Instruction Manual

18 Rev. 3

Calibration

Effects of dieletric shifts

To minimize the effects of shifts in the dielectric of the target liquid,

perform a closed dewar calibration (see page 21) at the expected operating

condition of the cryo-vessel. If this is not feasible, then calibrate the sensor

at atmospheric pressure and use the approximate calibration method to

compensate for the shift of the dielectric when the cryogenic liquid is

under pressure. For this type of approximate calibration, the reference

liquid will be the target liquid at atmospheric pressure — see page 25 for a

detailed discussion of the approximate calibration method. If any

questions exist in regard to calibration issues, contact AMI for assistance

in determining the optimal calibration strategy.



Note

All references to “dielectric constant” herein refer to the unitless

relative dielectric to

(ε

is the dielectric constant of a vacuum).

0 50 100 150 200 250 300 350 400 450 500

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

Diel-1 (saturated liquid) Diel-1 (saturated vapor)

Pressure (psi)

Diel - 1

Figure 3-1. Dielectric vs. pressure for nitrogen under saturated conditions.