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540B
STEP
CONTROL
POSITION
OPERATION
a
POWER
ON
Set the RANGE
switch to succeedingly
lower volt-
GALV
OPEN
age ranges
until
an
indication
between
50%
and
100%
SENSITIVITY
LOW
is obtained on the
PERCENT INPUT
meter. (Better
RANGE
1000v
transfer
resolution is
obtained with
readings closer
MODE
AC SEARCH
to
100%.)
b
SENSITIVITY
LOW
Tap the GAL V
switch against
the spring
tension to
MODE
AC TRANSFER
MOMENTARY
just
long
enough
to
see
if the GAL-
GALV
V
ANOMETER needle will
stay on scale.
Adjust
REFERENCE
COARSE
the
COARSE and MEDIUM
controls
until a zero
ADJUST
MEDIUM
reading is
obtained.
c
GALV
OPEN
Adjust the GALV ZERO
contr
ol for zero reading
on
SENSITIVITY
MED
the GALVANOMETER.
GALV
ZERO
d
GALV
LOCK
Adjust the MEDIUM and FINE controls for
zero
REFERENCE
MEDIUM
reading on the
GALVANOMETER.
ADJUST
FINE
e
GALV
OPEN
Adjust the
GALV
ZERO control for zero
reading
on
SENSITIVITY
HIGH
the GALVANOMETER.
GALV
ZERO
f
GALV
LOCK
Adjust
the
FINE
control
for a zero
reading on the
REFERENCE
GALVANOMETER.
ADJUST
FINE
g
GALV
OPEN
SENSITIVITY
LOW
h
MODE
DC SEARCH
Adjust the
de source voltage until
a
reading is
obtained on
the
P
E
RCENT
INPUT meter
t hat
is
equal to the
reading noted
in step
a.
i
MODE
DC TRANSFER
NOTE: DO
NOT
ADJUST THE
REFERENCE AD-
JUST CONTROLS IN
THIS MODE.
j
SENSITIVITY
LOW
Tap
the
GAL V
switch against
the
spring tension
to
GALV
MOMENTARY just long
enough to see if the
GAL-
V ANOMETER needle will stay on
s
cale. Adjust
the de source
voltage until
zer
o
is
obtained.
k
GALV
LOCK
Further refine the
adjustment
of the de source volt-
SENSITIVITY
MEDIUM
age until
zero reading on
t he
GALVANOMETER is
HIGH
obtained in
the HIGH SENSITIVITY position.
l
Record the exact de
source
voltage.
m
Repeat
steps
b through l at least three
times or until repeatibility
is attained. Record
the exact
de
voltage.
n
Reverse
the
input polarity to the
thermocouple
by
depressing
the
POLARITY switch.
Repeat
steps
b through
l at least three times
or until repeatibility
is attained. Record
the exact de
voltage
.
0
The
rms value
of the
unknown
ac
voltage
is
equal to the average of
the
two de voltages recorded
in
steps
1 and n.
NOTE:
If
a
test
report
from a standards
laboratory
is
used,
calculate the unknown
ac
voltage from the
following
equation:
Eac
=
(1
+ao
Edc
100
Where:
Edc
=
average of two de
voltages recorded
ao
=
Eac
-
Edc
100
=
ac to de percent
difference from
Edc
the test report
Figure 2-6. ME
ASURING
AN UNKNOWN AC VOLTAGE
2-7
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