DEVELOPMENT OF DISCRETE ARRAY TYPE LIQUID LEVEL INDICATOR FOR CRYOGENIC FLUIDS

摘要

In large cryogenic storage systems, the level of cryogenic fluids such as liquid nitrogen, liquid oxygen, etc., are usually monitored using capacitance type indicators. They are both heavy and inaccurate. We report here the development of discrete array type liquid level indicators. A special class of analog multiplexer IC, which operates at cryogenic temperatures, is used in the unit. Operating it at liquid helium temperature and switching the channels one million times without any failure tested the reliable operation of the IC at cryogenic temperature. The system is capable of detecting the liquid level of any cryogen. Only a software tuning is required for operation with each fluid. The developed unit has an active length of 400 mm and six regions with sensitivities ranging from +- 5 mm to +- 0.5 mm. Redundancy of level measurement is achieved through software. The interaction of the system that has 138 sensors to ambient electronics is through only 15 wires. The integrated unit has been cycled several times between room temperature and 77 K.