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Section
I11
Figure
3-3
Model 431B
POWER SUPPLY
0-300vdc
0-20ma
DIGITAL VOLTMETER
accuracy. 0.2%
MODEL
4318
Figure 3-3.
DC
Substitution Technique
1.
With
power
supply
turned
off,
connect
the
CAUTION
Model
431B
a s
shown
above.
Never
apply
more
than
20
ma
dc
to
the
DC
2.
Set
the Model
431B
for
normal
operation
on
the
CALIBRATION
&
SUBSTITUTION
termi-
appropriate
range
using
the
procedure
given
in
nals
of
the
Model
431B.
figure
3-2.
6.
Read
the
voltmeter
which
monitors
the
substitu-
3.
Apply
rf
power
a t
the
thermistor
mount
and
tion
current.
The
voltmeter
reading
can
be
note
and
record
the
reading
of
the
Model
431B
interpreted
a s
current
in
milliamperes
because
meter.
This
is
the
reference
for
the
substi-
the
voltage
is
measured
a c r o s s
1000
ohms.
tution
measurement.
This
current
is
Id,.
Note
7.
Calculate
power
in
mw
from
the
expression
A
second
digital
voltmeter,
in
parallel
with
a
1000-ohm
(*lo%,
1
watt)
resistor,
2
connected
in
s e r i e s
with
the
RECORDER
Power
(MW)
=
I
dc
Rd
output
of
the
Model
431B
will
increase
accuracy
of
reference
duplication.
4
lo3
where
Rd
=
operating
resistance
of
the
term-
4 .
Turn
off,
o r
disconnect,
the
rf
source.
istor
(100
or
200
ohms)
5.
Turn
power
supply
on;
adjust
the
output
voltage
and
Idc
=
substitution
current
in
milliamps
of
the
power
supply
until
the
reference
of
step
3
(from
step
6)
i s
duplicated.
A
potentiometer
arrangement
may
be
substituted
for
the
adjustable
power
9.
To
minimize
e r r o r
due
to
drift
in
either
the
supply.
However,
a t
least
10,000
ohms
must
reference
o r
substituted
power
level,
steps
1
remain
in
series
with
the
supply.
through
6
should
be
repeated.
A
*
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