American Magnetics 286 Multi-Sensor Liquid Level Instrument (CE-Marked) - Manual (Page 42)

28
Calibration
Approximate calibration
The Model 286 also provides preset approximate calibration factors
for common cryogens relative to liquid nitrogen, with both at
atmospheric pressure. The preset values may be selected in lieu of
entering a custom factor if the full active length of the sensor is
dipped (L
dipped
= L
active
).
Note
In contrast to the AMI Model 185/186 instruments, the approximate
calibration factor is retained in the Model 286 memory. Therefore,
the approximate calibration factor can be adjusted as desired at any
time without modifying the base MIN/MAX calibration.
Example: Purchased a 100" active length sensor for operation in
liquid argon at atmospheric pressure, however only liquid nitrogen
is available for calibration at a maximum depth of 30":
First, the sensor is dipped as far as possible into the liquid nitrogen
and cooled. The MIN point is then set as outlined in step 6. The
MAX point is set as outlined in step 7 while the sensor is
submerged 30" in liquid nitrogen. The dielectric constant for liquid
nitrogen is 1.4336 and for liquid argon is 1.53. Substituting all
values into the approximate calibration factor equation yields:
A value of 407.4 would be entered as a custom approximate
calibration factor as outlined in steps 6 and 7. The sensor is now
approximately calibrated for 100" active length operation in liquid
argon at 1 atm.
11. 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 if possible.
12. Proceed to the Operation section for directions for configuring the
instrument.
Approximate Calibration Factor
1.53 1 –
1.4336 1 –
------------------------- 100
Ч
100
30
--------- 407.4 = =