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Fluke 825A - Page 16

Fluke 825A
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FULL-SCALE
DEFLECTION
DC
500-0-500
50-0-50
5-0-5
0.5-0-0.5
10-0-10
No
effect
1-0-1
No
effect
0.
1-0-0.
1
No
effect
0.01-0-0.
01
No
effect
0.001-0-0.
001
No
effect
Figure
2-3.
2-6.
MEASUREMENT
OF
VOLTAGE
EXCURSIONS
ABOUT
A
NOMINAL
VALUE
a.
Perform
preliminary
operation
as
stated
in
para-
graph
2-3.
b.
Connect
voltage
to
be
observed
to
input
binding
posts.
If
meter
reads
to
the
left,
the
voltage
being
measured
is
negative;
set
polarity
switch
to
the
negative
position
in
this
case.
This
will
cause
meter
pointer
to
deflect
to
the
right.
c.
Set
RANGE
switch
to
lowest
range
which
will
give
an
on-scale
meter
indication
and
note
nominal
value
of
vol-
tage
indicated.
d.
Set
the
five
voltage
readout
dials
to
nominal
voltage.
e.
Turn
NULL
switch
to
lowest
position
that
will
allow
voltage
excursions
to
remain
on
scale.
f.
Read
voltage
excursions
from
meter.
Note
that
full
scale
right
and
left
meter
deflections
are
equal
to
the
NULL
voltage
setting.
Meter
deflection
to
the
right
in-
dicates
that
the
voltage
under
observation
has
increased
above
the
nominal
value
while
deflection
to
the
left
in-
dicates
it
has
decreased.
2-7.
USE
OF
825A
WITH
A
RECORDER
Recorder
output
binding
posts
and
an
output
level
control
are
provided
on
the
825A
for
monitoring
the
excursions
of
an
unknown
voltage
from
the
voltage
indicated
by
the
vol-
tage
dial
settings.
If
the
leakage
resistance
between
the
recorder
and
ground
is
less
than
10,000
megohms,
the
accuracy
of
the
825A
will
be
impaired.
Also,
both
input
posts
of
the
recorder
should
be
able
to
stand
500
volts
DC
to
ground.
Therefore,
the
John
Fluke
Model
A-70
Po-
tentiometric
Recorder
(manufactured
by
the
Texas
Instru-
ment
Co.)
is
recommended
for
this
application.
Set
up
the
recorder
as
follows:
a.
Connect
A-70
recorder
to
825A
voltmeter
with
teflon
leads
as
shown
in
figure
2-4.
2-4
VOLTAGE
DIALS
No
effect
No
effect
No
effect
No
effect
All
zero
All
zero
All
zero
All
zero
All
zero
VTVM
RANGES
NOTE
Do
not
ground
either
of
the
825A
output
ter-
minals
or
either
of
the
A-70
input
terminals.
If
any
of
these
terminals
are
grounded,
cur-
rent
will
be
drawn
from
the
825A
Kelvin-
Varley
divider
and
the
accuracy
of
the
825A
will
be
completely
destroyed.
b.
After
connecting
the
recorder,
perform
preliminary
operation
as
stated
in
paragraph
2-3.
с.
Check
for
excessive
leakage
as
follows:
(1)
Connect
a
voltage
to
the
input
of
the
825A
and
differentially
measure
its
potential.
(2)
Alternately
connect
and
disconnect
the
recorder
leads
from
the
output
terminals
of
the
825A
while
noting
the
meter
needle
deflection.
More
than
one-quarter
of
a
small
scale
division
deflection
indicates
that
excessive
leakage
has
been
introduced
by
the
recorder.
This
will
impair
the
accuracy
of
the
825A
voltmeter.
(3)
Disconnect
the
voltage.
d.
After
the
leakage
test
has
been
successfully
com-
pleted,
short
the
input
terminals
of
the
825A.
e.
Set
switches
on
the
825A
voltmeter
as
follows:
RANGE
50
NULL
10
voltage
read-
out
dials
10.
000
The
825A
meter
will
indicate
full
scale
deflection.
This
provides
up
to
a
maximum
of
approximately
20
millivolts
'
at
the
output
terminals
depending
on
the
setting
of
the
output
level
control.

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