INSTRUCTION MANUAL
MODELS 15OA, 150AR
MICROVOLT-AMMETERS
WARRANTY
We warrant each of our products to. be free
from defects in material and workmanship. Our
obligation under this warranty is to repair or
replace any instrument or part thereof (except
tubes and batteries) which, within a year after
shipment, proves defective upon examination.
To exercise this warranty, contact your Keithley
field engineering representative. You will be
given assistance and shipping instructions.
REPAIRS AND RECALIBRATION
Keithley Instruments and its international dis-
tributors maintain complete repair facilities.
To insure prompt repair or recalibration service,
please contact your Keithley field representative
before returning the instrument.
Estimates for repairs, normal recalibrations,
and
calibrations traceable to the National Bureau of
Standards are available upon request.
MODEL 150A
CONTEXTS
TABLE OF CONTENTS
section Page
INTRODUCTION. . . 1-l D. Zero Suppression. . . . . .
I.
II.
III.
IV.
SPECIFICATIONS .
OPERATION . . 3-l
Operating Controls.
A.
Preliminary Set-up. 3-l
B.
General Precautions
C.
D.
Measuring Voltages. 3-3
Measuring Current . 3-3
E.
Other Applications. 3-3
F.
CIRCUIT DESCRIPTION
2-l
3-l
3-2
4-l
Section
Other Controls. . . . . 4-2
E.
Power Supply. . . . . . .
F.
MAINTENANCE. . . . . .
V.
Trouble-Shooting. . . . 5-l
Excessive Output Noise. . 5-l
Output Not Zero . 5-2
220-Volt Operation. . . 5-2
VI. REPLACEABLE PARTS . . . .
Models 150A,
150AR Replaceable
Parts List . . . .
Input Circuit , . .
A.
AC Amplifier. . .
B.
DC Amplifier. . . .
C.
4-l
4-l
4-l
Model 1501 Replaceable Parts
List............
Model 1502 Replaceable Parts
List............
Voltage Resistance Chart. . 6-9
Schematic Diagram 12188D.
Page
4-2
4-2
5-l
6-1
6-2
6-7
6-7
6-11
9~ Change Notice
* Yellow Change Notice sheet is included only for instrument modifications
affecting the Instruction Manual.
0764R
i
MODEL 150A
1NTR0lxlc!rI0n
SECTION I
- INTRODUCTION
The Model 150A Microvolt-Ammeter is a stable, versatile instrument
for measuring extremely low level DC signals. It functions as a
voltmeter from one microvolt to one volt full scale, and as an
ammeter from one milliampere to one hundred micro-microamperes
full scale.
It also operates as a DC amplifier with gains up to
ten million for driving recorders.
The very low noise level of the Model 150A, together with its long
term stability make it ideal for many measurements requiring extreme power sensitivity.
Typical applications include measuring the output from strain gages,
thermopiles, thermocouples, bolometers, phototubes, ionization chambers,
scintillation counters, and barrier layer cells. Other apnlications
are found in cell studies, measurement of electrochemical potentials,
electrolytic corrosion studies, molecular weight analysis and Hall
effect studies.
In addition to its use as a direct indicator of minute potentials
and currents, the Model 150A may also be used as a null detector in
Wheatstone or Mueller bridges,
or with an external voltage source as
a meg-megohmmeter.
An important feature of the instrument is zero supnression up to
100 times full scale,
in place of the usual more limited meter zero.
This permits measurements of small signals in the presence of large
thermal EMF's or other masking DC signals.
l-l
MDLRL 15OA
SPECIFICATIONS
SECTION II -
SPECIFICATIONS
VOLllvIETw sF%xxlxcATIoRS
RANCE.:
Thirteen overlapping ranges in lx and p steps from one micrcvolt
to one volt full scale on a zero-center meter.
ZERO AccuRAcy: 2% of full scale on all ranges.
STABILITY:
After one hour,
+O.lmicrovolt +2 x 1O-5 R microvolt drift per
day, where R is the source resistance in ohms.
NOISE:
nlicmvo1t m3). At various
With the input shorted, less than 0.03 microvolt peak-to-peak (0.006
cmrce
r&sistances, she noise peak-to-peak in
microvolts is given by E = 6.5 x lo- (R + ZOoO)~, since the Input resistance is added to R, the source resistance.
INFUT RHISTANCE:
Tabulated below; if input shunting resistors are requested,
the Input resistance is loo kilohms on MICROVOLT ranges and one megohm on
MILLIVOIiT rages.
maximum murce resistancea specified on the l- and 3microvolt ranges also hold with shunting input resistors.
RAliOE
Input Resistance
Max. Source Resistance
lmicrovolt
3 micrcvolts
10 microvolts
30 micrcvolts
loo microvolts and
1 megohm
3 megohms
10 megohms
30 megohms
90 megohms
10 kilohms
30Mlom
100 kilohms
300 kilohms
1 megohm
above
RESPONSE SPEE!D (1% to VC$ of final value):
With maximum specified source resistance,
except the l-microvolt range,
where it is within two seconds.
Depends on ~0urc.e resistance.
less than one second on all ranges
With source resistance less than l@ of the maximum, response is within 0.5
second, except on the l-microvolt range, where It is within one second.
VOLTAOE ZERO SUPPRE!SS: Ranges of lo, 100, loo0 and 10,OoO micmvoltS; and
0.1, 1, 10 and loo millivolts, corresponding to the MICROVOLTS and MILLIVOLlB
positions on the FUNCTION switch.
Accuracy of the buckout ranges Is about
2% and stability is such that 100 times full scale may be suppressed.
RANLIES:
ampere (10'
Fi
een overlapping rangee in IX and p steps from 0.1
in
smpere) to loo0 microamperes (10'3 ampere) on a zero-center
SIIIJA-~~C~-
meter.
STABILTPY: After one hour', 22 x lO-ll ampere per day.
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2-l
sPFCLF1cATI0NS
MODEL 15OA
NOISE:
Less than 2 x 10-12
ampere peak-to-peak.
ACCURACY: Within 3% of full scale on all ranges.
VOLTAGE DROP:
100 microvolts on the MILLI-MICRO
AlmZRES ranges, one millivolt
on the MICROAMFERES ranges.
INFVT RESISTANCE: On the MICRCAMPERES
ranges the input resistance is equal
to 10-3 divided bx&the range in amperes. On the MILLI-MICROAMPERES ranges
it is equal. to 10
RESPONSE SPEED:
divided by the range in amperes.
One second maximum, except on the 0.1~milli-microampere
range, where it Is two seconds maximum.
CURRENT ZERO swpREss:
Up to 100 full scales on any range. Accuracy and
stability are the same as for the voltage zero suppress.
GENERAL SPECIFICATIONS
ouTHl* +
-I.0 volts at five milliemper s for full-scale deflection on any range.
Gain of dc amplifier is from 10 to lG 7 .
OUTPUT RmT.sTANcE:
60 CFS REJ-EZTION:
Less than 10 dms within the emplifierpassbend.
Greater than
50:
1.
-LNHJl! ISOLATION:
Neg8tiVe
volts with respect to the case.
terminal may be grounded or floating up to +&JO
A link is provided for grounding the negative
terminal to the case.
CONNECTORS: Input: Special receptacle.
Rear Output: Amphenol 8GPC2F
Front Output (Model15OAR): Binding posts.
'IUBE COMPLEMENT: TWO
one 6~~6, one
TOWER:
Lo5-125
6084.
v0lt.s OP
~~86,
210-250
one 0~2, one l2~T'7, two 12~x7, one 12&A, one 5651,
Mlts,
special order.
AccEssoRIEs SUPPLIED:
Model 1501 Low Thensal Test Leads; a length of low-
thermal solder; mating output plug.
ACCESSORIES AVAILABLE:
DIMENSIONS: Model 15OA:
Model 15OAR:
NET WEIGRTz Model 150A:
Model 15OAR:
Model 1502 Low Thermal Connector Pair.
U.-l/6 inches high x 7$ inches wide x ,13* inches deep.
7 inches high x 19 inches wide x 13 inches deep.
20
pounds.
22
pounds.
receptacle.
50
watts, 60 CPS.
50-CPS
models on
2-2
0763~
I&XIEL 15OA
OFTRAl'ION
A. o- c0mR0J.s
The controls of the Modell5OA exe simple and conveniently placed.
Their functions are as follows:
ON switch is located to the right of the panel meter.
l?UICTION stitch selects the fkuction which is to be used: MILLI-
vom, MIcmvoLm, MICRORANGE switch selects the full scale multiplier of the function
selected by the IBJNUTION switch.
tions are to be used for CURRENT measurements only.
ZEIiU SUPPRESS controls consist of the zero RA!K$E switch, which
selects the coarse range of suppressing voltage in discreet steps
and the zero SET potentiometer,
fine control, including settings through zero.
B.
PBELrnY SET-UP
SECTION
III -
OPElRATION
or MILLI-MICROAMPERES.
Note that the .3 and .l posi-
which
gives continuously variable
Connect the instrument to the power line. Unless otherwise marked the
unit may be used on IL7 volt, 60 cps line. To convert to 220-volt
operation, refer to the MAINTENANCE section.
is furnished, which grouuds the cabiuet.
Athree-wire line cord
If a three-wire receptacle
is not available, use the two-pin adapter furuished, and ground the
third lead to e.n external ground.
Set controls as follows:
FlJfEIIION: MILLIVOLTS
RANGE: loo0
.zEm s-s: OFF
Inptl~
Short the input leads together.
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3-l
MDDEL 150A
GENERAL PRECAUTIONS
C.
Source Resistance - In SECTION II - SPECIFICATIONS un-
1.
der INRJT RESISTANCE, the maximum source resistance for use with
each voltage range is specified. Reasonable operation is possible
with source resistance up to ten times greater than those specified;
however, the measurement will suffer from a considerable decrease in
speed of response, and measuring accuracy. If the instrument is
left completely open-circuited, the meter will generally drift off
scale on any voltage range. On current ranges this does not happen
because of the input shunting resistors.
Shielding - Since the instrument operates with a modulator fre-
2.
quency of 120 cps, it is no% generally sensitive to 60 cps pickup
unless it is large enough to overload the amplifier.
may be a source of difficulty when using the amplifier with high
impedances on the more sensitive voltage ranges and on the two or
three most sensitive current ranges. In these cases it is desirable
to shield the leads and the sources as completely as possible. In
some cases a simple low-pass filter at the input to eliminate fre-
quencies of about 1 cps and above will be helpful. No use is made
of an input filter in this instrument, since any input series impedance due to the filter will increase the input noise and the thermal
drift.
be grounded.
When operating above ground, the case of the instrument must
The pickup
Thermal E&iF - Extreme precautions have been taken in the input
3.
circuit to minimize thermal EMF's so that the residual EMF is less
than 0.6 microvolt.
copper. Any other metal will generate a thermocouple potential.
Lead solder is particularly troublesome.
a problem,
supplied with the instrument.
Input Noise:
Ir.
resistance and is approximately given by
where E is the rms noise,
assumed that the bandwidth of the instrument is about 1 cps and the
temperature is SOoF.
noise and compare results.
resistors approach the ideal resistor.
manganin resistors are used,a considerable thermal EMF of the re-
sistor material against copper will be observed.
Checking the Zero Point - At low levels, spurious E&W's may be
5.
generated simply by contact between the input leads and the terminals
under test.
adjust the zero after establishing a zero reference in the apparatus
under test.
bridge exciting voltage; or with a phototube, shield the tube from
light.
soldering should be done with the cadmium-tin solder
If possible,
For example,
'Ihe material used in the input circuit is pure
Where thermal EMF's are
The noise at the input is a function of input
E q 1.29 x lo-lo (R+2000)$
and R is the source resistance.
If noise is observed,
Also bear in mind that only wire-wound
always leave the instrument connected and
in bridge measurements, disconnect the
calculate the theoretica
However, if Evanohm or
It is
3-2
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