Datron 1061 Calibration And Servicing Handbook 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