Model
197A Autoranging Microvolt DMM
User’s Manual
MY MY
A GREATER MEASURE:~OF CONFIDENCE A GREATER MEASURE:~OF CONFIDENCE
WARRANTY
Keithley Instruments, Inc. warrants this product to be free from defects in material and workmanship for a period of I year
from date of shipment.
Keithley Instruments, Inc. warrants the following items for 90 days from the date of shipment: probes, cables, rechargeable
batteries, diskettes, and documentation.
During the warranty period, we will, at our option, either repair or replace any product that proves to be defective.
To exercise this warranty, write or call your local Keithley representative, or contact Keithley headquarters in Cleveland, Ohio.
You will be given prompt assistance and return instructions. Send the product, transportation prepaid, to the indicated service
facility. Repairs will be made and the product returned, transportation prepaid. Repaired or replaced products are warranted for
the balance of the original warranty period, or at least 90 days.
LIMITATION OF WARRANTY
This warranty does not apply to defects resulting from product modification without Keithley’s express written consent, or
misuse of any product or part. This warranty also does not apply to fuses, software, non-rechargeable batteries, damage from
battery leakage, or problems arising from normal wear or failure to follow instructions.
THIS WARRANTY IS IN LIEU OF ALL OTHER WARRANTIES, EXPRESSED OR IMPLIED, INCLUDING ANY
IMPLIED WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. THE REMEDIES PROVIDED HEREIN ARE BUYER’S SOLE AND EXCLUSIVE REMEDIES.
NEITHER KEITHLEY INSTRUMENTS, INC. NOR ANY OF ITS EMPLOYEES SHALL BE LIABLE FOR ANY DIRECT,
INDIRECT, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OF ITS
INSTRUMENTS AND SOFTWARE EVEN IF KEITHLEY INSTRUMENTS, INC., HAS BEEN ADVISED IN ADVANCE
OF THE POSSIBILITY OF SUCH DAMAGES. SUCH EXCLUDED DAMAGES SHALL INCLUDE. BUT ARE NOT LIMITED TO: COSTS OF REMOVAL AND INSTALLATION, LOSSES SUSTAINED AS THE RESULT OF INJURY TO ANY
PERSON, OR DAMAGE TO PROPERTY.
Keithley Instruments, Inc. * 28775 Aurora Road * Cleveland, OH 44 I39 * 440-248-0400 * Fax: 440-248-6 I68 * http://www.keithley.com
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 withstanding 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
this product and any associated instrumentation. Although some instruments and accessories would normally be used with non-hazardous voltages, there are situations whcrc hazardous conditions
may be present.
This product is intended for use by qualified personnel who recognize shock hazards and are familiar with the safety precautions required to avoid possible injury. Read the operating information
cweiully beiorc using the product.
The types of product osers arc:
Responsible body is the individual or group responsible for the use
and maintenance oi equipment, for ensuring that the equipment is
operated within its specifications and operating limits, and ior ensuring that operators are adequately trained.
Operators use the product ior its intended function. They most be
trained in electrical safety procedures and proper use of the instnment. They most bc protected from electric shock and contact with
hazardous live circuits.
Maintenance personnel perform routine procedures on the product
to keep it operating, ior example, setting the line voltage or replacing consumable materials. Maintenance procedures are described in
the manual. The procedures explicitly state if the operator may perform them. Otherwise, they should be performed only by service
pCIS”tttEl.
Service personnel arc trained to work on live circuits, and perform
safe installations and repairs of products. Only properly trained service personnel may perform installation and service procedures.
Keitbley products are designed ior “se with electrical signals that
are rated Installation Category I and Installation Category II, as described in the International Electratechnical Commission (IEC!)
Standard IEC 60664. Most measurement, conaol, and data I/O signals are Installation Category I and most not be directly connected
to mains voltage or to voltage sowces with high transientovcr-volt-
ages. Installation Category II connections require protection for
high transient over-voltages often associated with local AC mains
connections. The user should assome all measurement, control, and
data I/O connections zwe for connection to Category 1 sources unless otherwise marked or described in the Manual.
Exercise extreme caution when a shock hazard is present. Lethal
voltage may be present on cable connector jacks or test fixtures. The
American National Standards Institute (ANSI) states that a shock
hazard exists when voltage levels greater than 30V RMS, 42.4V
peak, or 60VDC are present. A good safety practice is to expect
that hazardous voltage is present in any unknown circuit before
measuring.
Users oi this product must be protected from electric shock at all
times. The responsible body must ensure that users are prevented
access and/or insulated from every connection point. In some cases,
connections must be exposed to potential human contact. Product
users in these circumstances must be trained to protect themselves
from the risk of electric shock. If the circuit is capable of operating
at or above 1000 volts, no conductive part of the circuit may be
exposed.
Do not connect switching cards directly to unlimited power circtdts.
They are intended to be used with impedance limited sources.
NEVER connect switching cards directly to AC mains. When connecting sources to switching cards, install protective devices to limit fault current and voltage to the card.
Before operating an instrument, make sore the line cord is connected to a properly grounded power receptacle. Inspect the connecting
cables, test leads, and jumpers for possible wear, cracks, or breaks
before each use.
When installing equipment where access to the main power cord is
restricted, such as rack mounting, a separate main input power disconnect device must be provided, in close proximity to the equipment and within easy reach of the operator.
For maximum safety, do not touch the product, test cables, or any
other instruments while power is applied to the circuit under test.
ALWAYS remove power from the entire test system and discharge
any capacitors before: connecting or disconnecting cables or jumpers, installing or removing switching cards, or making internal
changes, such as installing or removing jumpers.
Do not touch any object that could provide a current path to the common side oitbe circuit under test or power line (earth) ground. Always
make mea~uremem with dry hands while standing on a dry, insulated
surface capable of withstanding the voltage being measured.
The instrument and accessories must be used in accordance with its
specifications and operating instructions or the safety of the equipment may be impaired.
Do not exceed the maximum signal levels of the instruments and accessories, as defined in the specifications and operating inform%
lion, and as shown on the instrument or test fixture panels, or
switching card.
When fuses are used in a product, replace with same type and rating
for continued protection against fire hazard.
Chassis connections must only he used as shield connections for
measuring circuits, NOT as safety earth ground connections.
If you are using a test fixture, keep the lid closed while power is applied to the device under test. Safe operation requires the use of a
lid interlock.
Ifa@ screw is present, connect it to safety earth ground using the
wire recommended in the user documentation.
The n ! symbol on an instrument indicates that the user should refer to the operating instructions located in the manual.
Then
sure 1000 volts or more, including the combined effect of normal
and common mode voltages. Use standard safety precautions to
avoid personal contact with these voltages.
symbol on an instrument shows that it can source or mea-
The WARNING heading in a manual explains dangers that might
result in personal injury or death. Always read the associated information very carefully before performing the indicated procedure.
The CAUTION heading in a manual explains hazards that could
damage the instrument. Such damage may invalidate the warranty.
lnslrumentation and accessories shall not be connected to humans.
Before performing any maintenance, disconnect the line cord and
all test cables.
To maintain protection from electric shock and fire, replacement
components in mains circuits, including the power transformer, test
leads, and input jacks, must be purchased from Keithley Instrumerits. Standard fuses, with applicable national safety approvals,
may be used if the rating and type are the same. Other components
that are not safety related may be purchased from other suppliers as
long as they are equivalent to the original component. (Note that selected parts should be purchased only through Keithley Instruments
to maintain accumcy and functionality of the product.) If you are
unsure about the applicability of a replacement component, call a
Keithley Instruments office for information.
To clean an instrument, use a damp cloth or mild, water based
cleaner. Clean the exterior of the instrument only. Do not apply
cleaner directly to the instrument or allow liquids to enter or spill
on the insrmment. Products that consist of a circuit board with no
case or chassis (e.g., data acquisition board for installation into a
computer) should never require cleaning if handled according to instructions. If the board becomes contaminated and operation is affected, the board should be returned to the factory for proper
cleaning/servicing.
7JOl
197A 5%-D&$ Mukimeter Specifications
DCVOLTS
DCAMPS
.4CC”RMx”*
*(?&r*g + CO”rm,
Table of Contents
SECTION 1
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
1.10
SECTION
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
2.4.5
2.5
2.6
2.6.1
2.6.2
2.6.3 warmup
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
- General Information
INTRODUCTION ...................................................
FEATURES .........................................................
WARRANTY INFORMATION ........................................
MANUALADDENDA ...............................................
SAFETY SYMBOLS AND TERMS .....................................
SPECIFICATIONS.. .................................................
UNPACKING AND INSPECTION .....................................
USING THE MODEL 197A MANUAL .................................
INITIALOPERATION ...............................................
ACCESSORIES ......................................................
2 - Bench Operation
INTRODUCTION .........................................................................
HIGH ENERGY CIRCUIT SAFETY PRECAUTIONS
PREI’ARATIONFORUSE ..................................................................
LinePower .............................................................................
BatteryPackPower ......................................................................
BatteryCharging ........................................................................
FRONT AND REAR PANEL FAMILIARIZATION
Display
FrontPanelControls .....................................................................
InputTerminals .........................................................................
Current FuseReplacement
RearPanelSwitches .....................................................................
ERRORMESSAGES .......................................................................
OPERATINGCONDITlONS ................................................................
Environmental Conditions ................................................................
MaximumAllowableInputs ..............................................................
BASICBENCHMEASUREMENTS
PowerUp ..............................................................................
Relative Mode ..........................................................................
DCVoltageMeasurement .................................................................
TRMSACVoltageMeasurements ..........................................................
Microvolt Measurement Considerations
ResistanceMeasurements.. ...............................................................
Current Measurements (DC or TRMS AC)
ACI’lusDCMeasurements ...............................................................
dB Measurements .......................................................................
dB Measurement Considerations and Applications
MIN/MAX and 100 Point Data Logger Operation
DiodeTest ..............................................................................
........................................... 2-l
............................................. 2-2
................................................................................
................................................................
...............................................................................
..........................................................
....................................................
..................................................
...........................................
...........................................
2-l
2-2
2-2
2-2
2-2
2-2
2-4
2-4
2-4
2-5
2-5
2-5
2-5
2-5
2-b
2-b
2-b
2-b
2-7
2-8
2-8
2-9
z-11
z-12
2-13
2-15
2-16
2-16
2.8
2.8.1
2.8.2
2.8.3
2.8.4
TRMSCONSIDERATIONS
ACVoltageOffset
TRMSMeasurementComparison ..........................................................
CrestFactor
Extended Frequency Response ............................................................
............................................................................
.................................................................
.......................................................................
2-17
Z-17
2-17
2-17
2-17
SECTION
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
INTRODUCTION..
ENVIRONMENTAL CONDITIONS
RECOMMENDED TEST EQUIPMENT
INITIAL CONDITIONS ..................
VERIFICATION PROCEDURE ............
SECTION
4.1
4.2
4.3
4.4
4.5
4.5.1
4.5.2
4.6
4.6.1
4.6.2
4.6.3
4.6.4
4.6.5
4.6.6
4.6.7
4.6.8
INTRODUCTION
DISASSEMBLY INSTRUCTIONS
BATTERY PACK (Model 1978) INSTALLATION
LINE VOLTAGE SELECTION ...............................................................
FUSEREPLACEMENT ....................................................................
FRONTPANELCALIBRATION
3 - Performance Verification
.....................
.......
DC Voltage Accuracy Check ............
AC Voltage Accuracy Check ............
Resistance Accuracy Check .............
DC Current Accuracy Check ............
AC Current Accuracy Check ............
.................................................
.................................................
.................................................
.....
.................................................
.................................................
.................................................
.................................................
.................................................
.................................................
.................................................
4 - Maintenance
......................................................................... 4-1
............................................................ 4-l
...............................................
LineFuseReplacement ...................................................................
Current Fuse Replacement ................................................................
.............................................................
Recommended Calibration Equipment
Environmental Conditions
CalibrationSwitch
DC Voltage Calibration
ACVolageCalbration ...................................................................
FrequencyCompensation ................................................................
Resistance Calibration ...................................................................
CalibrationStorage
.......................................................................
................................................................ 4-6
................................................................... 4-6
......................................................................
.....................................................
3-l
3-l
3-1
3-l
3-2
3-2
3-3
3-4
3-6
3-7
4-3
4-4
4-5
4-5
4-5
4-5
4-6
4-6
4-7
4-7
4-9
4-10
List of Illustrations
SECTION
Figure 2-l
Figure 2-2
Figure 2-3
Figure 2-4
Figure 2-5
Figure 2-6
Figure 2-7
Figure 2-8
Figure 2-9
Figure Z-10
2 - Bench Operation
SECTION 3
Figure 3-1
Figure 3-2
Figure 3-3
Figure 3-4
Figure 3-5
Figure 3-6
Figure 3-7
Figure 3-8
Model 197A Front Panel
Model 197A Rear Panel
DC Voltage Measurements
TRMS AC Voltage Measurements
Four Terminal Zeroing
Two Terminal Resistance Measurement
Four Terminal Resistance Measurement
Current Measurement Between 2000mA and 20A
Current Measurements up to 2000mA
Typical ACV Frequency Response
- Performance Verification
Connections for DCV Verification
Connections for ACV Verification
Connections for 200R 2kQ and 2Okn Range Verification (4.terminal)
Connections for 2OOkQ through Ma Ranges Verification (2-terminal)
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 (2000mA to SOA)
.......................................................
.......................................................
................................
..................................
................................
..................................
........................
.........................
2-3
2-3
2-7
2-8
2-10
2-11
2.11
2-l 2
2-12
2.18
3-2
3-4
3-5
3-5
3-6
3-7
3-R
3-8
SECTION
Figure 41
Figure 42
Figure 43
Figure 4-4
Figure 4-5
Figure 4-6
4 - Maintenance
Model 197A Miscellaneous Parts
Display Assembly Exploded View
DC Voltage Calibration Configuration
AC Voltage Calibration Configuration
ZOO, 2k and 20k Four Wire Resistance Calibration
2OOk, 2M and 20M Two Wire Resistance Calibration.
.......................................................
......................................................
..................................................
..................................................
.........................................
......................................
4-2
4-4
4-7
4-8
4-9
4-10
List of Tables
SECTION
Table 2-1
Table 2-2
Table 2-3
Table 2-4
Table 2-5
Table 2-6
Table 2-7
Table 2-8
2 - Bench Operation
ErrorMessages .......................................................................
Model 197A Maximum Allowable Inputs
ResistanceRanges .....................................................................
dB Specifications for DC Volts (6000 Ref)
dB Specifications for AC Volts (6OOQ Ref)
Selectable Reference Impedances
Levels for Other Reference Impedances
Comparison of Average and TRMS Meter Readings
SECTION 3 -
Table 3-l
Table 3-2
Table 3-3
Table 3-4
Table 3-5
Table 3-6
SECTION
Table 4-l
Table 4-2
Table 4-3
Table 4-4
Table 4-5
Equipment Specifications
Limits for DC Voltage Verification
Limits for AC Voltage Verification
Limits for Resistance Verification
Limits for AC Current Verification
4 - Maintenance
lnput Terminal Identification ...........................................................
Recommended Calibration Equipment
DCVoltageCalibration ................................................................
.................................................
.................................................
.................................................
........................................................
..................................................
........................................
Performance Verification
...........................................
...................................
...................................
....................................
Limits for DC Current Verification
ACVoltageCalibration ................................................................
ResistanceCalibration .................................................................
...................................
...................................
...................................................
.............
.............
.............
.............
.............
.............
2-5
2-6
2-10
2-13
2-13
2-13
2-14
2-19
3-2
3-3
3-3
3-4
3-7
3-9
4-3
4-6
4-7
4-9
4-9
SECTION 1
General Information
1.1 INTRODUCTION
The Model 197A is a six function, 5-l/2 digit resolution
autoranging digital multimeter with a ?220,000 count
LCD (Liquid Crystal Display). This A/D range is greater
than the normal +199,999 count A/D used in many 5-l /2
digit DMMs. The 5-l /2 digit resolution allows the Model
197A tomeasureDC voltage for lpV/count to IOOOV. AC
voltage and current measurements are standard in the
Model 197A. TRMS ACV capability ranges from lpVv/
count to 750V. The Model 197A measures res&ance from
1rnQ to 22OMQ on seven resistance ranges. The Model
197A has six current ranges that measure current from
1nA (WA) to 10A.
The dB function makes it possible to compress a large
range of readings into a much smaller scope. Model 197A
dBm measurements can be referenced to 50,75,93,135,
300 or 6OOQ (default), but can be modified with the use of
the relative (REL) feature.
The Model 197A has two IEEE-488 interface options: The
Model 1972A and the Model 1973A. These optional inter-
faces enhance the capabilities of the Model 197A by allowing programmed control over the IEEE-488 bus. The
Model 1977-A 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 197A includes the following features:
1. Six Measurement Functions - DCV, ACV, DCA,
ACA, OHMS and dB all built in.
2. @EL) Relative Mode - The relative mode allows
offsets to be nulled out (e.g. test lead resistance for
low resistance measurements) and selects a variety
of reference impedances for dB measurements.
3. Digital Calibration - A non-volatile RAM stores
calibration constants and can be performed from the
front panel or over the IEEE-488 bus.
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
panel or over the IEEE-488 bus. In the talk-only
mode, the output rate can also be programmed.
5. Autoranging - The Model 197A includes a fast
autoranging feature for easier measurements.
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
eliminate the voltage from across the current carrying leads.
8. Sensitivity - The Model 197A has lpV, lmX2 and
1nA sensitivity. The 1pV of sensitivity allows minute
levels of offset, temperature etc. A ltisensitivity allows low current measurements without special
equipment. Measure leakage, bias and offset CUP
l-1
SECTION 1
General Information
rent. A lma sensitivity allows easy low resistance
measurements.
9. Electroluminescent
electroluminescent display backlight is used to enhance
the liquid crystal display under low light or dark
conditions.
10. dB Reference Impedances - Selectable dB reference
impedances of 5OQ 754 930, 1354 3OOn and 6OOn
(default).
Display Backlight - An
1.3 WARRANTY INFORMATION
Warranty information may be found on the inside front
cover of this manual. Should it become necessary to
exercise the warranty, contact your Keithley representative
or the factory to determine the proper course of action.
Keithley Instruments maintains service facilities in the
United States, United Kingdom and throughout Europe.
Information concerning the application, operation or
service of your instrument may be directed to the
applications engineer at any of these locations. Check the
inside front cover for addresses.
1.4 MANUAL ADDENDA
1.6 SPECIFICATIONS
Detailed Model 197A specifications may be found preceding the table of contents of this manual.
1.7 UNPACKING AND INSPECTION
The Model 197A 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 material in case reshipment is necessary. The following items are shipped with
every Model 197A order:
l
Model 197A Autoranging DMM
. Model 197A User’s Manual
. Model 1751 Safety Shrouded Test Leads
l
Additional accessories as ordered.
If an additional instruction manual is required, order the
manual package (K&Hey Part Number 197A-901-00). The
manual package includes an instruction manual and any
applicable addenda.
information concerning improvements or changes to this
instrument which occur after the printing of this manual
will be found on an addendum sheet included with this
manual. Be sure to review these changes before attempting
to operate or 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 197A.
The symbol
should refer to the operating instructions in this manual.
The symbol
tial of 1OOOV or more may be present on the terminal(s).
Standard safety practices should be observed when such
dangerous levels are encountered.
The WARNING
gers that could result in personal injury or death.
The
CAUTION
ards that could damage the instrument.
on the instrument denotes the user
A
on the instrument denotes that a poten-
A
heading used in this manual explains dan-
heading used in this manual explains haz-
1.6 USING THE MODEL 197A MANUAL
This manual contains information necessary for operating
and servicing the Model 197A Autoranging Microvolt
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
follows:
Section 2 contains detailed bench operation information
for the Model 197A.
Section 3 contains the information needed to verify the
accuracy of the Model 197A. l’erformance verification
can be done upon receipt of the unit or whenever the
basic accuracy of the instrument is in question.
Section 4 contains information on maintenance and calibration for the Model 197A.
NOTE
The Models 1973A and 1972A IEEE-488 interfaces come supplied with their own manual.
1-2
SECTION 1
General Information
1.9 INITIAL OPERATION
Perform the following steps in sequence to acquaint yourself with the basic operation of the Model 197A.
Verify that the instrument was not damaged in transit,
(see paragraph 1.7).
Carefully read over all safety information (see Section 2
Basic Operation).
Refer to paragraph 2.3 (Line Power) and set the line
voltage switch. Connect the female end of the power
cord to the AC receptacle on the rear of the Model 197A.
Plug the other end of the line 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 LO
input terminals. Connect the red test lead to the
HI terminal and the black test lead to the LO terminal. Short the test leads 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 button. V is still selected. The AC annunciator turns off.
5.
Select the autoranging OHMS by pressing in the
AUTO, and a buttons. DC must still be selected.
The n (omega) symbol is displayed. Press the
AC/DC button in (means select AC) and note the
“Err” message is displayed. This indicates an
invalid mode.
6.
Select AC or DC current by setting the AC/DC
button accordingly and pressing in the A button.
The annunciator that reflects the selected mode in
displayed. Note that current will not autorange.
The 10A and LO terminals must be used on the
10A range.
7.
Select dB by selecting AC or DC volts and pressing the dB button. The dB annunciator will turn
on and the default reference impedance (600R)
will be displayed momentarily. Pressing dB a sec-
ond time disables the dB measurement mode. To
select an alternate dB reference impedance,
enable dB as previously described, but hold in the
dB button to scroll through the alternate impedance selections. Release the dB button when the
desired dB reference impedance is displayed.
When finished, again press dB to exit the dB
mode.
The REL (relative) feature can be used with any
measurement function: Volts, Amps, Ohms, or
dB. For example, select the ohms function and
autorange. The display reads approximately
000.14OQ which is the test lead resistance. Press
the REL button. The REL annunciator is turned
on and the display reads OOO.OOOfi. The relative
level of 000.14n will be subtracted from all subsequent measurements. Press the REL button a second time to cancel the REL level.
To activate the 100 point DATA LOGGER with
minimum/maximum, press and hold in the
STOiCLR button. When the reading rate r=O is
displayed release the STO/CLR button. The ST0
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.
1 .lO ACCESSORIES
The following accessories can be used with the Model
197A.
MODEL 1010 SINGLE RACK MOUNTING KIT - Used to
mount one Model 197A in a standard 5-l /2” x 19” rack.
MODEL 1017 DUAL RACK MOUNTING KIT - Used to
mount two Model 197As in a standard 5-l/4” x 19” rack.
MODEL 1301 TEMPERATURE PROBE - A rugged low
cost temperature probe designed to allow precision temperature measurements from -55 to 150°C.
MODEL 1600A HIGH VOLTAGE PROBE -Extends DMM
measurements to 4OkV.
MODEL 1641 KELVIN TEST LEAD SET - Special clip
leads allow 4terminal measurements to be made while
making only two connections.
l-3
SECTION 1
General Information
MODEL 1651 50-AMPERE CURRENT SHUNT - The
external O.OOlQ il% 4.terminal shunt, permits current
measurements from 0 to 50A AC or DC.
MODEL 1681 CLIP ON TEST LEAD SET - Contains two
leads, 1.2m (48”) long terminated with banana plugs and
spring action clip probes.
MODEL 1682 R.F PROBE - Permits voltage measurements
from 1OkHz to 250MHz. AC to DC transfer accuracy is
ildB from 1OOkHz to 250MHz at IV, peak responding, calibrated in RMS of a sine wave.
MODEL 1684 HARD SHELL CARRYING CASE - Hard
vinyl case, 1OOmm x 3OOmm x 350mm (4” x 13” x 14”) has a
fitted foam insert with room for the Model 197A, an
instruction manual and small accessories.
MODEL 1685 CLAMP ON AC PROBE -Measure AC CUTrent by clamping on to a single conductor. Interruption of
the circuit is unnecessary. The Model 1685 detects currents
by sensing the changing magnetic produced by the current
flow.
MODEL 1751 SAFETY TEST LEADS-This test lead set is
supplied with every Model 197A. Finger guards and
shrouded banana plugs help minimize the chance of mak-
ing contact with live circuitry
MODEL 1754 UNIVERSAL TEST LEAD KIT - A 12 piece
test lead kit, with interchangeable plug-in accessories.
Included in the kit is one set of test leads (l-red, l-black),
two spade lugs, two standard banana plugs, two phone tips
(.06 DIA.) two hooks and miniature alligator clips (with
boots).
MODEL 1972A ANALOG OUTPUT IEEE-488 INTERFACE - The Model 1972A is an optional IEEE-488
interface that includes all of the logic necessary to interface
the Model 197A to the IEEE-488 bus. The Model 1972A is
similar to the Model 1973A however, it contains an analog
output. The analog output is a scaled output that follows
the display of the Model 197A. The Model 1972A is field
installable.
MODEL 1973A IEEE-488 INTERFACE -The Model 1973A
is an optional IEEE-488 interface for the Model 197A. This
interface adds extra versatility to the Model 197A by
allowing the hansmission of data and commands ova the
IEEE-486 bus. The interface provides all the logic necessary
to interface the Model 197A to the bus using standard
IEEE-488-1978 protocol. The Model 1973A is field
installable.
MODEL 1978 RECHARGEABLE BATTERY PACK - The
rechargeable battery pack allows off line or in the field
operation of the Model 197A. The pack typically provides
five hours operation from full charge. The battery pack
contains its own charging circuit and can be recharged
within 15 hours. The 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 ft.) in length and has a standard IEEE-488 connec-
tor at each end. The Model 7008-6 is 1.8m (6 ft.) in length
and has a standard IEEE-488 connector at each end.
l-4
SECTION
2
Bench Operation
2.1 INTRODUCTION
This section contains the information needed to prepare and
operate the Model 197A as a bench DMM. Bench operation
consists of using the Model 197A to perform basic voltage,
current, resistance and dB measurements. Also, the opera-
tion
of the data logger is covered. The capabilities of the
Model 197A can be enhanced with the addition of the
Model 1973A or Model 1972A IEEE-488 interface. IEEE
operation is covered in the Model 1973/1972 Manual. The
optional battery pack (Model 1978) is also covered in this
section.
2.2 HIGH ENERGY CIRCUIT SAFETY
PRECAUTIONS
To optimize safety when measuring voltage in high energy
distribution circuits, read and use the directions in the following warning.
WARNING
Dangerous arcs of an explosive nature in a high
energy circuit can cau8e *were personal injury
or death. If the meter is connected to a high
energy circuit when set to a current range, low
resistance range or any other low impedance
range, the circuit is virtually shorted. Dangerous
arcing can result even when the meter is set to a
voltage range if the minimum voltage spacing is
reduced.
When making measurements in high energy circuits use test
leads that meet the following requirements:
l
Test leads should be fully insulated.
l
Only use test leads that can be connected to the circuit
(e.g. alligator clips, spade lugs, etc.) for hands-off
measurements.
l
Do not use test leads that decrease voltage spacing. This
diminishes arc protection and creates a hazardous
condition.
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.
2. Attach the test leads to the circuit under test. Use appropriate safety rated test leads for this application.
3. Set the DMM to the proper function and range.
4. Energize the circuit using the installed connect-
disconnect device and make measurements without
disconnecting the DMM.
5. De-energize the circuit using the installed connect-
disconnect device.
6. Disconnect the test leads from the circuit under test.
CAUTION
The maximum common-mode input voltage (the
voltage behwen input LO and chassis ground)
is 500V peak. Exceeding this value may damage
the instrument.
2-l
SECTION 2
Bench Operation
2.3 PREPARATION FOR USE
2.3.1 Line Power
The Model 197A has a three-wire line cord which mates
with third-wire grounded receptacles. Connect the instrument to AC line power as follows:
1. Set the LINE VOLTAGE switch on the back of the
instrument to correspond to line voltage available.
Ranges are 105V-125V or ZlOV-250V 50/60Hz AC.
CAUTION
Be sure that the power line voltage agrees with
the indicated range on the panel of the instrument. Failure to observe this precaution may
result in instrument damage.
2. Connect the female end of the power cord to the AC
receptacle on the rear panel of the Model 197A. Plug in
the other end of the power cord into a properly
grounded receptacle.
WARNING
The Model 197A is equipped with a 3-wire
power cord that contains a separate ground
wire and is designed to be used with grounded
outlets. Failure to use a grounded outlet may
result in personal injury or death because of
electric shock.
of the power switch state. When the battery pack is first
installed, or if it is completely discharged, allow it to
charge for a minimum of 15 hours.
NOTE
For maximum battery efficiency only charge the
battery pack after it has become completely dis-
charged (BAT annunciator on). DO not make
measurements with BAT annunciator on as the
readings may be erroneous.
If the battery pack is not maintaining a charge (BAT off) for
five hours after a full 15 hour charge cycle, do the
following.
A.
Disconnect the Model 197A from line power.
8.
Turn on the Model 197A and leave it on to completely discharge the battery pack.
C.
Connect the Model 197A to line power and charge
the battery pack for 15 hours with power off.
D.
Repeat steps A through C three more times. The
battery pack should again be good for typically five
hours.
3. When the Model 197A is in use on line power, the battery charger maintains a trickle charge on the battery
pack.
2.3.2 Battery Pack Power
The Model 197A 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 197A for typically five hours. The BAT
annunciator turns on when the charge is insufficient to
maintain accurate readings.
2.3.3 Battery Charging
After the Model 1978 is installed in the Model 197A it can
be charged and recharged as follows:
1. Connect the instrument to line power as described in
paragraph 2.3.1.
2. The battery charge circuit is energized automatically
when the instrument is plugged into the AC line. The
rate at which the batteries charge is the same regardless
NOTE
The IEEE options (Model 1972A and Model
1973A) do not run off of battery power.
2.4 FRONT AND REAR PANEL
FAMlLlARlZATlON
Figure 2-1, Figure 2-2 and the following paragraphs, provide a brief description of the display, front panel controls,
input terminals, and rear panel switches.
2.4.1 Display
The Model 197A has a 5-l/2 digit liquid crystal display
(LCD). Positive polarity is implied by the absence of the
minus (-) sign The following annunciators are displayed
on the LCU.
2-2
SECTION 2
Bench Operation
REL
OCY
DATA LOGGER
00
STOICLR
Model 197A Front Panel
RCL
=y] 197A AUTORANGING MICROVOLT OMM
Figure 2-2.
BAT-Low battery indicator for the Model 1978.
AC -AC selected (DC implied by the absence of the AC
annunciator).
mV or V-Millivolts or volts.
0, kQ or MR -Ohms, kilohms or megohms.
p, mA or A - Microamps, milliamps or amps.
RMT (Remote) - Model 197A being controlled over the
IEEE-468 bus (Model 1973A or Model 1972A installed).
Model 197A Rear Panel
C - Model 197A in calibration mode.
AUTO - Autorange.
REL - Relative.
dB -Decibel measurement mode
ST0 -Data being stored.
RCL - Data being recalled. RCL flashes when buffer is full
during logging cycle.
2-3
SECTlON 2
Bench Operation
2.4.2 Front Panel Controls
ON/OFF - Pressing this button turns on the Model
197A. Releasing (out) this button turns the ins+n.nnent
off.
REL - (RELATIVE) -This button allows readings to be
made with respect to any baseline value. Also allows detailed information on REL.
dB - This button selects the dB function and is used
along with the ACV or DCV function. Measurements are
made in dBm referenced to 50, 75,93,135,300 or 6OOQ
(default). REL can be used to make any voltage level the
OdB reference point for dB measurements.
DATA LOGGER and MIN/MAX - 100 reading storage
capacity; records data at one of seven selectable rates
from 3 reading/second to 1 reading/hour or by manual
trigger (r=6). Also detects and stores maximum and minimum readings continuously while in the data logger
mode.
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, it selects the 10A range. There
is no autorange function for current.
2.
Manual ranging is accomplished by depressing the
appropriate range button.
2.4.3 Input Terminals
The input terminals are intended to be used with safety
shrouded test leads to help minimize the possibility of
contact with live circuits. Safety shrouded test leads
(Model 1751) are supplied with the Model 197A. Always
disconnect all unused test leads from the instrument.
HI and LO INPUT (Red and Black) -Use this pair of terminals for all volt, ohm, milliamp and dB measurements.
1. STO/CLR - Pressing this button initiates the logging sequence. Pressing this button a second time
turns off the data logger. For r=6 rate (manual trigger) every time a 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
storedinbufferlocationsO1 tolOZ.They aredepicted
on the front panel as follows: Buffer location #I is
represented by n=Ol.
AC/DC -This button is used along with the volts (V),
current (A), and dB functions. Depressing (in) this button
selects AC, releasing (out) this button selects DC. AC Q is
invalid condition. See Table 2-1.
V - Depressing this button selects the volts function.
IL - Depressing this button selects the ohms function.
The AC/DC button must be released (out).
A-Depressing (in) this button selects the current func-
tion. Up to 2A on red and black input jacks and up to 1OA
1OA and LO (White and Black) -Use this pair of terminals for measuring current up
to
10A (up to 2OA for 15
seconds).
OHMS Sense HI and LO - Use this pair of terminals
along with HI and LO input for four wire resistance
measurements.
2.4.4
Current Fuse Replacement
The current fuse protects the ZOO@ through 2OOOmA
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 aZO,OOO count display, the2Arange
can momentarily (approx. one minute) read
2.2A before the fuse will blow. This 10% overrange will not harm the instrument.
1. Turn off the power and disconnect the power line
and test leads.
2. Place the end of a tit-blade screwdriver into the slot
in the fuse holder on the front panel. Press in slightly
2-4
SECTION 2
Bench Operation
and rotate the fuse carrier on quarter turn counterclock-
wise. Release pressure and remove the fuse carrier and
the fuse.
3. Remove the defective fuse and replace it with the following type: ZA, 25OV, 3AG, normal-blow (Keithley
part number FU-13) or equivalent.
CAUTION
Use only the recommended fuse type. If a fuse
with a higher current rating is installed, instrument damage may occur.
2.4.5 Rear Panel Switches
The rear panel of the Model 197A is shown in Figure 2-2.
Note that if an IEEE-488 interface module (Mode 1972A or
1973A) is installed, a modified top cover (provided with
the interface) will be installed. The modified top cover has
clearance holes in the rear panel to provide access to the
interface connector(s) and switches. Refer to the Model
197311972 IEEE-488 Interface Instruction Manual for
details.
CALIBRATION - This slide switch is used to enable or
disable calibration of the Model 197A. In the ENABLED
position, calibration constants can be stored. In the DlSABLED position, newly entered calibration constants are
lost when the instrument is turned off. During normal
operation, keep this switch in the DISABLED position.
LINE VOLTAGE - This slide switch is used to match the
instrument to the available line power voltage.
2.5 ERROR MESSAGES
Table 2-l lists the error messages associated with basic
front panel operation. Note that the instrument has a num-
ber of other messages that are discussed in the appropriate
sections of the manual.
2.6 OPERATING CONDITIONS
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 of less than 80% up to 35°C. For ambient above
35°C &rate humidity 3% per C up to 50°C. If the instrument has been subjected to extremes of temperatures,
allow sufficient time for internal temperature to reach environmental conditions. Typically, it takes one hour to stabilize a unit that is 10yC (WF) out of the specified
temperature range.
2.6.2 Maximum Allowable Inputs
Table 2-2 lists the maximum allowable inputs for the Model
197A.
Display
r-mm--j
/--xq
(1
Table 2-I. Error Messages
Message Comments
RAM Error
Calibration Error Model 197Alocks up, but operation can be restored by pressing
(NVRAM Failure) any one of the four momentary pushbuttons. If restored,
Overrange
Invalid 52
Function (out) AC/DC pushbutton.
Model 197A locks up.
calibration is invalid as indicated by the flashing “C’
annunciator.
Overrange input applied to the Model 197A. Leading minus sign
indicates that input signal has a negative value.
“AC” and “Q” annunciators flash. Correct problem by releasing
2-5
SECTION 2
Bench Operation
Table 2-2. Model 197A Maximum Allowable Inputs
Function
DCV
ACV
DCA, ACA
a
Ranges Maximum Allowable Inputs
200mV, 2v
zo-1ooov
200mV, 2v 750Vrms, 1OOOV peak for less than 1Osec per minute 300Vrms, continuous.
20-750V 750Vrms, 1OOOV peak. 107*Hz maximum.
200~-2000mA
10A 10A continuous; 20A for 15%~ (unfused).
All 450V ueak AC or DC. 10 seconds oer minute. 350Vrms continuous.
1OOOVDC or peak AC for less than 1Osec per minute 300Vrms continuous.
1OOOVDC or peak AC.
107*Hz maximum.
2A, 250VDC
or rms (fuse protected).
2.6.3 Warm Up
The Model 197A requires one hour for warm up to achieve
rated accuracy.
2.7 BASIC BENCH MEASUREMENTS
Basic measurement techniques for using the Model 197A to
measure AC and DC volts, resistance, AC and DC current
and dB are covered in the following paragraphs. Also
included is the operation of the minimum/maximum and
100 point data logger.
WARNING
Before operating the Model 197A, observe all
previously mentioned safety precautions.
When testing high energy power circuits follow the instructions found in paragraph 2.2.
Failure to observe these and other safety pre-
cautions mentioned in this manual could result
in severe injury or death.
The LO terminal on the Model 197A is designed to float
above earth ground to avoid ground loop problems.
WARNING
Hazardous voltage may be applied to the LO
terminal. The maximum allowable voltage
between the LO terminal and chassis ground is
5OOV. Destruction of insulation, which could
present a shock hazard, may occur if the 500V
maximum is exceeded.
CAUTION
Do not exceed the maximum input limits
shown in Table 2-2.
2.7.1 Power up
NOTE
The software revision level of the Model 197A
can be displayed upon power up by running the
diagnostic program.
Turn on the Model 197A by pressing in the ON/OFF
switch. All zeroes are briefly displayed before going into
the measurement mode.
2.7.2 Relative Mode
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.
3. This reading is algebraically subtracted from all subsequent readings and displayed.
2-6
SECTION2
Bench Operation
A REL level can be established for any measurement
function (Volts, Ohms, Amps and dB) and ls effective
only on that function. Changing functions will not affect
a REL level already established. However, if another REL
level is set (on any function) the previous REL level is
cancelled. For example, place the Model 197A in the
ohms function and select the 20011 range. Short the test
leads and press the REL button. Note that the REL annunciator is on. Select DCV and note that the REL annunciator is off, indicating that there is not a REL level established for DCV. Switch back to ohms and note that the
REL level is still there. Again, go to DCV and set a REL
level of +lV. The REL annunciator turns on. Switch back
to ohms and note that the REL level for ohms is cancelled.
It is important to remember what the REL function does.
The REL function establishes a baseline. That baseline is
algebraically subtracted from all subsequent readings for
that function.
Once a REL level is established for a measurement function, that stored level will be the same regardless of what
range the Model 197A is on. For example, if +lV is established as the REL level on the 2OVDC range, +lV is also
the REL level for other DCV ranges.
The dynamic range of the display is ~400,000 counts. This
means that if a REL level of -2.OOOOOV is established, then
applying +1.99999V to the input displays +3.99999V.
Once the REL level is established, that level is algebraically subtracted from the input signal. For example: if a
+l.OOOOOV REL level is established, then applying a
+Z.OOOOOV level displays a +l.OOOOOV level.
The instrument accepts a f220,OOO count input before going into the overrange condition (OL). For example:
-l.OOOOOV REL level is established and 1.5OOOOV is applied. The instrument displays +2.5OOOOOV. If the input is
2.2OOOOV the instrument overranges.
2.7.3 DC Voltage Measurement
The Model 197A can make DC voltage measurements between 1pV and 1OOOV. The basic procedure is as follows:
1. Connect the test leads to the HI and LO INPUT terminals of the Model 197A.
2.
Select the DCV function.
3. Select a range consistent with the expected voltage.
For automatic range selection, press in the AUTO
button.
NOTE
To prolong instrument life, manual ranging is
recommended for routine measurements
above 200V.
4.
Connect the test leads to the source as shown in
Figure2-3. If the positive source terminal is connected
play shows a negative value. If the negative source
terminal is connected to the LO terminal, the display
shows a positive value.
5. Observe the display; If the “OL” message is shown,
select a 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 establishaproperbaselineforsubsequentrneasure-
to the
LO terminal of the instrument, the dis-
Figure 2-3.
DC Voltage Measurements
Input
Resistance =
> 1OOOM on 200mV and 2V Ranges.
10M.
except
2-7
SECTION 2
Bench Operation
ments on
that range. To zero the Model 197A use the fol-
lowing procedure:
1. Short the INPUT HI and LO test leads together.
2. Wait until the display reading settles. Noise and
thermal emfs may require a few moments to settle
out.
3.
Press the REL button.
The 2OOmV DC range and the ZOOR range require zero to
be set in order to achieve rated accumcy.
2.7.4
TRMS AC Voltage Measurements
The Model 197A can make TRMS AC voltage measurementsbetween lpVand750V. Tomeasure AC proceedas
follows:
1. Connect the test leads to the HI and LO terminals of
the Model 197A.
2. Select the ACV function.
3. Select a range consistent with the expected voltage.
For automatic range selection, press in the AUTO
button.
4.
Connect the test leads to the source as shown in
Figure 2-4.
NOTE
There is a small amount of offset (typically 50
counts or less) present when using the AC
function. Do not REL this level out. The reason for this is that the offset is generally negligible as compared to the input signal. For example:
offset = 22pV
applied signal = 20mV
display reading = xk20mV)z + (22~V)~
= do004 + 484 x lo-‘2
= .0200000121
This offset is seen as the last digit which is not
displayed on the Model 197A. Therefore, the
offset is negligible.
5.
Observe the display, if the “OL” message is shown,
select a higher range until a normal reading is displayed. Always use the lowest possible range to obtain the best resolution.
6. Take the reading from the display.
NOTE
See paragraph 2.8 for TRMS considerations.
When measuring AC signals disconnect any
test leads from the OHMS SENSE terminals.
2.7.5
Microvolt Measurement
Considerations
Accuracy Considerations - For sensitive measurements, other external considerations besides the Model
197A will affect the accuracy. Effects not noticeable when
working with higher voltages are significant in microvolt
signals. The Model 197A reads only the signal received at
its input; therefore, it is important that this signal be
properly transmitted from the source. The following
paragraphs indicate factors which affect accuracy, noise,
source resistance, thermal emfs and stray pick-up.
NoiseandSourceResistance-Thelimitofresolutionin
measuring voltages with the Model 197A is determined
Figure 2-4.
2-8
TRMS AC VoJtageMemrements
Caution: Maximum Input
RMS, lOOOV pk.
Input Impedance = 1MQ Shunted
/
by < 75pF
SECTION 2
Bench Operation
by the noise present. The displayed noise of the Model
197A is 1.5pV peak to peak. This noise is inherent in the
Model 197A and is the minimum amount present in all
measurements. The 1.5pV of noise is due to the insinment voltage noise. The noise at the Model 197A 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 resis-
tance and is given by the equation:
n2 = en* + (Lit)” + er2
where
n = total noise input.
= input voltage noise of the Model 197A.
en
i, = inputcurrentnoise.
IG = parallel combination of source resistance and
input impedance.
= Johnson noise of the source resistance.
e,
Even on the most sensitive range, the noise due to the
current is not applicable until R reaches approximately
1M.O. Thus, for an Rz of OR to 1MQ the noise at the input
is the inherent 1.5pV peak to peak. Beyond 1Ma the noise
due to IL becomes a limiting factor in the measurement.
Therefore, it is recommended that for sensitive
measure-
ments R be kept relatively low, if possible below 1MQ.
As an example of determining e, noise voltage generation
(due to Johnson noise of source resistance) assume that
the Model 197A is connected to a voltage source with an
internal resistance of 1MQ. At a room temperature of
20°C (29310, the p-p noise voltage generated over a
bandwidth of 1Hz will be:
er = 6.35 x lO”O jRxf
e, = 6.35 x 10-‘O 41 x 106) (1)
er = 0.635kV
Thus it is clear that optimum microvolt
measurements
with the Model 197A are possible with source resistance
as high as 1M.Q. However, this resolution will not be realized unless shielding is employed.
cuit should be shielded and the shield connected to the
Model 197A ground (particularly for low-level sources).
Improper shielding can cause the Model 197A to behave
in one or more of the following 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 197A away from strong AC magnetic sources. The
voltage induced due to magnetic flu is proportional to
the area of the loop formed by the input leads. Therefore,
minimize the loop area of the input leads and connect
each signal at only one point.
Thermal EMFs - Thermal emfs (thermoelectric poten-
tials) are generated by thermal differences between two
junctions of dissimilar metals. These can be large
com-
pared to the signal which the Model 197A can measure.
Thermal emfs can cause the following problems:
1.
Instability or zero offset is much higher than expected.
2.
The reading is sensitive to (and responds to) tem-
perature changes. This can be demonstrated by
touching the circuit, by placing a heat source near the
circuit or by a regular patten of instability (correspending to heating and air-conditioning systems or
changes in sunlight).
3.
To minimize the drift caused by thermal emfs, use
copper leads to connect the circuit to the Model
197A. A banana plug is generally sufficient and generates just a few microvolts. A clean copper conductor such as #lO bus wire is about the best for the application. The leads to the input may be shielded or
unshielded, as necessary. Refer to Shielding.
4.
Widely varying temperatures within the circuit can
also create thermal emfs. Therefore, maintain constant temperatures to minimize these thermal emfs.
A cardboard box around the circuit under test also
helps by
5.
The REL control can be used to null out constant off-
minimizing air currents.
set voltages.
2.7.6
Resistance Measurements
Shielding-The Model 197A is insensitive to AC voltages superimposed upon aDC signal at the input terminals. However, AC voltages which are extremely large
compared with the DC signal may erroneously produce a
DC output. Therefore, if there is AC interference, the cir-
The Model 197A can make resistance measurements be-
tween 1mQ and 22OMQ. The 2MQ 2OMn and 2OOMQ
ranges autorange when the I&Q button is selected. The
Model 197A provides automatic selection of 2-terminal
or 4-terminal resistance measurements. This means that
2-9
SECTION 2
Bench Operation
if the ohms sense leads are not connected, the measure
ment is done Z-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 or 4-terminal measurements on the 2OOQ range, zero must be set by the REL
function to obtain rated accurxy. For best results, on the
2OOQ, 2k.Q and 2OkQ 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:
1. Connect the test leads to the Hl and LO INPUT terminals. 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. If desired, use the autorange mode for automatic range selection.
4.
If readings are to be made on the ZOO&2 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. If 4-wire measurements are to be
made, short all four test leads as shown in Figure 2-5,
allow the reading to settle then press the REL button.
5. For 2-w& measurements connect the instrument as
shown in Figure 2-6. For 4-wire measurements, use
the connections shown in Figure 2-7,
Figure 2-5. Four Terminal Zeroing
CAUTION
The
maximum input voltage between the HI
andLO INPUT terminalsis45OVDC orpeak
AC for 10 seconds per minute, 350V RMS
contimmus.Donot exceedtbesevalues orinshument damage may occur. Table 2-3
shows the current output for various resistance ranges.
CAUTION
Incorrect readings will result if the resistance being measured is part of a live circuit.
6. Take the reading from the display.
NOTE
It is helpful to shield resistance greater than
106Q (1MQ) if a stable reading is expected.
Place the resistance in a shielded enclosure
and electrically connect the shield to the LO
input terminal of the Model 197A.
2-10
Range
200
2k
20
200
2M
20M
200M
k
k
Table 2-3. Resistance Ranges
MaxV Maximum Test Lead
Across
UnknOWn
Resistance for
<l Count Error 0
SECTION2
Bench Operation
Optional Shield
I-----
Caution: Maximum Input = 45oVUC
01 peak AC for 1 Oseclmin, 350”
RMS Continuous
1
‘igure 2-7.
2.7.7
Four Terminal Resistance Measurement
Current Measurements (DC or
TRMS AC)
The Model 197A can make DC or TRMS AC current
measurements between InA and 1OA (20A for 15 secends). If the expected current level is in question, make
the initial measurement
vent inadvertent blowing of the 2A current fuse which is
located on the front p&l.
For routine measurements above 1OA it is recommended that the Model 165150A shunt be
used.
on the 1OA range. This helps pre
NOTE
d
i
The test leads used
Optional Shield
I
Caution: Maximum Input = 45oVDC
or peak AC for 1 OsWmin. 35OV
RMS Continuous
NOTE
must
be rated to handle
20A. Twist the wires as shown in Figure 2-8 to
help in nkimidng external fields which
could affect the Model 197A or other equip-
ment.
Also, keep the test leads as short as pos-
sible to minimize voltage drop.
Select the AC4 or DCA function.
B.
- -. .-.
C. Select the lOA range.
The amps functions does
not autorange.
D. Connect the test leads to the current source as
shown in Figure 2-8 and take the reading from
the display.
1.
A.
For
current measurements
between 2000mA and
2OmA.
Connect the test leads to the 1OA and LO terminals of the Model 197A. Refer to Figure 2-8.
NOTE
Up to 5A may be applied continuously without degradation of the measurement due to
self heating effects. Above 5A derate 0.15%
rdg per amp for self heating, refer to specifica-
2-11
SECTION 2
Bench Operation
Figure 2-8. Current Measurement Between 2OOOmA and 20A
Caution: Maximum Input = IOA
tions that precede Section 1. For currents between 10A and 20A, specified accuracy can
only be obtained when measurements are
limited to a maximum of 15 seconds.
2. For current measurements up to 2OOOmA:
A. Connect the test leads to the INPUT HI and LO
terminals of the Model 197A.
B. Select the ACA or DCA function.
C. Select an appropriate range for the expected cur-
rent. The current function does not autorange.
D. Connect the test leads to the current source as
shown in Figure 2-9. If an overrange indication is
displayed, select a higher range until a normal
reading is shown. Use the lowest possible range
to obtain the best resolution.
E. Take the reading tkm.~ the display.
2.7.8 AC Plus DC Measurements
Use the Model 197A to measure TRMS on a signal which
has both AC and DC components.
l.
Measure and record theTRMS AC component as described in paragraph 2.7.4.
2.
Measure and record the DC component as described
in paragraph 2.7.3.
3.
Compute the row value from the following equation:
Em = dE%c + E*AC
Figure 2-9.
2-12
Caution: Maximum Input = 2A
Current Measurements up to 2000mA
SECTION2
Bench Oamtion
2.7.9 dB Measurements
The dB function makes it possible to compress a large
range of readings into a much smaller scope. The relationship between dB and voltage can be expressed by the
following equation.
dB=Z.Olog-
Vm
Tables 24 and 26 list the dB specifications for DC volts
and AC volts.
Table 2-4. dB Specifications for DC Volts
(600.Q Ref)
Linear
Counts
10-99 1dBm
100-999 O.ldBm
1000-9999 O.OldBm
10000-220,000 O.OldBm
Resolution Accuracv
A2dBm typical
+IdBm
+O.ldBm
9.02dBm
feature.
REL can also be used to make dB measurements
independent of impedance.
Table 2-6. Selectable Reference Impedances
The basic procedure for placing the instrument in the dB
mode is to first select AC or DC volts and then press the
dB button. The currently selected dB reference impedance will then be displayed briefly and the dB annunciatar will turn on. Note that on power up, the reference impedance will default to 6OOQ. To exit from the dB mode,
I
again press dB, or press the R or A function button.
dBm Measurements with Selectable Reference
Impedances
The Model 197A can make dB measurements referenced
to one of six selectable impedances. The selectable reference impedances are listed in Table 2-6. dB measure
ments referenced to other (non-selectable) impedances
can also be done. One method is to use the relative CREL)
Table 2-5. dB Specifications for AC Volts (6OOQ Ref)
r
dB Mode (Refi 6OO.Q)
I
Range Input
200mV
2V-750V
1mv to 2mv
(-58
to -52dBm)
2mv to 20mV
(-52
to -32dBm)
20mV to 200mV
(-32
to -12dBm)
2oomv to 750v
(-12
to +59.8dBm)
1okHz
dBm is defined as decibels above or below a 1mW reference. The default reference impedance (on power-up) of
the Model 197A is 6OOQ. With this reference impedance,
the Model 197A is designed to read OdBm when the voltage needed to dissipate 1mW through a 6000 impedance
is applied. That calculated voltage level is 0.7764V as derived from the basic power equation:
ZOHZ-
2.00
0.85
0.18
0.18
Accurac
1okI-h
2okHz 5okHz
3.00
1.10
0.18
0.18
&dBm)
2okHz-
-
2.00
0.28
0.28
2-13
SECTION 2
Bench Oneration
E=w
E = 6HY Wo600Q
E = 0.77456V
Thus with a 600R reference impedance the Model 197A
will read OdBm whenever 0.7746V is applied.
NOTE
Do not confuse reference impedance with input impedance. The input impedance of the
instrument is not modified in the dB mode.
To make dBm measurements referenced to one of the
selectable impedances, proceed as follows:
1. Connect the test leads to the INPUT HI and LO terminals of the Model 197A.
2. Select the ACV or XV function.
3. Select autorange for optimum resolution.
4. Press and hold the dB button to scroll through the
selectable reference impedances (see Table 2-6) Release the button when the desired reference impedance is displayed.
5. Connect the test leads to the voltage source.
6. Make the dBm reading from the display.
dBm Measurements with Other Non-Selectable
Reference Impedances
New ref 2
Offset (for dBm) = 10 log
6000
To make dBm measurements referenced to a non-selec-
table impedance, proceed as follows:
1. Choose the desired reference impedance.
2. Calculate or look up the offset value in Table 2-7 for
the desired reference impedance.
3. Determine dBm at the desired reference impedance
as follows:
dBm (at ref Z) = 197A reading-offset
Example: Make dBm measurements references to a
lOOf reference impedance.
Table 2-7. Levels for Other Reference
Impedances
offset
(6OOG Ref)
OdBm OdBW
8
50
-18.75 11.25
-10.79
75 - 9.03
93
135
150
300
600
1000
- 8.10
- 6.49
- 6.03
- 3.01
0.00
2.22
dBm measurements can be made with other reference
impedances. The most convenient method for using
other reference impedances is to algebraically subtract
the calculated dB offset for the desired reference impedance from the reading on the display of the Model 197A
Table 2-7 lists common reference impedances and the
corresponding offset values. The following equation can
be used to calculate the offset for impedances not listed in
Table 2-7.
2-14
Vrd. for OdBW = d=
Offset (for dBm) = 10 log
Offset (for dBW) = 10 log -3OdB
SECTION2
Bench
Operation
A. lOOn not listed in Table 2-7 so the offset must be
calculated as follows:
Offset = 10 log
Offset = -7.78dB
B. Subtract -7.78 from all subsequent displayed
readings on the Model 197A.
dBm measurements, referenced to another impedance,
can be read directly from the display of the Model 197A
by utilizing the REL feature, and an accurate voltage
source. The basic procedure is as follows:
1.
Calculate or look up the equivalent voltage level
(Table Z-7) for OdBm at the desired reference impedance.
Input that voltage level to the Model 197A.
2.
With the Model 197A in the dB mode, press the REL
3.
button.
4.
dBm measurements referenced to the desired impedance can now be read directly from the display of
the Model 197A.
dBW
Measurements
dBW is defined as decibels above or below a one watt reference. The procedure is the same as that found in paragraph 2.7.9 step 2. The only difference is that the reference point is OdBW (1W) rather than OdBm (1mW).
dBV
Measurements
dBV is defined as decibels above or below 1V (OdBV
point). This is a voltage relationship independent of impedance. The basic procedure is to simply subtract
2.22dB (Table 2-7) from all subsequent displayed readings on the Model 197A.
Relative dB Measurements
Just about any voltage level within the measurement
limit of the Model 197A can be established as the OdB
point. The basic procedure is to establish the level as the
OdB point by using RBL and making the desired dB measurement.
2.7.10 dB Measurement Considerations
and Applications
1. Typical Instrument Performance
Typically, the Model 197A will perform better than
its published dB specification. The following example will illustrate this uoint:
Using the Model 1’97A in the dB mode (6OOa ref)
A.
measure a 1mV RMS, 1kHz source &nmon application in the communications field). Typically, the Model 197A will read -57.7dBm.
The calculated dBm level for that source is
B.
-57.8dBm.
The O.ldBm error is considerably better
C.
tidBm specification. The specifications are intended to cover worst measurement conditions.
2. Measuring Circuit Gain/ Loss
Any point in a circuit can be established as the OdB
point. Measurements in that circuit are then referenced to that point expressed in terms of gain (+dB)
or loss (-dB). To set the OdB point:
A. Place the Model 197A in volts, autorange and dB.
B. Connect the Model 197A to the desired location
in the circuit.
C. Press the REL button. The display will read OdB.
D. Gain/Loss measurements can now be made ref-
erenced to the OdB point.
3. Measuring Bandwidth
The Model 197A can be used to determine the
bandwidth of an
Connect a si& generator to the input of the
A.
arn~lifier
as folkxvs:
i%+fie*.
Set the Model 197A to ACV and autorange.
B.
Connect the DMM and a frequency counter to
C.
the load of the amplifier.
Adjust the frequency of the signal generator un-
D.
til a peak AC voltage reading is measured on the
Model 197A.
Press the dB button and then press the REL but-
E.
ton. The OdB point is now established.
Increase the frequency input until the Model
F.
197A reads -3.OOdB. The frequency measured on
the frequency counter is the high end limit of the
bandwidth.
G.
Decrease the frequency input until the dB reading again falls to -3dB. The frequency measured
on the signal generator is the low end limit of the
bandwidth.
4. DeterminingQ
The Q of a tuned circuit can be determined as fol-
lows:
A. Determine the center frequency and bandwidth
as explained in paragraph 2.7.10 step 3.
B. Calculate Q by using the following formula:
Q = Center Frequency/Bandwidth
than
the
2-15
SECTTON 2
Bench Operation
2.7.11
MlNlMAX and 100 Point Data Log-
ger Operation
The data logger can store up to 100 readings and store the
minimum and maximum readings recorded during the
period that the data logger is active. The 100 points of
data are stored at one of seven selectable rates from three
per second to one reading per hour. Also,manual triggering is available (r=6). In the r=6 mode, one reading is
stored every time the STO/CLR button is pressed. Readings for
of three per second regardless of the selected rate. The
procedure for operating the data logger is as follows:
1. Connect the desired measurement
2. Logging Data:
minimum and maximum are sampled at the rate
configuration
to
the Model 197A. Make sure that the controls of the
Model 197A are set appropriately.
Press and hold the STO/CLRbutton. The follow-
A.
ing reading rates will scroll on the display:
rate/meaning
r=O kvery reading)
r=l (1 rdg/sec)
r=2 (1 rdg/lO set)
r=3 (1 rdg/min)
r=4 (1 rdg/lO min)
r=5 (1 rdg/hour)
r=6 (1 rdg every time STO/CLR is pressed)
NOTE
There is no need to select a rate if just mini-
mum/maximum readings are desired. Press
the STO/CLR button to start the logger.
c. The Model 197A displays the applied signal
and waits for the next manual rigger.
NOTE
The logging cycle can be terminated at any
time by pressing the STO/CLR button. This
shuts off the data logger. However, data is retamed and can be recalled at any time as long
as the instrument remains on. In the r=6
mode, press the RCL and the STO/CLR button to terminate the data logger cycle.
In the store mode (ST0 annunciator on) and when the
buffer is full (100 readings stored), the minimum and
maximum readings are continuously updated. When the
store mode is turned off the minimum and maximum
readings are not updated.
Data Retrieval-Data can be retrieved at any time,
3
but a flashing RCL annunciator indicates that the
maximum number of readings (100) have been
stored.
A. Press and hold in the RCL button. The display
scrolls through the data points and MIN/MAX
(LO/HI). The first data point displayed is the last
stored reading. The next two data points are the
HJ and LO readings made during that logging
cycle. Notice that the longer the RCL button is
held in the faster the data points scroll on the dis-
play.
B. Release the RCL button at the desired data point
and note the reading (data) on the display. The
data pointer can be incremented by steps of one
by momentarily holding in the RCL button.
2-16
Release the STO/CLR button when the desired
B.
reading rate is displayed. The ST0 annunciator
turns on and data is logged at the selected rate.
In the msnual trigger mode (r=6), a reading is
C.
stored every time the STO/CLR button is
pressed. The following sequence takes place after the STO/CLR button is pressed when in the
manual trigger mode.
a. The Model 197A stores the reading.
b. The buffer location number is briefly dis-
played. For example: Buffer location #l is
represented by n=Ol.
2.7.12 Diode Test
The 2k.Q and 2OOkS2 ranges can be used for testing semiconductor junctions as follows:
1.
Select the ohms function.
2.
Press the 2k and 200k button (diode symbols) in simultaneously.
3.
Display reads forward V drop of a silicon diode at
1.6mA (l.lmA for an LED), up to 2.2V. Red terminal
is positive. Accuracy is typically better than 1.5% of
reading.
T
SECTION 2
2.8 TRMS CONSIDERATIONS
Most DMMs actually measure the average value of an in-
put waveform but are calibrated to read its Rh4S equivalent. This poses no problems as long as the waveform be-
ing measured is a pure, low distortion sine wave. For
complex, nonsinusodial waveforms, however, measurements made with an averaging type meter can be grossly
inaccurate. Because of its TRMS (True Root Mean Square)
measuring capabilities, the Model 197A provides accurate AC measurement for a wide variety of AC input
waveforms.
2.8.1 AC Voltage Offset
Typically, the Model 197A displays 50 counts or less of
offset on AC volts with the input shorted. This offset is
caused by amplifier noise and offset of the TRMS converter. This offset does not affect the reading accuracy
and should not be zeroed out using the REL feature. Refer
to paragraph 2.7.4 step 4.
2.8.2
TRMS Measurement Comparison
nary sine wave with peak amplitude of 1OV. The average
value of this voltage is 6.37V, while its RMS value is
7.07V. Ifweapplythe 1.11 correction factor to theaverage
reading, it can be seen that both meters will give the same
reading, resulting in no error in the average type meter
reading.
The situation changes with the half-wave rectified sine
wave. As before, the peak value of the waveform is lOV,
but the average value drops to 3.18V. The RMS value of
this waveform is 3.86V, but the average responding meter will give 3.53V (3.18 x l.ll), creating an error of 11%.
A similar situation exists for the rectified square wave,
which has an average value of 5V and an RMS value of
7.07v. Here, the average responding meter gives a read-
ing of 5.55V 95 x 1.10, while the Model 197A gives a
TRMS reading of 5V. Other waveform comparisons can
be found in Table 2-8.
2.8.3
Crest Factor
The RMS value of a pure sine wave is equal to 0.707 times
its peak value. The average value of such a waveform is
0.637 times the peak value. Thus, for an average-responding meter, a correction factor must be designed in. This
correction factor, K, can be found by dividing the RMS
value by the average value as follows:
0.707
K=
0.637
By applying this correction factor to an averaged reading,
a typical meter can be designed to give the RMS equivalent. This works fine as long as the waveform is a pure
sine wave, but the ratios between RMS and average values of different waveforms are far from constant, and can
vary considerably.
TableZ-8 shows a comparison of common types of
waveforms. For reference, the first waveform is an ordi-
= 1.11
The crest factor of a waveform is the ratio of its peak value
to its RMS value. Thus, the crest factor specifies the dynamic range of a TRMS instrument. For sinusodial
waveforms, the crest factor is 1.414. For a symmetrical
square wave, the crest factor is unity.
The crest factor of other waveforms will, of course, depend on the waveform in question because the ratio of
peak to RMS value varies. For example, the crest factor of
a rectangular pulse is related to its duty cycle; as the duty
cycle decreases, the crest factor increases. The Model
197A has a crest factor of 3, which means the instrument
gives accurate TRMS measurements of rectangular
waveforms with duty cycles as low as 10%.
2.8.4 Extended Frequency Response
Figure 2-10 illustrates the extended frequency response
of the ACV ranges up to 1MHz.
2-17
SECTION 2
Bench Operation
‘igure 2-10
Typical ACV Frequency Response
2-18
Table 2-8. Comparison of Average and TRMS Meter Readings
SECTION 2
Bench
Operation
W*veform
Sine
+10--
0
47
Half-Wave Rectified Sine
Full-Wave Rectified Sine
Square
+,o- -
0
“a-
V2 Coupled
Peak
Value
1ov
1ov
1ov
1ov
RMS
Value
7.07v
5.oov
7.07v
lO.OOV
Average
Respondin$
Meter
Reading
7.07v
3.53v
7.07-v
ll.lOV
iC Coupled
TRMS
Meter
Reading
7.07v
5.oov
7.07v
lO.OOV
Averaging
Meter
Percent Error
0%
29.4%
0%
11%
Rectified Square Wave
Triangular Sawtooth
+,o-
0
%-
1ov
1ov
1ov
5.oov
1ov.J;
5.77v
5.55v
ll.lV l TJ
5.55v
5.oov
1ov l 47
5.77v
11%
l.llV 6 -1) y 1004
3.8%
2-19
SECTION
Performance Verification
3
3.1 INTRODUCTION
This section contains information necessary to verify that
the Model 197A’s performance is within specified accuracy.
Model 197A specifications may be found at the front of this
manual. Ideally, performance verification should be per-
formed when the instrument is first received to ensure that
no damage or change in calibration has occurred during
shipment. The verification procedure may also be per-
formed whenever instrument accuracy is suspect or follow-
i;lg calibration. If performance on any of the ranges or
functions is inconsistent with specifications, calibration
should be performed as described in Section 4.
NOTE
If the instrument does not meet specifications and
it is still under warranty (less than 12 months
since date of shipment), contact your Keithley
representative or the factory to determine the
action to be taken.
3.2 ENVIRONMENTAL CONDITIONS
All measurements should be made at an ambient tempera-
ture between WC and 28’C (65°F to 82’F) with a relative
humidity less than 80%.
3.3 RECOMMENDED TEST EQUIPMENT
Equipment for verifying the performance of the Model 197A
is listed in Table 3-1. Alternate equipment may be used as
long as equipment accuracy is at least equal to the specifications listed in Table 3-1.
NOTE
The verification limits in this section only reflect
the specifications of the Model 197A. They do not
include test equipment tolerance.
3.4 INITIAL CONDITIONS
Before performing the verification procedures, make sure
the Model 197A meets the following conditions:
1. If the instrument has been subjected to temperature
below 18°C (65°F) or above 28°C (WF), allow sufficient
time for the instrument to reach temperatures within the
range. Generally, it takes one hour to stabilize an instru-
ment that is 10°C @OF) outside of this range.
2. Turn on the Model 197A and allow it to warm up for one
hour. The instrument may be operated from either line
power or battery pack power, as long as the battery pack
has been fully charged as described in paragraph 2.3.3.
3-1
SECTION 3
Performance Verification
Table 3-1. Equipment Specifications
Mfg
Fluke
Model
343A
Fluke 5200A
Valhalla 2500E
Fluke 5450A
Fluke
5215A
Description
DC Voltage Calibrator
AC Voltage Calibrator
AC-DC Current Calibrator
Resistance Calibrator
Power Amplifier
Specifications
2oomv, 2v, 2ov, 2oov,
200mV, zv, 2ov, lOOV, SOHZ
1ooov ranges g.oos%
to
1okHz 9.05%
ZOO@, 2mA, 2OmA, 2OOm&2OOOmA, 1OA ranges
4.03%
DC, g.l% AC to 5kHz (at full scale)
IOOQ, lk!a, 1oks2,1ook!a ra”ges*O.05%; 1m.Q
range
9.01%; 1OMQ range 9.05%;
lOOMa 9.5%
IOOOV range: lOHz-30Hz 9.12%; 5OkHz-1OOkHz
20.10%; IOOV max @ 1ookHz = IOWz; 750v
max@=13kHz=10vHz
3.5 VERIFICATION PROCEDURE
The following paragraphs give the basic verification pro-
cedure
for the following functions DC volts, AC volts, re-
Do not exceed 1OOOV between the input HI
and LO terminals or damage to the instrument may occur.
CAUTION
sistance and current.
WARNING
The maximum common-mode voltage (voltage between input low and chassis ground)
is 500Vpeak. Exceeding this value may cause
a shock hazard. Some of the procedures in
this section may expose the user to dangerous voltages. Use standard safety precautions when such dangerous voltages are encountered.
2.
Connect the calibrator to the instrument as shown in
Figure 3-l.
3.
Set the calibrator to OV and enable the relative mode.
Leave the relative mode enabled for all DCV measurements. Check to see that the reading is OOO.OOOV
*l count.
4.
Apply a positive2OOmV to the HI and LO INPUT terminals. The reading must be within the limits specified in Table 3-2.
5.
For each remaining range, apply the required volt-
3.5.1 DC Voltage Accuracy Check
age as specified in Table 3-2 and verify that the readGg is Githin specifications.
1. Select the DC volt function and autorange. 6. repeat all checks with negative voltage.
Figure 3-l. Connections for DCV Verification
3-2
Performance
SECTION 3
Verification
Table 3-2. Limits for DC Voltage
Verification
197A Applied Allowable Readings
DCV Range DC Voltage (18°C to 28°C)
ZOOmV 2oo.ooomv 199.965 to 200.035
2v 2.00000 v 1.99976 to 2.00024
20 v 20.0000 v 19.9968 to 20.0032
200 v 200.000 v 199.968 to 200.032
1000 v 1000.00 v 999.83 to 1000.17
3.5.2
AC Voltage Accuracy Check
CAUTION
Do not exceed 750V RMS, 1OOOV peak
10’VHzbetweenHIandLOINPUTterminals
or instrument damage may occur.
1. Select the AC volts function and autorange. Do not
use REL to zero the offset in this procedure. Refer to
paragraph 2.7.4 step 4.
2. Connect the AC calibrator to the HI and LO INPUT
terminals of the Model 197A as shown in Figure 3-2.
3. Set the calibrator to output 2.OOOOOV at a frequency
of 50Hz. Verify that the reading is within the limits
specified in Table 3-3.
4. Repeat the 2.OOOOOV AC measurement at the other
frequencies specified in Table 3-3.
5. Check the 2OV, 200V and 750V ranges by applying
the required voltage and frequencies specified in
Table 3-3 and verifying that the readings are within
the specified limits.
197A AC
Range AC Voltage
2oomv
2v
20 v
200 v
750 v
Applied
2oo.ooomv
2.ooooov
2o.oooov
2oo.ooov
75o.ooov
‘Exceeds the V-Hz product.
Table 3-3. Limits for AC Voltage Verification
ZOHZ
197.900
to
202.100
1.97900
5oHz
199.200
to
200.800 201.400
199.200
to
2.02100
19.7900
to
2.ofo”soo
19.9200 19.8600
to
20.2100 20.0800
197.900 199.200
to
to
202.100 200.800
739.63
to
760.37
745.25 740.50
to to
754.75 759.50
1okHz
198.600
to
1.98600
to
2.01400
to
20.1400
198.600
2O:OO
2OkHZ
196.750
to
203.250
1.96750
to
2.03250
19.6750
to
20.3250
196.750
to
203.250
*
5OkHZ
189.600
to
210.400
1.93600
to
2.06400
19.3600
to
20.6400
193.600
to
206.400
*
1ookHz
189.600
to
210.400
1.93600
to
2.06400
19.3600
to
20.6400
3-3
SECTION 3
Performance
Figure 3-2. Connections for ACV Verification
Verification
3.53 Resistance Accuracy Check
Resistance verification is performed by connecting
known, precise resistance values to the HI and LO input
terminals and checking to see that the displayed reading
is within the required limits. Measurements on the 2004
2kQ and 2OkG ranges will be done using
configuration to minimi
ze
errors due to the voltage drop
across the test leads.
CAUTION
Donotexceed450VDCorpeakACforlOsec-
onds per minute, 350V nns continuous between the HI and LO INPUT terminals or the
instrument might be damaged.
1. Select the ohms function (AC/DC button must be
out) and the 2OOQ range.
2. Use Kelvin test leads (e.g. Keithley Model 1641) in
the input HI and LO, and then OHMS SENSE HI and
LO terminals. Short the leads together. Enable the
relative (REL) mode. Check to see that the display
reads 000.000. Leave the relative mode enabled for
the remaining resistance measurements.
3. Connect the 190n calibration resistor as shown in
Figure 33. Note that the 4-term&d configuration is
used for this measurement.
4. Check to see that the displayed reading is within the
limits specified in Table 3-4.
5. Connect a 1.9161 calibration resistor to the instrument as shown in Figure 3-3. Switch the instrument
the
4-terminal
to the 2kQ range. Verify that the displayed reading is
within the limits specified in Table 3-4.
6.
Connect a 19kn calibration resistor to the instrument
as shown in Figure 3-4. Switch the instrument to the
2OkQ range. Verify that the displayed reading is
within the limits specified in Table 3-4.
7. Connect a 19Ok.Q calibration resistor to the instrument as shown in Figure 3-4. Switch the instrument
to the 2OOkQ range. Verify that the displayed reading
is within the limits specified in Table 3-4. Note that
the 2-terminal configuration may be used on the
2OOkQ
and higher ranges.
8. Continue with each of the calibration resistance values listed in Table 3-4. Be sure to place the Model
197A on the correct range for each measurement.
The remaining readings may be done using 2-terminal configllration.
Table 3-4. Limits for Resistance Verification
197A
Range
200
2k
20k
200
k
2M
20M
ZOOM
Applied
Resistance
190.000 n
1.90000 kQ
19.0000 kQ
190.000 kc2
1.90000MR
19.ooooMQ
19o.oooMQ
Allowable Readings
(18°C to 28’C)
189.963 to 190.037
1.89964
to 1.90036
18.9949 to 19.0051
189.949 to 190.051
1.89931 to 1.90069
18.9770
to 19.0230
186.199 to 193.801
3-4
Figure 3-3. Connections for 20OQ 2kQand 2OkQ Range Verification (4.termimzl~
SECTION 3
Performance
Verification
Figure 3-4. Connections for 20fJkQ through MQ Ranges Verijication @terminal)
3-5
SECTION 3
Performance
Verification
3.5.4
DC Current Accuracy Check
5. Switch the Model 197A to the 2OmA range. Set the
calibrator to output +2O.OOOOmA. Verify that the dis-
DC current accuracy is checked by connecting a calibrated DC current source to the HI and LO INPUT terminals for up to 2OOOmA (10A and LO terminals for 20001x4
through lOA). The accuracy is then verified by referring
to Table 3-5 which shows the exact number of counts allowed in order to remain in the limit of the specifications.
played reading is within the limits specified in
Table 35.
6. Switch the Model 197A to the 2OOmA range. Set the
calibrator to output +2OO.OOOmA. Verify that the displayed reading is within the limits specified in
Table 3-5.
7. Switch the Model 197A to the 2OOOmA range. Set the
calibrator output +2OOO.OOmA. Verify that the read-
CAUTION
Do not exceed 2A to the HI and LO INPUT
terminals or the front panel amps fuse will
blow. Refer to paragraph 2.4.4.
1. Select the DC current function. Select the 20001x4
range.
2. Connect the instrument to the DC current calibrator
as shown in Figure 3-5. The HI side of the AMPS terminal should be connected to the HI terminal and
ing is within the limits specified in Table 3-5.
8. Set the Model 197A to the 10A range. Connect the
DC current to the 1OA and LO terminal as shown in
Figure 3-6.
NOTE
Be sure to connect the calibrator to the IOA
and LO terminals. Otherwise, applying the 5A
(as specified in Table 3-5) would blow the
front panel current fuse.
the LO side of the calibrator output should be connected to LO.
3. Set the calibrator to 00.000 and enable the relative
(REL) mode.
4. Verify that the displayed reading is within the limits limits specified in fable 3-5.
9. Apply t0.50000VDC to the current calibrator to output 5.0000A. Verify that the reading is within the
-
specified in Table 3-5. 10. Repeat steps 1 through 10 with negative current.
‘igure 3-5. Connections
3-6
for DC Current
DC Voltage
I I--.
Verification (ZOOpA to ZOOhA)
Hi Output
Lo output
1
Performance Verification
SECTION 3
DC Voltage
Calibrator ___ Calibrator
Model 34.M Model 2500E
Figure 3-6.
Table 3-5. Limits for DC Current Verification
197A
DC Range
2oo!.lA
2mA
2omA
2oomA
2ooomA
10 A
3.5.5
Connections
Applied
DC Current
2oo.oopA
2.ooooomA
2o.oooomA
2oo.ooomA
2ooo.oomA 1995.85 to 2004.15
5.0000 A
AC Current Accuracy Check
for
DC Current Verification (2000mA to 20AJ
Allowable Readings
m3”C to
28W
199.785 to 200.215
1.99785 to 2.00215
19.9785 to 20.0215
199.585 to 200.415
4.9735 to 5.0265
AC current accuracy is checked by connecting a calibrated AC current source to the HI and LO INPUT terminals for 200@ to 2OOOmA, 1OA and LO terminals for
2OOOmA to 2OA, and then verifying that the displayed
reading is within the specified range.
CAUTION
Do not exceed 2A between the HI and LO
PUT terminals or instrument damage might
occur. Refer to paragraph 2.4.4.
IN-
Hi Input
LO input
C”r,ent
1. Select the AC current function on the Model 197A.
Place the instrument in the 2OOOmA range.
2. Connect the AC calibrator to the Model 197A as
shown in Figure 3-7. Set the calibrator frequency to
1kH.z. Do not use the relative mode to zero the offset
in the AC mode.
3. Set the calibrator to output 200.000pA and switch the
Model 197A to the 200@ range. Verify that the displayed reading is within the limits specified in
Table 56.
4. Change the Model 197A to the 2mA range. Set the
calibrator to output 2.OOOOOmA. Verifj that the displayed reading is within the limits specified in
Table 3-6.
5. Change the Model 197A to the 2OmA range. Set the
calibrator to output 2O.OOOOmA. Verify that the displayed reading is within the limits specified in
‘raGle 3-6. -
6. Change the Model 197A to the 200mA range. Set the
calibrator to output 2OO.OOOmA. Verify that the displayed reading is within the limits specified in
Table 3-6.
7. Change the Model 197A to the 2OOOmA range. Set the
calibrator to output 2OOO.OOmA. Verify that the displayed reading is within the limits specified in
Tal& 3-6. -
8. Connect the calibrator to the Model 197A 10A and
LO terminals as shown in Figure 3-8. Change the
Model 197A to the 10A range.
3-7
SECTION 3
Performance Vm’fication
‘igure 3-7.
Connections for AC
Current
AC Voltage
Calibrator
Model ZOOA
Verification (2OOpA to 200CJmA~
Hi Input
LO Input
Model 2500E
Figure 3-8.
3-8
Model 343A Model 2500E
Connections for AC Current Verification (2000mA to 10AJ
Performance
SECTION 3
Verification
NOTE
Be SUE to connect the calibrator to the 10A
and LO terminals. Otherwise, applying the
5A (as specified in Table 3-6) would blow
the front panel current fuse.
Table 3-6. Limits for AC Current Verification
197A AC
Range AC Current
2001*A 200.000~A
Applied
2mA 2.ooooomA
20mA 20.0000mA
ZOOmA 200.000mA
2000mA 2000mA
10A 5.0000 A
20Hz
197.900
to
202.100
1.97900
to
2.02100
19.7900
to
20.2100
197.900
to
202.100
1979.00
to
2021.00
4.9150
to
5.0850
9. Set the calibrator to output 5.0000A. Verify that the
displayed reading is within the limts specified in
Table 3-6.
50Hz
198.300
to to
201.700
1.98300
to
2.01700
19.8300
to
20.1700
198.300
to
201.700
1983.00
to
2017.00
4.9400
to
5.0600
1OkHz
198.300
201.700
1.98300
to
2.01700
19.8300
to
20.1700
198.300
to
201.700
1983.00
to
2017.00
4.9400*
to
5.0600
195.750
to
204.250
1.95750
to
2.04250
19.5750
to
20.4250
-
3-9
SECTION
4
Maintenance
4.1 INTRODUCTION
This section contains installation, service and calibration
information for the Model 197A and Model 1978. Fuse
replacement, line voltage selection and troubleshooting procedures are also included in this section.
WARNING
The procedures described in this section are
intended for use by qualified service personnel
only. Do not perform these procedures unless
qualified to do so. Many of the steps covered in
this section expose the individual to potentially
lethal voltages that could result in personal
injury 01‘ death if normal safety precautions are
not observed.
4.2 DISASSEMBLY INSTRUCTIONS
If it is necessary to troubleshoot the instrument, replace a
component, or install an option, use the following disassembly procedure. Disassembly should be done in order that it
is presented since, in general,
ously performed procedure. Most parts referred to in the
following steps are shown in Figure 4-l.
each
step depends on a previ-
WARNING
Disconnect the line cord and any test leads from
the instrument.
Top Cover Removal
1. Turn off the power, disconnect the
all test leads from the terminals of the Model 197A.
2. Turn the unit over and remove the four screws from the
bottom of the case.
3. Turn the unit over again and separate the top cover from
the rest of the unit.
NOTE
When reinstalling the top cover, make sure to
properly position the tilt-bail/handle into the bottom cover.
IEEE-488 Interface Removal (If Installed)
The interface board is secured to the mother board by the 6pin male connector (l’1008) and a rear standoff. To remove
the interface board, gently lift it upward until it separates
from the connector and the standoff.
line cord and remove
4-1
SECTION 4
Maintenance
HOLDER BODY
CURRENT FUSE
LINE FUSE
FRONT PANELp=s&..,
Figure 4-l.
“FUNCTION 29465.5
0 FUNCTION 29465-7
A FUNCTION 29465.6
RANGE I71 294654
Model 197AMiscellaneous Parts
‘y EOnOM
SHELD
ATTERY PACK
FEET (4)
FE-10
WHITE: BJU-12-9
4-2
SECTION 4
Maintenance
Battery Pack Removal (If Installed)
The Model 1978 battery pack is mounted on top of the
mother board top shield. Perform the following steps to
remove the complete shield/battery pack assembly:
1. Disconnect the battery pack ribbon cable connector
from I’1009 on the mother board.
2. Remove the one screw that secures the top shield to
mother board. The screw is located at the rear of the
shield.
3. Carefully remove the shield/battery pack assembly
from the unit.
the
Display Board Removal
1. Disconnect the display board ribbon cable from the
mother board at J/I’1006.
2. Disconnect the input leads from the input jack terminals. Table 4-l provides terminal identification for reassembly.
3. Remove the front panel assembly from the unit.
4. The display board assembly is secured to the front
panel
with
three screws. Remove these three screws
and separate the display board assembly from the front
pXld.
5. The LCD (liquid crystal display) assembly is secured to
the display board by five tabs. To remove, gently push
the tabs away from the display board and pull the LCD
assembly away from the display board. The phosphor
layer of the electroluminescent backlight will remain
intact with the display board. An exploded view of the
display assembly is shown in Figure 4-2.
Table 4-1. Input Terminal Identification
Conductor
Input Terminal
INPUT HI
INPUT LO
0 SENSE HI
61 SENSE LO
10A INPUT
Insulator Color
Red
Black
Orange
Grey
white
Mother Board Removal
1. Disconnect the AC power receptacle from the mother
board at J/P1007.
2.
Remove the four case spacers.
3. Carefully lift the mother board out of the bottom case
cover.
WARNING
When reinstalling the mother board, make sure
the two switch guards are installed on the rear
panel CALIBRATION and LINE VOLTAGE
slide switches. These switch guards block
openings in the rear panel preventing access to
hazardous voltage.
4.3 BATTERY PACK (Model 1978) INSTALLATION
Refer to Figure 4-l and perform the following procedure to
install the battery pack:
WARNING
Disconnect the line cord and remove all test
leads from the terminals of the Model 197A.
1. Remove the top cover as explained in paragraph 4.2.
2. Remove the shield.
A. Remove the screw that secures the shield to the
mother
the shield.
B. Carefully pull up on either side of the shield.
C. Lift the shield out of the Model 197A.
3. Position the battery board as shown in Figure 4-1 and
secure it to the shield using the hvo supplied screws.
The screws are positioned through the shield into the
battely
4. Place the battery pack in the bracket and position on the
shield as shown. Route the two screws through the
shield into the bracket and tighten.
Do not allow the battery leads to short together
or damage to the batteries may occur.
5. Connect the red battery lead to the +RED terminal pin
on the battery board. Connect the black battery lead to
the -BLK terminal pin on the battery board.
Be careful not to reverse the wires (NOTE:
Reds to Red and Black to Black).
board.
The screw is located at the rear of
board fasteners.
CAUTION
CAUTION
4-3
SECTION 4
Maintenance
Window Bezel
175A-305
Mask
’ 175-306
Retainer
Backlight
DD-46
Strip Connector (2)
q cs-460.2
Fi,pre 4-2.
6. Carefully place the shield (with battery pack) back into
the Model 197A so that it seals properly on the two
spacers. Replace retaining screw in the shield.
Display Assembly Exploded View
NOTE
The retaining screw on
serves to connect the shield to circuit LO.
7. Connect the ribbon cable from the battery board to
I’1009 on the mother board. Make sure pin 1 on the
cable connects to pin 1 of l’1009. Refer to the detailed
drawing of Figure 4-l.
the rear of the shield also
CAUTION
Make a close visual inspection of the connections to ensure that they are properly connected. Otherwise, damage to the instrument
may result.
8. Reinstall the top cover as explained in paragraph 4.2
NOTE
The IEEE Interface options do not run off of battery power.
4.4 LINE VOLTAGE SELECTION
The Model 197A may be operated from either 105V-125V
or 21OV-25OV, 50-60Hz. A special transformer may be
installed for 90-1lOV or 195-235V operation. The instmment was shipped from the factory set for an operating
voltage marked on the front panel. To change the line volt-
age, proceed as follows:
1. Turn off the Model 197A and disconnect it from line
power.
2. Set the LINE VOLTAGE switch on the back of the
instrument to correspond to line voltage available.
Example: 1lOVAC is available, set the switch to
105V-125V.
CAUTION
Connect only to the line voltage selected.
Application of incorrect voltage can damage
the instrument.
3. Plug the power cord into a properly grounded outlet.
4-4
WARNING
Ground the instrument through a
properly
grounded receptacle before operation. Failure
to ground the instrument can result in severe
injury or death in the event of a short circuit or
malfunction.
4.5 FUSE REPLACEMENT
WARNING
Disconnect the instrument from the power line
and from other equipment before replacing
fuses.
4.5.1 Line Fuse Replacement
The line fuse is located internally in the Model 197A. For
exact fuse location refer to Figure 4-l. To replace the fuse
proceed as follows:
1. Remove the top cover as explained in paragraph 4.2.
2. If the Model 1973A or Model 1972A IEEE-488 interface
is installed, it must be removed to gain access to the
fuse. The IEEE board secured to the mother board by a
support post at the rear and connector l’1008. To
remove, lift the board up until it disengages from the
connector and support post.
3. Replace the blown fuse with the following type: 1/8A,
25OV, 3AG, Slo-Blo (Keithley Part Number FU-20).
CAUTION
Do not use a fuse with a higher rating than
specified or instrument damage may occur. If
the instrument persistently blows the fuse, a
problem may exist within the instrument. If so,
the problem must be corrected before operation may continue.
4. If the IEEE interface was installed, reinstall the interface
as follows:
Install the rear standoffs.
A.
Position the interface board above the rear stand-
B.
offs.
SECTION 4
MUiTltellaTlCe
C.
Guide the terminals of PlOOR and firmly push
down on that end of the board to mate the
connectors.
D.
Push down on the other side of the interface board
until it snaps onto the rear most standoff. Make
sure the board is properly seated on the other two
standoffs.
E.
Reinstall the modified top cover.
5. Reinstall the top cover as explained in paragraph 4.2
4.5.2 Current Fuse Replacement
The current fuse protects the ZOOpA through 2000mA
ranges from an input current greater than 2A. To replace
the current fuse, perform the following steps:
1. Turn off the power, disconnect the power line and
remove the test leads.
2. Place the end of a flat blade screwdriver into the slot of
the fuse holder on the front panel. Carefully press in
and rotate the fuse carrier one-quarter turn counterclockwise. Release pressure, remove the fuse and the
fuse carrier from the front panel.
3. Remove the defective fuse and replace it with the following type:
2% 25OV, 3AG, normal blow (Keithley Part Number
FU-13) or equivalent,
CAUTION
Use only the recommended fuse type. If a fuse
with a higher current rating is installed, instru-
ment damage may occur upon overload.
4.6 FRONT PANEL CALIBRATION
Calibration should be performed every 12 months, or if the
performance verification procedures in Section 3 show that
the Model 197A is out of specification. If any of the calibration procedures in this section cannot be performed properly, refer to the troubleshooting information in this
section. If the problem persists, contact your Keithley representative or the factory for further information.
WARNING
Do not push down on JlOO8. The male connector pins will
pass through JlOOS
and may cause
personal injury.
NOTE
ACA and DCA do not need to be calibrated.
These current ranges are calibrated when ACV is
calibrated.
4-5
SECTION 4
Maintenance
4.6.1 Recommended Calibration
Equipment
Calibration may be performed using the equipment listed
in Table 4-2. Alternate calibration equipment may be used
as long as the equipment’s accuracy is at least as good as
the specifications listed in Table 4-2.
4.6.2 Environmental Conditions
Calibration should be performed in an ambient temperature of 23’C k3”C and a relative humidity of less than 70%.
If the instrument has been subject to temperature outside
of this range, or to higher humidity, allow at least one additional hour for the instrument to stabilize before beginning
the calibration procedure.
4.6.3 Calibration Switch
The Model 197A is shipped from the factory with its external calibration switch in the DISABLED position. In this
position, calibration constants cannot be stored when
entered from the front panel or over the IEEE-488 bus. The
switch must be moved to ENABLED to allow calibration
constant storage.
The calibration switch is located in the middle of the rear
panel. Slide the switch to ENABLED. Plug in the line cord
and tom on the instrument. Press in the REL and dB pushbuttons simultaneously until the message “CAL” is displayed. Release the buttons. The unit is now in calibration
as indicated by the “C” annunciator.
WARNING
Some procedures require the use of high volt-
age. Take care to prevent contact with live circuits which could cause electrical shock
resulting in injury or death.
NOTE
Calibration may be stopped at any time and if
desired, only selected ranges may be calibrated.
4.6.4 DC Voltage Calibration
Select the DCV function. Connect the DC calibrator to the
Model 197A as shown in Figure 4-3.
NOTE
The following procedure must be performed in
the exact sequence listed.
1. Press the REL and dB buttons simultaneously until the
message “CAL” is displayed. Release the buttons. The
Model 197A is now in the calibration mode.
Description
DV Voltage Calibrator
AC Voltage Calibrator
Resistance Calibrator
Table 4-2. Recommended Calibration Equipment
Required Minimum Specifications
2oomV, 0.0030% + 0.5uv
2V, O.OOS% + 0.5PV
2ov, 0.003”% + 0.5PV
2ooV, O.OOS% + 0.5pv
lOOOv, O.OOS% + 0.5PV
(90 day accuracy)
2OOmV, 2V, 2OV, 200V and 750V ranges, *0.05%
19OQ 50ppm
1.9kQ 50ppm
19kQ50ppm
19Ok.Q 50ppm
1.9MQ 1OOppm
19MQ 500ppm
(90 day accuracy)
Fluke
5200A & 5215A
4-6
SECTION 4
Maintenance
The calibration mode is indicated by the “C” annunciatar on the front panel display.
2.
Select the 200mV range, short INPUT HI and LO, and
press the REL button (REL annunciator is on).
3. Set the calibrator to output +190.000mV.
4. Adjust the display to read 190.000 with the use of the
STO/CLR and RCL buttons. The STO/CLR button
increments the displayed reading. The RCL button decrements the displayed reading. The longer either button
is held in, the faster the displayed reading is modified.
5. Select the next range (2V) and set the calibrator output
to +1.9oooov.
6. Repeat step 4 to read 1.90000.
7. Reverse the calibrator leads in order to output
-1.9oooov.
8. Repeat step 4 to read -1.90000.
9. Repeat steps 2
ranges listed in Table 4-3.
through 4
for the remaining DC voltage
Table 4-3. DC Voltage Calibration
r
+1.90000 v
-1.90000 v
+19.0000 v
+190.000 v
Model 197A as shown in Figure 4-4. Steps l-6 must be performed in the exact sequence listed.
1. Select the AC voltage function and the 200mV range.
2. Set the calibrator to output 190.000mV at 500Hz.
3. Adjust the display using the STO/CLR and RCL buttons to rrad 19O.OOOmV AC.
4. Press the dB button and verify that the dB annunciator
is displayed.
5. Set the calibrator to output 19.000mV at 500Hz.
6. Adjust the displayed reading for 19.000mV.
7. Press the REL button and verify that the dB annunciator
is off.
8. Repeat steps 2 and 3 for
the remaining ranges using
Table 4-4 as a guide.
9. Store the new cal constants before proceeding. See paragraph 4.6.8.
4.6.6 Frequency Compensation
The following section is to be used to determine if frequency compensation should be performed on the Model
197A, and to perform frequency compensation if necessary.
This procedure requires the Model 197A to be warmed up
for at least one hour. Note that this section is not to be used
to verify that the Model 197A AC Voltage function is
within specifications. If desired refer to Section 3 Performance Verification.
4.6.5
With the Model 197A still in the calibration mode (“Y
annunciator on), connect the AC voltage calibrator to the
AC Voltage Calibration
WARNING
Steps 1 through 4 require the use of high voltage. Take care not to come into contact with live
circuits that could cause personal injury or
death.
4-7
SECTION 4
Maintenance
Model 5200A
Figure 4-4.
1. Select the 1OOOVAC range and set the calibrator to output 5oo.oov at 500~~. press the REL button (REL
annunciator turns on).
2. Set the calibrator to output 5OO.OOV at 2OkHz. Verify
that the reading on the Model 197A is 000.00 +150
COUII~S. Press REL (REL annunciator turns off).
3. Set the calibrator to output lOO.OOV at 500Hz and select
the ZOOVAC range. Press the REL button (REL anmmciator turns on).
4. Set the calibrator to output lOO.OOOV at 2OkHz. Verify
that the reading on the Model 197A is OOO.OOOV BOO
counts. FI~SS REL (REL annunciator tins off).
5. Set the calibrator to output lO.OOOOV at 500Hz and
select the ZOVAC range. Press REL (REL annunciator
turns on).
6. Set the calibrator to output lO.OOOOV at 2OkHz. Verify
that the reading on the Model 197A is 00.0000 1200
counts. Press REL (REL annunciator turns off).
If any of the above verifications are not met by the
Model 197A, the top cover must be removed and three
trimmer capacitors adjusted. The adjustments must be performed within 10 minutes after the top cover is removed so
that the circuit components will be close to normal operating temperature. The three trimmer capacitors (C103, Cl05
and C107) are accessible through the shield. The shield and
PC board must be secured to the bottom cover in order to
prevent movement. This assembly can be secured with two
scwvs and nuts (not supplied). Route the screws through
the bottom cover through the two brown spacers to the
shield. Secure the screws with the nuts.
AC Voltage Calibration Configuration
Model 5215
Also, use a flat blade, insulated calibration tool for all the
adjustments. Perform the following steps in the exact
sequence listed.
WARNING
Steps 1 through 4 require the use of high voltage. Take care not to come into contact with live
circuits that could cause personal injury or
death.
1. Select the 1OOOVAC range and set the calibrator to output 5oo.oov at 500~~. press the REL button (REL
annunciator turns on).
2. Set the calibrator to output 5OO.OOV at 2OkHz. Adjust
~103 for a reading 0f 000.00 *50 counts. PUSS REL (REL
annunciator turns off).
3. Set the calibrator to output lOO.OOV at 500Hz and select
the 200VAC range. Press REL (REL annunciator turns
OKI).
4. Set the calibrator to output lOO.OOV at 2OkHz. Adjust
Cl05 for a reading on the Model 197A of OOO.OOOV *50
c0unts. FNZSS REL (REL annunciator turns off).
5. Set the calibrator to output lO.OOOOV at 500Hz and
select the ZOVAC range. Press REL (REL annunciator
turns on).
6. Set the calibrator to output lO.OOOOV at 2OkHz. Adjust
Cl07 for a reading on the Model 197A of OO.OOOOV f50
counts.
7. Reinstall the top cover.
4-8
SECTION 4
Maintenance
Table 4-4. AC Voltage Calibration
Calibrator
I
Model 197A
Frequency
500Hz
500Hz
500Hz
500Hz
500Hz
190.000mV
19.000mV
1.90000 v
19.0000 v
190.000 v
4.6.7 Resistance Calibration
With the Model 197A in the calibration mode (“C” annunciator on), select the ohms function and connect the calibrator to the Model 197A as shown in Figure 4-5. Use the
following procedure and refer to Table 4-5 to calibrate the
ohms function.
1. Select the 2OOn range and set the resistance calibrator to
output zero ohms (short).
2. Press the REL button on the Model 197A. The REL
annunciator appears on the display and the display
reads zero (test lead compensation).
3. Set the calibrator to output 190Q. Adjust the display
using the STO/CLR and RCL buttons for a reading of
190.000R. Press REL (REL annunciator hwns off).
4. Select the 2kQ range and set the resistance calibrator to
output zero ohms (short). press REL (REL annunciator
turns on).
5. Set the calibrator to output 1.9kQ. Adjust the display for
a reading of 1.90000kQ.
6. Press the REL button and note that the REL annunciator
turns off.
7. Select the 2Okn range and set the resistance calibrator
output zero ohms (short). Press REL (REL annunciator
hlrns on).
8. Set the calibrator output to 19k0. Adjust the display for
a reading of 19.OOOOkG. Press REL (REL annunciator
turns off).
9. Repeat steps 7 and 8 for the 2OOk, 2M and 20M ranges
using Table 4-5 as a guide. For these ranges use the configuration shown in Figure 4-6.
Table 4-5. Resistance Calibration
Model 197A
Range
2000
2kn
20k!J
2ooka
2Mdl
20Mn
Zdibrator Voltage
190 R
1.9kR
19kfl
190kQ
1.9Mn
19MQ
Reading
190.000 R
1.90000kn
19.0000kn
19o.oookQ
1.9oooom
19.0000Mn
NOTE
Four terminal resistance measurements need
only be done when not using the REL feature.
Figure 4-5. 200, 2k and 20k Four Wire Resistance Calibration
4-9
SECTlON 4
Maintenance
Fiwrc ! 4-6. 200k. 2M and 20M Two Wire Resistance Calibration
4.6.6 Calibration Storage
To store the calibration constants, simultaneously press the
REL and dB buttons until the message “St&’ is displayed.
If instead the message “out” is displayed, then calibration
storage was not enabled and the calibration constants will
only be valid until the Model 197A is turned off.
Temporary calibration is denoted by the flashing “C”
annunciator.
To save calibration constants after “out” appears on the
display, slide the calibration switch to ENABLED. Press
REL and dB simultaneously until “CAL” appears on the
display. Then simultaneously press REL and dB until
“Star” is displayed. The calibration constants are now
stored and the Model 197A is ready for normal operation.
4-10
Service Form
Model No.
Serial No.
Date
Name and Telephone No.
Company
List all control settings, describe problem and check boxes that apply to problem.
a Intermittent
0 IEEE failure
0 Front panel operational
Display or output (check one)
0 Drifts
cl Unstable
0 Overload
0 Calibration only
0 Data required
(attach any additional sheets as necessary)
Show a block diagram of your measurement system including all instruments connected (whether power is turned on or not).
Also, describe signal source.
0 Analog output follows display
cl Obvious problem on power-up
0 AI1 ranges or functions are bad
0 Unable to zero
0 Will not read applied input
cl Certificate of calibration required
0 I’articular range or function bad; specify
0 Batteries and fuses are OK
0 Checked all cables
Where is the measurement being performed? (factory, controlled laboratory, out-of-doors, etc.)
What power line v&age is used?
Relative humidity?
Any additional information. (If special modifications have been made by the user, please describe.)
Other?
Ambient temperature?
Keithley Instruments, Inc.
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