Table of Contents
Advertisement
CIRCUIT
DESCRIPTION
MODELS 6108,
610BR ELECTROMETERS
FIGURE 17.
Block
Diagram
of Model
610B for
Guarded
Method
of Measuring
Resis-
tame.
Circuit
designatfons
refer
to schematic
diagram.
5106 is
the Multiplier
Switch;
R, is
the
resistor
for
a given
setting.
G
is
the unknown
resistor
being
measured;
E is
the voltage
source
(see
paragraph
3-5);
R, is
the
range
resistor
selected
with
the
Range Switch.
5104 is
the
GUARD terminal.
Ground
references
correspond
to the
schematic.
3-7.
POWER SUPPLY.
The power
supply
operates
from
the
line
voltage
and fur-
nishes
+250,
-265,
+21 and -10 volts
to the
differential
amplifier.
a.
A 24-volt
rms
output
from
the
power
transfomer,
T201,
is
full-wave
rectified
by diodes
D203 end D204 and is
filtered
by capacitor
C204.
The dc
voltage
across
C204 is
approximately
30 volts
dc.
b.
To obtain
a stable,
accurate
voltage,
the
output
of the
series
trms-
istor,
Q202,
is
regulated
by comparing
e sample
voltage
from dividers
R212
and R214 to the
zener
diode
reference,
D210.
If
e voltage
difference
exists,
ft
is amplified
by a differential
amplifier
consisting
of transistors
4204
and 4205.
The Si@'ld
is
further
amplified
by transistor
4203.
The output
of
4203 is applied
to Q202 to nullify
input
and load
variations.
Capacitor
C208 prevents
high-frequency
oscillations.
The +21 volts
at
the
output
of
the
regulator
powers
the
amplifier,
the
filament
of
the
electrometers,
and
is used as the
reference
supply
for
the OHMS ranges.
c.
Transistor
4203 operates
at a high
gain
by conneceing
its
collector
load
to a negative
regulated
supply.
The circuit
permits
linear
operation
of Q202
with
widely
varying
input
voltages.
To supply
Q203,
a 50-volt
output
of trans-
former
T201 is
half-wave
rectified
by diode
D201 and is
filtered
by capacitors
C203 and C205.
Resistor
R201 is
a dropping
resistor.
The voltage
across
the
zener
diode
D202 is
a stable
-10 volts,
which
is
supplied
to resistor
R209,
the
collector
load
resistor
of 9203,
and the
differential
amplifier.
26
1060
Advertisement
Table of Contents
