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845AR
3-22.
ISOLATION
CONVERTER
3-23.
The
isolation
converter drives
the
recorder
cut-
put
and meter
while providing
isolation
from
the
Model
845 amplifier
circuitry.
The
output signal
from
the
am-
plifier
is
applied
to the
transistors
Q113 and
Q114.
An
84
Hz
reference
drive signal
is
applied
to
the
bases
of
transistors
Q113
and
Q114 which
causes modulation
of
the
dc input signal
to
occur.
The
resulting
modulated
signal
is
coupled
to the
secondary
of
T203 where
tran-
sistors
Q203 and
Q204
demodulate secondary
signals
occur
ing at their
84
Hz
base
signal
rate.
Capacitor
C204
charges
to
the
peak
of
the
demodulated
signal
and
discharges through the
OUTPUT LEVEL
control Rl,
R211
through R213,
and
the
meter Ml. The meter
Ml
indicates the
polarity
and magnitude
of
the input voltage.
Capacitor
C3 and
resistor
R2
filter
the resulting
dc
out-
put voltage for the
recorder
output.
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