Datron 1061 - Page 31

lal
23
3.2.3.2
A
-
D
lnput
Control
The
analog
signal
from
the
DC
lsolator
is
applied
to
the
anarog
multiprexer
(M351
and
fed
to
the
input
of
the
buffer
(o36/M34).
This
in
turn
feeds
the
signal
to
the
integrator
comprising
of O35,
M2b
and
C9.
Control
of
the
multiplexer is
derived
from
the
Digital
assembly
via
opto-isolato6
M4,
M5
and
M6.
These
signals
control
the
sequence
of events,
allowing
first
the
signal,
then a
bias
voltage
of
the same
polarity
as
the
signal,
followed
by
opposite
polarity
reference
and
reference
+1 6
signals
to
the
buffer
and
integrator.
The
multiplexer
is
then
placed
in
a
reset
condition
ready
for
the
next
measurement
cycle.
Fig.
3.14 gives
the multiplexer
control
line
sequence
for
both
positive
and
negative
signals.
3.2.3.3 Reference
Supply
Voltages
and
Control
Logic
Power
REF 1
:
The
two
halves
of
M3g in
conjuncríon
with
zener
diodes D60
and
D59
form
the
positive
and
negative
refer-
ence
voltages
respectively,
D65
and
D64
being
'start-up'
diodes
(see
Fig.
3.15).
The
outputs
of
M39
(+11
and
-1
1
volts)
supply
the
defined current for the reference
zeners via R212
and
R38 respectively.
R19
and
R18
are selected by
Datron
so
that each zener
has
zero voltage/
temperature coeff icient.
The resistor
chains
R42-R43
and
R89-RgO
are binary
weighted values
allowing
the
set up
of the
exact nominal
REF 1
voltages,
of
+6.42Y,
by cutting
the appropriate
links.
REF 2
:
The second reference
is 1/16th
of REF
1. The
positive
and negative REF 1
voltages are divided
by R71,
R68 and R214, R7O
respectively.
The
power
supplies
for
the
logic
circuits
M35, M29,
M27, M28
and opto-isolators M1,
M4, M5 and M6 are also
derived
from M39
via zener
diodes
D61 and D62,
giving
supply voltages of
+8
volts.
.
Positive
signal
Negative
signal
Logic
levels
:
(0
=
-8V,
1
=
+8Vl
Fis
3.14 MULTIPLEXEB
CONTROL
LINE SIGNALS
b
a
c
b
a
STATE
STATE
1
0
0
0
0
1
1
1
0
1
0
1
1
1
1
o
0
1
1
0
1
1
I
1
1
1
o
I
0
1
1
1
1
0
0
1
R
ESET
srG
_BIAS
+REF
1
+REF
2
R ESET
RESET
SIG
+
BIAS
-REF
1
-REF
2
RESET
Æ?*
+15V
D65
R40
R213
+Ref 2
+Ref
1
871
R42
Ã211
R68
887
E
D
c
R43
A
R212
FIG.
3.15
POSITIVE
REFERENCE
CIRCUITRY
D6o*
*Dutron
Matched
pair