AMI 1700 - Figure 4-33 APPROX. CAL. VALUE Field; Figure 4-34 MAX CAL Values Edited

52 Rev. 2
Calibration
Capacitance-Based Level Calibration : Approximate Calibration Procedure
where L
dipped
is the length of the sensor dipped in the reference
liquid and L
active
is the active sensor length.
Note
If the target liquid is available for dipping (i.e. the reference liquid and
target liquid are the same), then the dielectric ratio, (
e
2
-1)/(e
1
-1),
becomes 1. If the full active length of the sensor can be dipped, then the
length ratio, L
active
/ L
dipped
, becomes 1.
Note that
e
1
= 1.454 for liquid nitrogen at -203°C at
atmospheric pressure. Dielectric constants for several liquids
are provided in the Appendix. The dielectric constant varies
with temperature and pressure, therefore for best accuracy use
the dielectric constant for the target liquid at the temperature
and pressure maintained in the containing vessel.
10. Touch the APPROX. CAL.
VALUE: field and using the
numerical keypad that pops
up, enter the Approx Cal
Value to be applied.
11. Press the APPLY button and
note that the Approximate
Calibration value will be used
to scale the MAX Calibration
frequency displayed adjacent
to the PERFORM MAX CAL
button and the value entered
into the APPROX. CAL.
VALUE field will vanish.
Note
The last approximate calibration factor is not retained in the instrument
memory, therefore the effects of repeated approximate calibrations are
cumulative.
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 minimum point is then set as outlined
Figure 4-33. APPROX. CAL. VALUE
field
Figure 4-34. MAX CAL values edited