u oori
1x10^-
<0
METEE
DEFLECTION PESCENT
OF
END-SCALE
1
RANGE NULL SENS CURVE RANGE NULL SENS CURVE
1000 100
E 10 1 c
10
D
.
1 B
1
C
.
01 B
1
.
1
B
.001 A
100 10 D 1 . 1
B
1 C .01 A
.
1
B .001 A
1
. 01
B .001 A
Figure
2-4.
OFF-NULL
DC
I
NPUT RESISTANCES
2-24.
TVM
MODE OPERATION
2-25.
The Model 893
can be used on the
TVM mode to
measure ac
volt^es
from
one millivolt to 1100
volts ac
or dc
voltages from 10
microvolts to 1100 volts dc
with
an accuracy of
±3%
of the selected range.
To operate
the
instrument on the TVM mode,
perform the
opera-
tions outlined
in the Preliminary (Iterating
Procedures
(paragraphs
2-9
and 2-10) and
proceed as follows:
a.
Place
the MODE switch
to the AC or +DC
position
that corresponds
to the
measurement source.
b.
Connect the
circuit to be measured
between the HI
and LO
INPUT termiisals. K
one side of
the voltage
source is
grounded, connect the
grounded side to
the LO INPUT
terminal.
c. Place
the RANGE switch to the lowest range pos-
sible that
maintains
an
on-scale meter deflection.
The meter
deflection multiplied
by
the RANGE
switch petition is the value of the measured
voltage.
Left or
right meter deflection during dc measure-
ments corresponds to a negative or
positive polar-
ity
of
the measured dc voltage.
d. Measurement of
ac
or dc voltages from
0.
02 to 0.
1
volts is accomplished
on
respective NULL
SENS
switch
positions
of
0.
001
to 0.
l. In
this applica-
tion, the RANGE switch is placed to the 1 VOLT
rai^e and
the Readout dials
to .
000 The re-
sulting meter deflection multiplied by
the
NULL
SENS
switch position is the value of the
measured
voltage.
2-26. DIFFERENTIAL MODE OPERATION
2-27.
An
improved accuracy of up to 250
times over
that of the TVM mode is
obtained when the instrument
is
operated
as
a differential voltmeter. To
operate the
instrument as
an ac or
dc
differential voltmeter, pro-
ceed as follows:
a.
Determine the approximate value of the measured
voltage
by
performing the TVM mode
measurements
described in paragraph
2-9
and
2-10.
b. Place
the MODE switch to the respective dc
polar-
ity
observed on the TVM mode
measurement and set
the Readout dials
to the TVM measurement value.
K
an ac measurement is being made,
leave the
MODE
switch in its AC position.
c.
Place the NULL SENS
switch
to
successively high
null
sensitivity
positions
and
adjust the Readout
dials to obtain a center-zero meter
deflection.
Whenever the
NULL SENS switch is placed
to a position other than 'TVM
on the dc meas-
urement mode,
a voltage corresponding to
the Readout dial
indications is present
be-
tween
the HI and LO INPUT
terminals. A
personnel
hazard
does not exist
as
the
source resistance
is 90 megohms on the
ono A
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