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MODEL `150
and
MODEL l5OR
' .
DC MICRO VOLT-AMMETER
INSTRUCTION MANUAL
KEITHLEY INSTRUMENTS, INC. "`1,
CLEVELAND, OHIO
SECTION
INTRODUCTLON . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..I.....
. 1 .'
SPECIl~ICA~IONS .,.,..*..*............**.........**.... II
OPJ3RATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. III
A. Operating Controls
B. Preliminary Set-up
C. General Precautions
1. source Reoistance
2. Shielding '
3. Thermal EMF
4. Input Noise
5. Checking the Zero Point
D. Meaouring Voltage
1. Direct Moaswement
2. Small varib.tions
3. Differential Voltages
E. Measuring Current
1. Dire& 14oasurcment
2. Small Variations
F. Other Applications
1. Null Indicutor
2. Megohmwter
CIRCUIT DESCRIPTION .,*............*.,*.,.,........... Iv
A. Input Circuit
B. AC Amplifier
C. DC Amplifier
D. Zero Supprension
E. Other Controls;
F. Power Supply
,,,,,..........*.......*,..*...,.......**.
MAINTENANCE V
General Notes
Trouble Shooting
Volta&c-Renistance Diagram
Circuit Schematic Diagram
Replaceable Parts List
SECTION I - INTRODUCTION
The Model 150 Micro Volt-Ammeter is a stable, versatile instrument
for measuring extremely low level DC signaln. It functions a6 a
voltmeter i9`om one microvolt to one volt full scale, and as an
ammeter from one milliampere to one hundred micro-microampere8
full scale., It aloo opcratev as a DC amplifier with gains up to
ten million for driving recordertl.
The very low noise level of the Model 150, together with ite long
term stability rrake it ideal for many meaouromcnto requiring c;:-
treme power nensitivity.
Typical applications include mca,suring the output from strain gages,
thermopilos, thermocouples, bolometers, phototubes, ionization chanlbtirs,
oclntillation countors, and barrier layer cells. Other applications
are found in cell studies, measurement of electrochemical potcn-cials,
electrolytic corrosion studies, molecular weight analysis and Hall
effect studies.
In addition to its use as a direct indicator of minute potentialo
and currents, the Mod01 150 may also be used as a null detec~tor In
Wheatstone or Mueller bridges, or with an external voltage source
ao a meg-me&ohmmeter. .
An important feature of the inritrument is zero supprenoion up to
100 times full scale, in place of the usual more limitod~ meter zero.
This permits measurements of small oignala in the presence of large
thermal EMF's or other masking DC signals.
I -1
SXTION II - SFXIFICATIOPIS
VOLTXTX~ SrPECIFICATIONS
RANGES: 13 overlapping ranges in lx and 3x sI;cps from 1
microvolt to 1 volt full wale on n zero-cqnt.cr mster.
Zl microvolt + 2 x lo-5 R o~icrovolts per day, -&rc i7 Is
the sourcerasiotancc in ohms.
NOISE : b!ith the input shdrted, less than 0.03 !?!.crovolt
peak to peak (0.006 microvolt RW). At variol+s source
impcdlances the noiw is given by E = 6.5 Y IO-+ (II +
2000); microvolts peak-to-peak since the ohmic input
reoistanco is added to R, the source resisfence.
_.
`2ccuRAcY: 25 of full scale on all rsngco.
INPUT AhTDSOURCERXSISTANCE: As tabulated bclov unless
resistors shunting ths input are requested, in which
case the input resistance i3 1OOK on the micrcvclt rxgcc
and 1 megohm on tho millivolt rangee. The rw~xilwn sowcc
res-lstanco specificatisns on the 1 and 3 n:crovolt ranges
hold with or without shuntine input resistance.
.
RANGE: Input Resistance Maximum
Greater thsn Source Hssistanca
1 microvolt 1 me&ohm 10~ ohms
3 microvolts 3 megohms 30~ ohms
10 microvolts 10 megohms 1OOk ohms
30 microvolts 30 megohms 300k ohms
100 microvolts 90 megohms 1 megohm
and above
F?ESPONSE SPEED: (10 to p@$ of full scale.). With maximum
specified source resistance, less than one second on all
ranges except the 1 microvolt renge whore it is two seconds.
b!ith source resistances less than 10% of maximw source
resistnnco, response io within 0.5 second on all ranges,
except the 1 microvolt range where it is within 1 second.
.I1 -1
VOLTAGE ZERO SUPPRESS: Rnngos, Off, plllo or minus 10, 100,
lOQ0 and 10,000 microvolto; and 0.1, 1.0, 10.0, 100.0
m~~l.:~vo.ltn corresponding to tho MICROVOLTS and MILLI-
VOLTS positions on tho function switch. Thu accuracy
of the oupproooion rangco 1s approximately 2C$ and the
stability is such that 100 times full scale may be
suppressed.
RANGES: 15 overlapping ranges in lx and 3x steps frown lo-lo
to 10-3 ampere full scale on a zero center meter.
STARILITY: After one hour warm-up, within plus or minlui 2 x
lo-11 ampere per day.
NOISE: Less than 2 x lo-12 ampere peak to peak.
ACCURACY: Plus or minus 3% of full scale on all rangon. '
VOLTAGE DROP: 100 microvolts on the millimicroampero ranges,
1 millivolt on the microampere ranges.
INPIJP RESISTANCE: Equal to 1 x 10m4 divided by current range
on microamperes. (Input resistance on the 10-j range Is
one ohm, rising to one megohm on the 10-l' ampere range).
RESPONSESEZD : 'One second except on the 10-l' range vhere
-.i it is two seconds.
CURlGNT ZERO SUPPRESS: A maximum of 100 times full scale zero
suppression on any range. Accuracy and stability are tho
same as for voltage zcrc suppress.
GENERAL SFECIFICAT';IONS
RECORDEROUTPUT: Plus or minIA 10 volts at five milliamperes
for full-scale deflection on any range.
OUTPUT IMPEDANCE: Less than 10 ohms belou 1 cps.
60 ~7.5 RFJECTION: Greater than 5O:l.
INPU!I' ISOLATION: Negative terminal may be grounded or floating
up to plus or minus 400 volts with respect to the case.
A link is provided for grounding the negatlvo terminal to
the case.
POWERREQUIREMWI'S: 11-f/230 volts, 30 watts, 60 cps only.
50 cps mod&s on special order.
II - 2
SECTION III - OPERATION
A. OPI?RATII:G COF!TROI.S
The controlo of the Modal 150 are simple and conveniently
placed. 'Their functions are as follo7m:
ON-OFF svitch is located to the right of the panel
motor.
FUNCTION switch selacto the function which is to be
used; millivolts, microvolts, ;r.icromporco or
mlllimicroampores.
RANGX switch selects the full scale c!ultiplier of
the function selected by the FUNCTI@N switch. __
Noto that the 0.3 and 0.1 positions are to be
used in current measurement only.
ZERO SUPPRESS controls consist of the ZERO IiANCX
switch which selects the course range of sup-
pressing voltage in discreet steps and the ZERO
SET potentiometer which gives continuously
variable fine control including settings through
zero I .
B. PREIJMINAPY SST-UP
Connect the instrument to the power line. Unless othcrvioc
marked the unit nay be used on 117 volt, 60 cps line. TO
convert to 220-volt operation, refer t0 the MAINTZ?!ANCE coctioll.
A three-wire line cord is furnished, which grounds the cabinet.
If a three-wire receptacle is not available, use tho two-pin
adapter furnished, and ground the third lead to an external
ground.
Set controls as follows:
Function: Millivolts
Range: 1000
Zero suppress: OFF
Input: Short the inputloads together.
III - 1
C. GmmAL PRlVzAIJTIOIIS
1. Source Xesistanco - In SL'CTLON II - SPECIPlCATIOMS under XPU'I'
AND SOURCE RE3IS?fJICE, the maximum source rcsistancc for uuo wit!,
each voltage range is opecifi.ed. Reasonable operation is Pcssi~b1.o
with source resistances up to ten times gcater than thcso s;jeci-
fied, however the measurement will surfer from a considerable dc-
crease in speed of response, and measuring accuracy. If the instru-
ment is, left completely open-circuited, the meter >:ill Cc.ncra1l.y
drift off scale on any voltage range. On current ranges ihis does
not happen bocauso of the input ohuntinC resistors.
2. Shielding - Since the instrument operates with a mo3~~lo.t~ fx-
quoncy of 120 cps, it is not generally sensitive to 60 cpn pickup
unless it is large enough to overload the amplifier. The pickup :n;y
be a source of difficulty when using the amplifier \Tith high imPeri-
axes ox the more sensitive voltage rzngcs and on the t-.zo or three
most sensitive current ranges. In these cases it is desirable to
shiold,thc leads and the source 3s completely as possible. In ooiae
cases a simple low-pass filter at the input to eliminate frec,uoncies
of about 1 cps and above will be helpi'ul. No use is made of an inout
filter in this instrument since any input series impcdxince 13.x to :he
filter will increase the input noise and the thermal drift. When o,p-
eratine above ground, the case of the instrument must be Croundcd.
3. Thermal EKF - Extreme precautions have been taken in the input
circuit to minimize thermal EMF's so that the residual FXF is less
than 0.6 microvolt. The material used in the input circuit is pure
copper. Any other metal will generat a thermoco)u?le potential.
Load solder is perticularly troublesome. lihero thermal EXF's are a
problem, soldering should be done with the cadmium-tin solder supplied
with the instrunont.
4. Input Noise: The noise at the input is a function of input re-
sistance and is approximately given by
E = 1.29 x 10-10 (R+2000)$
where E Is the IWS noise, and R is the source resistance. It Is as-
sumed that the bandwidth of the instrument is about 1 cps and the
temperature is 80