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Model DRC-91C/93C
9215.3
NOTES ON
CS-501
CAPACITANCE
SENSORS
9 2 1 5 . 3 . 1 Short-Term Stability
The
capacitance
sensor
provides
very
stable
temperature
control
over
long
periods
of
time.
However,
since
an
operational
"aging" phenomenon exists some care
must be exercised
in
their use.
The short-term (minutes to hours)
capacitance/temperature
drift
is
initiated by a thermal perturbation
of the sensor.
In order to minimize this short-
term drift, it is recommended that
approximately one hour be allowed
for the sensor to stabilize after
the initial cooldown.
The short-
term drift is then on the order of
a few tenths of miIIikelvin/minute
at
4.2K,
several millikelvin/minute
at 77K and one millikelvin/minute
at 305K.
For temperatures less
than 290K the short-term drift is
such that the equivalent tempera-
ture will decrease with time and
for temperatures above 290K will
increase with time.
9215.3.2
Thermal
Cycling
and
Reproducibility
Thermal
cycling
of
capacitance
sensors can produce variations in
capacitance/temperature
values
equivalent to several tenths of a
degree over the short term (days)
.
Thermal cycling over the long term
(weeks) can result
in
variations
that
exceed
a
degree.
These
variations are always such that the
equivalent
temperature
increases
with
time
and
with
increased
cycling.
The reduced capacitance
C(T)/C(4.2K)
for T<290K is stable
to within
±0.5K
on the average.
Also these variations do not create
instabilities and do not impair the
sensors
primary
function
as
a
2 .
Remove
the
four
screws that
control device in magnetic fields.
secure the calibration cover to
They also are not seen within a
its
clips and remove the cover.
temperature cycle.
Remove
the
two
back
panel
COPYRIGHT
2/88 LSCI
9215-3
9215 Capacitance Input
card
9 2 1 5 . 3 . 3
Magnetic
Field
Dependency
Magnetic field sensitivity is less
than ±0.15
%
at 4.2K and less that
±0.05 %
between 77K and 305K for
fields up to
18.7
Tesla.
9 2 1 5 . 3 . 4
Frequency
Dependence
For frequencies between
1
and
5
kilohertz the frequency sensitivity
is as follows:
-0.18k/kilohertz at 4.2K
-1K/kilohertz at 77K
+0.06K/kilohertz at
305K
9215.4
INSTALLATION
The
9215
can be installed in the
DRC-91C/93C as either Input A or
Input B.
The card
is
factory
installed if ordered with a DRC-
91C/93C Temperature Controller or
can be field installed at a later
date.
If field installation is
required,
use
the
following
procedure.
1 .
Set the POWER switch to
OFF
and
disconnect the power cord from
the unit.
Remove the three top
panel screws and slide the panel
off.
Note -on the calibration
cover the position of the Card
will occupy.
WARNING
To prevent
shock
hazard, t u r n
off
the
instrumen
t and discon-
nect it f r o m
AC
line
power and
all t e s t equipment
before
re-
moving
cover.
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