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33
1.4.2.
Analog
section
1.
4.2.1.
Direct
voltage
measurements (V~.)
Th'e
input
circuit
for
the
d.c.
voltage
measurements
is
shown
in Fig.
23.
The
various ranges are selected
by
reed relay switches,
which
connect
resistors
in parallel
with the
basic
attenuator.
The
table indicates
for
each range the attenuation
factor,
the
ADC
input
sensitivity
and
the range
relays.
The
basic
x
2 attenuation
is
given
by
the
network
comprising the
series
R101
section,
and
the
shunt path
R101, R103, R106.
Adjustment
of the
basic
x
2
attenuation
is
made
by
the
preset
potentiometer
R103.
Preset
R108
across
the
+10V
and
—10V
supply
provides
d.c.
balance.
The
200mV
sensitivity
is
achieved
by
using
the
lOOmV
range of the
ADC,
which
is
activated
by
the
RNGB
input
from
the
relay
control
D1908.
V
—
1
R,01
''
-
3
RANGE
ATTENUATION
ADC
in.
RANGE
RELAY
200mV
2
(RNGB)
lOOmV
^
V
\
V
20
V
20
1
V
K101
ReA
200
V
200
1
V
K102 ReB
2000
V
2000
1
V
K103 ReC
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