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MAINTENANCE
INSTRUCTION MANUAL
Digital MYllirneter
ModsIr
172A.
113A
given
in
the
performance
verification
tables
and should
be added
to
the
specified
accuracy
tolerance
of
the
instrument
to obtain
the
allowable
readings.
The
listed
"Source
Error"
assumes
that
the
test
equipment
has
been calibrated
to
the
manufact-
urerls
specifications.
a.
Initial
Conditions.
Before
beginning
the
verification
procedure,
the
instrument
must
meet
the
following
conditions:
I)
If
the
instrument
has been
subjected
to extremes
of
temperature,
allow
internal
temperatures
to stabilize
for
one
hour
minimum
at
the
environmental
conditions
speci-
fied
in Paragraph
6-3.
2)
Turn
on the
Model
172A/l73A
and allow
it
to stabilize
for
one hour.
The
instra-
ment may be powered
from
either
line
power
or from
battery
pack
power,
as long
a5 the
battery
pack
has been
fully
charged
a5 described
in Paragraph
2-3b.
WARNING
t
Some procedures
require
the
use of
high
voltage.
Take
care
to prevent
contact
with
live
circuits
which
could
cause
electrical
shock
resulting
in severe
bodily
injury
or death.
b.
Input
Resistance
Check.
(DC VOLTS).
I)
Select
DC V function.
2)
Select
MAN and 3 volt
range.
3)
Connect
the
DC Calibrator
(A)
to
the
Model
172A/l73A.
4)
Apply
I volt
dc to
the
Model
172A/l73A
and record
the
reading.
5)
Connect
the
I Megohm resistor
(G) between
calibrator
HI and
input
HI of
172A/l73A.
6)
Apply
I volt
dc to Model
172A/l73A
and verify
that
the
displayed
reading
is within
IO digits
of
the
reading
in step
4.
This
verifies
that
the
input
resistance
is
:>103n.
7)
Select
the
30 volt
DC range
using
UP RANGE pushbutton.
8)
Measure
the
input
resistance
between
HI and LO using
ohmmeter
(F).
9)
Input
resistance
should
be IO.megohms
*2-l/2%.
c.
DC Voltage
Accuracy
Check.
I)
Set
to DC Volts
and AUTO.
2)
Connect
the
DC Calibrator
(A)
to
the
instrument.
3)
Set
the
DC Calibrator
to
the
output
specified
in Table
6-2
4)
Verify
that
the
instrument
reading
is within
the
limits
specified.
5)
Repeat
steps
3) and 4) with
negative
voltages.
6-2
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