Fluke 825A - Specifications

SECTION 1
INTRODUCTION AND SPECIFICATIONS
1-1. INTRODUCTION
a. This instruction manual is for use with the 825A
series
Differential
DC
Voltmeters.
The
825A
voltmeters
are
available
with
either
a
standard
cell
or
a
Zener
diode
as
the
reference
element.
Models
containing
the
Zener
diode
option
are
denoted
by
a
/AG
in
the
model
number.
Both
the
standard
cell
option
and
the
Zener
diode
option
are
available
in
a
cabinet
model
or
a
model
designed
to
fit
a
standard
19
inch
rack.
Rack
models
are
denoted
by
an
R
immediately
following
the
825A
part
of
the
model
number.
b. The high accuracy, portability, and compactness
of
the
825A
make
this
instrument
ideal
for
the
precise
measurement
of
almost
any
DC
voltage.
Ease
of
opera-
tion,
inherent
protection
from
accidental
overload,
and
high
reliability
contribute
to
the
outstanding
performance
that
assures
suitability
for
both
production
line
testing
and
precision
laboratory
measurements.
This
instru-
ment
is
capable
of
being
used
as
a
vacuum
tube
volt-
meter,
as
a
precision
potentiometer,
and
as
a
meg-
ohmmeter
for
measurement
of
high
resistance.
It
can
also
be
used
to
measure
the
excursions
of
a
voltage
about
some
nominal
value.
One
feature
that
should
be
emphasized
is
that
no
current
is
drawn
from
the
unknown
source
when
balance
is
attained.
Thus
the
determination
of
the
unknown
potential
is
independent
of
its
source
resistance.
Тһе
825A
is
basically
used
for
measure-
ments
of
DC
voltages
from
0
to
500
volts.
However,
high
accuracy
measurements
to
30,
000
volts
DC
are
possible
with
precision
voltage
dividers
especially
de-
signed
for
use
with
the
Fluke
Model
800
Series
Differ-
ential
Voltmeters.
Ав
additional
features,
this
instru-
ment
contains
a
polarity
switch
for
equal
convenience
in
measuring
positive
or
negative
voltages
and
an
ad-
justable recorder output which makes the 825A particu-
larly
useful
for
monitoring
the
stability
of
almost
any
DC
voltage.
Furthermore,
the
825A
meter
has
taut-
band
suspension
which
eliminates
problems
due
to
meter
stickiness.
c. When used as a differential voltmeter, the 825A
operates
on
the
potentiometric
principal.
An
unknown
voltage
is
measured
by
comparing
it
to
a
known
adjust-
able reference voltage with the aid of a null detector.
An
accurate
standard
for
measurements
is
obtained
by
setting the reference supply with a standard cell for the
825A
and
825AR
and
with
a
Zener
diode
for
the
825A/AG
and 825AR/AG. Тһе known adjustable reference voltage
is provided by a 500 volt DC power supply and five
Kelvin-Varley decade resistor strings that are set ac-
curately by five voltage readout dials. In this way, the
500
volts
can
be
precisely
divided
into
increments
as
small
as
10
microvolts.
The
unknown
voltage
is
then
simply read from the voltage dials. In the highest null
sensitivity range, potential differences between the un-
known and the reference voltage of only 0. 001 volts will
cause full scale meter deflection.
d. The instrument is normally supplied ready for use
on 115 volts. Upon request, instruments are supplied
for 230 volts operation. If it becomes desirable to con-
vert from one mode of operation to the other, refer to
the instruction decal on the back of cabinet models or
on the cover in rack models.
1-2. DAMAGE IN SHIPMENT
Immediately upon receipt, thoroughly inspect for any
damage that may have occurred in transit. If any damage
is noted, follow the instructions outlined on the warranty
page at the back of this manual.
1-3. SPECIFICATIONS
AS A PRECISION POTENTIOMETER
ACCURACY: +0.02 % of input voltage from 0.1 volt
to 500 volts. «(0,02 % + 25 uv) below 0.1 volt.
Input Resistance
Recommended | per volt of input voltage
Null
Range* At 1% of Full
Null Scale Off Null
100 Meg
1,000 Meg
1, 000 Meg
10, 000 Meg
10,000 Meg
100, 000 Meg
100, 000 Meg
100, 000 Meg
RANGE
о
1
оо н н = =
1
1
1
0.
0.
0.
0
0
- 001 | Infinite
*Any null range may be used with any input vol-
tage range; recommended ranges are those most
useful.
500
50
5
0.5
1-1