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OPERATING
INSTRUCTIONS
INSTRUCTION
MANUAL
Digital Multimeter
Models
172A.
173A
3-a.
HOW TO MEASURE RESISTANCE.
The Modell72A/173A
measures
resistance
from
IO milli-
ohms/digit
to 300 megohms.
The maximum display
is
29999.
When the
display
exceeds
29999,
a 3 remains
lighted,
but
all
other
digits
are
blanked.
a.
HI Ohms Measurement.
When the
HI/LO
pushbutton
is
released
(set
to HI),
the
volt-
age developed
across
the
resistance
under
test
at
full
range
is
3 volts.
173A
measures
from
100 ms2 to 300 megohms
in HI mode.
The Model
172A/
I.
Set
to HI Ohms.
2.
Set
to 2 WIRE.
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.
4.
Connect
the
resistance
under
test
between
the
upper
set
of
HI and LO terminals.
5.
Observe
the
displayed
digits,
decimal
point
location,
and measurement
unit
(2,
Kn, or MR).
b.
LO Ohms Measurement.
When the HI/LO
pushbutton
is depressedtset
to LO),
the
volt-
age developed
across
the
resistance
under
test
at
full
range
is
300 miljjvolts.
The
Model
172A/l73A
measures
from
IO mR to 30 megohms
in LO mode.
I .
Set
to LO Ohms.
2.
Set
to 2 WIRE.
3.
Set
to AUTO.
4.
Connect
the
resistance
under
test
between
the
upper
set
of HI and LO terminals.
5.
Observe
the
displayed
digits,
decimal
point
location,
and measurement
unit
!n,
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
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