Keithley 172A User manual

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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 Mulllmrtw
Mod.1~ 17ZA. 173A
,ction
Page
INTENTS ......................................
.LuSTRATIoNs ...................................
GENERAL INFORMATION .............................. I-l
l-l. INTROOUCTION. .............................. 1-I
l-2. FEATURES ................................. l-1
l-3. WARRANTY INFORMATION. .......................... l-l
I-4.
CHANGE NOTICE .............................. I-I
l-5.
OPTIONAL MODEL 1728 RECHARGEABLE BATTERY PACK .............. l-1
1-6. OPTIONAL MODEL 1722 DIGITAL INTERFACE .................. I-I
1-7. OPTIONAL MODEL 1723 IEEE STANDARD 488 BUS INTERFACE ........... I-1
IECIFiCATIONS. .................................. I-'
INITIAL PREPARATION .............................. 2-l
2-1. GENERAL ................................ .2-l
2-2. INSPECTION. ............................... 2-l
2-3. PREPARATION FOR USE ........................... 2-I
OPERATING INSTRUCTIONS. ............................ 3-l
3-l. GENERAL .............................. ..3- 1
3-2. HOWTO SELECT POWER ........................... 3-l
;I;' HOWTO SELECT FUNCTION. ......................... 3-2
3-5: HOWTO SELECT RANGE ........................... 3-3
HOWTO MEASURE VOLTAGE. ......................... 3-4
3-6. HOWTO MEASURE CURRENT. (MODEL 172A ONLY) ................ 3-5
3-7. HOWTO MEASURE CURRENT. (MODEL 173A ONLY) ................ 3-6
3-8. HOW TO MEASURE RESISTANCE ........................ 3-7
3-9. FURTHER MEASUREMENT CONSIDERATIONS. ................... 3-8
3-10. HOWTO USE MODEL 172A/l73A OFF-GROUND .................. 3-11
3-11. HOWTO USE OPTIONAL PROBES AND SHUNTS .................. 3-12
3-12. HOWTO USE THE MODEL 1722 DIGITAL INTERFACE ............... 3-13
3-13. COMMENTS RELATIVE TO THE MODEL 172A/l73A SPECIFICATIONS ......... 3-25
3-14.
MODEL 1728 OPERATING Tips
. ACCESSORIES. .. ..... .................................................. if:;5
4-1. GENERAL..................................4- I
4-2. POWEROPTIONS .............................. 4-l
4-3. ISOLATED DIGITAL OUTPUT ......................... 4-1
4-4. RACK MOUNTING .............................. 4-i
4-5. PROBE AND SHUNTS. ............................ 4-4
4-6. CABLES AND CONNECTORS .......................... 4-5
4-7. MISCELLANEOUS .............................. 4-5
THEORY OF OPERATION .............................. 5-l
. 5-l. GENERAL.................................5- I
5-2. OVERALL OPERATION ............................ 5-l
5-3. INPUT SIGNAL CONDITIONING ........................ 5-l
5-4. A/O CONVERTER AND DIGITAL CIRCUITS (SCHEMATIC 29145E, SHEET 2). ..... 5-15
5-5. DISPLAY BOARD, SCHEMATIC 274040 ..................... S-21
5-6. POWER SUPPLY, SCHEMATIC 29145E. ..................... 5-21
MODEL 1728 RECHARGEABLE BATTERY PACK, SCHEMATIC 26758C. ......... 5-23
MODEL 1722 DIGITAL INTERFACE. ...................... 5-25
I
ii

INSTRUCTION MANUAL
Digital MultImeter
Models 172A. 173A
CONTENTS (CON'S)
iect ion
Page
;. MAINTENANCE.
6-i. GENERAL................................................................... ;I;
6-2. REQUIRED TEST EQUIPMENT. ........................ 6-l
PERFORMANCE VERIFICATION ........................ 6-l
CALIBRATION REQUIREMENTS ........................ 6-7
6-5.
PREPARATION FOR CALIBRATION. ...................... 6-8
6-6.
CALIBRATION PROCEDURE. ......................... 6-Y
6-7.
TROUBLESHOOTING AND REPAIR ....................... 6-15
6-8.
FUSE REPLACEMENT ............................ 6-21/Z
7. REPLACEABLE PARTS. .............................. 7-1
7-l. GENERAL.................................7- 1
7-2.
ORDERING INFORMATION .......................... 7-I
7-3.
FACTORY SERVICE. ............................ 7-l
7-4. REPLACEABLE PARTS LIST ......................... 7-l
CROSS REFERENCE OF MANUFACTURERS .................... 7-2
COVERS AND PANELS. ........................... 7-2
COMPONENT DESIGNATIONS FOR ~~-446. ................... 7-2
7-a. SCHEMATICS ............................... 7-2
7-Y.
COMPONENT LAYOUTS. ........................... 7-2
7-10.
SPARE PARTS KIT. ............................ 7-5
iii

INSTRUCTION MANUAL
Digital MuItlm*ter
Mod&172A.l73A
ILLUSTRATIONS
GURE NO. TITLE PAGE
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
Model l73A Front Panel ....................... 1-3
Bottom View Showing Line Cord. ................... l-4
Tilt Bail Positions. ........................ l-5
Dimensional Data .......................... 1-6
Rear Panel Showing Current Fuse. .................. 2-2
Model 1728 Rechargeable Battery Pack ................ 2-4
Installation of Battery Pack .................... 2-5
Front Panel Pushbutton Selection .................. 3-3
Typical Model 172A Current Display (DCnA). ............. 3-5
Typical Model l73A Current Display (ACmA). ............. 3-6
Typical 2 WIRE Resistance Measurement. ............... 3-7
Typical 4 WIRE Resistance Measurement. ...............
3-V
Semiconductor Diode and Transistor Testing ............. 3-10
Use of Multimeter Off Ground .................... 3-11
Model 1722 Digital Output Interface. ................ 3-14
Installation of Model I722 ..................... 3-15
Connector Pin Identification For ~1006 and PllOl .......... 3-17
Card-Edge Connectors (Model 1727 Cable Set). ............ 3-17
Location of Jumpers and Pull-ups on Model 1722 ........... 3-18
Model 1010 Single Rack Mounting Kit. ................ 4-2
Model 1017 Dual Rack Mounting Kit ................. 4-4
Overall Block Diagram of Model 172A/l73A .............. 5-2
Simplified Block Diagram of Signal Conditioning Circuits
................ 5-2
Simplified Schematic of DC Attenuator. ..... 5-6
Simplified Schematic of AC/DC Converter.
.....................................
5-7
Simplified Schematic of 173A I/V Converter 5-8
Simplified Schematic of Model l72A I/V Converter 5-8
Simplified Ohms Converter, Two-Wire Ohms Configuration ....... 5-10
Four-Wire Ohms Measuring Technique ................. 5-10
Simplified Schematic of Clamp. ................... 5-12
Simplified Schematic of Active Filter. ............. ., . 5-12
Simplified Block Diagram of A/D Converter. ............. 5-14
A/D Converter System Timing ....................
5-15
Simplified Schematic of A/D Buffer 5-16
Simplified Schematic of the A/D Converter,
.............................. 5-17
Simplified Schematic of 669 kHz Oscillator ........................... 5-19
Simplified Schematic of Reference Supply 5-20
Digital Display Multiplex Scheme
....................................... 5-22
Model 1722 Block Diagram . 5-24
Location of Calibration fidjustments. ................ 6-10
Location of Connectors and Test Points ............... 6-14
TOD and Bottom Cover Assembly ................... 7-3
iv

INSTRUCTION MANUAL
Digital Multimeter
Models 172A. 173A
GENERAL INFORMATION
-~- SECTION 1. GENERAL INFORMATION.
I-l.
INTROOUCTION. Thk Models, l72A and 173A Digital Multimeters are wide-range, general-
purpose measuring instruments, capable of measuring ac/dc voltage, ac/dc current and
resistance. (See Table 1-I for Specifications, Page l-2).
l-2. FEATURES.
a. Automatic Ranging and Polarity.
b. Manual Range Selection and Range Hold.
c. HI and LO Ohms Capability.
d. Line Operation.
e. Optional Battery Operation, Model 1728.
f. Floating Capability to +14OOV peak.
9. Optional Isolated Digital Interface, Model 1722/1723.
1-3. WARRANTY INFORMATION. The warranty is stated on the inside Front cover of the
manual. If there is a need for service, contact your Keithley representative or author-
ized repair facility as given in our catalog.
l-4. CHANGE NOTICE. Improvements or changes to the instrument not incorporated into
the manual will be explained on a change notice sheet attached to the inside back cover
of the manual.
l-5. OPTIONAL MODEL
1728 RECHARGEABLE BATTERY PACK. The Model 1728 is an accessory
battery pack which enables either line or battery operation. The Model 1728 has built-
in recharging circuitry. The Model 1728 is field-installed on the Model 172A/l73A chasis.
l-6. OPTIONAL MODEL 1722 DIGITAL INTERFACE. The Model 1722 is a field-installable
digital output option. It provides isolated open-collector ECD outputs and control lines.
1-7. OPTIONAL MOOEL 1723 IEEE STANDARD 488 BUS INTERFACE. The Model 1723 is a field-
installable digital interface option that provides logic and control functions necessary
to make the Model 172A or l73A bus compatible in accordance with the IEEE Standard 48B-
1975. Refer to the Instruction Manual for Model 1723 for operation and service instruction!
for this option.
IMPORTANT
The A Symbol can be found in various places in this Instruction Manual. Care-
fully read the associated CAUTION statements with regard to proper use and handling
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. This
symbol indicates those areas on the instrument which are potential shock hazards.
Carefully read the associated WARNING statements with regard to proper use and
handling of the instrument. Serious personal injury may result if these pre-
cautions are ignored.
l-l

GENERAL INFORMATION INSTRUCTION MANUAL
Digital Multimet*r
TABLE 1-1. Models 112A,.113A
SPECIFICATIONS

INSTRUCTION MANUAL
Digital Multimeter
Models 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

IN= I nub I I”N MANUAL
Digital Multimeter
Models 172A. 173A
r
TEST POINT “A”
FIGURE l-2. Bottom View Showing Line Cord.
1-4

INSTRUCTION MANUAL GENERAL INFORMATION
Digital Multimster
Models 172A. 173A
NORMAL BENCH POSITION
c I
-I I
LEVEL POSITION - TILTBAIL AT FRONT
HANGING POSITION
4%
45” POSITION
-I y
LEVEL POSITION - TILTBAIL AT REAR
FIGURE l-3.
Tilt Bail Positions.

GENERAL INFORMATION
INSTRUCTION MANUAL
Digital Multimeter
Models 172A. i73A
ht 5,-----lht 5,-----l
O~MENSIONS IN MILLIMETERS (INCHES)O~MENSIONS IN MILLIMETERS (INCHES)
FIGURE l-4. Dimensional Data
1-6

INSTRUCTION MANUAL
Digital Multimeter
Models 172A. 173A
INITIAL PREPARATION
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. Upon receiving the instrument, clieck for any obvious dam-
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.
2-3. PREPARATION FOR USE. The Model 172A/l73A is shipped ready-to-use. The instrument
can be powered from line voltage or from rechargeable nickel-cadmium batteries (when the
optional Model 1728 Rechargeable Battery Pack is installed).
a. Line Power. The Model 172A/l73A has an attached three-wire line cord which mates
with third-wire grounded receptacles (NEHA 5-l5P). The permanently installed line cord
is stored by wrapping the cord around the base of the instrument as shown in Figure 4.
CAUTION
A This instrument has an internal line power selector switch that must be set
to 234V position for operation above 125 volts rms, 50-60 Hz.
I. How to set the Internal Line Voltage Switch (S6Ol). The Model 172A/l73A has a
two position slide switch located on the main circuit board. For operation above 125
volts, the switch setting and fuse must be changed. The top cover must be removed to
gain access to the circuit board as described in MAINTENANCE section.
WARNING
t
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.
TABLE 2-l.
Summary of Standard and Optional Line Voltages.
----~ I I
1
/
Standard I
opt1 -nab
105 to 125 V rms 90 - 105 V rms - Transformer wiring
210 to 250 V rms must be modified.
2-l

INITIAL PREPARATION
INS: I ItUG I ION MANUAL
oigwd MYlllnle*er
Models 172A. 173A
FUSE F501
FIGURE 2-l. Rear Panel Showing Current Fuse.
2-2

INSTRUCTION MANUAL
Digital Multimeter
Models 172A. 173A
INITIAL PREPARATION
2.
Line Fuse Requirement. The Model 172A/l73A uses a single line fuse to protect
the line-operated power supply. The fuse is a 3 AB or 3 AG, slow-blow type. Rep lace
with I/4 ampere for II7 volts operation or l/8 ampere for 234 volrs.
IMPORTANT
A Replace fuse with correct rating, otherwise, damage to the instrument could result.
3. How to Replace the Line Fuse. The fuse is installed on the main circuit board
as shown in Figure 6-2 (Page b-14). The top cover must be removed to gain access to
the circuit board as described in Section 6.
FU-20 (1/8A) for 234V. Use Keithiey FU-I7 (l/4A) for II7 V;
WARNI NG
t
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
HAZARD.
CAUT I ON
A The fuse installed on the rear panel of the Model 172A/l73A is used only for
current range protection. This fuse is not a line voltage protection fuse.
-
b. Battery Power. To operate the Model 172A/l73A from batteries, the Model 1723
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).
NOTE
The Model 1728 Rechargeable Battery Pack can be installed by the user within me
Model 172A/l73A at any time. However, if the Model I722 Digital Output is
already installed, the Model 1728 cannot be used simultaneously.
I . How to Install the Model 1728 Rechargeable Battery Pack. The batteries furnisnec
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). See Figure 2-3.
=) Check the fuses on the Battery Pack. Three fuses are used. All are I ampere,
3AB or 3 AG, Slo-Blo types, Keithley Part Ho. FU-IO.
b) Check for proper installation of batteries in the Battery Pack. If reolace-
ment battery cells are to be insYalled, be certain to observe the proper polarity
of the individual cells as shown in Figure 2-3.
C) To install the Battery Pack, turn the instrument over so that the bottom cover
faces up. Loosen four slotted screws on the bottom cover. The screws are captive,
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. Carefully,
remove the top cover to gain access to the printed circuit board. There is a
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. Plug tile two
s-wire connectors (J401, J402) into the mating receptacles (P4Ol , ?402) taking care
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. Turn over t,\e instrument iiith
the bottom cover facing up and tighten down the four slotted-head screws.
2-3

INIT!AL PREPARATION
INSTRUCTION MANUAL
Digital Mullimatsr
Models 172A. 173.4
J401
J402
FIGURE 2-2. Model 1728 Rechargeable Battery Pack.
2-4

INSTRUCTION MANUAL
Digital Multimeter
Models 172A. 173A
INITIAL PREPARATION
WARNING
t
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
HAZARD.
FIGURE 2-3. Installation of Battery Pack.
2-5

INITIAL PREPARATION
INSTRUCTION MANUAL
Digital Multimeter
Models 172A1.173A
TABLE 2-2.
SummarY of Batteries Used in the Model 1728
Description Quantity Voltage Keithley Part NO.
I 2v "C" cell
(; AMP-HR) 7 8.4~ BA-30
+19.2V pack
(I&1.2v cells) I +19.2v BA-31
-19.2V pack,
(16-1.2V cells) I -19.2v BA-31
CAUTION
A The Model 1728 is shipped from the factory in an uncharged condition. There-
fore, the pack should be installed in the Model 172A/l73A and charged prior to
"Se.
2. How to Check Batteries.
a) The Model 172A/l73A has a built-in LO BAT indicator to permit easy determination
of battery condition. The Model 172A/l73A also has an indivicuai test point on the
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 .orma I
operating voltage. When the indicator turns on, the Model 172A/l73A shouio oe switched
to LINE or OFF to permit recharging of the Pack.
C)
The test point may be checked at any time using the Model l72A/173A or other
measuring instruments. The voltages are summarized in Table 2-3.
IMPORTANT
The instrument must be operated in BAT mode in order to obtain a valid battery
condition at test point "A". This will ensure that the batteries are supplying
power to the instrument. If the voltage is measured when the Model 172A/l73A is
operated in the LINE mode, a different reading may be observed since the batteries
are being charged.
TABLE 2-3.
Summary of Battery Voltage Levets (BAT mode)
I Test Acceptable Battery Levels Recharge Battery 1
Point Range Norma I If Below Tested
I I I I
I 4‘AlI I igv +
+20.5v
19v
I
BT402
I
3. How to Charge the Batteries. The Model 1728 provides built-in recharging cir-
cuitry. The Model 172A/l73A must be connected to line voltage. Recharging occurs at
the most rapid rate when the Model 172A/l73A is set to OFF. Typically, the recharge
time is 2.5 hours per hour of discharge. After the batteries have been fully charged,
eithhr turn the instrument on with the LINE switch (trickle charge condition) or dis-
connect the line cord to prevent overcharging of the batteries.
CAUTION
2-6
Overcharging the batteries will raise the internal temperature of the battery
pack and may shorten the life of the batteries.

INSTRUCTION MANUAL
Digital Multimeter
Models 172A. 173A
SECTION 3. OPERATING INSTRUCTIONS
OPERATING INSTRUCTIONS
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. The Model 172A/l73A may be powered from line voltage or re-
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.
NOTE
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. The Model 1728 features plug-in wiring and, as a result, no
modifications need to be made to the Model lJ2A/l73A chassis,
a. How to Operate from Line Power. The Model I
JZA/lJjA can be powereo from I ine volt-
age over four ranges from a minimum of 90 V rrn5 to a maximum of 250 V vs. Table 5-i
summarizes the line voltages permitted.
I. Set the internal line voltage switch to either ll7V or 234V.
2. Plug the line cord into source of line power.
3. Depress LINE pushbutton. NOTE
Power on will be indicated by a lighted display with one or more digits and mea-
surement unit showing. TABLE 3-1.
How to Set Line Voltage
b. How to Operate from Battery Power.
I Install the Model 1728 Rechargeable Battery Pack. (See Section 2, page 2-3.)
2. Depress BAT pushbutton.
3. If LO BAT indicator is lighted, the battery pack must be charged a minimum of 16
hours to provide fully charged operation of the Model l72A/l73A.
NOTE
To charge the Model 1728, release both LINE and BAT pushbuttons and connect rhe
line cord to line power. If it is desired to use the Model lJ2A/lJ3A immediately,
depress LINE. The Model lJZA/l73A will be useable for measurements although the
battery charging rate is decreased considerably.
4. If the LO BAT indicator is not lighted in BAT mode,the model 172A/173A maY be
used for measurements. 3-l

OPERATING INSTRUCTIONS
INSTRUCTION MANUAL
Digital MultImeter
Models ,72A. 173A
NOTE
The Model 1728 is shipped from the factory in uncharged condition. Therefore the
Model 1728 should be installed and charged prior to use. After the Model 1728 has
been charged for at least 16 hours, the Model 172A/l73A can be powered continuously
for at least 6 hours.
TABLE 3-2.
Summarv of Ooeration in LINE and BAT Modes
I
Condition of Instrument 1
Line Power Connected Line Power Connected Line Power Not Connected
Button Depressed 1728 npt installed
1728 installed 1728 installed
LINE ON
BAT OFF
ON
Battery trickle charged.
ON
Battery slowly discharged.
OFF
ON
NEITHER
LINE NOR BAT OFF OFF
Battery charged at max- OFF
3-3. HOWTO SELECT FUNCTION. Function is selected by means of four pushbuttons: DC/AC,
V, A and R.
a. v. This pushbutton must be used with DC/AC to select either DC voltage or AC
Voltage.
I. DC Voltage. Depress V. Release DC/AC.
2. AC Voltage. Depress V. Depress DC/AC.
b. A. This pushbutton must be used with DC/AC to select either DC current or AC
current.
I. DC Current. Depress A. Release DC/AC.
2. AC Current. Depress A. Depress DC/AC.
c. DC/AC. This pushbutton selects whether the selected voltage or current Function
will be AC or DC. When depressed, AC is selected.
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. However, it is possible to have all pushbuttons out which disconnects
the input HI and LO terminals and no measurement can be made. (The volts or
millivolts indicator will be lighted in this instance.) R overrides DC/AC. v or
A overrides HI/LO and 2 WIRE/4 WIRE.
3-2