Datron 1061 Calibration And Servicing Handbook 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.