Development of Superconducting Level Sensor for Liquid Helium Level Measurements

Liquid helium storage and transport Dewars of different types and different storage capacities are used in laboratories for experimental measurements at low temperatures. Liquid helium is used as a cryogen for cooling the sample to a temperature of 4.2 Kelvin. To measure the level of the liquid helium in the experimental cryostat or Dewar, imported superconducting level sensors are presently being used but are relatively expensive. In view of this, experimental work related to design and development of the superconducting level sensor based on NbTi superconducting wire was undertaken. This work includes the fabrication, characterization and calibration of the superconducting level sensor. The characterization work involves the measurement of the resistance of the level sensor at different levels of liquid helium in the Dewar for different values of excitation current to determine the optimum excitation current with a view to establish a single valued relationship between the measured resistance and the liquid helium level. A program has been written by using LABVIEW software to automate the characterization process. Based on the measurements, display system is being developed to display the level of liquid helium in the Dewar.