Fluke 825A - Page 17

825А
825А
Recorder
Output
DIFFERENTIAL
VOLTMETER
Source
Under
Measurement
A-70
Recorder
*If
the
recorder
should
be
jittery,
it
is
suggested
that
a
1,000
ohm
resistor
be
substituted
for
the
shorting
link.
Figure
2-4.
RECORDER
RECOMMENDED
CONNECTION
DIAGRAM
f.
Turn
the
output
level
control
until
the
recorder
de-
flection
obtained
is
that
desired
to
correspond
to
full
scale
deflection
of
the
825A.
g.
Remove
the
short
from
the
input
terminals
of
the
825A.
The
825A
and
the
recorder
are
now
ready
for
combined
use.
Proceed
as
instructed
under
paragraph
2-6.
2-8.
MEASUREMENT
OF
HIGH
RESISTANCES
One
of
the
important
features
of
the
825A
voltmeter
is
its
ability
to
be
used
as
a
megohmmeter
for
rapidly
measuring
high
resistances
from
1
megohm
to
250,
000
megohms.
The
following
equation
may
be
used
to
com-
pute
the
resistance
in
megohms
of
an
unknown
connect-
ed
to
the
input
binding
posts:
RUSO ires -1) megohms,
Rx = unknown resistance in megohms
E = voltage indicated by voltage readout
dials
- voltage indicated on meter
10 - megohms of input resistance of VTVM
circuit on 10, 1, and 0. 1 null range.
When
connecting
the
unknown
resistance
to
the
input
ter-
minals,
use
short
isolated
leads
to
prevent
measuring
leakage
resistance
between
the
leads.
a.
FROM
1
MEGOHM
ТО
500
MEGOHMS,
For
rapid
measurement
of
resistances
from
1
megohm
to
500
meg-
ohms,
proceed
as
follows:
(1) Perform preliminary procedure as stated in para-
graph 2-3.
(2) Set RANGE switch to 500 and NULL switch to 10.
(3) Connect unknown resistance between input ter-
minals.
(4) Adjust voltage readout dials for full scale meter
deflection.
(5) Subtract 10. 00 from the amount set on the voltage
readout dials to find the resistance of the unknown in
megohms.
b. FROM 500 MEGOHMS TO 5000 MEGOHMS. For
rapid measurements, of resistances from 500 to 5000
megohms, proceed as follows:
(1) Perform preliminary procedure as stated in para-
graph 2-3.
(2) Set RANGE switch to 500 and NULL switch to 1;
(3) Connect unknown resistance between input ter-
minals.
(4) Adjust voltage readout dials for full scale meter
deflection.
(5) Subtract 1.00 from the amount set on the voltage
readout dials and multiply the result by 10 to find the
resistance of the unknown in megohms.
с. FROM 5, 000 MEGOHMS ТО 50, 000 MEGOHMS, For
rapid measurements, of resistances from 5, 000 to 50, 000
megohms, proceed as follows:
(1) Perform preliminary procedure as stated in para-
graph 2-3.
(2) Set RANGE switch to 500 and NULL switch to 0.1.
(3) Connect unknown resistance between input ter-
minals.
(4) Adjust voltage readout dials for full scale meter
deflection.
(5) Multiply the amount set on the voltage readout
dials by 100 to find the resistance of the unknown in
megohms.
2-5