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Model
DRC-91C/93C
9215
Capacitance
Input
card
panel
and
on the DRC-93C
by
a
upper display hit the
key
sequence of key strokes from its
while still holding
down the
front panel.
Also the Sign of the
SCAN
key.
Similarly, to
temperature
coefficient
can
be
change the sign if in the lower
entered via the computer interface
display hit the
key while
using the
AC1C2
or BC1C2 command.
still holding down the
SCAN
key.
9 2 1 5 . 6 . 1
selection of
Temperature
4. Now let up on the
key (or
Coefficient Sign on the
DRC-91C
key) and then the
SCAN
key.
The sign to be used on the Tempera-
You should press the SENSOR key to
ture Coefficient of the capacitance
make
sure that the sign is as
is selected using Switch
1
of the
desired.
appropriate SENSOR ID located on
the rear panel of the DRC-91C.
9215.6.3
Selection of the Sign of
the Temperature Coefficient via the
When Switch
1
of the SENSOR ID is
Computer
Interface
closed the Temperature Coefficient
is Positive.
When Switch
1
of the
To select the sign of the tempera-
SENSOR ID is open, the Temperature
ture
coefficient
via
the
IEEE
Coefficient is Negative.
interface,
check
the
AC1C2
and
BC1C2 commands
in
the instrument
9215.6.2
Selection of Temperature
manual.
Coefficient Sign on the
DRC-93C
When a 9215 Capacitance Input Card
9215.7 PRINCIPLE
OF
OPERATION
is installed, pressing the SENSOR
key
will
display
for
the
ap-
The
9215-15
configuration provides
propriate channel either ±15-15 or
a charging current switched at a
-
±15-50;
the
-15
for the 9215-15
frequency of
5
kilohertz.
The
configuration or
-50
for the
9215-
frequency is precisely controlled
150
configuration.
The
(±)
sign
by
a
crystal
oscillator.
The
indicates whether the Temperature
operation
of
the
9215-150
is
Coefficient is positive or nega-
identical except that the frequency
tive.
The plus
(+)
means that the
is
1 kilohertz.
The
charging
Temperature Coefficient
is posi-
current produces a sawtooth voltage
tive. The minus
(-)
means that the
waveform
with
a
peak-to-peak
Temperature Coefficient
is nega-
voltage of about 7 volts.
Another
tive.
voltage of precise
amplitude is
generated which has a duty cycle
Select the Temperature Coefficient
dependent on the charging time of
sign from the front panel by using
the capacitor.
This waveform is
a combination of the SENSOR key,
averaged and filtered to produce a
SCAN
key and the
key and
positive DC voltage proportional to
key as follows:
the capacitance.
This Dc voltage
is sent to a
16
bit A/D converter
1 . Press and hold the SENSOR key.
on
the card.
The A/D converter has
a resolution of 50 microvolts and a
2.
While holding down the SENSOR
full scale input voltage of
3.0000
key, press the
SCAN
key.
volts.
With the
9215-15
Configura-
You may now let up on the SENSOR
tion the
3.0000
volts corresponds
key.
to a capacitance of
30
nanofarads;
and on the
9215-150
configuration
3.
To change the sign if in the
to
150
nanofarads.
The digitized
COPYRIGHT 2/88
LSCI
9215-5
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