Rev. 2 53
Calibration
Capacitance-Based Level Calibration : Closed Dewar Calibration Procedure
in step 2. The maximum point is set as outlined in step 3 while
the sensor is submerged 30" in liquid nitrogen. The dielectric
constant for liquid nitrogen is 1.454 and for liquid argon is 1.53.
Substituting all values into the approximate calibration factor
equation yields:
A value of 389.1 would be entered as the approximate
calibration factor as outlined in steps 6 and 7. The sensor is now
approximately calibrated for 100" active length operation in
liquid argon.
12. The sensor can now be installed in the dewar containing the target
liquid. The approximate calibration can be used until an open
dewar or closed dewar calibration can be performed with the target
liquid.
4.2.8 Closed Dewar Calibration
A calibration can be performed in a closed dewar system by monitoring the
liquid level while transferring the target liquid to an initially empty (or
near empty) dewar at a constant rate. In order to insure success with the
closed dewar technique, it is necessary to prepare the instrument by
presetting the calibration minimum and maximum calibration points
outside the estimated level range. If the instrument is not prepared in this
manner before the calibration procedure, it is possible to reach the
maximum calibration point of the instrument before the target vessel is at
the desired maximum level point. If minimum and maximum liquid level
indication is available via some other means (e.g. flow calculation, visual
determination, point sensors, etc.), then the presetting of the instrument is
not necessary.
4.2.8.1 Presetting the maximum and minimum calibration points
The following procedure should be performed before installation of the
sensor in the target cryo-vessel.
1. Connect the sensor coaxial cable to the BNC connector on the rear
panel of the instrument (Refer to “Connecting the Sensor to the
Instrument” on page 12). Do not connect the sensor. Energize the
instrument.
Approximate Calibration Factor
1.53 1–
1.454 1–
----------------------
100
100
30
---------
389.1==
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