Datron 1061 - Page 27

19
o9
o10
FIG.3.8
SIMPLIFIED
DIAGRAM
OF
ISOLATOR SWITCHING
Signal Out
o7
21 k6
9k
o6
RLT
RLl
Hi
o8
1k
100k
98k
9M9
*1
Lo
100mV
1V
10v
roov
1
000v
x31 .6
x3.16
+3.16
+31.6
+316
ON
ON
OFF
ON
OFF
OFF
OFF
OFF
ON
OFF
ON
ON
ON
ON
ON
OFF
OFF
OFF
I
The
various switching
combinations
for the
different
ranges are as
follows:-
Ranse
Gain
06 07
OB
09
O10
R Ll
The
output
from
the DC
lsolator,
test
point
(TL8l
is approximately
3.16
volts
(
x1/lõ
)
for a
full
range
(100,000)
input
by the
following
methods
(See
Fig' 3'9):-
100mV
Range
06
and O8
are
turned
on; all other
F.E.T.'s
are
turned
off
and RL1
energised'
Thus the
output
of
the
amplifier
is connected
to
its
inverting
inPut
via R 108,
R 109, R 1
10,
R111
and
O6,
an
attenuator
chain of
+31.6,
giving
the
amplifier an
overall
gain
of
X
31.6
08
connects the
preampli-
fier
directlY
to the
output'
lV Range
010
and
OB
are turned
on,
all
other
F.E.T.'s
are
turned
off
and RLl
energised.
The
output
of
the
amplifier
is connected
to
its
inverting
input
via R108,
R109,
R110,
R111
and
010, an attenuator
chain
of
+3.16,
giving
the amplifier
an
overall
gain
of
X
3.16.
OB connects
the
preamplifier dírectly
to
the output.
10
V
Range
09
and
07
are
turned
on; all
other F.E.T.'s
are
turned
off
and
RLl
energised.
Og
causes
the
amplifier
output to
be
directly
connected
to
¡ts
inverting
input,
giving
a
gain
of
un¡ty.
The
output
of
the amplifier
is
attenuated
bY
3.16
(Rl
14,
Rl 15)
before
being
passed
to the output
via
07
instead of
08.
100V
and
These
two
ranges
select the
1V and 10V
1000V
Ranges
ranges
respectively
but
a
+100
attenuator
(R149,
R156,
R143,
R148)
is
inserted
between
Hi
and the
preamplifier
input
when
RL1
is deenergised'
ON
OFF
OFF
OFF
OFF
OFF
OFF
ON
OFF
ON
OFF
OFF
OFF
OFF
ON
OFF
ON
OFF
DC
tl
fui.'.|1r,
,',,
The
configuration
of the
circuit
for each
range is
shown
in
Fig.
3.9'
Reference
should
be made to circuit
diagram
number
430328,
sheet
1,
for
the complete circuit.
Sheet 2
givei
tables
of
the
coding
on the
input
control
lines
(from
the
Analog
lnterface).
When
the
100V
or
1kV range
is
selected,
a
.100,
1OMQ
input
attenuator
(R143,
R156,
R149,
R148) is
incorporated
into
the
circuit.
This is
a
matched
set
of re-
sistors
for
low
temperature
coefficient.
The
selection
of a
lower
range
energizes
relay RLl
(via
O33),
causing
resistor
chaín
R119-R122
to
be
in series
with
the
Hi input.
Should
an
overload
signal
then
be
applied,
the
resistor
chain
límits
the
current
and
the
power
dissipation
is
such
that
lOOOV
can
be
applied
continuously.
The
amplifier
end of the
resistors
is
clamped
by
zener
díodes
D22,
D23 and
Ql
8,
O19
to
low,
thus
the
amplifier
input
can
never
exceed
approximately
+
24
volts.