Capacitive level meters for cryogenic liquids with continuous read-out

The operation of a variety of liquid level meters is briefly considered. Currently used continuous read-out level meters, whose operation is based on the difference between the dielectric constants of the gas and the liquid measured, are compared. The requirements for cryogenic application of these level meters are discussed. An electronic circuit for capacitance measurements with high stability and resolution better than 20 ppm is described along with construction details of capacitance transducers both for liquid nitrogen and liquid helium. The parameters of two particular level meters are reported as follows. For liquid nitrogen: measuring length 50 cm; overall error < 1% at full scale deviation (FSD); short time instabilities < 0.01% FSD; resolution better than 0.05 mm. For liquid helium: measuring length 60 cm; overall error < 5% FSD; short time instabilities < 0.2% FSD; resolution better than 1 mm.