Keithley 153 Service manual
INSTRUCTION MANUAL
MODEL 153
MICROVOLT-AMMETER
@COPYRIGHT 1974
J+ZEITHLEY INSTRUMENTS. INC.
CONTENTS
MODEL 153
SECTION
SPfTCIFICATIONS __-_-_____---__________________--
GENERAL DESCRIPTION _____--______-______----
1.
(-,pE~TION _______-__---______---------------
2.
APPLICATIONS __-______-__-_______-----------
3.
CIRCUIT DESCRIPTION ___-_______________-----
4.
SERVICING __-_____-___________-------------
5.
C&IBuTION _--_________--________--__-_---
6.
ACCESSORIES -_--___________--_______________
7.
REpuCpygjLE PARTS -------------------------
8.
SCHpJ.fATIC _____-_______-__-------------------
PAGE
iv
3
12
13
17
23
33
37
45
1174
MODEL 153
ILLLlSTRATIO!&
ILLUSTRATIONS
'i . Vo . .
Title
1 Model 153 Front Panel. ______________-_-_-_------------------2
Front pane1 Controls. -______----_---___--_----------------------
3 Rear panel Terminals. --___----_________--_____---------------_4 Thermal Sink Construction. _--___-_______-_____------------------
5 Using Model 153 with 4-Terminal Connections. ----_--------__-----
6
Null Circuit and Leeds and Northrup K3 Potentiometer. ----------7 Diagram Showing Currents in Solid State Circuits. --------------8 Circuit for Semiconductor Resistivity Measurements. ----- -------9 Model 153 Block Diagram. ____-___-___________________________
10 Wave Form at Junction of Diodes D301 and 0302. ----------------11
Wave Form at Junction of Resistor R302 and Capacitor C302B.
12 Wave Form at -13 Volt Supply. __--____________---_---------------13 Divider Connection for Multivibrator Frequency Adjustment. ------14 Wave Form of Multivibrator Output. --------------------------
15
lb
17
Wave Form for Tuned Multivibrator Output Across Resistor R121. ---
Wave Form for Input Modulator ElOl.
----------------------------
Demodulator Wave Form for Full-Scale Input on l-Volt Range.
18 Typical Model 153 Drift Chart. _____-_-_____-___-__----------19
20 Model 153 Inter&,=. __-_______--______-___----------------------21
22
23
24
25
26
27
28
29
30
31
32
33
Model 153 Interior. ----__--------_-_--------------------------
Capacitor, Tube, Battery, and Modulator Locations on PC-lob. -----
Resistor Locations on Printed Circuit Board PC-lob. ---- - ----- --
Component Locations for Printed Circuit Board PC-107.
_--_____Component Locations on Model 153 Rear Chassis Panel. ---- ----- -Component Locations on Range Switch Sl.
component Locations on Range Switch Sl.
-_------__------------_____-______-_-___-_---
Component Locations for Model 153 Power Supply and Multivibrator.
Keithley Instruments Model 1531 Gripping Probe. -_--_---_-e-s-Keithley Instruments Model 1532 Test Leads. ----___-----------Keithley Instruments Model 1533 Mating Connector. -------------Model 1483 Low-Thermal Connection Kit. _____-______________---Keithley Instruments Model 6012 Triaxial-to-Coaxial Adapter. _---Exploded View of Model 4005 Rack Mounting
Kit. ___-_____-____----
------
-----
Pap*
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1174
iii
SPECIFICATIONS
MODEL 153
KEITHLEY INSTRUMENTS.
INSTRUCTION MANUAL
CHANGE NOTICE
MODEL 153 MICROVOLT-AMMETER
INTRODUCTION: Since Keithley Instruments is continually improving pro-
duct performance and reliability, it is often necessary to make changes
to Instruction Manuals to reflect these improvements. Also, errors in
Instruction Manuals occasionally occur that require changes. Sometimes,
due to printing lead time and shipping requirements, we can't get these
changes immediately into printed Manuals. The following new change in-
formation is supplied as a supplement to this Manual in order to provide
the user with the latest improvements and corrections in the shortest
possible time.
to a Manual to minimize user error.
cated
Page 41, Replaceable Parts, Resistors should read as follows:
R172
R173
Pages 38 s 39, Replaceable Parts, Diodes, should read as follows:
D303
D304
in italics.
9.9kn O.l%, 1/3w w
100 n
Rectifier, l.OA, 8OOV lN4006
Rectifier, l.OA, 6OOV IN4006
Many users will transfer this change information directly
All changes or additions are indi-
O-l%, 1/3w w
15909
15909 1250-100R
1250-9.9KR
R-110-9.9??
R-110-100
MOT RF-38
MOT RF-38
I LN c.
22
22
27
27
MODEL 153
GENERAL DESCRIPTIO1i
SECTION 1.
l-l. GENIZAL.
The Keithley Model 153 Microvolt-Ammeter is a versatile dc instrument with high inp,:t
a.
impedance and low noise for measuring a wide range of voltages and currents.
ranyes are from 5 microvolts full scale to 1000 volts, and its current ranges are from
?l
lo-
scales.
higher ranges to ?3% of full scale on the 10 and 30-microvolt ranges.
current ranges varies from +2% of full scale on the 3 x 10v9
24% of full scale on the 3 x lo-11 ampere and lower ranges.
tance for the lo-microvolt range is 20 megohms. If a lower resistance is wanted, a front
panel switch control allows shunting a 2-megohm resistor across the input.
0.06 microvolt rms. In ut noise on the most sensitive current range with the input open
is less than 0.1 x lo-
ampere full scale to 0.1 ampere.
Accuracy for the voltage ranges varies from 21% of full scale on the 3-millivolt a-.?
b.
Input resistance is 200 megohms for the l-millivolt and higher ranges. Input resis-
c.
Input noise on the most sensitive voltage range with the input shorted is less thar.
d.
13
ampere rms.
GENERAL DESCRIPTION
Its voltage
The Model 153 has zero-center and zero-left meter
Accuracy for tjle
ampere and higher ranges to
1-2.
Line frequency rejection is good; a power line or twice power line frequency which is 40 db
(p-:~“c) greater than full scale affects readings less than 0.5%. Isolation greater than
10') -..,~s from ground permits use in floating circuits.
a:: .in ammeter varies from 1 megohm on the lo-L1 ampere range to 1 ohm on the O.l-ampere
range. Voltage drop varies from 10 microvolts to 100 millivolts, depending upon the
range used.
on any range. The l-milliampere capability permits use with recording galvanometers.
Output resistance is less than 10 ohms with the output potentiometer set for maximum out-
put.
l-3. APPLICATIONS.
as contact potentials, vacuum tube electrode potentials,
electro-chemical potentials, and power supply voltages.
with various voltage generating transducers such as piezo-electric generators, Hall effect
generators and strain gauges.
FEATURES.
The Model 153 has excellent resolution for potentiometric null detector applications.
a.
h
The Model 153 uses the voltage drop method to measure currents.
Recorder output is fl volt dc at up to 1 milliampere for full-scale meter deflection
=.
Drift is less than +2 microvolts per 24 hours.
As a voltmeter, the Model 153 is ideal for measuring a wide variety of voltages such
a.
biologically generated emf's,
Other applications include use
Input resistance
The Model 153 is also ideal for most null detector applications.
b.
sensitive ranges, power sensitivity is better than 5 x lo-21 wtt.
~iloating capability make the Model 153 an ideal null detector for any bridge or potentio-
meter.
1174
On the three most
High ac rejection and
1
I
GENERAL DESCRIPTION
MODEL 153
2
FIGURE 1,
Model 153 Front Panel.
1174
MODEL 153
OPERATION
SECTION 2. OPERATION
2-1. FRONT PANEL CONTROLS AND TERNINALS.
a. METER Switch. The METER Switch has four positions. POWER OFF shuts off the in-
strument; this also short circuits the meter,
ment.
for center zero operation (lower meter scales).
b.
and one for current inputs. In the VOLTS INPUT R-2M position,
proximately 2 megohms.
mum for the range being used.
tions as an ammeter.
c.
one of 17 voltage and 21 current ranges.
to full-scale deflection for the range selected with the RANGE Switch.
METER + and METER - determine meter polarity.
FUNCTION Switch. The FUNCTION Switch has three positions, two for voltage inputs
In the VOLTS R-OPEN position, input resistance is at the maxi-
(See Table 1.) In the AMPS position, the Model 153 func-
RANGE Switch. The RANGE Switch selects the full-scale instrument sensitivity for
allowing accurate mechanical zero adjust-
CENTER ZERO sets the instrument
input resistance is ap-
The 10 or 3 of the top meter scale corresponds
d. ZERO Control.
20 microvolts,
higher ranges use a 1OOO:l divider,
range.
e. INPUT Receptacle. The INPUT Receptacle is a Teflon-insulated Triaxial type con-
nector. Its center terminal is the circuit high; the inner shield is circuit low (circuit ground); the outer shield is chassis ground.
2-2.
a. DC OUTPUT ADJ Control.
Both the output
from 0 to 1.05 volts; output resistance varies to 7.5 kilohme maximum.
b. Output Binding Posts.
f;r case ground; LO is circuit ground; HI is the output connection.
!-:: link is for connecting the LO Post to the G Post.
C. 117-234 Switch. The screwdriver-operated slide switch sets the Model 153 for 117
or 234-volt ac power lines.
d.
210-250 volt operation, use a l/4 ampere, 3 AG Slow Blow fuse.
It has much less effect on other ranges.
REAR PANEL CONTROLS AND TERMINALS.
FUSE. For 105-125 volt operation, use a l/2 ampere, 3 AG Slow Blow fuse.
so it is most effective on the microvolt ranges. Since the II-volt and
voltage
The ZERO Control allows precise meter zeroing. Its range is about
the Control is also somewhat effective on the 3-volt
This Control sets the amplitude of the output voltage.
and reszstance vary wxtn the control setting. Voltage span is
Three posts are used for the l-volt recorder output. G is
The furnished short-
For
e. Power Cord. The 3-wire power cord with the NEMA approved 3-prong plug provides a
ground connection for the cabinet. An adapter for operation from 2-terminal outputs is
provided.
NOTE
The Model 153 INPUT Receptacle is a Triaxial connector.
nect bnc-type connectors to it may damage both.
1174
Any attempt to con-
3
OPERATION
MODEL 153
FUNCTION
SWITCH -
(S1)
INPUT
RECEPTACLE-
(Jl)
-MECHANICAL
ZERO
METER
-SWITCH
.(S3)
ZERO
-CONTROL
(R155)
I I
RANGE SWITCH
(S2)
FIGURE 2.
Front Panel Controls.
I
MODEL 153
OPERATION
- ..-. ,.
3
FIGURE 3.
Rear Panel Terminals.
OPERATION MODEL 153
2-3. PRELIMINARY PROCEDURES.
Check the 117-234 Switch and the Fuse for the proper ac line voltage.
a.
Set the controls as follows:
b.
METER Switch
POWER OFF
RANGE Switch 1 VOLT
FUNCTION Switch
Check meter zero.
Connect the power cord and set the METER Switch to +.
C.
If necessary,
needle should be at zero with the input shorted.
VOLTS INPUT R-2M
adjust with the meter mechanical zero.
If the meter is not exactly at zero
with the input shorted after approximately 20 minutes,
tentiometer, R125 for exact meter zero.
(See paragraph 5-5.) For maximum accuracy, al-
low the Model 153 to warm up approximately 30 minutes.
To cancel any zero offset,
d.
Adjust the front panel ZERO Control.
ty.
2-4.
for all ranges,
VOLTAGE MEASUREMENTS.
Voltage measurements can be made with either of two input resistances:
a.
or a higher resistance, from 20 megohms to 200 megohms depending upon
short the input high to low and reduce
the range.
Generally, it is better to use the higher input resistance (obtained by setting
1.
the FUNCTION Switch to VOLTS OPEN).
To maintain the accuracy of measurements, the input resistance should be 100 times the source resistance.
resistance by ranges.
Within one minute, the
meter
adjust the internal BIAS ADJ Po-
meter
sensitivi-
2 megohms
(See Table l-l for input
With the higher input resistance,
2.
open due to extraneous sisal pickup.
soma meter deflection may occur with the input
To reduce this pickup and also to speed recovery
from input overloads when measuring low impedance sources, use the 2:megohm input resistance (obtained by setting the FIJNCTION Switch to VOLTS (R-2M).
Connect the voltage source to the INPDT Receptacle. Use properly shielded and
b.
grounded leads. Refer to paragraphs 2-8 and following for suggestions and cautions.
Set the RANGE Switch to the highest voltage range. Turn the METER Switch to CENTER
c.
ZERO for the correct polarity for the input signal. Increase the Model 153 sensitivity
until the meter shows the greatest on-scale deflection.
On the 3-volt and higher ranges,
the Model 153 will withstand overloads to 1000 volts without damage. On the lower ranges,
momentary overloads to 1000 volts will cause only temporary instability and zero offset.
Prolonged overloads will damage components and cause increased noise and slower response
speeds.
I
6
1174
MODEL 153
OPERATION
TABLE 1.
and Maximum Current Overload by Ranges.
Model 153 Voltage Input Resistances and Current Input Resistance, Voltage Drop
Maximum Current Overload is tllc p,r~'atcst curr~p.t
for the ralli;e xliich will not damage tliti range resistor.
vo1tag e
Range
Inpur Rcsistancc current Input
:~tll FLTC'rION
Renfie
Resistance
Voltage
Drop GUI-rent
..:itcll sft to
OPEN
R-211
10 microvolts -20 Mu -1.8 M. 10 picoamps 1 M. 10
,I"
(milliampcr:
30 micro\~i,lts -50 M -1.9 x 30 picoamps 1 ?1 30 ,.v 0 . i
100 microi~olts -200 hl~ -2 El 100 picoamps 1 T.1 100 ,:v 0.5
300 microvolts -200 )I. -2 Mu 300 picoamps 1 bl, 300 ;i" 0 . 5
1 millivolt -200 M -2 M 1 nanoamp 1 hl 1 m\ 0.5
3 millivolts -200 K -2 M. 3 nanoamps 1 x 3 rn" 0.5
10 millivolts -200 M. -2 M. 10 nanoamps 1 Mu 10 mv 0.5
30 millivolts -200 Mu -2 MY 30 nanoamps 100 k:~ 3 mv 1.6
100 millivolts -200 Mu -2 M. 100 nanoamps 100 k~. 10 mv 1.6
300 millivolts -700 Mu -2 M' 300 nanoamps 10 k:: 3 mv 5
1 volt
-200
i
M:
-2 M? 1 microamp 10 k:. 10 mv 5
3 volts 200 MT -2 MC 3 microamps 1 kl. 3 rn" 16
10 volts 200 M: -2 MS 10 microamps 1 k:: 10 mv 16
30 volts 200 Mu: -2 I-Ii: 30 microamps 100 1. 3 mv 50
Maximum
Overload
0.5
100 volts 200 M: -2 w 100 microamps 100 :. 10 mv 50
300 volts 200 M1 -2 Ml? 300 microamps 10 1. 3 mv 160
1000 volts 200 M? -2 I% 1 milliamp 10 7. 10 mv 160
3 milliamps -1 n 3 mv 500
10 milliamps -1 R 10 mv 500
X rnil.~icatupS 21 R 30 mv 500
100 milliamps -1 r! 100 mv 500
2-5. CURRENT MEASUREMENTS.
Set the FUNCTION Switch to AMPS. Select the range using the
RANGE Switch. Make sure low resistance leads are used to connect the source to the Model
153 input to minimize input voltage drop.
Refer to Table 1 for the voltage drop by ranges
and for the maximum allowable current overload which will not damage the instrument. On
all ranges momentary overloads will only cause temporary zero offset end instability.
Prolonged overloads exceeding the values in Table 1 may damage the current-sensing resistars.
2-6.
line ground,
FMATING OPERATION
a. The Model 153 can be connected Qetween two potentials,
It
can be floated up to -500 volts off ground.
neither of which is at powr
Triaxial connectors are
especially useful when operating the low terminal at a different potential from the ground
terminal.
1174
7
OPERATING INSTRUCTIONS
For best results with floating operation, follow the steps below:
b.
Remove the shorting link from the LO or GND Post on the rear panel.
1.
Connect the unknown source to the Model 153, connecting the lowest impedance
2.
paint to the input low.
corders used with this operation,
grounded.
Operate as described inparagraph 2-4.
since the low of the Model 153 output is no longer
MODEL 153
Do not ground any re-
Use triaxial cable and connectors for floating operation.
3.
A complete outer shield
protects the operator.
4. Make sure the chassis is grounded.
Use the G Post on the rear panel or the ground
pin of the power cord.
2-7. RECORDER OUTPUT.
Model 153 output for full-scale meter deflection on any range is adjustable from 0
a.
to *1.05 volts at up to 1 milliampere.
Output polarity is positive. Output resistance
is less than 10 ohms with the DC OUTPUT ADJ Control set for maximum output; resistance varies
with the Control setting to 7.5 kilohms maximum.
If the Model 153 is used for floating
measurements, do not ground the recorder connected to the output.
When recording with the Model 153 "se the Keithley Model 370 Recorder. The output
b.
of the Model 153 is sufficient to drive the Model 370 without the "se of any recorder
preamplifiers. The Model 370 allows maximum capability of the Model 153.
It has 1% line-
arity, 10 chart speeds and can float up to ?500 volts off ground. Using the Model 370
with the Model 153 avoids interface problems which may be encountered between a measuring
instrument and a recorder.
To "se the Model 370 with the Model 153 connect the high and low binding posts on
c.
the Model 153 rear panel to the sama posts on the Model 370.
if differential measurements are being made.
Adjust the easily accessible Calibration
Do not ground the Model 370
Control on the Model 370 for full-scale recorder deflection.
2-8.
INPUT CONNECTIONS.
a. The Model 153 INPUT Receptacle is a triaxial type; its mating connector is the
Keithley Model 1533.
For input leads to the Model 153, Keithley Instruments, Inc., has
the Model 1534 Special Low-Thermal Triax Cable which can be connected directly to the
Model 1533 Connector.
The Connector is made to acconrmodate the 0.145-inch outer diameter
of the Cable.
b. For best connections to the input,
Section 7.
This will enable the Model 153 to be used under the best conditions.
use the accessory probes and leads described in
Other
considerations for making sure the Model 153 is properly connected are listed in the
following paragraphs.
c.
Carefully shield the input connection and the source being measured.
shielding is thorough,
any alteration in the electrostatic field near the input circuitry
Unless the
will cause definite meter disturbances.
8
1174
MODEL 153
OPERATING INSTRUCTIOXS
d. Use high resistance,
low-noise materials - such as Teflon (recommended), polyethy-
lene or polystyrene - for insulation. The insulation leakage resistance of leads shx*Jld
be greater than 500 megohms to maintain the Model 153 input resistance.
age reduces the accuracy of readings from high impedance sources.
the cable must also be high:
tween shields.
The Model 1534 Cable meets these requirements.
1000 volts center conductor to inner shield; 500 volts be-
Voltage breai:d3jm of
Triasial cables used
Excessive lea;:-
should be a low-noise type which employ a graphite or other conductive coating brt!ieen
the dielectric and the surrounding shield braid.
e. Any change in the capacitance of the measuring circuit to ground will cause extran-
eous disturbances.
For instance, cable flexture changes the cable capacitance and thus
affects meter readings. Make the measuring setup as rigid as possible and tie down connec-
ting cables to prevent their movement. If a continuous vibration is present, it may appear at the output as a sinusoidal signal and other precautions may be necessary to iso-
late the instrument and the connecting cable from the vibration.
f. For low impedance measurements, unshielded leads and the Model 6012 Adapter ma)
be used.
Since the circuit low and ground are connected with the Adapter, do not
use
it
for off-ground measurements.
NOTE
Keithley Instruments, Inc., has several booklets available on low voltage measurements and low current high resistance measurements. A list is available from
Keithley Instruments, Inc., or its representative.
2-V. ACCURACY CONSIDERATIONS. For sensitive measurements - 100 millivolts and below -
other considerations besides the instrument affect accuracy.
Effects not noticeable when
working with higher voltages are very important with microvolt signals. The Model 153
only reads the signal received at its input; therefore,
it is important that this signal
be properly transmitted from the source. The following paragraphs indicate factors which
affect accuracy: thermal emf's,
2-10.
THERMAL EMF'S.
Thermal emf's (thermo-electric potentials) are generated by thermal gradients be-
a.
tween any two junctions of dissimilar metals.
shielding and circuit connections.
These can be significatn compared to the
signals which the Model 153 can measure.
Thermal emf's can cause the following problems:
b.
Metal instability or zero offset much higher than normal.
1.
Note, though, the
Model 153 may have some offset (paragraph 2-3).
Meter is very sensitive to ambient temperature
2.
VariStiOnS.
ing the circuit, by putting a heat source near the circuit,
instability,
corresponding to heating and air conditioning systems or changes in sun-
or by a regular pattern of
This is seen by touch-
light.
1174
9
OPERATING INSTRUCTIONS
To minimize the drift caused by thermal emf's, use the same metal or metals having
c.
low thermo-electric powers in the input circuit.
have thermo-electric
ture difference of
emf of 2.5 microvolts.
owers within about *0.25 wv/'C of copper.
1
C between one of these metals and copper will generate a thermal
10
At the other extreme, germanium has a thermo-electric power of
Gold, silver and low-thermal solder
This means even a tempera'-
about 320 uv/°C, and silicon will develop about 420 pv/oC against copper.
handbooks contain tables of thermo-electric powers of materials.
circuit is of copper, the best juntion is copper to copper.
However, copper oxide in the
Since the Model 153 input
MODEL 153
Standard physical
junction or differences in processing of two pieces of copper can cause thermal emf's Of up
to 0.2 microvolt oer oC.
The Model 1483 Kit contains all necessary equipment to make
low-thermal joints. See Section
7.
very
d. Maintaining constant temperatures
F?pf ~~5~%~~~~~~:~~~~~d~~~~~~~~ Es
and similar sources which vary temperature.
Minimize thermal gradients by-placing all
junctions physically close on a large heat
sink.
with a non-metallic abrasive such as Scotch
Brite before making a connection. Crimp to-
gether the ends of each copper wire; bolt
the lugs for each connection point together;
mount all stacks of lugs on a thick metal
plate having high thermal conductivity.
Thermal conductivity between the junctions
and the heat sink can be kept at a high
level by using mica washers or high conduc-
tivity ceramics for electrical insulation.
the effects of thermal emf's. Use only
cadmium-tin low-thermal solder (Model conductivity.
1503), such as supplied in the Model 1483
Kit, for soldered connections. Unlike
metals controlled oil bath or a good heat sink is used.
the thermoelectric power of the materials in the junction and the temperature difference
between the junctions.
Thoroughly clean all copper leads
Several other techniques will reduce
e.
including regular solder
FIGURE 4.
Thermal Sink Construction.
Connect leads or lugs as close as possible.
Separate only with insulation of high heat
- may be used and low thermal emf's obtained if a wellThermal voltages may be calculated from
2-11. SHIELDING.
Generally, the Model 153 is insensitive to ac voltages superimposed upon a dc signal
a.
at the input terminals.
signal can cause erroneous readings.
apparatus in the measurement circuit together and ground at one point.
However, ac voltages which are very large compared with the dc
Usually it is sufficient to connect the cases of all
This provides a
"tree" configuration, which minimize ground loops. Also floating the instrument (para-
graph 2-6) will minimize ground loops.
The connnon point at which all shields are connect-
ed should be as near as possible to the circuit low of the Model 153 at its input.
Improper shielding can cause the Model 153 to react in one or more of the following
b.
ways :
10
1174
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