as it is usually termed, the error signal.
The error signal is amplified by a standard three stage ac amplifier consist-
ing of Vl and.V2a. V2b is an output cathode-follower which drives the feed-
back loop, Rll8, R143, RI& and RU5; and the meter and output circuits.
The gain of the smplifier is varied slightly to compensate for the absence or
presence of the input transformer by shunting RU.4'and Rl45 across R143 in
the Milliohm position. The MILLIOHM TRIM control is used to calibrate the
milliolnu ranges. The divided output of Rl18 and R143 through R145 is applied
to RlG2 and returned to the input, completing the feed-back loop. A feed-
back factor of 40 db assures high gain stability. The fact that all potentials
used in the smplifier are closely regulated, also helps assure a high degree
of gain stability and complete freedom from line bounce.
0273 15
CIRCUIT DESCRIPTION % MODEL 503
2
tu
>
ml
91 g
5 "T
FQur&ll. AC Amplifier Schematic Diagram 0273
16
MODEL 503 CIRCUIT DESCRIPTION
The amplifier is stabilized against low frequency oscillation by two sets
phase-advance interstage couplings, ~106, C105, R106 and R107 between the
two halves of Vl and by CllO, Clog, R1l.l and Rll2 between Vlb and V2a. Each
network introduces an appropriate attenuation and phase lead to prevent os-
cillation and give adequate phase margin. C104, R105; ~108; and Cl13 and
Rll6; are individual high-frequency oscillation stoppers.
3-4.!lXE SYNCHXONOUS DEMXLWICR, METERANDOlJTPDT: (Fig. 12) The output of
V2b is coupled through Cll5 and Rllg to a demodulator bridge circuit con-
sisting of D103 through DlO6. The bridge is driven through Rlk6 and R147 from
the collectors of Q7 and Q8. Since the center tap of the collector winding is
at ground, the drive signal is balanced to ground. When the junction of D103
and DlO5 is positive with respect to the junction of DlO4 and D106, the diodes
are conducting and the junction between Rllg and RI20 is effectively grounded.
When the polarity is reversed, the bridge is open circuited. Therefore, the
signal is rectified in this manner. The output travels through ~120, ~l21
and then is split. Part of the current drives the meter and the remainder
the output. RI21 is the calibration control. It is located on the front
panel. On the CAL position of the range switch, RI27 is switched in and
this potentiometer is used to correct the meter reading if necessary. RI25
allows calibration of the recorder terminal.
RI22 RI24
R Dl06
DIOS .L R
M
G II O-I
MA Rl2f
I T-
1
>-
A ZERO
T BAL A
TRANSISTOR TRANSISTOR
COLLECTOR COLLECTOR
ae at
Figure 12. Synchronous Demodulator Meter - Output
0273 17
SERVICING MODEL 503
SECTION 4. SERVICING
The Model 503 should not require periodic maintenance. Occasional
verification of the calibration (either section 2-14 or 4-2) and
the dc balance (zero balance) should reveal any need for adjustment.
If difficulty is encountered, read completely the following material:
4-1. Trouble Shooting Guide
Servicing is quite straight forward as the 503 employs only two
vacuum tubes and eight transistors, all of which are conservatively
operated within their ratings. No matched or critically selected
components are used.
The usual caution should be observed when soldering to the printed
circuit board as excessive heat will damage the board,
In servicing, bear in mind all operating voltages are obtained from
the 12 volt transistor regulator, either directly or through the
transistor inverter.
Reference should be made to Circuit Schematic DR 146280 for voltage
values and other circuit parameters.
In case of complete failure to operate, the fuse, line cord and
power source should all be checked. If these are all found satis-
factory, use the following detailed service procedure to isolate
the trouble:
1. POWERSUPPLY:
a. THE AC POWER TRANSFORMER AND FILTER RECTIFIER CIRCUITRY
(Figure 8): Set the RANGE SWITCH to the 3 milliohm posi-
tion with ZERO OPERATE switch in ZERO position. Remove
transistor Q-l from the circuit and measure the voltage
across C203. (See schematic notes for recommended type
VTVM). If approximately 25 volts dc is indicated, this
portion of the circuit is in proper working order. Note
that neither terminal of C203 is grounded.
Measure voltage across D202, which should be between -9
to -12 volts with respect to ground. If not, check
diodes D201 and D202.
b. THE SUPER REGULATED12 VOLT SUPPLY (See Figure 9): Re-
place transistor Q-l in the circuit. Determine that the
regulated 12 volts across C205 does not vary more than 5
mv with line voltages from 105 volts to 125 volts. Use
a variable autotransformer to supply the line voltage.
(General Radio Variac).
If no voltage is present or the 12 volts are not regu-
lated, check components in this portion of the circuit.
18 0577
MODEL
503 SWVICING
2. 40 CFS TRANSISTOR INVRRTER (Figure 10): .With the range switch
set at 3 milliohms, connect the current test leads to an oscillo-
scope. Observe a 40 cps square wave with a peak to peak amplitude
of about 20 volts. If thisis present, measdre +260 volts dc
across C2Op. If no square wave is observed, or the B+ is absent,
check the components in this portion of the circuit.
NOTE: FORSECTIONS AND 4 THE RANCE
3 SWITCHSHOULD IN CAL POSITION
BE
WITH THE Z,li'RO-OmD SWITCH THE OPERATE
IN POSITION.
3. THE AC VACUCM TUBEVOLIKZTER. (Figure 11): Be sure both vacuum
tube filaments are heated and the pilot lsmp is lit. Since the
pilot lamp is in parallel with the filament of Vl and the com-
bination is in series with the filament of V2 across the I2 volt
regulator, some service information is provided by its brilliance.
If it lights normally, .it may be assumed the supply is working
properly. If it is brighter than normal, Vl is probably burned
out. If the lamp is not lit, either V2 is burned out, or the
pilot itself is open. The instrument will operate without the
pilot lamp, but since the life of Vl will be reduced, it should
be replaced.
If it is determined the tubes are operating proper& proceed as
follows: Measure at the iunction of Cl02 and RlOl a 4 millivolt
peak to peak square wave. This indicates the test current is
properly reaching the amplifier through the range switch. Should
there be no signal, or one of improper magnitude. inspect the range
switch for faulty operati,>n or component failure.
Next, check the voli;age between pin 8 ,:f V2 and ground. This
should be a square wave voltage of abcu~t 10 volts peak to peak.
A distortion in/or absence o; this signal indicates a faulty
AC amplifier.
4. SYNCHRONOUS DRMCIXJLA~R METER
- OllTKlT (Figure 12): Connect an
oscilloscope to the ,Junction of !i.-119 and RI.20 and compare this
wave forn,with Figure 13.
Figure 13
A distortion or absence of this wave form Is an indication of a
faulty demodulator.
0273 19
SERVICING MODEL 503
4-3. CALIBRATION: The procedure of Section 2-14.calibrates the 503 on then
1000 range. Other ranges should be within specification once thisrange
is properly calibrated. If the user wishes to further verify the
CALIEGWPION, to calibrate for a given range or point, the following
or
procedures are reconunended:
1. OHMRANGES: A standard resistor of at least 0.05% accuracy is
reconrmended. ~T'hestandard should be selected to 3/4 of full scale
of range in question, or to the value of the measurement to be
made. The slotted control on the front panel will adjust the
meter needle for proper deflection.
2. MILLIOHMRWG~: To calibrate the milliohm ranges,. an appropriate
low value standard resistor is required. Leeds & Northrup Type
4221-B, 100 milliohms; Type 4222-B - 10 milliohms: and Type 4223-B,
1 milliohm are all suitable. Using one of these resistors or
their equivalent, adjust the "MILLIOHM CAL'" (Figure 14) for the
proper meter reading.
20 0273
MODEL 503 SERVICING
FIalm14. Model 503 Internal Component6 Tacations (Top Removed).
0273 21
R134
R137 rR133
7
.31
.R130
D102
\-R127
\ \
\ b129
REPLACEABLEPARTS MODEL 503
SECTION 5; REPLACEABLE PARTS
5-1. REPLACEABLEPARTS LIST. The Replaceable Parts List describes the com-
ponents of the Models 503 and 503C Milliohmmeters and 5031 Current and Voltage
Leads. The List gives the circuit designation, the part description, a sugges-
ted manufacturer, the manufacturer's part number and the Keithley Part Number.
The name and address of the manufacturers listed in the "$ffg, Code" column
are contained in Table 6.
5-2. 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)
must be ordered from Keithley Instruments, Inc. 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 Department, Keithley Instruments, Inc.
ampere Mfg. Manufacturer
MtF Metal Film
CbVar Carbon Variable Mil. No. Military Type Number
CerD Ceramic, Disc MY Mylar
Comp Composition
CompV Composition Variable R
DCb Deposited Carbon
P pica (10-l*)
EMC Electrolytic, metal cased
ETB Electrolytic, tubular P micro (10m6)
ETT Electrolytic, tantalum
V volt
f farad Var Variable
k kilo (103) w watt
ww Wirewound
M or meg mega (106) or megohms WWVar Wirewound Variable
m milli (10-3)
TABLE 5. Abbreviations and Symbols.
24 0273
MODEL 503 REPLACEABLEPARTS
MODELS 503, 503C REPLACEABLEPARTS LIST
(Refer to Schematic Diagram 14628D for circuit designations.)
CAPACITORS
Circuit Mfg. Mfg. Keithley
Desig. Value Rating TYPO Code Part No. Part No.
Cl01 .Ol vf 50 v MY 84411 601PE C41-.OlM
Cl02 0.1 pf 50 v MY 84411 601PE C41-O.lM
Cl03 100 pf 15 v ETB 72699 TDLOO-15 Cll-100M
Cl04 220 pf 1000 v CerD 72982 831X5R221K c22-22OP
Cl05 1 Kf 200 v MY 13050 107-21 C66-1M
Cl06 .005 pf 1000 " CerD 72982 81125V502P C22-.005M
Cl07 100 pf 15 v ETB 72699 TDlOO-15 Cll-100M
Cl08 .02 pf 1000 " CerD 72982 841Z5V203P C22-.02M
Cl09 1 {lf 200 v MY .13050 107-21 C66-1M
Cl10 .047 uf 200 v MY 14655 WMF2S47 C66-.047M
Cl11 100 pf 15 " ETB 7.2689 TDlOO-15 Cll-100M
Cl12 20 IJf 250 v ETB 56289 TVA1508 C27-20M
Cl13 .002 vf 1000 " CerD 72982 8OlZ5V202P C22-.002M
b114 270 pf 500 v Mica 84171 DM15-271J C21-270P
Cl15 10 pf 200 " PMC 72354 X10316 C69-10M
Cl16 56 jpf 6v ETT 05397 K56-J6KS C70-56M
Cl17 56 pf 6v ETT 05397 K56-J6KS C70-56M
c201 20 pf 250 v ETB 56289 TVA1508 C27-20M
c202 500 uf 50 " FNC 14655 AA0160 C57-500M
C203 500 I*f 50 v EMC 14655 AA0160 C57-500M
C204 .Ol i.Lf 1000 v CerD 72982 811Z5V103P C22-.OlM
C205 500 pf 25 v FM2 14655 AA0120 C58-500M
C206 0.22 pf 50 " MY 84411 601PE C41-0.22M
C207 40-40-2oKf 450 " ENC 56289 TVL3786 C33-40/40/20M
DIODES
Circuit Mfg. Keithley
Desig. TYPO Number Code Part No.
DlOl Rectifier, lA, 800V lN4006 MOT RF-38
Dl02 Rectifier, lA, 800V lN4006 MOT RF-38
D103 Silicon lN645 01295 RF-14
D104 Silicon lN645 01295 RF-14
D105 Silicon lN645 01295 RF-14
DlO6 Silicon lN645 01295 RF-14
D107 Silicon lN645 01295 RF-14
D201 Rectifier, lA, 800V lN4006 MOT RF-38
D202 ZCSX?r lN715 12954 DZ-22
0576 25
REPLACEABLEPARTS MODEL 503
DLOIIES (Cant ' d)
Circuit Mfg. Keithley
Desig. Type Number C0de Part No.
D203 Silicon lN1563A 04713 RF-19
D204 Silicon lN1563A 04713 RF-19
D205 ZellGX lN936 04713 DZ-5
D206 Silicon lN645 01295 RF-14
~207 Rectifier, lA, 800V 1~4006 MOT RF-38
D2Og Rectifier, lA, 800V 1~4006 MOT RF-38
D209 Silicon lN645 01295 RF-14
MISCELLANEOUSPARTS
Circuit Mfg. Keithley
Desig. Description Code Part No.
DS-1 Pilot Light Assembly, Red lens (Mfg.
No. 5100) 72765 PL-5R
--- Bulb, Miniature bayonet base (Mfg.
No. 47) 08804 PL-4
Fl (117 v) Fuse, 0.5 amp, (Mfg. No. 312.500) 75915 W-6
Fl (234 v) Fuse, 0.25 amp, (Mfg. No. 3120.25) 75915 FU-9
--- Fuse Holder (Mfg. No. 342012) 75915 FH-3
Jl Receptacle, VOLTAGE (Mfg. No. XLR-3-32) 71468 cs-71
52 Receptacle, CURRENT(Mfg. No. XLR-3-32) 71468 cs-71
--- Jacb, Mate of Jl and J2 (Mfg. No.
XLR-3-11C) 71468 CS-72
53 Receptacle, Microphone, OUTPUT
(Mfg. NO. 80PC2F) 02660 CS-32
--- Plug, Microphone, Mate of 53 (Mfg.
No. 80MC2M) 02660 cs-33
54 (c) Receptacle, Output (Mfg. No. 126-221) 02660 CS-81
J5 Cc) Same as 54, but does not have jumper
--- Plug, Mate of J4 and 55 (Mfg. No.
126-220) 02660 CS-82
Kl (c) Relay, SPDT 80164 RL-3
Ml (4 Meter ◦ Jabse Service Manual Search 2024 ◦ Jabse Pravopis ◦ onTap.bg ◦ Other service manual resources online : Fixya ◦ eServiceinfo