Keithley 173A, 172A Service manual
Models 172A, 173A
Instruction Manual
Contains Operating and Servicing Information for the
Models 172A, 173A Digital Multimeter
Publication Date: August 1978
Keithley Instruments, Inc.
Instrument Division
Cleveland, Ohio, U.S.A.
Document Number: 29662, Rev. B
INSTRUCTION MANUAL
Digltal Multlmster
Models
172A. 173A
INSTRUCTION MANUAL
Digital Multimeter
MODELS 172A/173A
COPYRIGHT 1978, KEITHLEY INSTRUMENTS, INC.
PRINTEU APRIL, 1981, CLEVELAND, OHIO, U.S.A.
DOCUMENT NO. 29662, REV. B
CONTENTS
INSTRUCTION MANUAL
DigItal
Mod.1~
Mulllmrtw
17ZA. 173A
,ction
INTENTS ......................................
.LuSTRATIoNs
GENERAL INFORMATION
l-l.
l-2.
l-3.
I-4.
l-5.
1-6.
1-7.
IECIFiCATIONS.
INITIAL PREPARATION
2-1.
2-2.
2-3.
OPERATING INSTRUCTIONS.
3-l.
3-2.
;I;'
3-5:
3-6.
3-7. HOW TO MEASURE CURRENT. (MODEL 173A ONLY)
3-8.
3-9.
3-10.
3-11.
3-12.
3-13.
3-14.
. ACCESSORIES.
4-1.
4-2.
4-3.
4-4.
4-5.
4-6.
4-7.
THEORY OF OPERATION
. 5-l.
5-2.
5-3.
5-4.
5-5.
5-6.
...................................
INTROOUCTION.
FEATURES
WARRANTY INFORMATION.
CHANGE NOTICE
OPTIONAL MODEL 1728 RECHARGEABLE BATTERY PACK
OPTIONAL MODEL 1722 DIGITAL INTERFACE
OPTIONAL MODEL 1723 IEEE STANDARD 488 BUS INTERFACE
GENERAL
INSPECTION.
PREPARATION FOR USE
GENERAL
HOW TO SELECT POWER
HOW TO SELECT FUNCTION.
HOW TO SELECT RANGE
HOW TO MEASURE VOLTAGE.
HOW TO MEASURE CURRENT. (MODEL 172A ONLY)
HOW TO MEASURE RESISTANCE
FURTHER MEASUREMENT CONSIDERATIONS.
HOW TO USE MODEL 172A/l73A OFF-GROUND
HOW TO USE OPTIONAL PROBES AND SHUNTS
HOW TO USE THE MODEL 1722 DIGITAL INTERFACE
COMMENTS RELATIVE TO THE MODEL 172A/l73A SPECIFICATIONS
MODEL 1728 OPERATING Tips
GENERAL..................................4- I
POWER OPTIONS
ISOLATED DIGITAL OUTPUT
RACK MOUNTING
PROBE AND SHUNTS.
CABLES AND CONNECTORS
MISCELLANEOUS
GENERAL.................................5- I
OVERALL OPERATION
INPUT SIGNAL CONDITIONING
A/O CONVERTER AND DIGITAL CIRCUITS (SCHEMATIC 29145E, SHEET 2).
DISPLAY BOARD, SCHEMATIC 274040
POWER SUPPLY, SCHEMATIC 29145E.
MODEL 1728 RECHARGEABLE BATTERY PACK, SCHEMATIC 26758C.
MODEL 1722 DIGITAL INTERFACE.
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Page
I-l
l-1
l-l
I-I
l-1
I-I
I-1
I-'
2-l
.2-l
2-l
2-I
3-l
..3- 1
3-l
3-2
3-3
3-4
3-5
3-6
3-7
3-8
3-11
3-12
3-13
3-25
if:;5
4-l
4-1
4-i
4-4
4-5
4-5
5-l
5-l
5-l
5-15
S-21
5-21
5-23
5-25
I
ii
INSTRUCTION MANUAL
Digital MultImeter
Models 172A. 173A
CONTENTS (CON'S)
iect ion
;. MAINTENANCE.
6-i.
6-2. REQUIRED TEST EQUIPMENT.
6-5.
6-6.
6-7.
6-8.
REPLACEABLE PARTS.
7.
7-l.
7-2.
7-3.
7-4.
7-a.
7-Y.
7-10.
GENERAL
PERFORMANCE VERIFICATION
CALIBRATION REQUIREMENTS
PREPARATION FOR CALIBRATION.
CALIBRATION PROCEDURE.
TROUBLESHOOTING AND REPAIR
FUSE REPLACEMENT
GENERAL.................................7- 1
ORDERING INFORMATION
FACTORY SERVICE.
REPLACEABLE PARTS LIST
CROSS REFERENCE OF MANUFACTURERS
COVERS AND PANELS.
COMPONENT DESIGNATIONS FOR ~~-446.
SCHEMATICS
COMPONENT LAYOUTS.
SPARE PARTS KIT.
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Page
;I;
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6-l
6-7
6-8
6-Y
6-15
6-21/Z
7-1
7-I
7-l
7-2
7-2
7-2
7-2
7-2
iii
ILLUSTRATIONS
INSTRUCTION MANUAL
Digital MuItlm*ter
Mod&172A.l73A
GURE NO.
1-l
l-2
l-3
l-4
2-l
2-2
2-3
;::
::i
;:;
3-7
3-a
3-9
3-10
3-11
3-12
4-l
4-2
5-l
::;
5-4
5-5
5-6
5-J
5-a
5-9
5-10
5-11
5-12
;:;;
:I;;
::g
6-l
6-2
J-1
TITLE PAGE
Model l73A Front Panel
Bottom View Showing Line Cord.
Tilt Bail Positions.
Dimensional Data
Rear Panel Showing Current Fuse.
Model
Installation of Battery Pack
Front Panel Pushbutton Selection
Typical Model 172A Current Display (DCnA).
Typical Model l73A Current Display (ACmA).
Typical 2 WIRE Resistance Measurement.
Typical 4 WIRE Resistance Measurement.
Semiconductor Diode and Transistor Testing
Use of Multimeter Off Ground
Model 1722 Digital Output Interface.
Installation of Model I722
Connector Pin Identification For ~1006 and PllOl
Card-Edge Connectors (Model 1727 Cable Set).
Location of Jumpers and Pull-ups on Model 1722
Model 1010 Single Rack Mounting Kit.
Model 1017 Dual Rack Mounting Kit
Overall Block Diagram of Model 172A/l73A
Simplified Block Diagram of Signal Conditioning Circuits
Simplified Schematic of DC Attenuator. .....
Simplified Schematic of AC/DC Converter.
Simplified Schematic of
Simplified Schematic of Model l72A I/V Converter
Simplified Ohms Converter, Two-Wire Ohms Configuration .......
Four-Wire Ohms Measuring Technique
Simplified Schematic of Clamp.
Simplified Schematic of Active Filter.
Simplified Block Diagram of A/D Converter.
A/D Converter System Timing
Simplified Schematic of A/D Buffer
Simplified Schematic of the A/D Converter,
Simplified Schematic of 669 kHz Oscillator
Simplified Schematic of Reference Supply
Digital Display Multiplex Scheme
Model 1722 Block Diagram .
Location of Calibration fidjustments.
Location of Connectors and Test Points
TOD and Bottom Cover Assembly
1728
Rechargeable Battery Pack
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173A
I/V Converter
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.,
.
1-3
l-4
l-5
1-6
2-2
2-4
2-5
3-3
3-5
3-6
3-7
3-V
3-10
3-11
3-14
3-15
3-17
3-17
3-18
4-2
4-4
5-2
5-2
5-6
5-7
5-8
5-8
5-10
5-10
5-12
5-12
5-14
5-15
5-16
5-17
5-19
5-20
5-22
5-24
6-10
6-14
7-3
iv
INSTRUCTION MANUAL
Digital
Multimeter
Models
-~-
172A. 173A
SECTION 1.
GENERAL INFORMATION
GENERAL INFORMATION.
I-l.
purpose measuring instruments,
resistance.
l-2.
1-3. WARRANTY INFORMATION. The warranty is stated on the inside Front cover of the
manual.
ized repair facility as given in our catalog.
l-4.
the manual will be explained on a change notice sheet attached to the inside back cover
of the manual.
l-5.
battery pack
in recharging circuitry.
INTROOUCTION. Thk Models, l72A and 173A Digital Multimeters are wide-range, general-
capable of measuring ac/dc voltage, ac/dc current and
(See Table 1-I for Specifications, Page l-2).
FEATURES.
a. Automatic Ranging and Polarity.
Manual Range Selection and Range Hold.
b.
HI and LO Ohms Capability.
c.
Line Operation.
d.
e. Optional Battery Operation, Model 1728.
Floating Capability to +14OOV peak.
f.
Optional Isolated Digital Interface, Model 1722/1723.
9.
If there is a need for service,
CHANGE NOTICE. Improvements or changes to the instrument not incorporated into
OPTIONAL MODEL
which enables either line or battery operation.
1728
RECHARGEABLE BATTERY PACK.
The Model 1728 is field-installed on the Model 172A/l73A chasis.
contact your Keithley representative or author-
The Model 1728 is an accessory
The Model 1728 has built-
l-6. OPTIONAL MODEL 1722 DIGITAL INTERFACE.
digital output option. It provides isolated open-collector ECD outputs and control lines.
1-7.
installable digital interface option that provides logic and control functions necessary
to
1975.
for this option.
OPTIONAL MOOEL 1723 IEEE STANDARD 488 BUS INTERFACE. The Model 1723 is a field-
make the Model 172A or l73A bus compatible in accordance with the IEEE Standard 48B-
Refer to the Instruction Manual for Model 1723 for operation and service instruction!
IMPORTANT
The A
fully read the associated
of the instrument. Damage to the instrument may occur if these precautions are
ignored.
The \ symbol can be found in various places in this Instruction Manual.
symbol indicates those areas on the instrument which are potential shock hazards.
Carefully read the associated
handling of the instrument.
cautions are ignored.
Symbol can be found in various places in this Instruction Manual.
CAUTION
statements with regard to proper use and handling
WARNING
Serious personal injury may result if these pre-
The Model 1722 is a field-installable
Care-
This
statements with regard to proper use and
l-l
GENERAL INFORMATION
TABLE 1-1.
SPECIFICATIONS
INSTRUCTION MANUAL
Digital Multimet*r
Models 112A,. 113A
INSTRUCTION MANUAL
Digital
Models
--
Multimeter
172A. 173A
GENERAL INFORMATION
FUNCTION AND UNITS DISPLAY (mV)
I
INPUT HI AND LO. UPPER
PAIR
FIGURE l-1.
Model 173A Front Panel.
1-3
r
TEST POINT “A”
IN= I nub I I”N MANUAL
Digital Multimeter
Models 172A.
173A
1-4
FIGURE l-2.
Bottom View Showing Line Cord.
INSTRUCTION MANUAL
Digital Multimster
Models 172A. 173A
NORMAL BENCH POSITION
GENERAL INFORMATION
I
c
I
-I
LEVEL POSITION - TILTBAIL AT FRONT
4%
45”
POSITION
HANGING POSITION
-I y
LEVEL POSITION - TILTBAIL AT REAR
FIGURE
l-3.
Tilt Bail Positions.
GENERAL INFORMATION
INSTRUCTION MANUAL
Digital Multimeter
Models 172A.
i73A
1-6
ht 5,-----l ht 5,-----l
O~MENSIONS IN MILLIMETERS (INCHES) O~MENSIONS IN MILLIMETERS (INCHES)
FIGURE l-4.
Dimensional Data
INSTRUCTION MANUAL
Digital Multimeter
Models 172A. 173A
SECTION 2. INITIAL PREPARATION.
2-i. GENERAL. This section provides information needed for incoming inspection and
preparation for use.
2-2. INSPECTION. The Model 172A/173A was carefully inspected both mechanically and
electrically before shipment.
ages which may have occurred during transit. Report any damages to the shipping agent.
To verify the electrical specifications, follow the procedures given in Section 6.
Upon receiving the instrument, clieck for any obvious dam-
INITIAL PREPARATION
2-3.
can be powered from line voltage or from rechargeable nickel-cadmium batteries (when the
optional Model 1728 Rechargeable Battery Pack is installed).
with
is stored by wrapping the cord around the base of the instrument as shown in Figure 4.
PREPARATION FOR USE. The Model 172A/l73A is shipped ready-to-use. The instrument
Line Power. The Model 172A/l73A has an attached three-wire line cord which mates
a.
third-wire grounded receptacles (NEHA 5-l5P). The permanently installed line cord
CAUTION
This instrument has an internal line power selector switch that must be set
A
to 234V position for operation above 125 volts rms, 50-60 Hz.
How to set the Internal Line Voltage Switch (S6Ol).
I.
two position slide switch located on the main circuit board.
volts,
gain access to the circuit board as described in MAINTENANCE section.
t
the switch setting and fuse must be changed.
WARNING
Disconnect the line cord before removing the top cover of the instrument.
Line voltage is present at various points on the circuit board and represents
a SHOCK HAZARD.
NOTE
Optional line voltage range is available when wiring modifications are made to
transformer T60l
as
shown on schematic 29145E.
The top cover must be removed to
The Model 172A/l73A has a
For operation above 125
----~
1
/
Summary of Standard and Optional Line Voltages.
Standard
105 to 125 V rms
210 to 250 V rms
TABLE 2-l.
I
opt1 -nab
90 - 105 V rms -
Transformer wiring
must be modified.
I
I
2-l
INITIAL PREPARATION
FUSE F501
INS: I
ItUG
I ION
oigwd MYlllnle*er
Models 172A. 173A
MANUAL
2-2
FIGURE 2-l.
Rear Panel Showing Current Fuse.
INSTRUCTION MANUAL
Digital
Models 172A. 173A
Multimeter
Line Fuse Requirement. The Model 172A/l73A uses a single line fuse to protect
2.
the line-operated power supply. The fuse is a 3 AB or 3 AG, slow-blow type.
with I/4 ampere for II7 volts operation or l/8 ampere for 234 volrs.
IMPORTANT
Replace fuse with correct rating, otherwise, damage to the instrument could result.
A
3.
How to Replace the Line Fuse.
as shown in Figure 6-2 (Page b-14).
the circuit board as described in Section 6.
FU-20 (1/8A) for 234V.
Disconnect the line cord before removing the top cover of the instrument. ‘Line
voltage is present at various points on the circuit board and represent a SHOCK
t
HAZARD.
The fuse installed on the rear panel of the Model 172A/l73A is used only for
A
current range protection.
Battery Power. To operate the Model 172A/l73A from batteries, the Model 1723
b.
Rechargeable Battery Pack must be installed. The /*ode1 1728 can be either field or
factory-installed (at the time the Model 172A/l73A is purchased).
This fuse is not a line voltage protection fuse.
The fuse is installed on the main circuit board
The top cover must be removed to gain access to
Use Keithiey FU-I7 (l/4A) for II7 V;
WARN I NG
CAUT I ON
-
INITIAL PREPARATION
Rep lace
NOTE
The Model 1728 Rechargeable Battery Pack can be installed by the user within me
Model 172A/l73A at any time.
already installed, the Model 1728
How to Install the Model 1728 Rechargeable Battery Pack.
I .
with the Model 1728 are already installed in the battery pack. The battery pack in-
cludes 7 rechargeable “C” cells (l.2V, 2 AMP Hr) and two 19.2 volt packs (sixteen I.?‘/cells per pack).
Check the fuses on the Battery Pack. Three fuses are used.
=)
3AB or 3 AG, Slo-Blo types, Keithley Part Ho. FU-IO.
b) Check for proper installation of batteries in the Battery Pack.
ment battery cells are to be insYalled,
of the individual cells as shown in Figure 2-3.
To install the Battery Pack,
C)
faces up.
that is they cannot be removed completely. Turn over the instrument with the top
cover facing up, taking care to hold the top and bottom covers together.
remove the top cover to gain access to the printed circuit board.
connection between the top cover and the main circuit board which must be temporaril
removed in order to free the top cover. Check to see that the four insulating
spacers are in position on the circuit board as shown in Figure 2-3.
s-wire connectors (J401, J402)
to orient the connectors as shown. Place the Model I728 in position on tne spacers
with the pack oriented as shown in Figure 2-3. Replace the connector from the top
cover to the circuit board. Replace the top cover.
the bottom cover facing up and tighten down the four slotted-head screws.
See Figure 2-3.
Loosen four slotted screws on the bottom cover.
However, if the Model I722 Digital Output is
cannot be used simultaneously.
The batteries furnisnec
All are I ampere,
If reolace-
be certain to observe the proper polarity
turn the instrument over so that the bottom cover
The screws are captive,
There is a
Plug tile two
into the mating receptacles (P4Ol
Turn over t,\e instrument iiith
, ?402) taking care
Carefully,
2-3
INIT!AL PREPARATION
J401
INSTRUCTION MANUAL
Digital Mullimatsr
Models 172A. 173.4
J402
2-4
FIGURE 2-2. Model 1728 Rechargeable Battery Pack.
INSTRUCTION MANUAL
Digital Multimeter
Models 172A. 173A
Disconnect the line cord on the instrument before the Battery Pack is installed.
Line voltage is present at various places on the circuit board and is a SHOCK
t
HAZARD.
INITIAL PREPARATION
WARNING
FIGURE 2-3. Installation of Battery Pack.
2-5
INITIAL PREPARATION
Description
I 2v "C" cell
(; AMP-HR)
TABLE 2-2.
SummarY of Batteries Used in the Model 1728
Quantity
7
Voltage
8.4~
Keithley Part NO.
INSTRUCTION MANUAL
Digital Multimeter
Models 172A1.173A
BA-30
+19.2V pack
(I&1.2v cells)
-19.2V pack,
(16-1.2V cells)
The Model 1728 is shipped from the factory in an uncharged condition.
fore, the pack should be installed in the Model 172A/l73A and charged prior to
A
"Se.
How to Check Batteries.
2.
The Model 172A/l73A has a built-in LO BAT indicator to permit easy determination
a)
of battery condition.
bottom panel usually needed only for troubleshooting purposes 'See Figure l-2).
b) The LO BAT indicator will be lighted when the Battery Pack goes be
operating voltage.
to LINE or OFF to permit recharging of the Pack.
The test point may be checked at any time using the Model l72A/173A or other
C)
measuring instruments.
The instrument must be operated in BAT mode in order to obtain a valid battery
condition at test point
power to the instrument.
operated in the LINE mode,
are being charged.
The Model 172A/l73A also has an indivicuai test point on the
When the indicator turns on,
The voltages are summarized in Table 2-3.
"A". This will ensure that the batteries are supplying
I
I
CAUTION
IMPORTANT
If the voltage is measured when the Model 172A/l73A is
a different reading may be observed since the batteries
+19.2v
-19.2v
the Model 172A/l73A shouio oe switched
BA-31
BA-31
There-
.orma I
TABLE 2-3.
Summary of Battery Voltage Levets (BAT mode)
I
I
Battery
Tested
BT402
the recharge
I
I
cuitry.
the most rapid rate when the Model 172A/l73A is set to OFF.
time is 2.5 hours per hour of discharge.
eithhr turn the instrument on with the LINE switch (trickle charge condition) or dis-
connect the line cord to prevent overcharging of the batteries.
2-6
Test
Point
4 ‘Al I
How to Charge the Batteries.
3.
The Model 172A/l73A must be connected to line voltage.
Overcharging the batteries will raise the internal temperature of the battery
pack and may shorten the life of the batteries.
Acceptable Battery Levels Recharge
I I I
I
Range
igv +
+20.5v
Norma I If Below
The Model 1728 provides built-in recharging cir-
After the batteries have been fully charged,
CAUTION
19v
Recharging occurs at
Typically,
1
I
INSTRUCTION MANUAL
Digital Multimeter
Models 172A. 173A
OPERATING INSTRUCTIONS
SECTION 3.
3-l. GENERAL. This section provides information needed to operate the tlodel l72A/iJjh
for measurement of voltage, current and resistance.
3-2. HOW TO SELECT POWER.
chargeable nickel-cadmium batteries (when the Model 1728 is installed). The Model 172.V
lJ3A hasa built-in line-voltage power supply and power cord.
The accessory Model 1728 Recharqeable Battery Pack may be ordered at the time of
purchase of the Model lJ2A/lJ3A or may be purchased and field-installed at a later
time if so desired.
modifications need to be made to the Model lJ2A/l73A chassis,
How to Operate from Line Power.
a.
age over four ranges from a minimum of 90 V rrn5 to a maximum of 250 V vs.
summarizes the line voltages permitted.
Set the internal line voltage switch to either ll7V or 234V.
I.
2. Plug the line cord into source of line power.
Depress LINE pushbutton.
3.
The Model 172A/l73A may be powered from line voltage or re-
The Model 1728 features plug-in wiring and, as a result, no
OPERATING INSTRUCTIONS
NOTE
The Model I
NOTE
JZA/lJjA can
be powereo from I ine volt-
Table 5-i
Power on will be indicated by a lighted display with one or more digits and measurement unit showing.
TABLE 3-1.
How to Set Line Voltage
How to Operate from Battery Power.
b.
Install the Model 1728 Rechargeable Battery Pack.
I
2. Depress BAT pushbutton.
If LO BAT indicator is lighted,
3.
hours to provide fully charged operation of the Model l72A/l73A.
To charge the Model 1728,
line cord to line power.
depress LINE. The Model lJZA/l73A will be useable for measurements although the
battery charging rate is decreased considerably.
release both LINE and BAT pushbuttons and connect rhe
If it is desired to use the Model lJ2A/lJ3A immediately,
the battery pack must be charged a minimum of 16
NOTE
(See Section 2, page 2-3.)
If the LO BAT indicator is not lighted in BAT mode,the model 172A/173A maY be
4.
used for measurements.
3-l
OPERATING INSTRUCTIONS
The Model
Model 1728 should be installed and charged prior to use.
been charged for at least 16 hours,
for at least 6 hours.
1728
is shipped from the factory in uncharged condition. Therefore the
Summarv of Ooeration in LINE and BAT Modes
INSTRUCTION MANUAL
Digital MultImeter
Models ,72A. 173A
NOTE
After the Model 1728 has
the Model 172A/l73A can be powered continuously
TABLE 3-2.
I
Line Power Connected
Button Depressed 1728 npt installed
LINE
BAT OFF
NEITHER
LINE NOR BAT
3-3.
V, A and R.
Voltage.
current.
will be AC or DC. When depressed, AC is selected.
HOW TO SELECT FUNCTION.
a. v.
I.
2.
b. A.
I.
2.
c.
This pushbutton must be used with DC/AC to select either DC voltage or AC
DC Voltage.
AC Voltage.
This pushbutton must be used with DC/AC to select either DC current or AC
DC Current.
AC Current.
DC/AC.
This pushbutton selects whether the selected voltage or current Function
ON
OFF OFF
Function is selected by means of four pushbuttons:
Depress V. Release DC/AC.
Depress V. Depress DC/AC.
Depress A. Release DC/AC.
Depress A. Depress DC/AC.
Condition of Instrument
Line Power Connected
1728
Battery trickle charged.
Battery slowly discharged.
Battery charged at max-
Line Power Not Connected
installed 1728 installed
ON
ON
OFF
ON
OFF
1
DC/AC,
3-2
d. R.
Depress R to measure resistance.
NOTE
V, A, and R pushbuttons are interlocked so that only one pushbutton is depressed
at a time.
the input HI and LO terminals and no measurement can be made.
millivolts indicator will be lighted in this instance.)
A overrides HI/LO and 2 WIRE/4 WIRE.
However,
it is possible to have all pushbuttons out which disconnects
(The volts or
R overrides DC/AC.
v or
INSTRUCTION MANUAL
Digital Multimeter
Models 17’2A. ,73A
OPERATING INSTRUCTIONS
FIGURE 3-l. Front Panel Pushbutton Selection.
3-4. HOW TO SELECT RANGE. The Model 172A/l73A provides automatic or manuai ranging.
The AUTO/MAN pushbutton determines the ranging mode, where AUTO = fully automatic
ranging.
AUTO. When released, the Model l72A/173A
a.
automatically selects the appropriate
range in accord with the following rules.
I. When the display exceeds 29999 the Model lj’2A/l73A upranges (that is. it changes
to less sensitivity and the decimal point moves appropriately).
2.
When the display reaches 02599 the Model 172A/l73A downranges (that is, it
changes to greater sensitivity and the decimal point moves appropriateiy).
MAN. When depressed,
b.
the range is placed to hold.
The user can cause the Model
172mto uprange or downrange by using the UP RANGE and DN RANGE pushbuttons.
When DN RANGE is momentarily depressed, the Model 172A/i73A will downrange one
I.
decade of sensitivity. Each time the pushbutton is depressed and released, one down-
range will occur until most sensitive range is obtained.
When UP RANGE is momentarily depressed,
2.
decade of sensitivity.
Each time the pushbutton is depressed and released, one uprange
the Model 172A/l73A will uprange one
will occur until least sensitive range is obtained.
3-3
OPERATING INSTRUCTIONS
INSTRUCTION MANUAL
Digital Multimeter
Models 172A. 173A
?-5.
ranges :
HOW TO MEASURE VOLTAGE.
0.3v, 3V, 3OV, 300V and \zOOV DC (IOOOVAC).
The Model 172A/l73A measures ac and dc voltage in five
CAUTION
Table 3-3 gives the maximum
Do not exceed these volt-
A
Maximum input voltage depends on the range selected.
allowable continous input for each range on AC and DC.
ages or damage to the instrument will occur.
TABLE 3-3.
Maximum Allowable Continuous Input
Range
0.3v
3 v
30 v
300 v
AC Voltage (ACV)
1000v rms
1000v rms
IOOOV rills
1ooov rnls
DC Voltage (DCV)
1200V peak"
12OC'v peak*
12OOV peak
12OOV peak
1000 v IOOOV rms 12OOV peak
*Overload on manual range not to exceed 600 volts continuous or 1200~ for 3 seconds.
The Model \72A/l73A detects dc voltages from i10 microvolts/digit to
,l%$&?%%.O display).
The maximum display is 29999. When the display exceeds
pggg, a 3 remains lighted, but all other digits are blanked. The display blinks above
1199.9 volts on the highest range.
I. Set to DC Volts.
2. Set to AUTO.
Connect the Signal to be measured between HI and LO terminals.
3.
(The terminals
are designed to accept banana style plugs, such as Keithley part no. BG-5 or accessory
test leads such as Model 1681 Clip-On Test Leads.)
Observe the displayed digits, polarity sign, decimal point location, and measure-
4.
ment unit (mV or V).
AC Voltage.
b.
volts (1000.0 display).
a 3 remains lighted, but all other digits are bianked.
If no polarity sign is indicated, a positive polarity is implied.
The Model iJ2A/i73A detects ac voltages from 10 microvolts rms to 1000
The maximum display is 29999. When the display exceeds 29999,
The display blinks above 999.9
volts on the highest range.
Set to AC Volts. (The AC indicator should be lighted.)
I.
Set to AUTO.
2.
Connect the signals to be measured between HI and LO terminals.
3.
(The terminals
are designed to accept banana style plugs, such as Keithley part no. BG-5 or accessory
test leads such as Model 1681 Clip-On Test Leads.)
Observe the displayed digits, decimal point location, and measurement unit (mV
4.
or V).
3-4
INSTRUCTION MANUAL
Digital Multimeter
Models 172A. 173A
OPERATING INSTRUCTtONE
3-6.
in two ranges:
DMM is capable of displaying 2.9999A.
A
amperes.
MAN mode it is possible to select 30A, 300A t 3000A Ranges,but2A Max is still the limit.
to 2 amperes vn5. When the input exceeds 2 amperes, the current Fuse will blow.
HOW TO MEASURE CURRENT. (MODEL 172~0~~~).
0.3A, and 2A.
The Model 172Ais protected by a 2 ampere fuse on all ranges.
a replacement Keithley Part No.
holder. (See Figure 2-l).
a. DC Current. The Model 172Adetects dc currents from ?I0 microamperes/digit to r2
When the input exceeds 2 amperes, the current fuse will blow. When using the
1. Set to DC Amperes.
Set to AUTO.
2.
Connect the signal to be measured at the HI terminal.
3.
4. Observe the displayed digits, polarity sign, decimal point location, and measure-
ment unit (mA, or A).
AC Current. The Model l7ZA DMM detects ac currents from IO microamperes rnsidigir
b.
Set to AC Amperes. (The AC indicator should be lighted).
1.
Set to Auto.
2.
Connect the signal to be measured at the HI terminal.
3.
Observe the displayed digits,
4.
mA or AC A).
If no polarity sign is indicated, a positive polarity is implied.
The current is limited by the current fuse even thouqh the
CAUTION
FU-13 should be installed in the rear panel fuse
decimal point location and measurement unit !AC
The Modell72A measures ac and dc current
If the fuse is blown,
FIGURE 3-2. Typical Model 172ACurrent Display (DCmA).
3-r
OPERATING INSTRUCTIONS
INSTAUCTION MANUAL
Digital Multimeter
Models 172A. 1?3A
3-7.
A
amperes. The maximum display is 29999.
lighted, but all other digits are blanked.
to 3 amperes rms.
remains lighted, but all other digits are blanked.
HOW TO MEASURE CURRENT. (MOOELl73AONLY.) The Mode1173A measures ac and
dc current in five ranges: 0.3mA. 3mA, 30mA, 0.3A, and 3A.
CAUTION
The Model 173A DMM is protected by a 3 ampere fuse on al I ranges.
blown, a replacement Keithley Part No.
fuse holder. (See Figure 2-l).
a. DC current.
I. Set to DC Amperes.
2. Set to AUTO.
Connect the signal to be measured at the HI terminal.
3.
4. Observe the displayed digits, polarity sign, decimal point location, and measure-
ment unit (,A, mA, or A). If no polarity sign is indicated, a positive polarity is
implied.
AC Current.
b.
1. Set to AC Amperes. (The AC indicator should be lighted.)
The Modell73A DMM detects dc currents from +I0 nanoamperes to 23
The Model 173ADMM detects ac currents from IO nanoamperes
The maximum display is 29999.
FU-2 should be installed in the rear panel
When the display exceeds 29999, a 3 remains
When the display exceeds 29999, a 3
If the fuse is
rms/digi t
2. Set to AUTO.
Connect the signal to be measured at the ill terminal.
3.
4. Observe the displayed digits, decimal point location, and measurement tinit (ACiA,
AC ma, or AC A).
3-6
FIGURE 3-3. Typical Model l73A Current Display (ACmA).
INSTRUCTION MANUAL
Digital Multimeter
Models 172A. 173A
OPERATING INSTRUCTIONS
3-a. HOW TO MEASURE RESISTANCE.
ohms/digit to 300 megohms. The maximum display is 29999.
The Modell72A/173A measures resistance from IO milli-
When the display exceeds
29999, a 3 remains lighted, but all other digits are blanked.
a.
HI Ohms Measurement.
age developed across the resistance under test at full range is 3 volts.
173A
measures
I.
2.
from 100 ms2 to 300 megohms in HI mode.
Set to HI Ohms.
Set to 2 WIRE.
When the HI/LO pushbutton is released (set to HI), the volt-
The Model 172A/
NOTE
When the Model l72A/l73A IS set to 2 WIRE,the lower set of HI and LO input terminals
is not connected. When set to 4 WIRE, the higherset of HI an(7 LO input terminals
is used as “voltage sensing” terminals.
See Section 3-9 for more detailed infor-
mation.
3. Set to AUTO.
Connect the resistance under test between the upper set of HI and LO terminals.
4.
Observe the displayed digits, decimal point location, and measurement unit (2,
5.
Kn, or MR).
b.
LO Ohms Measurement.
When the HI/LO pushbutton is depressedtset to LO),
age developed across the resistance under test at full range is 300 miljjvolts.
Model 172A/l73A measures from IO mR to 30 megohms in LO mode.
the volt-
The
Set to LO Ohms.
I .
2. Set to 2 WIRE.
Set to AUTO.
3.
Connect the resistance under test between the upper set of HI and LO terminals.
4.
Observe the displayed digits, decimal point location, and measurement unit !n,
5.
Kn, or Mfi).
This illustration is typical of a 2-terminal ohmmeter design.
When measuring resistance less than ICOOohms it may be necessary
to use the 4-wire mode to eliminate the measuring error of the test leads.
For example a pair of IOft leads made from 18 AWG copper wire has 0.14 ohms resistance.
FIGURE 3-4. Typical 2 WIRE Resistance Measurement.
3-7
OPERATING INSTRUCTIONS
INSTRUCTION MANUAL
Digital Multimeter
Model. ,72A. 173A
3-V.
FURTHER MEASUREMENT CONSIDERATIONS.
DC Voltage Measurements.
a.
I.
Overloads.
When
the display exceeds _tlZOO.OV DC all digits blink to indicate
an overload condition.
Input Resistance.
2.
IO MO on the 3OV, 3OOV, and 3000V ranges.
considered when evaluating total accuracy of measurement.
Accuracy.
3.
a % of range.
The Model l72A/l73A accuracy is specified in terms of % of reading and
For a full range reading of 299.99 mV DC the accuracy of measurement
would be t (0.03 mV + 0.01 mV) or 20.04 mV.
Input resistance is 1,000 Mf? on the 3OOmV and 3V ranges:
The effects of circuit loading should be
(See Accuracy.)
Measurements from relatively high source
resistances could cause an additional reading error. The amount of error due to
loading can be determined by the following relationship:
% error = 100 x Rs i (Rs + RI)
where
Rs = source resistance in ohms
RI = input resistance of Model 172A/173A inohms
4. Self-Test Feature. The Model 172A/I73A has a bottcm
functional check in DC Volts. To use this feature,
circled 8 contact.
Verify a display of approximately 5 volts dc with V depressed. -o
connect the input HI terminai :o
cover
voltage contacf for
check dc current, depress A and verify a disolay of 1.3 mA (172~): I mA (i73A).
AC Voltage Measurements
b.
I. Overloads.
When the display exceeds 1000.0 V AC (
rms) all digits blink to in-
dicate an overload condition.
2. Input Impedance.
picofarads.
The effects of circuit loading should be considered when evaluating the
total accuracy of measurement.
3.
AC-to-DC
ConverSiOn.
calibrated in terms of the root-mean-square (rms) of a sine wave.
The input impedance is 2 megohms shunted by less than 50
(See Accuracy.)
The Model 172A/173A operates as an average-readinq
The calibration is
exact for sinusoidal waveforms in the specified frequency range.
Frequency Response.
4.
The frequency range given in the specifications is the mini-
mum and maximum frequencies which accuracy is valid.
Accuracy.
5.
many digits.
additional reading error.
[72A/173A accuracy is specified in terms of % of reading and so
Measurements from relatively high source impedance could cause an
The amount of error due to loading can be determined by
the following relationship:
voltmeter.
% error = 100 x Zs fSZin
where Zs = source impedance
Zin = effective input impedance of tlodel 172A/l73A
6. Self-Test Feature. The Model 172A/l73A has a bottom cover voltage contact for
functional check in AC volts. To use this feature,
connect the input HI terminal to
circled A contact. Verify a display of approximately 6 volts ac. To chec.i ac current,
depress A and verify a display of 1.2 mA.
NOTE
AC Self-test features are operable on line power only.
3-8
INSTRUCTION MANUAL
Digital Multimeter
Models 172A. 173A
Current Measurements.
c.
OPERATING INSTRUCTIONS
I. Overloads.
Shunt Resistance.
2.
input terminals at full range.
Fuses are as follows: Modell72A: 2A Model 173A: 3A
The Model 173Adevelops approximately 300 millivolts across the
The172Ahas 1.3 R on all ranges.
For example, on the 300 milli-ampere range the shunt resistor is 1.3 ohm, which results
in a voltage drop of 0.3 x I.3 = 390 millivolts at full range.
ACCUrXy.
3.
so many digits.
sistance is not greater than 1000 times the shunt resistor.
l72A/l73A accuracy is specified in terms of a % of reading and
An additional reading error should be considered if the source re-
The amount of error can
be determined by the following relationship:
where Rin = shunt resistance of the Model 172A/i73A
Rs = source resistance.
Resistance Measurements.
d.
Maximum Allowable Voltage Input.
I.
The maximum input should not exceed 250V ~~15
sine wave or ?25OV dc.
Polarity of Ohms.
2.
The Model 172A/l73A provides a positive voitaqe at the PI
terminal.
Maximum Open-Circuit Voltage.
3.
HI or LO ohms,
the maximum voltage developed between HI and LO is +5 'dolts.
When the HI and LO terminals are open in either
This illustration is typical of a 4-terminal measuring technique
using a separate Voltmeter and Current Source.
The Model 1?2A/l73A
combines these features.
"HI" LEADS
"LOW" LEADS
When using the 4-WIRE method, connect one
'lcurrent" leads to R SOURCE input.
;?SOURCE
HIGH
9 SOURCE LOW
Pair Of
connect a
second pair of "voltage" leads to HI and LO.
Then set to 4 WIRE.
Care should be taken to connect "current" leads
and "voltage" leads properly. The LO terminal
and n Source low must always connect to the same
side of the unknown resistance.
FIGURE 3-5.
Typical 4 WIRE Resistance Measurement.
3-9
OPERATING INSTRUCTIONS
INSTRUCTION MANUAL
Digital MuWmeter
Model.
172A. 173A
4.
terminals
Four-terminal Measurements.
to the DMM ohmmeter source.
The 4-WIRE mode connects the lower set of n SOURCE
As shown in Figure 3-5 the lower terminals
are the current carrying terminals while the upper terminais are the voltage sensing
terminals.
This arrangement eliminates the error due to voltage drop across the cur-
rent-carrying leads.
Semiconductor Diode and Transistor Testing.
5.
test diodes and transistors to determine the relative condition of the device.
semiconductor diodes,
forward direction.
I milliampere.
Since the HI terminal is positive with respect to LO terminal, con-
nections should be made as shown
the voltage applied must be sufficient to cause conduction in the
The “HI OHMS” mode provides a voltage up to 3 volts at a current upto
in
Figure 3-6 to cause forward conduction of diodes.
The Model 172A/l73A can be used to
For
Since the maximum current is available on the 3 KR range, depress AUTO/MAN (Set to
MAN) and manually range to the 3 KR range (down-range).
6. Self-Test Feature. The Model 172A/l73A has a bottom cover voltage contact for
functional check in OHMS. To use this feature,
Connect input HI terminal to circled C contact.
place theDMH in OHM!; and 2-lWIRE mode.
Verify a display of approximately 10
ki lohms.
3-10
CONDUCTION
CONDUCTION
H’ (+)
EMITTER-TO-BASE
9
LO- B
ANODE
TYPICAL DIODE
TYPICAL PNP TRANSISTOR
FIGURE 3-G. Semiconductor Diode and Transistor Testing.
INSTRUCTION MANUAL
Digital Multimeter
Models 172A. 173A
OPERATING INSTRUCTIONS
3-10.
ground at potentials of up to i14OOV. Isolation from the “LO” terminal to power line
ground is specified at IOOOMQ, or 10'0 (shunted by 3OOpF). Typically, the isolation
resistance from LO to GNO is two decades greater than IO30 (IO 1 Q).
excellent isolation,
loading (from LO to GND) of a floating source. At IOOOV above ground, the Model 172A/
173Awill require, typically, only IOnA from the source. The excellent isolation also
accounts for the high common-mode rejection ratio of the Model 172A/l73A. Even with the
“HI” terminal driven and a source resistance of IkR, 1000 VDC (from HI to GNO) will
produce typically only 1OuV DC error. This error voltage is determined directly from
the ratio of the source resistance to the “isolation”
The “isolation”
present. In the Model 172A/l73A this capacitance is specified at 3OOpF. At a frequency
of 60H2, 300 picofarads has a reactance of approximately IOHR.
driven and a source impedance of IkR, a IOOOV p-p, 60 Hz, common-mode signal will
produce a voltage of only IOOmV p-p across the input terminals.
p-p signal will be further rejected by the input filter and A-D converter 50 that the
total rejection at the digital display is at least I20 dB
impedance). For DC voltage measurements,
the Model 172A/l73A LO terminal is driven, rather than the HI terminal.
a need for even greater isolation from LO to power line ground, or where there is a need
to float at potentials greater than 1400 volts above power line ground the Model 1728
Battery Pack should be used.
HOW TO USE MODEL 172A/l73A OFF-GROUND. The "LO"
operating the Model 172A/l73A off ground results in very little
, - lOOOV -
IOllrl
10-BA
capacitance from LO to GND is important when AC common-mode signals are
'across Ik = I x IkR = 10-a x IO3 = IDuVDC
rejection is much greater than specified when
terminal can be operated off
Because of this
resistance (See Figure 3-7).
With the HI terminal
This IOOmV
(HI driven, IkR source
Where there is
+
1
EXTERNAL
SOURCE
1 ooov
DC
ilNpT[--------
FIGURE 3-7.
RESISTANCE
GROUND
Use of Multimeter Off Ground.
-1
/
I
I
I
I
_-;
3-11
OPERATING INSTRUCTIONS
INSTRUCTION MANUAL
Digital Multimeter
Models 172A. 173A
3-11. HOW TO USE OPTIONAL PP9BFS AND SHUNTS.
Model 1600 High Voltage Probe. Set the Model 172A/l73A to DC volts and 30 volt
a.
ra”gtZ. The input resistance on the 30 volt range is IO megohms so that no shunt resistor
is needed. The Model 1682 has a 1OOO:l division ratio. For maximum safety review the
instructions furnished with the Model 1600 probeabove 30kV, switch to the 300V range.
CAUTION
The alligator clip (ground) must be connected to the source low so that high volt-
A
age is not applied between low and ground.
occur if the alligator clip is r!otconnected.
Model 1682 RF Probe. Set the Model 172A/l73A to DC volts and 30 volt range. The
b.
Severe damage to the instrument will
Model 1682 has a IVdc output corresponding to 1 V rms input over the range 100 kHz to
TOO MHz.
IMPORTANT
For use on the 3 volt range the banana plug adapter (with IO megohm resistor)
should be used since the Model 172A/l73A
input resistance is >I000 megohms on the
3 volt and 0.3 volt ranges.
Model 1685 Clamp-On AC Current Probe.
c.
Set the Model 172A/l73A to AC volts and 0.3
volt range. The Model 1685 provides a 0.1 volt rms output corresponding to a I ampere
rms input.
Review the instructions furnished with the Model 1685 to achieve best pos-
sible accuracy.
Model 1651 Current Shunt.
d.
and 0.3 volt range.
Connect the voltage leads to the Model 172A/l73A input terminals.
Set the Model l72A/l73A to AC or DC volts (as appropriate)
Connect separate-leads (not furnished) between the source and the Model 1651 hex-head
bolts.
The Model 1651 shunt resistance is 0.001 ohm which produces a sensitivity of I
millivolt per ampere.
3-12
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