TM 9-4935-282-34
803D
2-2. ZEROING INSTRUCTIONS
b. Turn RANGE switch to lowest range that will allow an
on-scale reading and note approximate value of unknown
From time to time, it may be necessary to adjust the internal
voltage as indicated on upper meter scale.
meter zero control. This will normally be done a somewhat
c. If meter reads to the left, turn AC - DC polarity switch
more frequent intervals than complete instrument calibration.
to the negative position. The meter needle will deflect to the
Proceed as follows:
light. This is because polarity of unknown voltage is negative.
a. Mechanically zero the meter with the adjustment
d. Noting the position of illuminated decimal light, set
screw on the front of the meter case. If the instrument is in the
five voltage readout dials to approximate voltage determined in
case, it must be shut off for at least three minutes prior to this
step b. For example, if approximate voltage is 35 volts, the
adjustment. If out of case, another method would be to short
decimal light between the B and C voltage readout dials will be
out the internal meter terminals prior to zeroing.
illuminated. Therefore, set A dial to 3, B dial to 5, and C, D,
b. Set power switch to ON and allow a 20 minute
and E dials to 0.
warmup period.
e. Set NULL switch to successively more sensitive null
c. Set RANGE switch to 5 or 0.5 volts, voltage readout is
ranges, as indicated in figure 2-2, and adjust voltage readout
to zero, and NULL switch to VTVM.
dials for zero meter deflection in each null position. When the
d. Adjust R232, null detector ZERO ADJ, for ze ro meter
meter needle indicates to the right, the voltage under
deflection. This control may be reached through the ventilation
measurement is greater than the voltage set on the voltage
holes in the cabinet model (see figure 4-3). In the rack model,
readout dials. When the indication is to the left, the voltage is
an identified access hole is provided on the rear panel.
less than that set on the readout dials.
f. Read unknown voltage directly from the five voltage
2-3. PRELIMINARY OPERATION
readout dials.
The following procedure prepares the voltmeter for operation:
INPUT
*RECOMMENDED
VOLTAGE
NULL
a. Connect power plug to a 115 volt AC power source. If
RANGE
SETTING
instrument has been wired for 230 volt operation, connect to
230 volts AC.
50-500
10 then 1
(then 0.1 for voltages
NOTE
from 50 to 100 volts)
The round pin on polarized three-prong
plug connects instrument case to power
5-50
1 then 0.1
system ground. Use three-to-two pin
(then 0.01 for voltages
adapter supplied with instrument when
from 5 to 10 volts)
connecting to a two-contact receptacle.
For personnel safety, connect short lead
0.5-5
0.1 then 0.01
to a suitable ground.
(then 0.001 for voltages
from 0.5 to 1 volt)
b. Set controls on 803D voltmeter as follows:
0-0.5
0.01 then 0.001
RANGE
500 volts
NULL
VTVM
*Any null range may be used with any input voltage range;
AC - DC polarity
+ (positive)
recommended settings are those most useful.
all voltage
0 (zero)
readout dials
power
ON
Figure 2-2. RECOMMENDED NULL SETTINGS
c. After a warmup period of at least ten minutes,
2-5. OPERATION AS AN AC DIFFERENTIAL VOLTMETER
advance OPERATE-CALIBRATE switch against spring tension
to CALIBRATE, and adjust internal 500 volt DC reference
a. After completing preliminary operation set AC-DC
supply with CALIBRATE control for zero meter deflection.
polarity switch to AC.
Release OPERATE-CALIBRATE switch.
b. Connect unknown AC voltage to input binding posts.
c. Turn RANGE switch to lowest range that will allow an
2-4. OPERATION AS A DC DIFFERENTIAL VOLTMETER
on-scale reading and note approximate value of unknown
voltage as indicated on upper meter scale.
a. After completing preliminary operation, connect
d. Noting the position of illuminated decimal light, set
unknown voltage to input binding posts. If one side is
five voltage dials to approximate voltage determined in step c.
grounded, always connect it to the lower input post (middle
For example, if approximate voltage is 35 volts, the decimal
post).
light between the B and C voltage dials will be illuminated.
Therefore, set A dial to 3, B dial to 5, and C, D, and E dials
to 0.
2-3
