Keithley 179A Service manual
Instruction Manual
Model 179A
TRMS Multimeter
01982, Keithley Instruments, Inc.
Cleveland, Ohio, U.S.A.
Document Number 32430
SPECIFICATIONS
DC AND TRMS AC AMPS
20 A A 0.5%+2d* l%+lEdt 0.5” ,Ornll
*Add 0.1 %rdg above 15A fo, self-testing.
tlktir max.
MAXIMUM INPUT: 24 250” DC o, rms (fuse protected, except ‘or 20A
range: l5A continuous. 20A for 1 minute lunfusedl.
TEMPERATTURE COEFFlClENT OF-18°C Et 28°-!XioC,:
DC f,O.Ol% +O.Zd,,T.
AC * lO.O7% +2dlPC.
CREST FACTOR Iratio of peak value to rms valuel: 31.
SETTLING TIME: DC: 1 second to within 1 digit of final reading. AC: 2
seconds to within 15 digits of final reading.
MAXIMUM OPEN CIRCUIT VOLTAGE: 5”
GENERAL
DISPLAY: Five 0.5” LED digits. appropriate decimal position and polarity
indication.
CONVERSION PERIOD: 4OOms.
OVERRANGE INDICATION: Display blinks all zmoes above 19999 counts.
MAXIMVM COMMON MODE VOLTAGE: ,400” oeak.
EWI,R,ONMENT: Operating: 0’
0
c. storage: -25T to +l35oc.
POWER
: 105-125” 0, 210-250” bvitch selectedl. go-,lO” available.
50~60 Hz, 5.5w. Optional B-hour batmy pack. Model 1788.
DIMENSIONS. \n
13%” x 9%” x WY,“,. Netweigirt l.Skg 14 Ix).
ACCESSORIES SUPPLIED: ,nst,wtio” Manual md Mode, ,691 Tesf
Leads.
IEIGHT: 85mm high x 235mm wide x 275mm deco
‘-55°C. 0% to 80% relative humidity up
ACCESSORIES AVAILASLE:
Model 1010: Single Rack Mounting Kit
Model 1017: Dual Rack Mounting Kit
Model 1301: Temperature Probe
Model 1600A: High Voltage Probe ,4Ok”,
Model 1651: 50.Ampere Current Shunt
Model 1581: Clip-On Test Lead Set
Model ISSZA: RF Probe
Model 1683: Universal Test Lead Kit
Model 1584: Herd She,, Carwing Case
Model ,885: Clamp-On AC Probe
Model 1591: General Purpass Test Lead Set
Model 1788: Rechargeable Smtery Pack
Model 1792: Isolated SCD Output
Model 1793: isolated IEEE-488 O”f,,uf
Model 7008-3: IEEE~488 Cable (3 ft.1
Model 7008-6: IEEE-488 Cable 18 tt.,
TABLE OF CONTENTS
PARAGRAPH
SECTION 1 GENERAL INFORMATION
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
2.1
2.1.1
2.1.2
2.1.3
2.2
2.2.1
2.2.2
2.3
2.3.1
2.3.2
2.3.3
2.3.4
2.3.5
3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8
3.9
3.10
4.1
4.2
4.2.1
4.2.2
4.2.3
4.3
4.3.1
4.3.2
Introduction.
Features .....................................
Warranty Information ... ...
ManualAddenda.........~
Safety Symbols and Terms
Unpacking and Inspection ..
Optional Accessories ..........................
Specifications ....... ~, .....
SECTION 2 OPERATION
Preparation for Use.,
LinePower........~.~...........~
Battery Pack Power
Battery Charging
Operating lnsfructi”ns
Environmental Conditions ...... ........
Front Panel Familiarization ..... ...... ....
DMMMeasurements ...........................
DC Voltage Measurement ...... .. ... ..
TRMS AC Voltage Measurement ..
Resistance (111 Measurement ...... ............
Current Measurement IDC or TRMS ACI .. ...
AC and DC Measurement ... .. ...... .. ..
SECTION 3 PERFORMANCE VERIFICATION
Introduction. ........ ...... ..... ... .....
Environmental Conditions ..... ......... .. ...
Recommended Test Equipment .... ..... ......
PerformanceVerification Procedure ....... .. ...
Initial Conditions .. ~,
DCVoltsVerification ...........................
AC Volts Verification
Resistance Verification.
DC Current Verification
AC Current Verification
SECTION 4 THEORY OF OPERATION
Introduction., .......... .... ~, ....... ......
Overall Operation ...
Attenuation ...................................
............
Signal Conditianing
Ohms Cowersian
A/D Converter ....
DC”o,ts........~~
AC”“,ts.............~...~
TITLE PAGE
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.. ~, ... .. .. ...
... ......... ..
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... ..... ...............
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..
.. ... .. ... .........
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.....
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.. .. ... .. .......
......
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.. .........
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~, .... ...
..
.....
.. .. .. ...
..... .. ........
.. .. .........
~,
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.. ... ... .......
.. ... ...........
..................
~,
...
.....
4.4
4.5
4.5.1
4.5.2
4.6
4.6.1
4.6.2
4.6.3
4.6.4
4.7
2~1
4.8
2~1
4.9
2-l
4.10
2-1
2~1
2-1
2~1
5.1
2-3
5.2
2-3
5.2.1
2~4
..
2-4
2~4
2~5
3-1
3~1
3-1
3~1
3~1
3~1
3-2
3-2
3-2
3-2
4-1
4~1
4~1
4-1
4~ 1
4~2
4~2
4~2
5.2.2
5.2.3
5.2.4
5.3
5.4
5.4.1
5.5
5.6
5.7
6.1
6.2
6.3
6.4
6.5
6.6
SECTION 5 MAINTENANCE
Introduction., ~,
Calibration Procedure
Rccommendcd Tesr Equipment
Environmental Canditions
Calibration Shield Installation
Calibration Adjustments
Batten/ Pack iModel 17881 installation
Troubleshooting ~. ~.
Troubleshooting Procedure
Special Handling of Static Sen&e Devices
Batten/ Charge Voltage Adjustments
Fuse Replacement ~.
SECTION 6 REPLACEABLE PARTS
Introduction ~~~ ,.,, .~,.~ ~~,,,
Replaceable Parts ~. ~, ~.
Ordering Information ~.
Factory Service ~, ~, ~. ~,
Component Location Drawings
SchematicDiagram ~, ~, ~.
~, ~, ~,
~. 4~2
4~2
4-2
4~2
4~3
4-3
4~3
4-3
4-3
4~4
4-4
5~1
51
5~1
5~1
5-1
5-l
52
5-2
53
5-3
5~3
5-4
6-l
6- 1
6-l
6~1
6-l
6~1
LIST OF TABLES
LIST OF FIGURES
TABLE
3-2
3~3
3~4
3-5
4~1
4-2
4-3
4-4
5~1
5~2
53
5~4
5-5
5-6
6-l
6~2
6~3
6-4
TITLE PAGE
Model 179A Maximum Allowable Inputs
Recommended Test Equipment for
Performanceverification ........................ 3-1
DC Voltage Performance Check .................. 3~2
AC Voltage Performance Check .................. 3-2
Resistance Peformance Check
DC Current Performance Check .................. 3-2
Full Scale A/D Inputs ........................... 4-2
DC Attenuation and Gain Setting Components ..... 4-2
AC Attenuation Gain Setting Components ......... 4-3
Resistance Range Setting Components ............ 4-3
Recommended Test Equipment
Calibration Adjustments ......................... 5-2
Voltage Levels ................................. 5-3
Signal Tracing Levels ...........................
Model l79A Static Sensitive Devices .............. 5-4
Fuse Replacement ............................. 5-5
Model l79A Mother Board PC-492, Parts List ...... 6.2
Model 179A Display Board PC-485, Parts List ...... 6.4
Model 1788 Battery Pack PC-451. Parts List ........ 6.5
Recommended spare parts ...................... 6~5
...................
for
Calibration ..... 5-l
2-4
3-2
5-4
FIGURE
2-1
2-2
2-3
2-4
2-5
2-6
2-7
4-1
4-2
4-3
6-l
6-2
6-3
6-4
6-5
TITLE PAGE
Rear View Showing Line Switch
Front Panel Familiarization
DC Voltage Measurement
AC Voltage Measurement
Resistance(R) Measurement.
Current Measurement Up to 2000mA
Current Measurement Between 2000mA and 20A.
Simplified Signal Flow Block Diagram,
Model 179A DMM
Attenuation and Ohms Conversion
AID Converter Function
Miscellaneous Parts
Model 179A Display Board PC-485, Component
Location Drawing 29663
Model 1788 Battery Pack PC-451. Component
Location Drawing i9007 :. .‘.
Model 179A Display Board PC-492, Component
Location Drawing 32045
Model 179A and 1788, Schematic Diagram 32046.
... ............
..... ... ......
.....................
.....................
.................
...........
2~2
2~2
2~3
2-4
2~4
2-5
2~5
4~1
4~1
4-4
6~1
6~6
6-6
SECTION 1
GENERAL INFORMATION
1.1 INTRODUCTION
The Model 179A is a precision 4% digit TRMS multimeter
useful for measurement of AC and DC voltage, AC and DC
Current and resistance. Ranges and accuracies are listed in
the detailed specifications which precede this section,
Ranges and functions are zselected with front panel push
buttons (see Figure Z-2). The decimal point is also po$
tioned by the selected range push button. Polarity of the
measured signal is automatically displayed.
1.2 FEATURES
The Model 179A includes the following features:
l
TAMS AC measurement capability gives waveforminsensitive measurement accuracy to applications such as
solid-state regulator design, measurement of powcr
transformer input currents and capacitor ripple currents.
. AC and DC CURRENT ranges allow continuous
measurements of up to 15A or periodic measurement up
to ZOA.
l
1OpV AC and DC sensitivity
l
HI-LO Ohms. In the HI mode, enough voltage can be applied to semiconductors to turn them on for a test. LO can
be used for in-circuit measurements without turning on
semiconductor junctions. Full-scale compliance voltage is
2V on Hf. 200mV on LO.
. 1kV protection on II. 1OOOV overload protection on ohms
eliminates accidental damage due to improper function
selection.
. Optional BCD output. The Model 1792 Isolated BCD Out-
put may be ordered and is field installable.
l
Optional IEEE-488 data output. The Model 1793 IEEE-488
Interface can be ordered with the unit, or can be easily
field-installed with a screwdriver. It is powered internally
from the instrument, With the interface and any of the low
c”?.t controllers now on the market. it is possible to set up
an economical, automated test system that saves the time
of manually recording, transcribing and entering large
amounts of measurement data.
1.3 WARRANTY INFORMATION
Warranty information is provided on the inside front cover
of this manual. If there is a need to exercise the warranty.
contact the Keithley representative in your area to determine the proper action lo be taken. Keithley maintains come
plete repair and calibration facilities in the United States.
West Germany. Great tlritain, France, the Netherlands.
Switzerland and Austria. Information concerning the appli~
cation, operation or sewice of your instrument mav be
directed to the applications engineer at any of the previously
mentioned locations. Check thr inside front cover of this
manual for addwsst!s
1.4 MANUAL ADDENDA
Improvements or changes to tilis manuill will t,l, r~x~:la~ned
on an addendum in<:/udcd with this manuals
1.5 SAFETY SYMBOLS AND TERMS
Safety symbols used in this manual are as follows:
The symbol
A
on the instrument denotes that
the user should refer to the operatin:, instructions~
The symbol
1OOOV or more may bc present
on the
instrument
on
the ternlir,al(si
derrotcs Ihilt
The WARNING used in the manual exl~ia~ns rls~q,:!~ :~u!
could result in personal injury or death
The CAUTION used in illis manual axpla~n:; hazards ~hrft
could damage the instrument.
1.6 UNPACKING AND INSPECTION
The Model 179A is inspecred both mecflai~~cally ano c1e.c
tricallv before shipments Upon receiving tfw Modui 179A
unpack all items from the shipping container and check for
any obvious damage Illat may have “CCIIIZ’~ dc,rir\!j i~i~ns~t
Report any damage to the shipping agent, Rela~n anti use
the original packqing tmatcriais 11 rcst,ipmen: 1s rnccessarv
The following items are sflipped with all Modal 179A urtitils
- A Model 179A TRMS Multimeter
l
A Model 179A Instn~ctior Manual
l
A Model 1691 tane~;rl Purpose To51 Lead Set
l
Optional accessories per request
1.7 OPTIONAL ACCESSORIES
A wide range of accessories are available to facilitate the use
of the Model 179A DMM. extend its range. and adapt it for
additional uses.
1. Model 1010 Single Rack Mounting Kit To mount one
bench DMM in a standard 5%” x 19” rack mounting.
2. Model 1017 Dual Rack Mounting Kit&To mount two
berlcfi DMMs in a standard 5%” I 19” rack amounting
3. Model 1301 Temperature Probe A rugged low cost
temperature probe deslgncd to allow precision
temperature rneasuremcn~s from ~55“C to 150°C
1-l
Range: -55oc to 15ooc
Output: lmVI°C; compatible with any DMM with at
least 10MII input impedance
Accuracy: kZ°C from O” to 100°C; f3”C from -55’
to O°C and 100° to 150°C
Power: 9V alkaline or C-Zn (NEDA 16041 battery.
4. Model 1600A High Voltage Probe extends the DMM to
40kV.
Maximum Input: 40kV DC or peak AC to 300Hz
Input Resistance: IOOOMR
Division Ratio: 1OOO:l (into lOMa)
Ratio Accuracy (into lOM12 DMM): +2.5% from 1kV
to 40kV DC; -3dB at 300Hr AC
Operating Temperature: O” to 50°C
5. Model 1651 50.Ampere Current Shunt-The external
0.00112 + 1%.
measurements from O-50A DC and 20.50A AC.
6. Model 1681 Clip-On Test Lead Set contains two leads,
1.2m (48 inches) long terminated with banana plugs and
spring action clip-on probes.
7. Model 1682A RF Probe permits voltage measurements
from IOOkHz to 250MHr.
AC to DC transfer accuracy: +ldB from 1OOkHz
to 250MHz at IV, peak responding, calibrated
in rms of a sine wave. compatible with instruments
with lOML2 input resistance
Voltage Range: 0.25V to 15V rms
Maximum Allowable Input: 42V AC peak, ZOOV (DC
+ AC peak1
8. Model 1683 Universal Test Lead Kit consists of two test
leads. 1.2m (48 inches) long with 12 screw-in tips, 2
banana plugs, 2 spade lugs, 2 alligator clips with boots,
2 needle tips with chucks and 4 heavy duty tip plugs.
9. Model 1684 Hard Shell Carrying Case-Hard vinyl case,
1OOmm x 300mm x 350mm (4” x 13” x 14”) has a fitted
4.terminal shunt permits current
foam insert with room for the Model 179A, instruction
manual and small accessories.
10. Model 1685 Clamp-On AC Probe measures AC current
by clamping onto a single conductor. Interruption of the
current path is unnecessary. The Model 1685 detects
current by sensing the magnetic field produced by the
current flow.
Range: 2, 20 and 200A rms
Accuracy: i-4% of range at 60Hz; *6% of range at
5OHz
Temperature Coefficient: iO.O5%/‘C on 20A and
200A range; +0.3%/OC on 2A range
Maximum Allowable Current: 300A rms
Maximum Conductor Voltage: 600V rms
Conversion Ratio: O.lV/A rms
11. Model 1691 General Purpose Test Lead Set consists of
two 0.9lmm (36 inches) test leads with probe tips terminated in banana plugs.
12. Model 1788 Rechageable Battery Pack provides six
hours minimum operation from full charge, recharges
within 14 hours and is field installable.
13. Model 1792 Isolated BCD Output provides parallel BCD
data output including sign, overrange and busy. Field installable.
14. Model 1793 Isolated IEEE-488 Interface-Field in-
stallable option provides isolated data output. Switchselectable TALK ONLY or ADDRESSABLE modes.
Mounts within and powered by the Model 179A. Model
7008 IEEE-488 cable is available.
1.8 SPECIFICATIONS
For Model 179A detailed specifications, refer to the
specifications that precede this section.
1-2
SECTION 2
OPERATION
2.1 PREPARATION FOR USE
The Model 179A is shipped ready to use. The instrument
may be powered from line voltage or from rechargeable bat-
teries (when the optional Model 1788 Rechargeable Battery
Pack is installedl.
21.1 Line Power
The Model 179A is provided with 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 an the back of the instrument to correspond to line voltage available. Ranges are
105 to 125 volts and 210 to 250 volts AC as shown in
Figure 2-l.
CAUTION
Connect only to the line voltage
selected. Application of incorrect
voltage can damage the instrument.
2. Plug the power cord into a properly grounded outlet.
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 short circuit or malfunction.
2.1.2 Battery Pack Power
The Model 179A may also be operated from rechargeable
sealed lead-acid batteries contained in the optional Model
1788 Battery Pack. The battery pack will operate the 179A
for up to six hours. Circuits within the battery pack will
automatically shut down the instrument when the battery
charge is insufficient to maintain accurate readings. Refer to
Section 5, paragraph 5.3 for installation procedures.
2.1.3 Battery Charging
After the Model 1788 Battery Pack is installed in the Model
179A it can be charged and recharged as follows:
1. Connect the instrument to line power as described in
paragraph 2.1.1.
2. With the power switch off, the battery charge circuitry is
automatically engerized to charge the battery at the max-
imum rate. When the battery pack is first installed, or if it
is completely discharged, allow it to charge for at least 14
hours,
NOTE
For maximum battery life, do not allow the
battery pack to remain completely discharg-
ed. Constant charging will not harm either
the battery pack or the instrument. Allowing
the batten, pack to discharge below 7.2V
and remain discharged will ruin the battery
pack.
3. When the 179A is in use on line power, the bart~?ry
charger maintains a trickle charge on the battery pack.
2.2 OPERATING INSTRUCTIONS
2.2.1 Environmental Conditions
All measurements should be made at iii, ;Imlwnt
temperature within the range of O°C to 55°C. anti with a
relative humidity of 0% to 80% up to 35OC. For instliii w:~s
above 35OC derate humidity 3% per “C up to 55”C, If tilt sn
strument has been subjected to extremes of temperature,
allow sufficient time for internal temperatures to react1 cnw
ronmental conditions. Typically, it takes orx hwIr !o
stabilize a unit that is 10°C 118”Fl out of spei:lf!ixi
temperature range.
2.2.2 Front Panel Familiarization
The following text and Figure 2~2 provide a brief description
of the front panel controls, input terminals and display.
ON/OFF Depressing (in) this push button turns the ins
strument on for either battery power lif the Model 1788 is
installed) or line power. Releasing (out1 this push button
turns the instrument off.
NOTE
In the OFF position, the Model 1788 !if in
stalled) will be charging if the instrument 1s
connected to line power.
AC/DC This switch is used along with the volts IV1
and current (A) functions. Depressing linl this push butt
ton selects AC and releasing lout) this push button
selects DC.
LO/HI This feature is used along with the !! funcllon.
The front panel push button selects the LO or HI mode
for the 20kR. 200k12 and 2000kU ranges. Depressiw the
push button lin) selects LO and releasing the push button
selects HI. On the 2kI2 range the Model 179A is in rhc LO
mode, regardless of the push button position. On the
20MR range the Model 179A is in the HI mode,
regardless of the push button position.
2-l
These adjustments are used only for calibration. They are not intended for
adjustment during operation.
Figure 2-l. Rear View Showing Line Switch
2-2
MlNUS SIGN DISPLAYED
PLVS SIGN IMPLIED
OVERRANGE IS INDICATED BY A FLASHING “0000” EXCEPT
ON THE 1000 VOLT RANGE
‘MENT
Figure 2-2. Model 179A Front Panel View
A. Use the HI mode for measurements in the 20k. 200k.
2000k and 20M ranges. Full range voltage drop is 2
volts and is sufficient to cause forward conduction of
semiconductor junctions. The HI terminal is positive.
B. Use the LO mode for measurements in the 2k, 20k.
200k and 2000k ohm ranges. Full range voltage drop
is 2OOmV. Maximum open circuit voltage is 5V on all
ranges.
4. Function Selection
A. R Depressing this push button selects the ohms
function.
B. V Depressing this push button selects the volts
function.
C. A Depressing this push button selects the current
function.
5. Range Selection Select the desired range by depress-
ing the appropriate push button.
6. Input
A. 20 AMP jacks (grey and black) Use this pair exclu-
sively for measuring current up to 20A.
6. INPUT jacks (red and black1 Use this pair for current
measurements up to 2000mA and all other
measurements.
7. Zero Adjustment The from panel zero adjustment nulls
input offset on the 20, 200 and 1200 DC voltage ranges
and on all resistance ranges. Typically. this adjustment
need not be performed more often than once a week
unless the instrument is operated at ambient temperatures outside the range of 1WC to 28OC. Zero the instrument as follows:
A. Turn on the power and select LO II and the 200k
range.
E
Plug in test leads and short them. Adjust the zero adjustment pot on front panel to obtain a reading of
0000 +3 digits.
NOTE
The zero adjustment may also be used for
lead compensation on a particular R range.
2.3 DMM MEASUREMENTS
1. Turn on and zero the instrument as described in
paragraph 2.2.2 step 7. Zero the instrument before the
first use or whenever the instrument is used outside the
temperature range of 18OC to 28OC. and weekly during
normal use.
2. TRMS The Model 179A measures the true root mea”
square of a signal within the frequency range of 45 to
20kHz The maximum crest factor for rated accuracy to
3. Crest Factor (CF) is the ratio of the peak voltage to the
r”X
Vdtag‘3
CF = V
e-
Some typical crest factors:
Sine wave: CF =E
Square wave: CF = 1
Triangular wave: CF =w
Positive pulse train: CF- l/Vdufy cycle (duty cycle
forCF=3is0.11)
NOTE
There will be some additional measurement
error for signals with a crest factor greater
than 3lCF> 3).
CAUTION
Do not exceed the maximum allowable
inputs of the 179A or instrument
damage that is not covered by the warranty, may occur. See Table 2-l for max-
imum inputs.
WARNING
Exercise extreme caution when measuring voltage thaf present a shock hazard
hazard to the user. The American National Standard Institute (ANSI) etetes
that e shock hazard exists when voltage
levels greeter then 30 volts rms or 42.4V
peak are present. A good safety practice
is to expect that hazardous volfages ere
present in sny unknown circuit fo be
measured, until actual conditions are
verified.
2.3.1 DC Voltage Measurement
1. Select DC V function.
2. Select desired range.
3. Connect the unknown DC voltage to fhe INPU~r jacks of
the Model 179A as shown in Figure 2~3.
4. Note reading on display.
NOTE
Accuracy is specified for 2000 counts and
above. The method of calibrating the converter may yield an offset up to 50 digits with
the input shorted, This does not affect the
instrument’s accuracy.
Figure 2.3. DC Voltage Measurement
2-3
Table 2-1. A Model 179A Maximum Allowable Inputs
2.3.2 TRMS AC Voltage Measurement
1. Select AC V function
2. Select desired range.
3. Connect the unknown AC voltage to the INPUT jacks of
the Model 179A as shown in Figure 2-4.
4. Note the reading on display.
-Maximum Inputs
450V rms continuous; 1200V peak, for
lo seconds per minute.
1200V peak.
1OOOV rms; 1400V peak; 107WHz.
2A, 250V DC or rms (fuse protected)
15A continuous, 20A for 1 minute (50% duty
cycle1
450V rms sine wave; 1OOOV peak, for
lo seconds per minute.
Figure 2-4. AC Voltage Measurement
2.3.3 Resistance III) Measurement
1. Select the 12 function.
2. Select the HI mode or the LO mode (see paragraph 2.2.2
SteD 31.
3. Connect the unknown resistance (RI to the INPUT jacks
of the 179A as shown in Figure 2-5.
4. Note reading on display.
Figure 2-5. Resistance InI Measurement
2.3.4 Current Measurement IDC or TRMS AC)
NOTE
To prevent measurement errors, connect the
current test leads to either the 20A jacks or
the normal INPUT jacks. Disconnect all circuits from the unused jacks.
WARNING
To prevent electrical shock, remove
power from the circuit to be measured
before connecting the Model 179A.
1. For current measurements up to 20OOmA:
A. Select the ACA or DCA function,
B. Select the desired range (up to 2000mA).
C. Connect the unknown current to the INPUT jacks of
the Model 179A as shown in Figure 2-6.
D. Note reading on display.
2. FW current measurements between 2000mA and 20A:
A. Select the ACA or DCA function.
B. Depress the 20A range switch.
C. Connect the unknown current to the 20 AMP jacks of
the Model 179A as shown in Figure 2.7.
D. Note the reading on display.
2-4
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