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OPERATING
INSTRUCTIONS
INSTRUCTION MANUAL
Digital MuWmeter
Model.
172A. 173A
4.
Four-terminal
Measurements.
The 4-WIRE
mode connects
the
lower
set
of
n SOURCE
terminals
to
the
DMM ohmmeter
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.
5.
Semiconductor
Diode
and Transistor
Testing.
The Model
172A/l73A
can be used
to
test
diodes
and transistors
to determine
the
relative
condition
of
the
device.
For
semiconductor
diodes,
the
voltage
applied
must
be sufficient
to cause
conduction
in
the
forward
direction.
The "HI
OHMS" mode provides
a voltage
up to 3 volts
at
a current
upto
I milliampere.
Since
the
HI terminal
is
positive
with
respect
to LO terminal,
con-
nections
should
be made as shown
in
Figure
3-6 to cause
forward
conduction
of
diodes.
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,
place
theDMH
in OHM!; and 2-lWIRE mode.
Connect
input
HI terminal
to circled
C contact.
Verify
a display
of
approximately
10
ki lohms.
CONDUCTION
EMITTER-TO-BASE
CONDUCTION
H' (+)
9
LO-
B
ANODE
TYPICAL
DIODE
TYPICAL
PNP TRANSISTOR
FIGURE 3-G.
Semiconductor
Diode
and Transistor
Testing.
3-10
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