Keithley 197 Service manual
Instruction Manual
Model
197
Autoranging Microvolt
DMM
0
Keit hley Instruments, Inc.
Cleveland,
Document Number 197-901-01
Ohio,
U.S.A.
DC
VOLTS
RANGE LUTION RESISTANCE 22'-24"C 18"-28'C
-
200mV
2V
20
200
loo0
*Relative to calibration accuracy.
NMRR:
Greater than 6OdB at
MAXIMUM ALLOWABLE INPUT:
minute on the 200mV and 2V ranges; 300V rms continuous).
SETTLING TIME
dB
MODE
0.OldB above
TRMS
RANGE 50Hz* 1OkHz' 20kHz'
200mV
2V - 200V
~ ~~~ ~~ ~ ~ ~ ~~~
750V
'Above
1800
MAXIMUM ALLOWABLE INPUT:
minute on 200mV and 2V ranges, 300V
3dB
BANDWIDTH:
INPUT IMPEDANCE:
1.1MR
paralleled by 75pF on
SETTLING TIME:
dB
MODE
RANGE INPUT lOkHz 20kHz 50kHz 100kHz
2V - 750V 200mV to 750
200mV 20mV to 200mV 0.18
RESOLUTION:
DC
AMPS
RANGE RESOLUTION
200 uA
2mA lOnA 0.3V
20mA 100nA 0.3V
200mA
2000mA
10
"Above 5A derate
*'When properly rereod.
OVERLOAD PROTECTION: mA
10A
Input: 20A for
SETTLING TIME:
TRMS
AC
RANGE BURDEN ZOHz
200pA - 20mA 0.3V
200mA 0.3V
2ooOmA
10
*Above 1800 counts. "1kHz max. Above 5A derate
SETTLING TIME:
RESO- INPUT 24
1
V
V
v
10
100
1
rV
pV
pV
ImV
OmV
>iGR
>
1GR
iiMR
1OMR
1OMR
"When properly zeroed.
50Hz.
60Hz
lO00V
1
second to within 3 counts of final reading
(ref:
ma):
Accuracy: &(0.02dB+I count) above -78dBm. Resolution:
0.5%
of range
"OLTsACCURACY (1
2OHz-
1.00+100
1.00+700
1.25+100
*'Above
counts.
3JOkHr typical.
1MR paralleled by less than 75pF
1
second to within
(ref: 600R):
Yr.)
50Hz-
0.35+100
0.35+100
0.75+100 1.0+200 1.8+250 3+400
18000
counts.
750V
rms,
rms
200mV,
2V and 2OV ranges. Capacitively coupled.
0.1
%
20Hz- 10kHz- 20kHz- 5OkHz-
V
(-
12 to 59.8dBmj
(-32 tn -12dBmj
2mV to 20mV
(-52 to -32dBm)
1mVto 2mV 2.00 3.00
(-58 to -52dBm)
0.OldB above 0.5% of range.
1
nA
1
PA 0.3V 0.2
10
A
pA
100
pA 0.3V 0.75+15'
0.15%
rdg per amp for self-heating.
15s.
unfused.
1
second to within 3 count5 of final reading.
0.18
0.85
MAXIMUM ACCURACY
VOLTAGE 18"-28'C
BURDEN
Input: 2A fuse (250V), externally accessible.
AMPS
MAXIMUM 18'-28"c
VOLTAGE
A 0.3V
0.8V
1
second to within
-
50Hz 50Hz - lOkHz 10kHz - 30kHz
1.0+100
l.O+IOO
1
OflW
1.5+100**
0.1%
*0.1%.
dc
or
18"-28"C
lOkHz
0.6+200
0.6+200
IOOOV
continuous). lO'V*Hr maximum.
of final reading on range.
ACCURACY
0.3V
0.8V
ACCURACY
of final reading.
ACCURACY
*(%rdg+counts)
Hr.,*
0.007+2 0.016+3
0
005+2 0.011+2
0
m6+2 0.015+2
0.006+2 0.015+2
0.007+2 0.015+2
peak ac (less than
on
range.
~~
*(%rdg+counts)
20kHz - 50kHz-
-
50kHz'* 100kHz"
1.5+250 5+400
1.5+250 3+400
peak (less than
on
200V and 750V ranges.
(
+-dBm)
0.18 0.28
0.18
1.10
0.8+100
08+100
08+100
1.0+100'*
0.15%
0.28 0.65
2.00
-
*(%rdg+counts)
0.1
0.1
0.1
0.2 +I5
(1
Yr.)*
+(%rdg+counts)
rdglamp for self-heating.
10
+15'*
+I5
+I5
+I5
**
1 Yr.,
seconds per
10
seconds per
0.50
~
-
(1
Yr.)
2 + 250
-
-
-
OHMS
RANGE
200
n
2 kR*
20 kQ lOOmR 400pA 4.0V 0.014+2 0.026+2
200 kR*
2MR"
20MR"'
200MR**
'When properly zeroed.
CONFIGURATION:
MAXIMUM ALLOWABLE INPUT:
rms
continuous.
OPEN-CIRCUIT VOLTAGE:
DIODE TEST:
nominal.
SETTLING TIME:
RESO- NOMINAL ACROSS 24 HI.. 1
LUTION I-SHORT
1mR
1OmR
1
R
10
n
100
R
10
kR
'*Appropriate range selected automatically in MR.
Automatic 2-
Display reads junction voltage
2 seconds to within 3 counts of final reading on range.
OUTPUT
MAX
v
ACCURACY
~
?(%rdg+counts)
UNKNOWN 22 -24°C 18
2mA
2mA 4.0
40pA 4.0V 0.014+2 0.026+2
4
aA
400nA 4.0V
400
nA
or
4-terminal.
450V dc
+5V.
or
peak ac
05V
4.0V
5.0V
up
001
V
0.01
0.02 +2 0.035+2
0.10
2.00
10
seconds per minute. 350V
to 2.2V Test Current: 1.6mA
+2' 002 +3'
+2 0 018+2
+2 0.12 +2
+1
2.00
Yr.
-28°C
GENERAL
DISPLAY:
RANGING:
RELATIVE:
DATA LOGGER
CONVERSION RATE:
OVERRANGE INDICATION: "OL"
CREST FACTOR
MAXIMUM COMMON MODE VOLTAGE:
COMMON MODE REJECTION RATIO (1kR
TEMPERATURE COEFFICIENT (Oo-lS0C & 28 -50-C):
ENVIRONMENT:
WARMUP:
POWER:
DIMENSIONS, WEIGHT:
ACCESSORIES SUPPLIED:
ACCESSORIES AVAILABLE:
*220,oo0 count LCD.
indication.
dc amps
Model
Model 1017:
Model 1301: Temperature Probe
Model 1600A. High Voltage Probe
Model 1641
Model 1651: 50-Ampere Current Shunt
Model
Model 1682A: RF Probe
Model 1684:
Model
Model 1751: Safety Test Leads
Model 1754:
Model 1972:
Model 1973: IEEE-488 Interface
Model 1978: Rechargeable Battery Pack
Model 7008-3: IEEE-488 Digital Cable (3
Model 7008-6: IEEE-488 Digital Cable
Model 8573.
Auto
or
manual
made with respect to baseline value Front panel annunciator indicates REL mode.
six selectable rates from 3 readingslsecond to
ing. Also detects and stores maximum and minimum readings continuously while
data logger mode.
SOHr, 6OHz
accuracy specification)/'C.
linearily derate 3% RH/"C, 35"-50"c. Storage: -25' to 60-C.
50-60Hz,
in.
I'ushbutton allows zeroing of
and
MIN/MAX:
(ratio
+0.1%.
Operating: O"-5O0C; less than
1
hour to rated accuracy.
105-125V or 210-25OV (external switch selected).
12V.A. Optional 5-hour battery pack, Model 1978.
X
10%
in.). Net weight 1.8kg
Single Rack Mounting Kit
1010:
Dual Rack Mounting Kit
Kelvin Test Lead Set
:
Clip-On Test Lead Set
1681:
Hard Shell Carrying Case
1685:
Clamp-On Ac Probe
Universal Test Lead Kit
IEEE-488 with Analog Output
IEEE-488 Interface for IBM
(use with 1972l3)
0.45
in. height; polarity, function, range. and status
on
dc volts, ac volts, and ohms: manual on ac amps and
on
range readings. Allows readings to be
100
reading storage capacity: records data at one of
1
reading;hour
3 readings/second.
of
Greater than 6OdB in ac volts.
displayed.
peak value to rms value),
89mm high X 235mm wide X 275mm deep (31 2 in.
Model 1751 safety te5t leads, instruction manual.
500V
peak
unbalance): Greater than 12OdB at dc,
80%
(3
Ibs., 14
OL
1.
ft
)
(6
it.)
IT
or
by manual trigger-
AC FUNCTIONS:
*
(0.1
X
applicable one year
relative humidity up to 35'C:
90-llOV
3.
available;
+1
X
in
91
4
Specifications subject to change without notice
TABLE
OF
CONTENTS
SECTION 1-GENERAL INFORMATION
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
1.10
2.1
2.2
2.3
2.3.1
2.3.2
2.3.3
2.4
2.4.1
2.4.2
2.4.3
2.4.4
2.5
2.6
2.6.1
2.6.2
2.6.3
2.7
2.7.1
2.7.2
2.7.3
2.7.4
2.7.5
2.7.6
2.7.7
2.7.8
2.7.9
2.7.10
2.7.11
2.7.12
2.8
2.8.1
2.8.2
2.8.3
2.8.4
Introduction
Features
Warranty Information
ManualAddenda
Safety Symbols and Terms.
...
Specifications
Unpacking and Inspection
Using the Model
Initial Operation
Accessories
...........
..............................................
....
......................................
..............................
.........................................
.
197
Manual
... ................................................................
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.............................
......................................................
......................................................
......................................................
SECTION 2-BENCH OPERATION
Introduction
High Energy Circuit Safety Precautions
Preparation For Use
LinePower
BatteryPackPower
Battery Charging.
Front Panel Familiarization
Display
Front Panel Controls
Input Terminals
Current Fuse Replace
ErrorMessages
Operating Conditions.
Environmental Conditions
Maximum Allowable Inputs
WarmUp
Basic Bench Measurements
PowerUp
Relative Mode
TRMS
Microvolt Measurement Considerations
Resistance Measurements
Current Measurements (DC or TRMS
AC Plus
dB Measurements
dB Measurements Considerations and Applicatio
MIN/MAX and
Diode Test
TRMS
AC
Voltage Offset
TRMS
CrestFactor
Extended Frequency Response
....................
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.....
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....................................
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..................................
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...
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...
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......................................................
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................
......................................................
......................................................
................................
..............................
...........................................
................................
ent
..................
AC
Voltage Measurements
..............................
......................
AC)
DC
Measurements
..............
100
Point Data Logger Operatio
....................
Considerations
.............
Measurement Comparison
.........................................
..........
.
......................................................
.......................
..........
..........
.................
.........
.....................
...........................................
......................
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......
...........
...........................................
...............
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..................
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..................
.....................
..................
......................
......................
....................
....................
..........
........
..........
..........
..........
.........
......
1-1
1-1
1-1
1-1
1-1
1-2
1-2
1-2
1-2
2-1
2-1
2-1
2-1
2-2
2-2
2-2
2-2
2-3
2-3
2-3
2-4
2-4
2-4
2-4
2-4
2-4
2-5
2-5
2-6
2-6
2-7
2-8
2-9
2-10
2-13
2-14
2-14
2-14
2-14
i
SECTION
3-
PERFORMANCE VERIFICATION
3.1
3.2
3.3
3.4
3.5
3.5.1
3.5.2
3.5.3
3.5.4
3.5.5
4.1
4.2
4.3
4.3.1
4.3.2
4.3.3
4.3.4
4.3.5
4.3.6
4.4
4.4.1
4.4.2
4.4.3
4.4.4
4.5
4.6
4.7
Introduction
Environment itions
Recommended Test Equipment
Initial Conditions
..
Verification Procedure
DC Voltage Accuracy Check
AC Voltage Accuracy Check
Resistance Accuracy Check
DC Current Accuracy Check
AC Current Accuracy Check
........................................................
......
..................
.............................
........
..................... ............................
...........
............
...........
.............
.................................................
..................................................
SECTION 4-THEORY OF OPERATION
Introduction
Overall Functional Description
Analog Circuitry.
Multiplexer
Input Buffer Amplifier
AC Converter
PIA
Display Board
Digital Calibration
Model
..................................................
........................................................
........................
................................................
.......
.....
.................................................
.................................................
.....
......................
1978
Battery Option
. . ......................................................
.................................................
......................................................
.......................................................
...
............................
...................
............................
.....................................
.......................
..................................
.............
.....................................
................
........................
...........................
............................
......
...........................................
........................
.................
3-1
3-1
3-1
3-1
3-2
3-2
3-3
3-5
4-1
4-1
4-1
4-1
4-1
4-1
4-1
4-4
4-5
4-5
4-5
4-6
4-6
4-6
4-7
5.1
5.2
5.3
5.4
5.5
5.5.1
5.5.2
5.6
5.6.1
5.6.2
5.6.3
5.6.4
5.6.5
5.6.6
5.6.7
5.6.8
5.7
5.7.1
5.7.2
5.7.3
-___
ii
SECTION 5-MAINTENANCE
Introduction
Top Cover Removal/Installation
Battery Pack (Model
Line Voltage Selection
Fuse Replacement
Line Fuse Replacement
Current Fuse Replacement
Front Panel Calibration
Recommended Calibration Equipment
Environmental Conditions
Calibration Jumper
DC Voltage Calibration
AC Voltage Calibration
Frequency Compensation.
Resistance Calibration
Calibration Storage
Troubleshooting
PowerUpSequence
Self Diagnostic Program
Power Supply and Battery Pack (Model
....................................
1978)
Installation
...................
.................................................
....
....................................
.
.................
...........................................
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............................................. ............
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.......................................
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...................................
......................................
........................................
.......................................
1978)
Checks
......................................
............................
.............................
....
....................
........................
.......
...............
...................
..........
5-1
5-1
5-1
5-2
5-2
5-2
5-2
5-4
5-4
5-4
5-4
5-5
5-5
5-5
5-7
5-7
5-8
5-8
5-8
5-9
ild
5.7.4
5.7.5
5.8
A/D Converter and Display
Signal Conditioning
.......................
Special Handling of Static Sensitive Devices
................
.....
SECTION 6-REPLACEABLE PARTS
.......
.......
.......
......................
......................
......................
...
......
......
...
....
......
5-9
5-9
5-9
6.1
6.2
6.3
6.4
6.5
Introduction
Replaceable Parts
Ordering Information
Factory Service
..............................
..........................
.......................
............................
.......
..
......
..
......
..
......
Schematic Diagrams and Component Location Drawings
......................
..
......................
..
......................
..
......................
..
.........................
...
..
...
...
...
..
........
...
......
......
......
....
6-1
6-1
6-1
6-1
6-1
...
Ill
LIST
OF
TABLES
2-1
2-2
2-3
2-4
2-5
2-6
2-7
3-1
3-2
3-3
3-4
3-5
3-6
5-1
5-2
5-3
5-4
5-5
5-6
5-7
5-8
5-9
5-10
ErrorMessages
Model 197 Maximum Allowable Inputs
Resistance Range Output Values
dB Specification for DC Volts (600fl Ref)
dB Specification for AC Volts (600fl Ref)
Levels for Other Reference Impedances
Comparison of Average and
Recommended Test Equipment
Limits for DC Voltage Verification
Limits for AC Voltage Verification
Limits for Resistance Verification
Limits for DC Current Verification
Limits for AC Current Verification
Recommended Calibration Equipment
DC Voltage Calibration
ACVoltageCalibration
Resistance Calibration
Recommended Troubleshooting Equipment
Model 197 Troubleshooting Mode
.........................................................
.......
..........................................................
............................. ................
..................................................
...................................................
TRMS
...............................................
.................................................................
................................................
Meter Readings
...........................................................
..............
........................................................
................................................
............
........................................................
.....................................................
.................................................
.....................................
Power Supply and Battery Pack (Model 1978) Checks
DisplayBoardChecks
A/D Converter Checks
Model 197 Static Sensitive Devices
.................................................................
...............................
.......................................................
.........
.................................
......................................
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....
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........
..........
........
.......................................
..............
2-4
2-5
2-8
2-10
2-11
2-12
2-15
3-1
3-2
3-3
3-3
3-4
3-6
5-4
5-5
5-6
5-7
5-8
5-10
5-12
5-12
5-13
5-13
6-1
6-2
6-3
Model197PartsList
Display Board. Parts List
....................................................................
................................................................
Model 1978 Battery Pack. Parts List
.......................................................
6-3
6-6
6-6
iv
LIST
OF
ILLUSTRATIONS
2-1
2-2
2-3
2 -4
2-5
2-6
2-7
2-8
2-9
3-1
3-2
3-3
3-4
3-5
3-6
3-7
3-8
4-1
4-2
4-3
4-4
4-5
4-6
Model 197 Front Panel
DC Voltage Measurements
TRMS AC Voltage Measurements
Two Terminal Resistance Measurement
Four Terminal Resistance Measurement
Four Terminal Zeroing
Current Measurements Between 2
Current Measurements up to 2000mA
Typical ACV Frequency Response
Connections for
Connections for ACV Verification
Connections for 200, 2k and 20k Range
Connections
for
Connections for DC Current Verification (200pA to 2000mA)
Connections for DC Current Verification (2000mA to 20A)
Connections for AC Current Verification (200pA to 2000mA)
Connections for AC Current Verification (2OOOmA to 10A)
Simplified Block Diagram
JFET Multiplexer
Simplified Schematic of the Input Buffer Amplifier
.......................
...................
........................................................
.................................
.................................
.... ....................
....
DCV
.........
Verification
.........................................
.........
.......................................................
...
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................................
...
...............................
200k through MU Ranges Verification (2-Terminal)
..................................
...................................
..................................
...................................
....
............
........................................................
........................................................
..........................................
............................
Input Configuration During 2- and 4-Terminal Resistance Measurements
Resistance Measurement Simplified Circuit
A/D Converter
...........
.................................................
................................................
....................
..................
..................
........................
2-2
2-6
2-7
2-9
2-9
2-9
2-10
2-10
2-15
3-2
3-3
3-4
3-4
3-5
3-5
3-6
3-6
4-2
4-3
4-3
4-4
4-5
4-6
5-1
5-2
5-3
5-4
5-5
5-6
5
-7
6-1
6-2
6-3
6-4
6-5
6-6
6-7
Model
DCI
197
I<TJ~:II
ON
Miscellaneous Parts
REVISION
C
........
....
DC Voltage Calibration Configuration
AC Voltage Calibration Configuration
.................................................
................................................
...................................................
...................................................
200, 2k and 20k Four Wire Resistance Calibration
200k. 2M and 20M
Segment Identification
Display Assembly, Exploded View
Model 1978 Battery Pack, Compone
Two
Wire Resistance Calibratic
...............................
................................................
ion Drawing, Dwg
Mother Board, Component Location Drawing, Dwg
Display Board, Component Location Drawing, Dwg
Mother Board, Schematic Diagram, Dwg
Display Board, Schematic Diagram, Dwg
.
No
.
.
No
197-106
.
197-116
Model 1978 Battery Pack, Schematic Diagram, Dwg
.
.
.
No
No
No
.
197-100
.
197-110
......
.....
.
1978-106
...........
.............................
.
No
.
1978-100
............
.............................
................
.............................
......
..........
...............
. .
.................
...
.........
.......
5-3
5-5
5-5
5-7
5-7
3-7
5-9
6-1
6-7
6-11
6-13
6-15
6-17
vlvi
SAFETY
PRECAUTIONS
The following safety precautions should be observed before operating the Model
This instrument is intended for use by qualified personnel who recognize shock hazards and are familiar with the
safety precautions required to avoid possible injury. Read over the manual carefully before operating this instrument.
Exercise extreme caution when a shock hazard is present at the instrument's input. The American National Stan-
dards Institue (ANSI) states that a shock hazard exists when voltage levels greater than 30V rms
present.
measuring.
Inspect the test leads for possible wear, cracks or breaks before each use.
leads that have the same measure of safety as those supplied with the instrument.
For optimum safety do not touch the test leads or the instrument while power is applied to the circuit under test.
Turn the power off and discharge all capacitors, before connecting or disconnecting the instrument. Always
disconnect all unused test leads from the instrument.
Do
line (earth) ground. Always make measurements with dry hands while standing on a dry, insulated surface,
capable
A
good safety practice is to expect that a hazardous voltage
not touch any object which could provide a current path to the common side of the circuit under test or power
of
withstanding the voltage being measured.
is
present in any unknown circuit before
If
any defects are found, replace with test
197.
or
42.4V peak are
Exercise extreme safety when testing high energy power circuits (AC line
tion.
Do
not exceed the instrument's maximum allowable input as defined in the specifications and operation section.
or
mains, etc). Refer to the operation sec-
SECTION
GENERAL INFORMATION
1.1
INTRODUCTION
The Model 197 is a six function,
autoranging digital multimeter with a
(Liquid Crystal Display). This
normal +-199,999 count
5%
The
voltage from 1pV/count to
measurements are standard in the Model 197. TRMS ACV
capability ranges from IpVlcount to
measures resistance from 1mQ to 220MQ on seven resistance
ranges. The Model 197 has six current ranges that measure
current from 1nA (lO-9A) to 10A.
digit resolution allows the Model 197 to measure
A/D
A/D
used in many
1OOOV.
5?h
digit resolution
+-220,000
range is greater than the
count LCD
5?h
digit DMMs.
DC
AC
voltage and current
750V.
The Model 197
1
6.
5%
Digit Resolution-The Model 197 has a +220,000
count A/D that surpasses the more common k199,999
count A/D.
Four
7.
8.
1.3
Terminal Ohms-These terminals are used to
eliminate the voltage drop across the current carrying
leads.
Sensitivity-The Model 197 has 1pV, ImQ and 1nA sensitivity. The IpV of sensitivity allows minute levels of offset, temperature etc. A 1nA sensitivity allows low current
measurements without special equipment. Measure
leakage, bias and offset current. A ImQ sensitivity allows
easy low resistance measurements.
WARRANTY INFORMATION
The dB function makes
of readings into a much smaller scope. The Model 197 dBm
measurements are referenced to the standard
but can be modified with the use of relative
The Model 197 has two IEEE-488 interface options: The
Model 1972 and the Model 1973. These optional interfaces
enhance the capabilties of the Model 197 by allowing programmed control over the IEEE-488 bus. The Model 1972 also
includes an analog output. The bus commands are the same
for each interface and respond to IEEE-488 protocol.
1.2
FEATURES
The Model 197 includes the following features:
Six Measurement Functions-DCV, ACV, DCA, ACA,
1.
OHMS
(REL) Relative Mode-The relative mode allows offsets to
2.
be nulled out (e.g. test lead resistance for low resistance
measurements) and selects a variety of reference impedances for dB measurements.
Digital Calibration-A non-volatile
3.
tion constants and can be performed from the front panel
or
Data Logger-A data storage buffer is included to allow
4.
up to
internally stored at a user selectable rate. The buffer may
be read and controlled from the front panel
IEEE-488 bus. In the talk-only mode, the output rate can
also be programmed.
Autoranging-The Model 197 includes a fast autoranging
5.
feature for easier measurements.
and dB all built in.
over the IEEE-488 bus.
100
readings and minimum/maximum readings be
it
possible to compress a large range
600Q
impedance
(REL)
feature.
RAM
stores calibra-
or
over the
Warranty information may be found on the inside front cover
of this manual. Should
warranty, contact your Keithley representative
to determine the proper course of action. Keithley Instruments maintains service facilities in the United States,
United Kingdom and throughout Europe. Information con-
cerning the application, operation
ment may be directed to the applications engineer at any of
these locations. Check the inside front cover for addresses.
1.4
MANUAL ADDENDA
Information concerning improvements or changes to this instrument which occur after the printing
found on an addendum sheet included with this manual. Be
sure to review these changes before attempting to operate
service the instrument.
1.5
SAFETY SYMBOLS AND TERMS
The following safety symbols and terms are used in this
manual or found on the Model 197.
The symbol
refer to the operating instructions in this manual.
The symbol &n the instrument denotes that a potential
1OOOV
of
ard safety practices should be observed when such dangerous
levels are encountered.
A
or
more may be present on the terminal(s). Stand-
it
become necesary to exercise the
or
the factory
or
service of your instru-
of
this manual will be
or
on the instrument denotes the user should
1-1
The
WARNING
that could result in personal injury
The
CAUTION
that could damage the instrument.
heading used in this manual explain dangers
heading used in this manual explain hazards
or
death.
NOTE
The Models 1973 and 1972 IEEE-488 interfaces
come supplied with their own instruction
manual.
1.9 INITIAL OPERATION
1.6 SPECIFICATIONS
Detailed Model 197 specifications may be found preceding
the table of contents of this manual.
1.7 UNPACKING AND INSPECTION
The Model 197 Autoranging Microvolt DMM was carefully
inspected, both electrically and mechanically before shipment. Upon receiving the instrument, carefully unpack all
items from the shipping carton and check for any obvious
signs of physical damage that may have occurred during transit. Report any damage to the shipping agent. Retain and use
the original packing materials in case reshipment is necessary.
The following items are shipped with every Model 197 order:
Model 197 Autoranging DMM
Model 197 Instruction Manual
Model 1751 Safety Shrouded Test Leads
Additional accessories as ordered.
If
an additional instruction manual is required, order the
manual package (Keithley Part Number 197-901-00). The
manual package includes an instruction manual and any applicable addenda.
1.8 USING THE MODEL 197 MANUAL
This manual contains information necessary for operating
and servicing the Model 197 Autoranging Microvolt DMM
and the Model 1978 Rechargeable Battery Pack. The informa-
tion is divided into the following sections.
1.
Section 2 contains detailed bench operation information
for the Model 197.
2. Section 3 contains the information needed to verify the accuracy of the Model 197. Performance verification can be
done upon receipt of the unit
curacy of the instrument is in question.
3.
Information concerning theory of operation, maintenance
and servicing is contained in Sections 4 through
or
whenever the basic ac-
6.
Perform the following steps in sequence to acquaint yourself
with the basic operation of the Model 197.
Verify that the instrument was not damaged in transit, (see
paragraph 1.7).
Carefully read over all safety information (see Section
Basic Operation).
Refer to paragraph 2.3 (Line Power) and set the line voltage
switch. Plug the power cord into a properly grounded
receptacle. If the Model 1978 is installed the charging circuit
is activated.
Acquaint yourself with the front panel controls as follows:
1.
Turn on the instrument using the ON/OFF button. All of
the zeroes are briefly displayed.
2. Connect the supplied test leads to the HI and
minals. Connect the red test lead to the HI terminal and
the black test lead to the
together.
3. Select AC volts and autoranging by pressing in the
AC/DC, V and AUTO buttons. The AC, AUTO and mV
annunciators are displayed. Pressing in any of the other
range buttons activates manual ranging. This is indicated
by the absence of the AUTO annunciator.
4. Select DC volts by releasing (out position) the AC/DC
V
button.
5.
Select the autoranging OHMS by pressing in the AUTO,
and
symbol is displayed. Press the AC/DC button in (means
select AC) and note that the "Err" message is displayed.
This indicates an invalid mode.
6.
Select AC or DC current by setting the AC/DC button ac-
cordingly and pressing in the A button. The annunciator
that reflects the selected mode
rent will not autorange. The 10A and
be used on the 10A range.
7. Select dB by selecting AC
button. The dB annunciator is now displayed. Press the dB
button to take the instrument out of the dB mode.
8.
The REL (relative) feature can be used with any measurement function: Volts, Amps, Ohms
select the ohms function and autorange. The display reads
approximately 000.1403, which is the test lead resistance.
Press the REL button. The REL annunciator is turned on
and the display reads 000.0003. The relative level of
000.143 will be subtracted from all subsequent
measurements. Press the REL button a second time to
cancel the REL level.
is still selected. The AC annunciator turns off.
3
buttons. DC must still be selected. The 3 (omega)
LO
terminal. Short the test leads
is
displayed. Note that cur-
or
DC volts and pressing the dB
or
LO
input ter-
LO
terminals must
dB. For example,
2
1-2
9. To activate the
minimum/maximum, press and hold in the STO/CLR button. When the reading rate r=O is displayed release the
STO/CLR button. The STO annunciator turns on. Press
the RCL button and the last data point is briefly displayed
followed by the reading (data). Other data points can be
displayed by holding in the RCL button. Turn off the
DATA LOGGER by pressing the STO/CLR button again.
100
point DATA
LOGGER
with
1.10 ACCESSORIES
The following accessories can be used with the Model 197
MODEL
mount one Model 197 in a standard 5%’’
MODEL 1017 DUAL RACK MOUNTING KIT-Use to
mount two Model 197s in a standard
MODEL
temperature probe designed to allow precision temperature
measurements from -55 to 150°C.
MODEL 1600A HIGH
measurements to 40kV.
Model 1641 Kelvin Test Lead Set-Special clip leads allow
4-terminal measurements to be made while making only two
connections.
MODEL 1651 50-AMPERE CURRENT SHUNT-The external
measurements from 0 to 50A
MODEL 1681 CLIP ON TEST LEAD SET-Contains two
leads, 1.2m (48”) long terminated with banana plugs and
spring action clip probes.
1010
SINGLE RACK MOUNTING KIT-Used to
X
19” rack.
5Y4”
X
19” rack.
1301 TEMPERATURE PROBE-A rugged low cost
0.001Q
VOLTAGE
f
1 % 4-terminal shunt, permits current
PROBE-Extends
AC
or DC.
DMM
MODEL 1751 SAFETY TEST LEADS-This test lead set is
supplied with every Model 197. Finger guards and shrouded
of
banana plugs help minimize the chance
with live circuitry.
MODEL 1754 UNIVERSAL TEST LEAD KIT-A 12 piece
test lead kit, with interchangeable plug-in accessories. Included in the
lugs,
two hooks and miniature alligator clips (with boots).
MODEL 1972 ANALOG OUTPUT IEEE-488 INTERFACEThe Model 1972 is an optional IEEE-488 interface that in-
cludes all of the logic necessary to interface the Model 197 to
the IEEE-488 bus. The Model 1972 is similar to the Model
1973 however,
put is a scaled output that follows the display of the Model
197. The Model 1972 is field installable.
MODEL 1973 IEEE-488 INTERFACE-The Model 1973 is an
optional IEEE-488 interface for the Model 197. This interface
adds extra versatility to the Model 197 by allowing the
transmission of data and commands over the IEEE-488 bus.
The interface provides all the logic necessary to interface the
Model 197 to the bus using standard IEEE-488-1978 protocol.
The Model 1973 is field installable.
MODEL 1978 RECHARGEABLE BATTERY PACK-The
rechargeable battery pack allows off line or in the field operation of the Model 197. The pack provides typically five hours
operation from full charge. The battery pack contains its own
charging circuit and can be recharged within
battery pack is field installable.
MODEL 7008 IEEE-488 DIGITAL CABLE-Useful for con-
necting the 1973 to the IEEE-488 bus. The Model 7008-3 is
0.9m (3
at each end. The Model 7008-6 is 1.8m (6
a standard IEEE-488 connector at each end.
kit
is one set of test leads (1-red, 1-black), two spade
two standard banana plugs, two phone tips (.06 DIA.)
it
contains an analog output. The analog out-
ft.)
in length and has a standard IEEE-488 connector
making contact
10
hours. The
ft)
in length and has
MODEL 1682A RF PROBE-Permits voltage measurements
AC
from 100kHz to 250MHz.
+IdB from 1OOkHz to 250MHz at
calibrated in RMS of a sine wave.
MODEL 1684 HARD SHELL CARRYING CASE-Hard
vinyl case, 100mm
has a fitted foam insert with room for the Model 197, an in-
struction manual and small accessories.
MODEL 1685 CLAMP ON
rent by clamping on to a single conductor. Interruption of the
circuit is unnecessary. The Model 1685 detects currents by
sensing the changing magnetic field produced by the current
flow.
X
300mm X 350mm (4”
to DC transfer accuracy is
1V,
peak responding,
X
13”
AC
PROBE-Measures AC cur-
X
14”)
MODEL 8573 IEEE-488 INTERFACE-The Model 8573 is an
IEEE-488 standard interface designed to interface the
or
XT
computers to Keithley instrumentation over the
IEEE-488 bus. The interface system contains two distinct
parts: an interface board containing logic to perform the
necessary hardware functions and the handler software
(supplied on disk) to perform the required control functions.
These two important facets of the Model 8573 join together to
give the IBM advanced capabilities over IEEE-488 interfaceable instrumentation.
IBM
PC
1-311-4
SECTION
2
BENCH OPERATION
2.1
INTRODUCTION
This section contains the information needed to prepare and 4. Energize the circuit using the installed connect-disconnect
operate the Model 197 as a bench
consists of using the Model 197 to perform basic voltage, cur- DMM
rent, resistance and
the data logger is covered. The capabilities of the Model 197
can be enhanced with the addition of the Model 1973 or
Model 1972 IEEE-488 interface.
the Model 1973 Instruction Manual. The optional battery
pack (Model 1978) is also covered in this section.
2.2
HIGH ENERGY CIRCUIT SAFETY
dB
measurements. Also, the operation of 5. ~~-~~~~~i~~
DMM.
IEEE
Bench operation
operation is covered in
PRECAUTIONS
To
Optimize safety
distribution circuits, read and use the directions in the following warning.
Dangerous arcs
high energy circuit can cause severe personal injury or death.
nected to a high energy circuit when set to
a current range, low resistance range or any
other low impedance range, the circuit is
virtuallv shorted. Dangerous arcing can
result even when the meter is set
range
reduced.
when
measuring
WARNING
of
an explosive nature in a
If
the meter is con-
if
the minimum voltage spacing is
in
to
voltage
high energy third-wire grounded
2. Attach the test leads to the circuit under test. Use ap-
propriate safety rated test leads for this application.
3.
Set the
device and make measurements without disconnecting the
disconnect
6,
Disconnect the
2.3
2.3.1
The Model 197 has a three-wire line cord which mates with
AC
1.
Set the LINE VOLTAGE switch on the back of the instrument to correspond to line voltage available. Ranges are
105V-125V or 210v-250V 50/60Hz
2. Plug the power cord into a properly grounded outlet.
DMM
to the proper function and range.
~~
.
the
device.
test
circuit
leads
using the installed connect-
from
the
circuit
under
PREPARATION FOR USE
Line
Power
Connect
line
power
as
follows:
CAUTION
Connect only to the line voltage selected.
Application
damage the instrument.
of
incorrect voltage can
AC.
the
instrument
test,
to
When making measurements in high energy circuits use test
leads that meet the following requirements:
Test leads should be fully insulated.
Only use test leads that can be connected to the circuit (e.g.
alligator clips, spade lugs, etc.) for hands-off measurements.
Do not use test leads that decrease voltage spacing. This
diminishes arc protection and creates a hazardous condi-
tion.
Use the following sequence when testing power circuits:
1.
De-energize the circuit using the regular installed connect-
disconnect device such as the circuit breaker, main switch,
etc.
WARNING
Ground the instrument through a properly
grounded receptacle before operation.
Failure to ground the instrument can result
in severe injury or death in event of a short
circuit or malfunction.
NOTE
Although the Model 197 is specified at 50 and
60Hz the instrument may be operated
and 440Hz.
at
400Hz
2-1
2.3.2 Battery Pack Power
The Model 197 may be operated from rechargeable sealed
nickel-cadmium batteries contained in the optional Model
1978 Rechargeable Battery Pack. The battery pack will
operate the Model 197 for typically five hours. (NOTE: The
Model 197 uses the most power on the amps function and also
2OOQ,
in the
turns on when the charge is insufficient to maintain accurate
readings. Refer to paragraph 5.3 for installation procedures.
2kQ or 750VAC ranges). The BAT annunciator
2.3.3 Battery Charging
If the battery pack is not maintaining a charge
10
for five hours after a full
following.
A. Disconnect the Model 197 from line power.
B.
Turn on the Model 197 and leave
discharge the battery pack.
C. Connect the Model 197 to line power and charge the
10
battery pack for
D.
Repeat steps A through C three more times. The battery pack should again be good for typically five hours.
3.
When the Model 197 is in use on line power, the battery
charger maintains a trickle charge on the battery pack.
hours with power off.
hour charge cycle, do the
it
on to completely
(BAT
off)
After the Model 1978 is installed in the Model 197
charged and recharged as follows:
1.
Connect the instrument to line power as described in
paragraph 2.3.1.
2.
With the power switch off, the battery charge circuitry is
automatically energized to charge the battery at the max-
imum rate. When the battery pack is first installed, or
is completely discharged, allow
of
10
hours.
For maximum battery efficiency only charge the
battery pack after
charged (BAT annunciator on). Do not make
measurements with BAT annunciator on as the
readings may be erroneous.
it
has become completely dis-
NOTE
it
to charge for a minimum
-1
it
197
AUTORANGING
can be
if
NOTE
The
IEEE
options (Model 1972 and Model 1973)
do not run off of battery power.
2.4
FRONT
it
Figure
description of the display, front panel controls and input terminals.
2.4.1
The Model 197 has a
The minus sign is displayed. The plus sign is implied by the
absence of the minus sign. The following annunciators are
displayed on the
2-1,
Display
MICROVOLT
PANEL FAMILIARIZATION
and the following paragraphs, provide a brief
5%
digit liquid crystal display (LCD).
LCD.
DMM
~
I
I
2-2
w
200m
*
QSENSE
u
I
BAT-Low battery indicator for the Model 1978.
AC-AC selected (DC implied by the absence of the AC annunciator).
AC/DC-This button is used along with the volts
(A),
rent
AC, releasing (out) this button selects
condition. See Table 2-1.
and dB functions. Depressing (in) this button selects
DC.
AC
!2
(V),
cur-
is invalid
or
mV
O,
p,
RMT
IEEE-488 bus (Model 1973
C-Model 197 in calibration mode.
AUTO-Autorange.
REL-Relative.
dB-Decibel measurement mode.
STO-Data being stored.
RCL-Data being recalled. RCL flashes when buffer is full
during logging cycle.
V-Millivolts or volts.
kO or MO-Ohms, kilohms
mA or A-Microamps, milliamps
(REMOTE)-Model 197 being controlled over the
or
megohms.
or
amps.
or
Model 1972 installed).
2.4.2 Front Panel Controls
ON/OFF-Pressing this button turns on the Model 197.
Releasing (out) this button turns the instrument off.
REL-(RELATIVE)-This button allows readings to be made
of
with respect to any baseline value. Also allows zeroing
range readings. See paragraph 2.7.2 for more detailed infor-
mation on
dB-This button selects the dB function and is used along
with the ACV or DCV function. Measurements are made in
dBm referenced to
voltage level the OdB reference point for dB measurements.
DATA LOGGER and MIN/MAX-100 reading storage
capacity; records data at one
reading/second
(r=6).
readings continuously while in the data logger mode.
REL.
600O.
REL
can be used to make any
of
seven selectable rates from
to
1
reading/hour
Also detects and stores maximum and minimum
or
by manual trigger
on
V-Depressing this button selects the volts function.
0-Depressing this button selects the ohms function. The
AC/DC button must be released (out).
A-Depressing (in) this button selects the current function.
Up to 2A on red and black input jacks and up to 10A with the
black and white input jacks. Refer to paragraph 2.4.3.
RANGE BUTTONS
1.
Depressing AUTO button allows volts and ohms to
autorange. In current,
autorange function for current.
2.
Manual ranging
propriate range button.
it
selects the 10A range. There is no
is
accomplished by depressing the ap-
2.4.3 Input Terminals
The input terminals are intended to be used with safety
shrouded test leads to help minimize the possibility
with live circuits. Safety shrouded tests leads (Model
are supplied with the Model 197. Always disconnect all un-
from
used test leads
HI
and
LO
INPUT (Red and Black)-Use this pair of ter-
minals
1OA
measuring current up to 10A (up to 20A
OHMS Sense HI and LO-Use this pair of terminals along
with HI and
3
for
all volt, ohm, milliamp and dB measurements.
and
LO
(White and Black)-Use this pair of terminals for
LO
the instrument.
for
15 seconds).
input for four wire resistance measurements.
2.4.4 Current Fuse Replacement
of
contact
1751)
1.
STO/CLR-Pressing this button initiates the logging se-
a
quence. Pressing this button
data logger. For
reading is desired, press the STO/CLR button.
2. RCL-Pressing and holding in this button scrolls the data
pointer. To read the data at a certain point, simply release
the button. The logged readings are stored in buffer locations
01
to 102. They are depicted on the front panel as
follows: Buffer location
r=6
rate (manual trigger) every time a
#1
second time turns off the
is represented
___
by n=01.
-
-
Tne current fuse protects the 200pA through 2000mA ranges
from an input current greater than 2A. To replace the current
fuse, perform the following steps:
NOTE
The front panel current fuse (F101) is rated at
2A. With a 220,000 count display, the 2A range
can momentarily (approx. one minute) read
2.2A before the fuse will blow. This
range will not harm the instrument.
1.
Turn off the power and disconnect the power line and test
leads.
2. Place the end of a flat-blade screwdriver into the slot in the
fuse holder on the front panel. Press in slightly and rotate
the fuse carrier one quarter turn counterclockwise. Release
pressure and remove the fuse carrier and the fuse.
3. Remove the defective fuse and replace
type: 2A, 250v, 3AG, normal-blow (Keithley part number
FU-13)
or
equivalent.
10%
over-
it
with the following
of less than 80% up to
humidity 3% per "C up to 50°C.
subjected to extremes of temperature, allow sufficient time for
internal temperature
Typically,
(18°F) out of the specified temperature range.
it
takes one hour to stabilize a unit that is 10°C
35°C.
For ambient above 35°C derate
If
the instrument has been
to
reach environmental conditions.
2.6.2 Maximum Allowable Inputs
Table 2-2 lists the maximum allowable inputs for the Model
197.
CAUTION
Use only the recommended fuse type. If a
fuse with a higher current rating is installed, instrument damage may occur.
2.5
ERROR MESSAGES
Table 2-1 lists the error messages associated with basic front
panel operation. Note that the instrument has
other messages that are discussed in the appropirate sections
of the manual.
a
number of
2.6 OPERATING CONDlTlONS
2.6.1 Environmental Conditions
All
measurements should be made at an ambient temperature
within the range of 0°C to 50°C, and with a relative humidity
Table
2-1.
2.6.3 Warm Up
The Model 197 requires one hour for warm
rated accuracy.
up
2.7 BASIC BENCH MEASUREMENTS
Basic measurement techniques for using the Model 197 to
measure AC and DC volts, resistance,
and
dB
are covered in the following paragraphs.
ed is the operation of the minimum/maximum and
data logger.
WARNING
Before operating the Model
previously mentioned safety precautions.
When testing high energy power circuits
follow the instructions found in paragraph
2.2.
Failure to observe these and other safe-
Error
Messages
AC
197,
observe all
and
Also
to achieve
DC
current
includ-
100
point
2-4
3isplay
LC
Err
--
~
Message
I
~
Q11(
Invalid D Function
Comments
Model 197 locks up. See Section 5 for troubleshooting information.
Model 197 locks up, but operation can be restored by pressing
any one of the four momentary pushbuttons. If restored,
calibration is invalid as indicated by the flashing "C" annunciator.
See Section
Overrange input applied to the Model 197. Leading minus sign
indicates that input signal has a negative value.
"AC" and
(out) AC/DC Dushbutton.
5
for troubleshooting information.
"Q"
annunciators flash. Correct problem by releasing
2-3
Table
2-2.
Model
197
Maximum Allowable Inputs
-7
Function
DCV
ACV
DCA, ACA
Q
ty precautions mentioned in this manual
could result in severe injury or death.
The
LO
terminal on the Model 197 is designed to float above
earth ground to avoid ground loop problems.
WARN I NG
Hazardous voltage may be applied to the
LO
terminal. The maximum allowable voltage between the
ground is
which could present a shock hazard, may
occur
Do not exceed the maximum input limits
shown in Table
2.7.1
Power
The software revision level of the Model 197 can
be displayed upon power up by running the
diagnostic program. See Section
ance, for more information.
Turn on the Model 197 by pressing in the
All
zeroes are briefly displayed before going into the measure-
ment mode.
If
the Model 197 does not enter the measurement
mode, refer
if
the
Up
500V.
500V
to
LO
Destruction
maximum is exceeded.
CAUTION
2-2.
NOTE
NOTE
section 5.7.1.
Ranges
200mV, 2V
20-1OOOV 1000VDC or peak AC.
i
~OO~V,
'
20-75OV
~
200p-2000mA
I
1 OA
1
terminal and chassis
All
of
5,
1
'
~
2v
insulation,
Mainten-
ON/OFF
Maximum Allowable Inputs
1000VDC or peak AC for less than 10sec per minute.
300~rms continuous.
750Vrms, 1OOOV peak for less than 10sec per
minute.
300Vrms, continuous. lO7*Hz maximum.
750Vrms, IOOOV peak. l07.H~ maximum.
2A, 250VDC or
10A continuous; 20A for 15sec (unfused).
450V peak AC
350Vrms continuous.
switch.
rrns
(fuse protected).
or
DC,
10
seconds per minute,
2.7.2
3.
Relative
When the relative mode is selected with an on-scale reading
on the display the following occurs:
1.
The REL annunciator is displayed.
2.
The next reading is stored.
This reading is algebraically subtracted from all subse-
quent readings and displayed.
A
REL level can be established for any measurement function
(Volts, Ohms, Amps and dB) and
function. Changing functions will not affect a
already established. However,
any function) the previous
ple, place the Model 197 in the ohms function and select the
200Q
range. Short the test leads and press the REL button.
Note that the REL annunciator is on. Select DCV and note
that the
REL
that the
REL
back
celled.
It
REL
braically subtracted from all subsequent readings
function.
Once a
that stored level will be the same regardless of what range the
Model 197 is on.
REL level on the 20VDC range,
other DCV ranges.
REL
level established for DCV. Switch back to ohms and note
REL
level of
to
ohms and note that the
is important to remember what the
function establishes a baseline. That baseline
REL
Mode
is
effective only on that
if
another
REL
level is cancelled.
annunciator is off, indicating that there is not a
level is still there. Again,
+lV.
The REL annunciator turns on. Switch
REL
level for ohms
REL
level is established for a measurement function,
For
example,
if
+1V is established as the
+
1V
is
I
1
I
REL
REL
level is set (on
For
exam-
go
to
DCV and set
is
function does. The
is
for
also the REL level
level
a
can-
alge-
that
for
2-5
The dynamic range
means that
applying +1.99999V to the input displays +3.99999V.
Once the REL level is established, that level is algebraically
subtracted from the input signal.
+
1
.OOOOOV
f2.OOOOOV level displays a
if
of
the display is
a
REL
level of -2.OOOOOV is established, then
REL level is established, then applying a
+1.OOOOOV
-+400,000
For
example:
level.
counts. This
if
a
7
The instrument accepts a +220,000 count input before going
(OL).
into the overrange condition
REL
level is established and 1.50000V is applied. The instrument displays +2.500000V. If the input is 2.20000V the instrument overranges.
2.7.3
The Model 197 can make DC voltage measurements between
DC
Voltage Measurement
1pV and
1.
2. Select the DCV function.
3. Select a range consistent with the expected voltage. For
IOOOV.
Connect the test leads to the
of the Model 197.
automatic range selection, press in the
To prolong instrument life, manual ranging is
recommended for routine measurements above
200v.
The basic procedure is as follows:
NOTE
For example:
HI
and
LO
AUTO
-1.OOOOOV
INPUT
button.
terminals
CAUTION.
o/
I
The 200mV DC range and the 2000 range require zero to be
set in order to achieve rated accuracy.
2.7.4
The Model
between
1.
2. Select the ACV function.
3.
4.
MODEL
Figure
TRMS
Connect the test leads
Model 197.
Select a range consistent with the expected voltage.
automatic range selection, press in the AUTO button.
Connect the test leads to the source as shown in Figure 2-3.
197
2-2.
AC
197
can make TRMS AC voltage measurements
1pV
and 750V. To measure AC proceed as follows:
INPUT RESISTANCE = 10M. EXCEPT
>
lOOOM
DC
Voltage Measurements
Voltage Measurements
to
the
HI
on
1OOOV
MAXIMUM INPUT
200mV
and
LO
and
2V
terminals
RANGES
of
the
For
4.
Connect the test leads to the source as shown in Figure 2-2.
If
the positive source terminal is connected to the
minal of the instrument, the display shows a negative
If
value.
LO
5. Observe the display;
higher range until a normal reading is displayed. Always
use the lowest possible range for the best resolution.
6.
Take the reading from the display.
The term "when properly zeroed" means that the user must
establish a proper baseline for subsequent measurements on
that range. To zero the Model 197 use the following pro-
cedure:
1.
Short the INPUT
2. Wait until the displayed reading settles. Noise and thermal
emfs may require a few moments
3. Press the
2-6
the negative source terminal is connected to the
terminal, the display shows a positive value.
If
the
"OL"
message is shown, select a
HI
and
LO
test leads together.
to
settle out.
REL
button.
LO
ter-
NOTE
There is a small amount of offset (typically 50
counts
tion.
this is that the offset is generally negligible as
compared to the input signal.
offset
applied signal
displayed reading =\(20mV)2
This offset is seen as the last digit which is not
displayed on the Model 197. Therefore, the offset is negligible.
5.
Observe the display,
higher range until a normal reading is displayed. Always
use the lowest possible range to obtain the best resolution.
or
less) present when using the
Do
not REL this level out. The reason for
=
22pV
=m-+484
=
.0200000121
=
20mV
x
10-iZ
if
the
AC
For
example:
+
(22pV)Z
"OL"
message is shown, select a
func-
6. Take the reading from the display
NOTE
See paragraph
When measuring
leads from the OHMS SENSE terminals.
-INPUT
MODEL
197
2.8
for TRMS considerations.
AC
signals disconnect any test
IMPEDANCE
BY
<
75pF
=
IMR
SHUNTED
R,
=
parallel combination of source resistance and input impedance.
e, = Johnson noise of the source resistance.
on
Even
is
Thus, for an R, of
inherent 1.5pV peak to peak. Beyond
to R, becomes a limiting factor in the measurement.
Therefore, it is recommended that
ments R, be kept relatively 10~7,
As
(due to Johnson noise of the source resistance) assume that the
Model 197 is connected to a voltage source with an internal
resistance of
p-p noise voltage generated over a bandwidth
most sensitive range, the noise due to the current
not appreciable until R, reaches approximately
OQ
to
lMQ,
the noise at the input is the
1MQ
the noise due
for
sensitive measure-
if
possible below
an example of determining e, noise voltage generation
1MQ.
At
a
=
e,
e, = 6.35
room temperature
6.35
X
10-10
X
lO-lO\r(lx
\J
R
X
10m
of
20°C
of
f
1MQ.
(293K),
1Hz
will be:
lMQ.
the
Figure
2.7.5
Accuracy Considerations-For sensitive measurements, other
external considerations besides the Model
accuracy. Effects not noticeable when working with higher
voltages are significant in microvolt signals. The Model 197
reads only the signal received at its input; therefore,
portant that this signal be properly transmitted from the
source. The following paragraphs indicate factors which af-
fect accuracy, noise, source resistance, thermal emfs and
stray pick-up.
Noise and Source Resistance-The limit of resolution in
measuring voltages with the Model 197 is determined by the
noise present. The displayed noise of the Model 197 is 1.5pV
peak to peak. This noise is inherent in the Model 197 and is
the minimum amount present in all measurements. The 1.5pV
of noise is due to the instrument voltage noise. The noise at
the Model 197 input increases beyond this minimum when the
noise current passes through a resistor thus generating a
voltage noise. The total noise becomes a function of the
source resistance and is given by the equation:
2-3.
TRMS
AC
Voltage Measurements
Microvolt Measurement Considerations
197
will affect the
it
is im-
=
en2
+
n2
(inRs)2
+
er2
e, = 0.635pV
Thus
it
is clear that optimum microvolt measurements with
the Model 197 are possible with source resistances as high as
1MQ.
However, this resolution will not be realized unless
shielding is employed.
Shielding-The Model 197 is insensitive
DC
superimposed upon a
However,
with the
Therefore,
shielded and the shield connected to the Model 197 ground
(particularly for low-level sources). Improper shielding can
cause the Model 197 to behave in one
ing ways:
1. Unexpected offset voltages.
2.
Inconsistent readings between ranges.
3.
Sudden shifts in reading.
To minimize pick up, keep the voltage source and the Model
197 away from strong
duced due to magnetic flux is proportional to the area
loop formed by the input leads. Therefore, minimize the loop
area of the input leads and connect each signal at only one
point.
AC
voltages which are extremely large compared
DC
signal may erroneously produce
if
there is
AC
signal at the input terminals.
interference, the circuit should be
AC
magnetic sources. The voltage in-
to
AC
voltages
a
DC
output.
or
more of the follow-
of
the
where
n
=
total noise input.
=
input voltage noise of the Model 197.
en
in
=
input current noise.
Thermal EMFs-Thermal emfs (thermoelectric potentials) are
generated by thermal differences between two junction
dissimilar metals. These can be large compared
which the Model 197 can measure. Thermal emfs can cause
the following problems:
to
the signal
of
2-7
1.
Instability
2. The reading is sensitive to (and responds to) temperature
changes. This can be demonstrated by touching the circuit,
by placing a heat source near the circuit
pattern of instability (corresponding to heating and airconditioning systems or changes in sunlight).
3. To minimize the drift caused by thermal emfs, use copper
leads to connect the circuit to the Model 197.
plug is generally sufficient and generates just a few
microvolts.
is about the best for the application. The leads to the input
may be shielded
Shielding.
4.
Widely varying temperatures within the circuit can also
create thermal emfs. Therefore, maintain constant temperatures to minimize these thermal emfs.
box around the circuit under test also helps by minimizing
air currents.
5. The REL control can be used to null out constant offset
voltages.
2.7.6
The Model 197 can make resistance measurements between
1m3 and 22OM3. The 2M3, 20MQ and 200MQ ranges
autorange when the
provides automatic selection of 2-terminal
resistance measurements. This means that
leads are not connected, the measurement is done &terminal.
If
the sense leads are connected the measurement is done
4-terminal. For 4-terminal measurements, rated accuracy can
be obtained as long as the maximum lead resistance does not
exceed the values listed in Table 2-3. For 2-terminal
4-terminal measurements on the 2003 range, zero must be set
by the REL function to obtain rated accuracy. For best results
on the 2003, 2k3 and 2Ok3 ranges, it is recommended that
4-terminal measurements be made to eliminate errors caused
by the voltage drop across the test leads that occurs when
2-terminal measurements are made. To make resistance
measurements, proceed as follows:
or
zero offset is much higher than expected.
A
clean copper conductor such as
or
unshielded, as necessary. Refer to
Resistance Measurements
M3
button is selected. The Model 197
or
by a regular
A
banana
#lo
bus wire
A
cardboard
or
4-terminal
if
the ohms sense
or
1.
Connect the test leads to the HI and
If four-wire measurements are to be made, connect an additional set of leads to the OHMS SENSE terminals.
NOTE
The Model 1641 Kelvin test lead kit is ideal for
low resistance 4-terminal measurements.
2. Select the ohms function.
3.
Select a range consistent with the expected resistance.
desired, use the autorange mode for automatic range selection.
4.
If
readings are to be made on the 2OOQ range, zero the instrument to obtain rated accuracy. To zero the instrument
for resistance measurements: Short the test leads together
after disconnecting them from the measured circuit:
4-wire measurements are to be made, short
leads as shown in Figure 2-6, allow the reading to settle
REL
then press the
5.
For 2-wire measurements connect the instrument as shown
in Figure 2-4. For 4-wire measurements, use the connections shown in Figure 2-5.
The maximum input voltage between the
HI
and LO INPUT terminals is
peak AC for
RMS
values or instrument damage may occur.
Table
various resistance ranges.
Incorrect readings will result if the
resistance being measured is part
circuit.
6. Take the reading from the display.
continuous. Do not exceed these
2-3
button.
CAUTION
10
seconds per minute,
shows the current output for
CAUTION
LO
450V
INPUT
all
DC or
350V
of
a live
terminals.
four test
If
if
2-8
Range
200
2k
20 k
,
200 k
200M
tesolutior
lm3
1
OmQ
1
OOmQ
1Q
10
0
100
Q
10
k3
Table
I-S
hort
2mA
2mA
400pA
40 pA
4 PA
400 nA
400 nA
2-3.
Resistance Ranges
Across
Unknown
4.0V
4.0V
5.0V
Maximum Test Lead
Resistance for
(1
Count Error
10
(Q)
32
100
320
Ik
3.2k
10k
NOTE
It
is helpful to shield resistance greater than 106Q
(1MQ)
resistance in a shielded enclosure and electrically
connect the shield to the
the Model 197.
-
if
a stable reading is expected. Place the
LO
input terminal of
OPTIONAL SHIELD
__
RESISTANCE
2.7.7
Current Measurements
(DC
or TRMS
AC)
The Model 197 can make DC or TRMS AC current
measurements between 1nA and 10A (20A for
the expected current level is in question, make the initial
measurement on the 10A range. This helps prevent inadvertent blowing of the 2A current fuse which is located on the
front panel.
I
I
NOTE
For routine measurements above 10A
recommended that the Model 1651 50A shunt be
used.
15
seconds).
it
If
is
Figure
MODEL 197
2-4.
Two
MODEL 197
Figure
CAUTION: MAX INPUT
or PEAK AC for lOsec/min, 350V
[
RMS CONTINUOUS
=
450VDC
Terminal Resistance Measurement
OPTIONAL SHIELD
I-----
CAUTION: MAX INPUT = 450VDC
or
pk
AC for 10sec/min, 350V RMS
CONTINUOUS.
2-5.
Four Terminal Resistance
-
-
---
Measurement
1.
For current measurements between 2000mA and 20A.
to
A. Connect the test leads
the Model 197. Refer
The test leads used must be rated to handle 20A.
Twist the wires as shown in Figure 2-7
minimizing external fields which could affect the
I
I
Model 197 or other equipment. Also, keep the
test leads as short as possible
voltage drop.
B.
Select the ACA or DCA function.
C. Select the 10A range. The amps function does not
autorange.
D. Connect the test leads to the current source as shown in
Figure 2-7 and take the reading from the display.
Up to
5A
may be applied continuously without
degradation of the measurement due to self
heating effects. Above
amp for self heating, refer to specifications that
precede Section
20A, specified accuracy can only be obtained
when measurements are limited to a maximum
of
15
seconds.
1.
the 10A and
to
Figure 2-7.
NOTE
NOTE
5A
derate
For
currents between 10A and
to
0.15%
LO
terminals
to
help in
minimize
rdg per
of
INPUT
LO
OHMS SENSE LO
OHMS SENSE HI SHORT
Figure 2-6. Four Terminal Zeroing
2.
For
current measurements up to 2000mA:
A.
Connect the test leads to the INPUT
minals
B.
Select the ACA or DCA function.
C.
Select an appropriate range for the expected current.
The current function does not autorange.
of
the Model 197.
HI
and
LO
ter-
2-9
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