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DATA PRECISION 938 User Manual

DATA PRECISION 938
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42-5124
MODEL
938
During
Step
2
(INT
switches
are
closed),
the
A/D
input
is
con
nected
to
the
buffer
amplifier,
whose
output
is
connected
in
series
with
the
zero
compensation
of
the
previous
step,
and
the
net
value
charges
capacitor
C7.
During
Step
3
(DE
switches
are
closed),
the
pair
of
DE
switches
are
closed
to
connect
the
voltage
across
C6
to
the
A/D
input
with
the
proper
polarity
convention
in
order
to
reduce
the
voltage
previously
built
up
on
integrating
capacitor
C7
in
Step
2.
4.5.2
Digital
Section
of
the
A/D
Converter.
The
digital
section
of
the
A/D
converter
contains
counters
and
logic
circuitry
with
which
to
develop
the
3-step
timing
signals
and
to
generate
driving
signals
for
each
of
the
seven
segments
of
the
3
full
display
decades,
as
well
as
the
driving
signal
for
the
MSB
“
1
”
.
This
section
of
the
IC
also
includes
the
circuitry
to
determine
and
drive
the
negative
polarity
sign,
when
required,
in
the
display,
to
sense
an
out-of-range
condition,
and
to
blank
the
digits.
The
chip
also
provides
the
driving
signal
for
the
liquid
crystal
display
back
plane
in
proper
synchronism
with
the
signals
for
the
display
elements.
Figure
4-7.
Analog
Section
of
the
A/D
Converter
R14
4-10
MODEL
938
PRINCIPLES
OF
OPERATION
4.5.3
Converter
Timing
The
three
steps
in
the
A/D
conversion
cycle,
that
occur
asyn
chronously
with
the
4
phases
of
the
charge/discharge
cycles
in
the
signal
conditioning
circuits,
complete
an
A/D
conversion
at
the
nominal
rate
of
2
per
second.
A
typical
waveform
pattern
for
the
A/D
timing
waveforms,
referred
to
the
output
of
the
in
tegrator,
is
shown
in
Figure
4-8.
4.6
DISPLAY
The
liquid
crystal
display
used
in
the
Model
938
is
a
low
power
device,
whose
back
plane
power
is
furnished
directly
by
the
A/D
converter
chip,
while
the
digit
segments
are
synchronously
driven
by
independent
lines
from
the
A/D
chip
(7
segment
drivers
for
each
of
3
digits,
1
driver
for
the
MSD,
and
1
for
the
negative
polarity
sign).
Drivers
for
the
decimal
points
(3)
and
for
the
“
LO
BAT
”
indicator
are
gated
with
the
back
plane
power
drive
through
Exclusive
OR
gates.
4-11

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DATA PRECISION 938 Specifications

General IconGeneral
BrandDATA PRECISION
Model938
CategoryMeasuring Instruments
LanguageEnglish