Most applications hold liquids with below-freezing boiling points, such as nitrogen and methane, in thermally insulated vertical cryogenic tanks. Still, the tank will always have a gas pressure head for the liquid-vapour. Also, these fluids have low oxygen permeability, or Dk values, which make radar devices a poor choice for cryogenic level measurement.
Cryogenic level measurement using a differential pressure transmitter
Differential pressure transmitters can compensate for the vapor pressure head and measure the level accurately. Also, wet or dry legs with some slant will help reduce turbulence from boiling and condensing outside the insulation. If you use wet legs, then you should use liquids with low freezing points.
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