Step Frequency Time Domain Reflectometry for Distributed Temperature Sensing

Intelligent Automation Inc (IAI) is partnering with Boeing to develop an innovative distributed temperatures sensor based on Electrical Time/ Frequency Domain Reflectometry. The core idea is the development of a simple, practical, yet robust electrical equivalent of Fiber Braggs Grating using thermistor based frequency tuned circuits. The step frequency Time Domain Reflectometer (TDR) is used for generating input signals using Direct Digital Synthesis (DDS). These input signals are fed into an appropriately temperature rated coaxial cable (which traverses the entire span of the cryostat to be monitored) with single ended access and minimum attenuation. On this coax cable are frequency tuned thermistor circuits that respond only to certain frequencies. The cryogenic narrow band pass filters are designed to admit only a narrow band of frequencies. Essentially at any given time the step frequency TDR interrogates only a particular thermistor element of the circuit. The use of electrical rather than optical methods allows use of materials and components that have been thoroughly tested at cryogenic temperature, reducing risk. We plan to leverage several key technologies (Time Domain Reflectometer, Step frequency Radar) developed under other ongoing programs at IAI, thus further mitigating the technical risks.