Design and development of heater control circuit without temperature sensor for monitoring hydrogen in argon

A thin film based tin oxide sensor is developed to monitor low levels of hydrogen (concentration ranging from 5 to 75 ppm) in the cover gas plenum of the fast breeder test reactor. The heater and the sensor patterns are integrated on a miniature alumina substrate, and necessary electrical leads are incorporated into it. For proper functioning of the sensor, the heater has to be maintained at a constant temperature of 350 °C. This paper gives an outline of the electronics developed to measure the sensor signal and to control the heater temperature. The major challenge in this work is that there was no provision for embedding a temperature sensor on the heater surface due to physical constraints. This constrained the maintenance of a constant heater temperature for the proper functioning of the sensor. This led us to develop and demonstrate a heater control circuit without a temperature sensor to maintain a fixed temperature for monitoring hydrogen in argon, and electronics for the above-mentioned circuitry is discussed.