Table of Contents
Advertisement
MODEL 630 POTENTIOMETRIC ELECTROMETER
CIRCUIT DESCRIPTION
SECTION
3.
CIRCUIT
DESCRIPTION
3-1.
GENERAL. The Model 630 Potentiometric
Electrometer
measures
voltage
by the potentio-
metric
(null)
method.
The variable
known voltage
is an ultra-stable
500-volt
reference
supply
used in conjunction
with
a precision
5-dial
Kelvin-Varley
divider.
Electronic
referencing
of the 500-volt
output
to a zener
diode
standard
maintains
the reference
sup-
ply's
stability
and accuracy.
This
method eliminates
repeated
manual
standardization.
The difference
between
the divider
output
and the unknown voltage
is indicated
by the
null
detector,
a vibrating-reed
electrometer.
At null
the unknown voltage
can be read
directly
from the in-line
dials
of the Kelvin-Varley
divider.
The input
and null
detector
are fully
guarded
to avoid
leakage.
NOTE
_.__ -_
__ l_..l...-__
- 1_1o ^-... __-__-
__.^ _~ _^..... -.
..,..,.. ..^.
.
GUARDED,
VIBRATING-REED
NULL
DETECTOR
Guard
5.DIAL
KELVIN-VARLEY
DIVIDER
REFERENCE
VOLTAGE
SUPPLY
INPUT
500 v
SUPPLY
Zener
Reference
FIGURE 8.
Simplified
Model 630 Circuit
Diagram.
3-2.
REFERENCE VOLTAGE SUPPLY.
Unregulated
voltage
from transformer
T201 is rectified
by a silicon
half-wave
reziifier,
D301, and is filtered
by capacitors
C302 and C303A.
The voltage
then
is applied
to the regulator
series
pass tube,
V3004.
Regulator
tube V3005 is used to keep the
screen
of V3004 at a constant
potential.
b.
To obtain
a stable,
accurate
voltage,
the 500-volt
output
of V3004 is sampled by a
divider
network
of wirewound
resistors,
R325 to R330.
The divider
network
ratio
is ad-
justed
with
potentiometer
R327 to better
than 0.01%.
Light
modulator
E302 compares the
sample voltage
from the divider
network
to the voltage
across
zener
diode,
D302.
Any dif-
ference
between
the
two
voltages
is chopped by E302 and amplified
by a 2-stage
ac-coupled
amplifier,
V3001.
'L"ne amplified
output
of V3001 is converted
to a dc signal
by light
modulator
~301 and then is amplified
by the two-stage
differential
dc amplifier,
V3002
and V3003.
The amplifier
output
is applied
to the grid
of the series
tube,
~3004,
to
1165
13
Advertisement
Table of Contents
