An optical-fibre refractometric liquid-level sensor for liquid nitrogen

This paper presents a prototype optical-fibre refractometric liquid-level sensor which can access the static and dynamic levels of liquid nitrogen in large cryogenic systems. This version of the sensor is intended for use in various tests of cryogenic systems such as used in rocketry, during the design stage. The sensor employs a vertical linear array of 140 highly sensitive optical-fibre refractometric transducers. The liquid-level measurement range is 1.6 m with a resolution of up to 5 mm. The optical transducers are multiplexed using a matrix-type optical-fibre network which employs a robust level tracking algorithm. This type of sensor can be used for measuring the level of other cryogenic liquids such as liquid hydrogen.