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DATA PRECISION 938 User Manual

DATA PRECISION 938
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42-5124
MODEL
938
Figure
4-4.
System
Block
Diagram
4-4
MODEL
938
PRINCIPLES
OF
OPERATION
As
shown
in
the
illustration,
the
A/D
converter
operates
on
the
values
of
voltage
connected
to
two
pairs
of
inputs:
the
INPUT
and
the
REFERENCE.
A
sequence
of
switching
actions
perform
ed
by
the
four
output
signals
of
a
control
logic
programming
block
determine
the
the
circuit
configurations
that
develop
values
of
the
voltage
signals
for
each
of
these
two
inputs
to
the
A/D
converter.
The
four
phases
in
the
signal
conditioning
pro
cess
are:
4>1,
4>2,
<i>3,
and
4>4.
<i>1:
During
which
the
capacitor
to
be
measured
(Cy)
is
charg
ed
to
an
initial
nominal
value
depending
upon
the
value
of
capacitance
and
the
range
scale
selected
(but
not
exceeding
2.8
volts).
$2:
During
which
Capacitor
C4
and
C5
are
charged
in
series
to
the
initial
value
of
the
capacitor
under
test.
4>3:
During
which
the
capacitor
under
test
Cy
is
discharged
through
a
range-selected
resistor.
The
resulting
current
is
averaged
over
a
number
of
cycles
of
this
interval
and
converted
into
a
voltage
on
C3
by
the
filtering
action
of
R9
and
C3.
4>4:
During
which
the
value
of
the
C
t
voltage
at
the
end
of
the
discharge
interval
of
4>3
is
stored
on
C4.
As
a
result,
the
voltage
on
C5
represents
the
difference
between
the
initial
and
final
values
of
capacitance
on
C
t
-
It
is
the
REFERENCE
input
to
the
A/D.
Figure
4-5
derives
the
result
in
a
more
rigorous
fashion.
4-5

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DATA PRECISION 938 Specifications

General IconGeneral
BrandDATA PRECISION
Model938
CategoryMeasuring Instruments
LanguageEnglish