Design, Fabrication, and Characterization of an Interdigitated Micro-Capacitive Level Sensor Coupled with Signal Conditioning Circuit

Abstract Capacitance-based fluid level switches are extensively used to control cryogen flow in cryogenic storage systems. Despite their popularity, these switches typically require expensive fabrication techniques and complex read-out circuitry; they often have the disadvantages of being heavy and having a large thermal mass. This paper introduces a novel cryogenic liquid point level sensor based on an interdigitated capacitor (IDC) integrated with a signal conditioning circuit on a PCB. The design leverages PCB manufacturing techniques to optimize the sensor’s electrode configuration, resulting in a compact and efficient solution. The signal conditioning circuit utilizes matched monostable multivibrators and an Exclusive OR (XOR) gate to convert capacitance changes into stable DC voltage signals. This device can precisely sense cryogen levels and provide fast, reliable switching signals for external control valves. The dynamic response of the sensor in liquid nitrogen (LN 2 ) is analyzed and presented, demonstrating its potential to improve the accuracy and efficiency of cryogenic liquid-level measurement systems.