Fluke 825A - Preliminary Operation

b. Set power switch to ON and allow а 20 minute
warmup period.
c. Set RANGE switch to 5 or 0.5 volts, voltage read-
out dials to zero, and NULL switch to 0.001 volt.
d. Adjust R232, VTVM ZERO ADJ, for zero meter
deflection. This control may be reached through the
ventilation holes in the cabinet model (see figure 4-4).
In the rack model, an identified access hole is provided
on the rear panel. If the meter cannot be zeroed, clean
chopper as outlined in paragraph 4-2c.
2-3. PRELIMINARY OPERATION
The following procedure prepares the voltmeter for
operation.
a. Connect power plug to a 115 volt AC power source.
If instrument has been wired for 230 volt operation,
connect to 230 volts AC
NOTE
The round pin on polarized three-prong plug
connects instrument case to power system
ground. Use three-to-two pin adapter Sup-
plied with instrument when connecting to а
two-contact receptacle. For personnel
Safety, connect short lead to suitable ground.
b. Set controls on 825A voltmeter as follows:
RANGE 500 volts
NULL VTVM
polarity * (positive)
all voltage 0 (zero)
readout dials
power ON
c. After a warmup period of at least ten minutes, ad-
vance
OPERATE-CALIBRATE
switch
against
spring
ten-
sion
to
CALIBRATE,
and
adjust
internal
500
volt
DC
re-
ference
supply
with
CALIBRATE
control
for
zero
meter
deflection.
Release
OPERATE-CALIBRATE
switch.
2-4. OPERATION AS A DC DIFFERENTIAL VOLT-
METER
a. After completing preliminary operation, connect
unknown voltage to input binding posts. If one side is
grounded,
always
connect
it
to
the
lower
input
post
(middle post).
b. Turn RANGE switch to lowest range that will allow
an
on-scale
reading
and
note
approximate
value
of
un-
known
voltage
as
indicated
on
upper
meter
scale.
c. If meter reads to the left, turn polarity switch to
the
negative
position.
The
meter
needle
will
deflect
to
the
right.
This
is
because
polarity
of
unknown
voltage
is negative.
d. Noting the position of illuminated decimal light,
set five voltage readout dials to approximate voltage
determined in step b. For example, if approximate vol-
tage is 35 volts, the decimal light between the B and C
voltage readout dials will be illuminated. Therefore,
set А dialto 3, В dialto 5, and C, D, and E dials to 0.
825A
e. Set NULL switch to successively more sensitive
null ranges, as indicated in figure 2-2, and adjust voltage
readout dials for zero meter deflection in each null posi-
tion. When the meter needle indicates to the right, the
voltage under measurement is greater than the voltage
set on the voltage readout dials. When the indication is
to the left, the voltage is less than that set on the readout
dials.
*RECOMMENDED
NULL
SETTING
10 then 1
(then 0. 1 for voltages
from 50 to 100 volts)
1 then 0.1
(then 0. 01 for voltages
from 5 to 10 volts)
0.1 then 0.01
(then 0.001 for voltages
from 0.5 to 1 volt)
0.01 then 0.001
*Any null range may be used with any input vol-
tage range; recommended settings are those most
useful.
Figure 2-2. RECOMMENDED NULL SETTINGS
f. Read unknown voltage directly from the five voltage
readout dials.
2-5. OPERATION AS A CONVENTIONAL VTVM
If it is desired to use the instrument as a VTVM only,
additional ranges can be made available by converting the
NULL ranges to УТУМ ranges. This is made possible by
setting the voltage readout dials to zero. Proceed as
follows:
a. Perform preliminary operation procedures as stat-
ed in paragraph 2-3.
b. Consult figure 2-3, and select full scale voltage
deflection desired. If the approximate value of the vol-
tage to be measured is unknown, select the 500 volt
range initially.
€. Set RANGE switch, NULL switch, and voltage dials
as indicated for the range selected.
d. Connect voltage to be measured to input binding
posts. Deflection to the right indicates that unknown DC
voltage is of positive polarity.
e. Read voltage from upper or lower scale as listed
in figure 2-3.
2-3