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..
.
CONTROLS
TERMINALS
CIRCUIT
AND
LOCATION
SYMBOL
FUNCTIONAL DESCRIPTION
INDICATORS
NULL switch
Front panel
S3
Set to VTVM for determining the approximate
value of unknown voltage prior to differential
measurements.
Five null voltage ranges of 10, 1,
0.1, 0. 01, and 0. 001 volts are used for differ-
ential measurements. These ranges represent
full scale differences between the unknown voltage
and the amount of preCision internal reference vol-
tage that is set on the voltage readout dials.
A,B,C,D,
and
E
Front panel
S6, S7,
Provide an in- line readout of the amount of internal
voltage readout
S8,S9,
reference voltage necessary to null the unknown
dials
SlO
voltage.
Decimal lights
Front panel
DSl, DS2,
Serve as decimal points for the voltage readout
003, 004
dials. A different light illuminates for each
. .
position of the RANGE switch .
Poiarity switch
Front panel
S5
Changes polarity of 825A to match polarity of
un-
.
.
known voltage . With this switch in the positive
position, the polarity of the upper input binding
post is positive with respect to the lower input
.
binding post (middle post) .
Output
..
Rear panel of
J4,J5
Provided for attaching a recorder to monitor vol-
te.r:minals
825A, front
tage excursions.
panel of 825AR
Outjlut level
Rear panel of
Rl
Varies the output level of the output binding post
control.
..
825A, front
from
O
to approximately 20 millivolts full scale
.
.
panel of 825AR
deflection .
Meter.
. Front panel
Ml
Indicates approximate voltage when 825A is in VTVM
mode and difference between unknown and internal
~·
..
reference voltage when 825A is
in
differential mode .
. .
..
·The upper scale, 500-0-500, is used when the NULL
switch is set to VTVM.
At all other times, the
lower scale, 1-0-1, is used.
Mechanical ·
Meter.ca.Se
..
None
Sets meter to zero mechanically. Thfs adjustment
zero control
.shoul<;l be used only after instrument has been
..
turned off for at least three minutes or when the
ineter terminals have been shorted .
.
Fuse
Rear panel ·of
Fl
Fuse holder protrudes from instrument to provide
825.A.,· front
easy access to the fuse.
panel of 825AR.
.
..
..
Figlire 2-1.: CON';rRO.LS, TERMINALS, AND INDICATORS.
(Sheet 2 of 2)
2-2. ·ZEROING INSTRUCTIONS
From time to time, it may be necessary to .adjust the in-
ternal rreter zero control.
ThlS
will normally be done at
somewhat more frequent intenrals than complete· instru-
ment calibration.. Proceed as .follows:
·
2-2
a. · Mechanically zero the meter with the adjustment
. sc;rew on the front of the meter case.
If
the instrument
is in the case,· it must be shut off for at least three
.minutes prior to this adjustment.
If
out of case, another
method would be to short out the meter terminals prior
to zeroing.
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