Development of a complete cold electronic based discrete level sensor

Abstract

A complete cold electronics based cryogenic level sensor with six discrete levels is presented here. Each level consists of a series arrangement of 3 diodes separated by 1 mm distance, forming a series-parallel diode arrangement. The method of feeding a constant current to only one selected level at a time has greatly improved the current requirement to (1-2mA). Likewise, multiplexing and monitoring the voltage across one level at a time using a cold electronics multiplexer circuit has negated the shortcoming of reduced sensitivity at higher number of levels. The level is determined by the series voltage of the diodes obtained from the output of op-amp circuit and corresponding to the delta diode voltage, digitization of the voltages has been done to represent immersed or exposed diodes in LN2. With this seriesparallel method of measurement, both the shortcomings of conventional diode based level sensors namely; requirement of large supply current for diodes and the thermal-voltage saturation error at higher levels are improved. Experimental results from the calibration are also presented here.