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MODEL 630 POTENTIOMETRIC ELECTROMETER
CALIBRATION
results
when the resistors
are immersed
in an oil
bath
to hold
the ambient
temperature
variations
to
+O.Ol%.
e.
Procedures
for
the Reference
Voltage
Supply
Stability
Test.
1.
After
the saturated
standard
cell
and the resistor
divider
network
are placed
in
the oil
bath,
allow
sufficient
time
for
the cell
to stabilize
at ~35°C.
(Consult
Keith-
ley Instruments,
Inc.,
or its
representative
for
details.)
Connect
the standard
cell
to the circuit
after
turning
on the 500-volt
supply.
Set the Model
630 controls
as
follows:
DETECTOR INPUT Switch
1010 OHMS
RANGE Switch
500
Reference
Voltage
Dials
4
9 9.9 9 10
NULL Switch
10 Mv
POLARITY Switch
OFF
Connect
the resistor
divider
network
across
the Model
630's
reference
voltage
supply,
the positive
side
of the divider
input
to the wiper
arm of the last
Reference
Voltage
Switch,
S306, and the negative
side
of the divider
to the LO terminal
on the Model
630
front
panel.
2.
Connect
the Model 150B and the recorder
as shown in Figure
12.
Set the Model
1500
to the 3-volt
range.
Advance
the Model
630 POLARITY Switch
to -I- to put 500 volts
across
the divider.
If
the Model
150B reads
two volts,
the standard
cell
and the divider
vol-
tages
are improperly
connected
in series.
If
the circuit
is correct,
the Model
l50B
will
read zero.
Increase
the Model
15OB's sensitivity
to the O.l-millivolt
range.
If
it
reads
more than
20 microvolts,
adjust
the 500 V CAL potentiometer,
R327 (Figure
20),
shunting
the divider.
NOTE
Any adjustment
of potentiometer
R327 requires
all
other
ranges
to be calibrated,
3.
After
l-hour
warm-up,
the drift
of the entire
system
should
not exceed i-25 micro-
volts
in 24 hours.
5-7.
OSCILLATOR ADJUSTMENT.
a.
The oscillator
circuit
drives
the light
modulator,
vibrating
capacitor
and bridge.
demodulator.
Before
adjusting
the oscillator,
make sure
the reference
voltage
supply
is operating
correctly.
b.
Connect
the Type 503 Oscilloscope
Vertical
Input
to the plate
and low side
of tube
V1003 (Figure
15) and the Horizontal
Input
to the Model
200CD Oscillator.
Adjust
the
oscillator
frequency
to approximately
94 cps with
potentiometer
R210 (Figure
18).
The
Model
630 oscillator
is then adjusted
for minimum meter
noise
-
normally
within
a cycle
of 94 cps.
Disconnect
the Oscilloscope
before
adjusting
potentiometer
R210.
The
Oscilloscope
will
cause a small
loading
error.
1067R
27
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