Using Bi-2223 Ag Clad Tape As a Liquid Nitrogen Level Sensor

Abstract

The dramatic resistance change in the superconducting-normal transition temperature range enables a high Tc superconductor to be considered for use as a liquid nitrogen level sensor. A (Bi,Pb)2Sr2Ca2Cu3O10+x Ag clad superconducting wire is tested as a continuous liquid nitrogen level sensor to investigate the possibility for this application. The (Bi,Pb)2Sr2Ca2Cu3O10+x Ag clad superconducting wire has approximately 110 K critical temperature, with more flexible and stable properties compared with bulk shape ceramic high Tc superconductors. The voltage drops across the sensor are tested with different immersion length in liquid nitrogen. The voltage signal is sensitive to liquid nitrogen level change, and this signal can be optimised by controlling the transport current. The problems of the Ag clad superconductor are that the Ag sheath thermal conductivity is very high, and the sensor normal resistance is low. These are the main disadvantages for using such a wire as a continuous level sensor. However a satisfactory accuracy can be achieved by control of the transport current. A different configuration of the wire sensor is also designed to avoid this thermal influence.