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Model 197A AutorangingMicrovolt DMM
User'sManual




MY




A GREATER MEASURE:~OF CONFIDENCE
Model 197AAutoranging Microvolt DMM
User's Manual




01990, Keithley Instruments, Inc.
All rights reserved.
Cleveland, Ohio, U.S.A.
Third Printing, February 2001
Document Number: 197A-901.01 Rev. C
SAFETY PRECAUTIONS
The following safety precautions should be observed before operating the Model 197A.


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 Standards
Institute (ANSI) states that a shock hazard exists when voltage levels greater than 30V ms or 424V peak are present. A
good safety practice is to expect that a hazardous voltage is present in any unknown circuit before measuring.


Inspect the test leads for possible wear, cracks or breaks before each use. If any defects are found, replace the test leads.


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.


Do not touch any object which could provide a current path to the cmnmon side of the circuit under test or power line
(earth) ground. Always make measurements with dry hands while standing on a dry, insulated surface, capable of with-
standing the voltage being measured.


Exercise extreme safety when testing high energy power circuits (AC line or mains, etc). Refer to High Energy Circuit
Safety Precautions found in paragraph 2.2.


Do not exceed the instrument's maximum allowable input as defined in the specifications and operation section.


Instrumentation and accessories should not be connected to humans.
Safety Precautions

The following safety precautions should be observed before using Exercise extreme caution when a shock hazard is present. Lethal
this product and any associated instrumentation. Although some in- voltage may be present on cable connector jacks or test fixtures. The
struments and accessories would normally be used with non-haz- American National Standards Institute (ANSI) states that a shock
ardous voltages, there are situations whcrc hazardous conditions hazard exists when voltage levels greater than 30V RMS, 42.4V
may be present. peak, or 60VDC are present. A good safety practice is to expect
This product is intended for use by qualified personnel who recog- that hazardous voltage is present in any unknown circuit before
nize shock hazards and are familiar with the safety precautions re- measuring.
quired to avoid possible injury. Read the operating information Users oi this product must be protected from electric shock at all
cweiully beiorc using the product. times. The responsible body must ensure that users are prevented
The types of product osers arc: access and/or insulated from every connection point. In some cases,
connections must be exposed to potential human contact. Product
Responsible body is the individual or group responsible for the use
users in these circumstances must be trained to protect themselves
and maintenance oi equipment, for ensuring that the equipment is
from the risk of electric shock. If the circuit is capable of operating
operated within its specifications and operating limits, and ior en-
at or above 1000 volts, no conductive part of the circuit may be
suring that operators are adequately trained.
exposed.
Operators use the product ior its intended function. They most be
Do not connect switching cards directly to unlimited power circtdts.
trained in electrical safety procedures and proper use of the instn-
They are intended to be used with impedance limited sources.
ment. They most bc protected from electric shock and contact with
NEVER connect switching cards directly to AC mains. When con-
hazardous live circuits.
necting sources to switching cards, install protective devices to lim-
Maintenance personnel perform routine procedures on the product it fault current and voltage to the card.
to keep it operating, ior example, setting the line voltage or replac-
Before operating an instrument, make sore the line cord is connect-
ing consumable materials. Maintenance procedures are described in
ed to a properly grounded power receptacle. Inspect the connecting
the manual. The procedures explicitly state if the operator may per-
cables, test leads, and jumpers for possible wear, cracks, or breaks
form them. Otherwise, they should be performed only by service
before each use.
pCIS"tttEl.
When installing equipment where access to the main power cord is
Service personnel arc trained to work on live circuits, and perform
restricted, such as rack mounting, a separate main input power dis-
safe installations and repairs of products. Only properly trained ser-
connect device must be provided, in close proximity to the equip-
vice personnel may perform installation and service procedures.
ment and within easy reach of the operator.
Keitbley products are designed ior "se with electrical signals that
are rated Installation Category I and Installation Category II, as de- For maximum safety, do not touch the product, test cables, or any
other instruments while power is applied to the circuit under test.
scribed in the International Electratechnical Commission (IEC!)
ALWAYS remove power from the entire test system and discharge
Standard IEC 60664. Most measurement, conaol, and data I/O sig-
any capacitors before: connecting or disconnecting cables or jump-
nals are Installation Category I and most not be directly connected
ers, installing or removing switching cards, or making internal
to mains voltage or to voltage sowces with high transientovcr-volt-
changes, such as installing or removing jumpers.
ages. Installation Category II connections require protection for
high transient over-voltages often associated with local AC mains Do not touch any object that could provide a current path to the com-
connections. The user should assome all measurement, control, and mon side oitbe circuit under test or power line (earth) ground. Always
data I/O connections zwefor connection to Category 1 sources un- make mea~uremem with dry hands while standing on a dry, insulated
less otherwise marked or described in the Manual. surface capable of withstanding the voltage being measured.
The instrument and accessories must be used in accordance with its The WARNING heading in a manual explains dangers that might
specifications and operating instructions or the safety of the equip- result in personal injury or death. Always read the associated infor-
ment may be impaired. mation very carefully before performing the indicated procedure.

Do not exceed the maximum signal levels of the instruments and ac- The CAUTION heading in a manual explains hazards that could
cessories, as defined in the specifications and operating inform% damage the instrument. Such damage may invalidate the warranty.
lion, and as shown on the instrument or test fixture panels, or lnslrumentation and accessories shall not be connected to humans.
switching card. Before performing any maintenance, disconnect the line cord and
When fuses are used in a product, replace with same type and rating all test cables.
for continued protection against fire hazard. To maintain protection from electric shock and fire, replacement
components in mains circuits, including the power transformer, test
Chassis connections must only he used as shield connections for leads, and input jacks, must be purchased from Keithley Instru-
measuring circuits, NOT as safety earth ground connections. merits. Standard fuses, with applicable national safety approvals,
may be used if the rating and type are the same. Other components
If you are using a test fixture, keep the lid closed while power is ap-
that are not safety related may be purchased from other suppliers as
plied to the device under test. Safe operation requires the use of a
long as they are equivalent to the original component. (Note that se-
lid interlock.
lected parts should be purchased only through Keithley Instruments
[email protected] screw is present, connect it to safety earth ground using the to maintain accumcy and functionality of the product.) If you are
wire recommended in the user documentation. unsure about the applicability of a replacement component, call a
Keithley Instruments office for information.
The n ! symbol on an instrument indicates that the user should re- To clean an instrument, use a damp cloth or mild, water based
fer to the operating instructions located in the manual. cleaner. Clean the exterior of the instrument only. Do not apply
cleaner directly to the instrument or allow liquids to enter or spill
Then symbol on an instrument shows that it can source or mea- on the insrmment. Products that consist of a circuit board with no
sure 1000 volts or more, including the combined effect of normal case or chassis (e.g., data acquisition board for installation into a
and common mode voltages. Use standard safety precautions to computer) should never require cleaning if handled according to in-
avoid personal contact with these voltages. structions. If the board becomes contaminated and operation is af-
fected, the board should be returned to the factory for proper
cleaning/servicing.




7JOl
197A 5%-D&$ Mukimeter Specifications
DCVOLTS
.4CC"RMx"*
*(?&r*g+ CO"rm,




DCAMPS
Table of Contents
SECTION 1- General Information
1.1 INTRODUCTION ...................................................
1.2 FEATURES .........................................................
1.3 WARRANTY INFORMATION ........................................
1.4 MANUALADDENDA ...............................................
1.5 SAFETY SYMBOLS AND TERMS .....................................
1.6 SPECIFICATIONS.. .................................................
1.7 UNPACKING AND INSPECTION .....................................
1.8 USING THE MODEL 197A MANUAL .................................
1.9 INITIALOPERATION ...............................................
1.10 ACCESSORIES ......................................................


SECTION 2 - Bench Operation
2.1 INTRODUCTION ......................................................................... 2-l
2.2 HIGH ENERGY CIRCUIT SAFETY PRECAUTIONS ........................................... 2-l
2.3 PREI'ARATIONFORUSE .................................................................. 2-2
2.3.1 LinePower ............................................................................. 2-2
2.3.2 BatteryPackPower ...................................................................... 2-2
2.3.3 BatteryCharging ........................................................................ 2-2
2.4 FRONT AND REAR PANEL FAMILIARIZATION ............................................. 2-2
2.4.1 Display ................................................................................ 2-2
2.4.2 FrontPanelControls ..................................................................... 2-4
2.4.3 InputTerminals ......................................................................... 2-4
2.4.4 Current FuseReplacement ................................................................ 2-4
2.4.5 RearPanelSwitches ..................................................................... 2-5
2.5 ERRORMESSAGES ....................................................................... 2-5
2.6 OPERATINGCONDITlONS ................................................................ 2-5
2.6.1 Environmental Conditions ................................................................ 2-5
2.6.2 MaximumAllowableInputs .............................................................. 2-5
2.6.3 warmup ............................................................................... 2-b
2.7 BASICBENCHMEASUREMENTS .......................................................... 2-b
2.7.1 PowerUp .............................................................................. 2-b
2.7.2 Relative Mode .......................................................................... 2-b
2.7.3 DCVoltageMeasurement ................................................................. 2-7
2.7.4 TRMSACVoltageMeasurements .......................................................... 2-8
2.7.5 Microvolt Measurement Considerations .................................................... 2-8
2.7.6 ResistanceMeasurements.. ............................................................... 2-9
2.7.7 Current Measurements (DC or TRMS AC) .................................................. z-11
2.7.8 ACI'lusDCMeasurements ............................................................... z-12
2.7.9 dB Measurements ....................................................................... 2-13
2.7.10 dB Measurement Considerations and Applications ........................................... 2-15
2.7.11 MIN/MAX and 100 Point Data Logger Operation ........................................... 2-16
2.7.12 DiodeTest .............................................................................. 2-16
2.8 TRMSCONSIDERATIONS ................................................................. 2-17
2.8.1 ACVoltageOffset ....................................................................... Z-17
2.8.2 TRMSMeasurementComparison .......................................................... 2-17
2.8.3 CrestFactor ............................................................................ 2-17
2.8.4 Extended Frequency Response ............................................................ 2-17


SECTION 3 - Performance Verification
3.1 INTRODUCTION.. ..................... ................................................. 3-l
3.2 ENVIRONMENTAL CONDITIONS ....... ................................................. 3-l
3.3 RECOMMENDED TEST EQUIPMENT ..... ................................................. 3-1
3.4 INITIAL CONDITIONS .................. ................................................. 3-l
3.5 VERIFICATION PROCEDURE ............ ................................................. 3-2
3.5.1 DC Voltage Accuracy Check ............ ................................................. 3-2
3.5.2 AC Voltage Accuracy Check ............ ................................................. 3-3
3.5.3 Resistance Accuracy Check ............. ................................................. 3-4
3.5.4 DC Current Accuracy Check ............ ................................................. 3-6
3.5.5 AC Current Accuracy Check ............ ................................................. 3-7


SECTION 4 - Maintenance
4.1 INTRODUCTION ......................................................................... 4-1
4.2 DISASSEMBLY INSTRUCTIONS ............................................................ 4-l
4.3 BATTERY PACK (Model 1978) INSTALLATION ............................................... 4-3
4.4 LINE VOLTAGE SELECTION ............................................................... 4-4
4.5 FUSEREPLACEMENT .................................................................... 4-5
4.5.1 LineFuseReplacement ................................................................... 4-5
4.5.2 Current Fuse Replacement ................................................................ 4-5
4.6 FRONTPANELCALIBRATION ............................................................. 4-5
4.6.1 Recommended Calibration Equipment ..................................................... 4-6
4.6.2 Environmental Conditions ................................................................ 4-6
4.6.3 CalibrationSwitch ....................................................................... 4-6
4.6.4 DC Voltage Calibration ................................................................... 4-6
4.6.5 ACVolageCalbration ................................................................... 4-7
4.6.6 FrequencyCompensation ................................................................ 4-7
4.6.7 Resistance Calibration ................................................................... 4-9
4.6.8 CalibrationStorage ...................................................................... 4-10
List of Illustrations
SECTION 2 - Bench Operation
Figure 2-l Model 197A Front Panel 2-3
Figure 2-2 Model 197A Rear Panel 2-3
Figure 2-3 DC Voltage Measurements 2-7
Figure 2-4 TRMS AC Voltage Measurements 2-8
Figure 2-5 Four Terminal Zeroing 2-10
Figure 2-6 Two Terminal Resistance Measurement 2-11
Figure 2-7 Four Terminal Resistance Measurement 2.11
Figure 2-8 Current Measurement Between 2000mA and 20A 2-l 2
Figure 2-9 Current Measurements up to 2000mA 2-12
Figure Z-10 Typical ACV Frequency Response 2.18


SECTION 3 - Performance Verification
Figure 3-1 Connections for DCV Verification ....................................................... 3-2
Figure 3-2 Connections for ACV Verification ....................................................... 3-4
Figure 3-3 Connections for 200R 2kQ and 2Okn Range Verification (4.terminal) ........................ 3-5
Figure 3-4 Connections for 2OOkQ through Ma Ranges Verification (2-terminal) ......................... 3-5
Figure 3-5 Connections for DC Current Verification (200pA to 2000mA) ................................ 3-6
Figure 3-6 Connections for DC Current Verification (2000mA to 20A) .................................. 3-7
Figure 3-7 Connections for AC Current Verification (200pA to 2000mA) ................................ 3-R
Figure 3-8 Connections for AC Current Verification (2000mA to SOA) .................................. 3-8


SECTION 4 - Maintenance
Figure 41 Model 197A Miscellaneous Parts ....................................................... 4-2
Figure 42 Display Assembly Exploded View ...................................................... 4-4
Figure 43 DC Voltage Calibration Configuration .................................................. 4-7
Figure 4-4 AC Voltage Calibration Configuration .................................................. 4-8
Figure 4-5 ZOO,2k and 20k Four Wire Resistance Calibration ......................................... 4-9
Figure 4-6 2OOk, 2M and 20M Two Wire Resistance Calibration. ...................................... 4-10
List of Tables
SECTION 2 - Bench Operation
Table 2-1 ErrorMessages ....................................................................... 2-5
Table 2-2 Model 197A Maximum Allowable Inputs ................................................. 2-6
Table 2-3 ResistanceRanges ..................................................................... 2-10
Table 2-4 dB Specifications for DC Volts (6000 Ref) ................................................. 2-13
Table 2-5 dB Specifications for AC Volts (6OOQ Ref) ................................................. 2-13
Table 2-6 Selectable Reference Impedances ........................................................ 2-13
Table 2-7 Levels for Other Reference Impedances .................................................. 2-14
Table 2-8 Comparison of Average and TRMS Meter Readings ........................................ 2-19


SECTION 3 - Performance Verification
Table 3-l Equipment Specifications ........................................... ............. 3-2
Table 3-2 Limits for DC Voltage Verification ................................... ............. 3-3
Table 3-3 Limits for AC Voltage Verification ................................... ............. 3-3
Table 3-4 Limits for Resistance Verification .................................... ............. 3-4
Table 3-5 Limits for DC Current Verification ................................... ............. 3-7
Table 3-6 Limits for AC Current Verification ................................... ............. 3-9


SECTION 4 - Maintenance
Table 4-l lnput Terminal Identification ........................................................... 4-3
Table 4-2 Recommended Calibration Equipment ................................................... 4-6
Table 4-3 DCVoltageCalibration ................................................................ 4-7
Table 4-4 ACVoltageCalibration ................................................................ 4-9
Table 4-5 ResistanceCalibration ................................................................. 4-9
SECTION 1
General Information


1.1 INTRODUCTION 1.2 FEATURES

The Model 197A is a six function, 5-l/2 digit resolution The Model 197A includes the following features:
autoranging digital multimeter with a ?220,000 count
LCD (Liquid Crystal Display). This A/D range is greater 1. Six Measurement Functions - DCV, ACV, DCA,
than the normal +199,999 count A/D used in many 5-l /2 ACA, OHMS and dB all built in.
digit DMMs. The 5-l /2 digit resolution allows the Model 2. @EL) Relative Mode - The relative mode allows
197A tomeasureDC voltage for lpV/count to IOOOV. AC offsets to be nulled out (e.g. test lead resistance for
voltage and current measurements are standard in the low resistance measurements) and selects a variety
Model 197A. TRMS ACV capability ranges from lpVv/ of reference impedances for dB measurements.
count to 750V. The Model 197A measures res&ance from 3. Digital Calibration - A non-volatile RAM stores
1rnQ to 22OMQ on seven resistance ranges. The Model calibration constants and can be performed from the
197A has six current ranges that measure current from front panel or over the IEEE-488 bus.
1nA (WA) to 10A. 4. Data Logger -A data storage buffer is included to
allow up to 100 readings and minimum/maximwn
readings beintemallystored at auserselectablerate.
The buffer may be read and controlled from the front
The dB function makes it possible to compress a large panel or over the IEEE-488 bus. In the talk-only
range of readings into a much smaller scope. Model 197A mode, the output rate can also be programmed.
dBm measurements can be referenced to 50,75,93,135, 5. Autoranging - The Model 197A includes a fast
300 or 6OOQ (default), but can be modified with the use of autoranging feature for easier measurements.
the relative (REL) feature. 6. 5-l/2 Digit Resolution - The Model 197A has a
2220,000 count A/D that surpasses the more corn-
man 1199,999 count A/D.
7. Four Terminal Ohms-These terminals are used to
The Model 197A has two IEEE-488 interface options: The eliminate the voltage from across the current carry-
Model 1972A and the Model 1973A. These optional inter- ing leads.
faces enhance the capabilities of the Model 197A by al- 8. Sensitivity - The Model 197A has lpV, lmX2 and
lowing programmed control over the IEEE-488 bus. The 1nA sensitivity. The 1pV of sensitivity allows minute
Model 1977-Aalso includes an analog output. The bus levels of offset, temperature etc. A ltisensitivity al-
commands are the same for each interface and respond to lows low current measurements without special
IEEE-488 protocol. equipment. Measure leakage, bias and offset CUP


l-1
SECTION 1
General Information



rent. A lma sensitivity allows easy low resistance 1.6 SPECIFICATIONS
measurements.
Detailed Model 197A specifications may be found preced-
9. Electroluminescent Display Backlight - An
ing the table of contents of this manual.
electroluminescent display backlight is used to enhance
the liquid crystal display under low light or dark
conditions. 1.7 UNPACKING AND INSPECTION
10. dB Reference Impedances - Selectable dB reference
impedances of 5OQ 754 930, 1354 3OOn and 6OOn The Model 197A Autoranging Microvolt DMM was care-
(default). fully inspected, both electrically and mechanically before
shipment. Upon receiving the instrument, carefully unpack
all items from the shipping carton and check for any obvi-
1.3ARRANTY INFORMATION ous signs of physical damage that may have occurred dur-
ing transit. Report any damage to the shipping agent.
Warranty found on the inside front Retain and use the original packing material in case reship-
cover of t it become necessary to ment is necessary. The following items are shipped with
exercise the warranty,ntact your Keithley representative every Model 197A order:
or the factory to determine the proper course of action.
Keithley Instruments maintains service facilities in the l Model 197A Autoranging DMM
United States, United Kingdom and throughout Europe. . Model 197A User's Manual
Information concerning the application, operation or . Model 1751 Safety Shrouded Test Leads
service of your instrument may be directed to the l Additional accessories as ordered.
applications engineer at any of these locations. Check the If an additional instruction manual is required, order the
inside front cover for sses. manual package (K&Hey Part Number 197A-901-00). The
manual package includes an instruction manual and any
applicable addenda.
1.4 MANUAL ADDENDA
information concerning improvements or changes to this
instrument which occur after the printing of this manual
1.6 USING THE MODEL 197A MANUAL
will be found on an addendum sheet ined with this This manual contains information necessary for operating
manual. Be sure to review these changes before attempting and servicing the Model 197A Autoranging Microvolt
to operate or service the instrument. DMM and the 1978 Rechargeable Battery Pack. This section
of the manual contains general information and an initial
operation procedure. The rest of the manual is organized as
1.5 SAFETY SYMBOLS AND TERMS follows:
The following safety symbols and terms are used in this Section 2 contains detailed bench operation information
manual or found on the Model 197A. for the Model 197A.
Section 3 contains the information needed to verify the
The symbol A on the instrument denotes the user
accuracy of the Model 197A. l'erformance verification
should refer to the operating instructions in this manual.
can be done upon receipt of the unit or whenever the
on the instrument denotes that a poten- basic accuracy of the instrument is in question.
The symbol A
tial of 1OOOV or more may be present on the terminal(s). Section 4 contains information on maintenance and cal-
Standard safety practices should be observed when such ibration for the Model 197A.
dangerous levels are encountered.
NOTE
The WARNING heading used in this manual explains dan- The Models 1973A and 1972A IEEE-488 inter-
gers that could result in personal injury or death. faces come supplied with their own manual.

The CAUTION heading used in this manual explains haz-
ards that could damage the instrument.




1-2
SECTION 1
General Information



1.9 INITIAL OPERATION ond time disables the dB measurement mode. To
select an alternate dB reference impedance,
Perform the following steps in sequence to acquaint your- enable dB as previously described, but hold in the
self with the basic operation of the Model 197A. dB button to scroll through the alternate imped-
Verify that the instrument was not damaged in transit, ance selections. Release the dB button when the
(see paragraph 1.7). desired dB reference impedance is displayed.
Carefully read over all safety information (see Section 2 When finished, again press dB to exit the dB
Basic Operation). mode.
Refer to paragraph 2.3 (Line Power) and set the line The REL (relative) feature can be used with any
voltage switch. Connect the female end of the power measurement function: Volts, Amps, Ohms, or
cord to the AC receptacle on the rear of the Model 197A. dB. For example, select the ohms function and
Plug the other end of the line cord into a properly autorange. The display reads approximately
grounded receptacle. If the Model 1978 is installed, the 000.14OQ which is the test lead resistance. Press
charging circuit is activated. the REL button. The REL annunciator is turned
Acquaint yourself with the front panel controls as on and the display reads OOO.OOOfi.The relative
follows: level of 000.14n will be subtracted from all subse-
1. Turn on the instrument using the ON/OFF quent measurements. Press the REL button a sec-
button. All of the zeroes are briefly displayed. ond time to cancel the REL level.
2. Connect the supplied test leads to the HI and LO To activate the 100 point DATA LOGGER with
input terminals. Connect the red test lead to the minimum/maximum, press and hold in the
HI terminal and the black test lead to the LO ter- STOiCLR button. When the reading rate r=O is
minal. Short the test leads together. displayed release the STO/CLR button. The ST0
3. Select AC volts and autoranging by pressing in annunciator turns on. Press the RCL button and
the AC/DC, V, and AUTO buttons. The AC, the last data point is briefly displayed followed
AUTO, and mV annunciators are displayed. by the reading (data). Other data points can be
Pressing in any of the other range buttons acti- displayed by holding in the RCL button. Turn off
vates manual ranging. This is indicated by the the DATA LOGGER by pressing the STO/CLR
absence of the AUTO annunciator. button again.
4. Select DC volts by releasing (out position) the
AC/DC button. V is still selected. The AC annun-
ciator turns off. 1 .lO ACCESSORIES
5. Select the autoranging OHMS by pressing in the The following accessories can be used with the Model
AUTO, and a buttons. DC must still be selected. 197A.
The n (omega) symbol is displayed. Press the
MODEL 1010 SINGLE RACK MOUNTING KIT - Used to
AC/DC button in (means select AC) and note the
mount one Model 197A in a standard 5-l /2" x 19" rack.
"Err" message is displayed. This indicates an
invalid mode. MODEL 1017 DUAL RACK MOUNTING KIT - Used to
6. Select AC or DC current by setting the AC/DC mount two Model 197As in a standard 5-l/4" x 19" rack.
button accordingly and pressing in the A button. MODEL 1301 TEMPERATURE PROBE - A rugged low
The annunciator that reflects the selected mode in cost temperature probe designed to allow precision tem-
displayed. Note that current will not autorange. perature measurements from -55 to 150