3-20.
Front Panel
3-21.
The front panel
serves
as an
interface between the
operator
and
the 8502A controller. The display is
multi-
plexed
by the
controller
by
means of addressing the front
pane! for
each
digit. One direct address,
two
indirect
addresses, and the accompanying
data determine which
digit or annunciator and
which segments will
light. An in-
direct
address requires a previous,
valid direct address to
set
up
the indirect response.
Another direct address enables
the switch matrix to be read
to determine
if
any function
changes are
desired. The cycle of updating each digit
and
annunciator and reading the
switch matrix requires approxi-
mately 28
msec and is a continual
cycle.
Input terminals,
J1 -J5, are
physically located on the front
panel but have
no electrical
interaction with the front panel.
3-22.
DC Signal Conditioner
3-23. DC signals from either the input terminals or
optional signal
conditioners (Ohms or Current Shunts)
are routed
through
the DC Signal
Condilioner
to be
brought v/ithiri
the range
of the A/D Converter
(±
20V).
Figure
3-6
is a block diagram of the DC Signal
Conditioner,
For
ease in
arithmetic
manipulations in
the microprocessor,
all gains and attenuations
In
the 8502A are powers of
eight. Gain
or
attenuation factors
are selected
by
the micro-
processor
addressing the module. Data from the
data bus is
latched into the control circuitry and used to select relays
in
the attenuator .and switches in the amplifier feedback
circuit.
The combination of the attenuator
and
feedback-
controlled
amplifier
give gain or attenuation factors of one,
eight, or sixty -four.
3-24.
Active Filter
3-25.
The
purpose of tJie Active Filter
module is to
multiplex
dc
signals
to the A/D Converter and to switch
analog filters
into
the signal conditioner inputs. Figure
3-7
is
a block diagram of the FUter/External Reference
module. Five filter modes
may be selected from the
front
panel.
For
external reference measurements,
the signal
Figure
3-6.
DC
Signal Conditioner Block Diagram
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