Design of closed-loop analyzer for micromachined thermal conductivity sensor

The hydrogen gas is used for cooling of turbine generators for long years. The reasons of this usage are high thermal conductivity and low density of hydrogen. Since hydrogen is highly explosive, safety must be fully respected. Continuous monitoring of hydrogen concentration in the generator cooling cycle is so important to almost completely eliminate fire hazards. Thermal conductivity sensors are especially suited to measure hydrogen concentration since hydrogen possesses the highest thermal conductivity off all known gases. It is therefore possible to measure concentration of hydrogen in air by the measurement of thermal conductivity of a hydrogen-air mixture. The Thermal conductivity meter must allow the measurement of hydrogen concentration between 0 and 100 vol. % with a good accuracy and reproducibility. It is hard to achieve a satisfactory accuracy by fixed gain closed-loop or open-loop analyzer over the entire range of concentration. Consequently, we design a self-tune closed-loop analyzer. The purpose of this paper is to demonstrate the results obtained from implementation of this analyzer for a MEMS-based thermal conductivity sensor on a 32-bit DSP-based system.