Fluke 893A - 2-30. APPLICATIONS

100 and 1000 volt ranges, however,
this
potential can damage high input impedance
semiconductor devices such
as
field
effect
transistors.
d. The Readout, dial digit indications correspond to the
magnitude of the measured voltage. If dc measure-
ments have been performed, the MODE switch po-
sition indicates the polarity of the
measured dc
voltage
.
2-28.
OPTIONAL RECORDER
OUTPUT
OPER-
ATION
2-29.
Instruments equipped with the
-02
option provide
an isolated recorder output
voltage
which
is available
at the
rear panel terminals. The recorder output dc
voltage
is adjustable from zero to ±0.
2
volts dc for
a
full-scale
meter
deflection and is used
to
drive
a center-
zero recorder. To utilize the recorder output voltage,
proceed as follows:
a. Connect the recorder to
the
rear panel RECORDER
OUTPUT
terminals.
The
LO
RECORDER OUTPUT
terminal is
connected to chassis ground of the Model
893. If
a
ground reference is undesirable,
q)erate the Model 893 on battery power with
its
line
cord disconnected
from
line
power.
b. Turn the recorder on and place the Model 893 con-
trols to the following positions:
POWER ON/LINE-OPR
RANGE 10
NULL SENS 1
MODE +DC
Readout dials 1 . 00 W
c. Connect the shorting link between the HI and LO
INPUT terminals and adjust the RECORDER OUT-
PUT LEVEL control for the desired left full-scale
indication on the recorder. The
left full-scale
meter
is
now plotted and from this information the
right full-scale point
can be
determined.
d. Remove the shorting link from between the HI
and
LO INPUT terminals and proceed with the desired
measurement. The external recorder will now
re-
cord
all
meter excursions of the Model
893.
2-30.
APPLICATIONS
2-31.
INTRODUCTION
2-32.
The Model 893 AC DC Differential Voltmeter,
because of its calibrated meter end-scale and high dc
mode input impedance, can be used in many special
applications. These applications,
to mention a few, are;
measurement
of
ac or dc voltage excursions about
a
nominal value, measurement of extremely high resist-
ances, operation
as a
dc null detector, and measure-
ment
of DBM.
2-6
2-33.
MEASUREMENT OF
VOLTAGE EXCURSIONS
ABOUT
A NOMINAL VALUE
2-34.
Whenever the instrument
is operated on the dif-
ferential
mode, the meter end-scale is calibrated
to be
a
known voltage by the position
of the NULL
SENS
switch, thus allowing rapid
determination of
any volt-
age
excursions about
a nominal value. For
example,
by selecting a null sensitivity of
, 1
with
the
RANGE
switch
on any voltage
range, the full left or right
scale
meter deflection represents
±0. 1 volts deviation
from
the Readout dial settings. To
measure voltage
excur-
sions about a nominal value, proceed
as follows:
a. Perform the Preliminary
Operating Procedures
of
paragraph
2-9
and
2-10,
b.
Determine
the nominal value of the
ac or dc volt-
age
being
measured, using the
TVM mode on the
Model
893. Refer to paragraphs 2-24
and
2-25
for
the TVM mode operating
procedures.
c. Place the Readout dials to the nominal
value of the
voltage
measured
in
step b and select
the desired
full-scale
meter sensitivity with the
NULL SENS
switch. The voltage
excursions about the Readout
dial settings can
now be determined by
the
left
or
right
meter deflections.
2-35.
MEASUREMENT
OF EXTREMELY
HIGH RE-
SISTANCES
2-36.
The Model
893 can be used as a megohmmeter
for measurements of high
resistances from 10 to 10
®
megohms with a typical accuracy
of ±5%, To operate
the instrument
as a megohmmeter,
perform the Pre-
liminary Operating Procedures described
in paragraphs
2-9
and
2-10
and proceed
as
follows:
a.
Place the
Model 893 controls to the following posi-
tions
:
POWER
ON/LINE OPR
RANGE
10
NULL
SENS
.
01 (.
001 if the
R
is
greater than
10^®)
MODE +DC
Readout dials
0. 00 00
The 10 volt range
has been used only
as
an
example in
step a. Other
voltage ranges
may
be
used to provide high resistance
measurements
at different voltage
levels.
b. Connect the unknown resistance between
the HI and
LO INPUT terminals.
Use
short
isolated leads to
prevent measuring the leakage resistance between
the
leads.
c. Rotate the Readout dials to
obtain
a meter deflec-
tion of
-1
and use the following calculations
tn de-
termine the value
of
the
unknown resistance.
893A