Abstract
Concentration sensor using a hot-wire and sonic nozzle to measure the gas composed of two kinds of gases is fabricated by MEMS technology. When to measure the concentration, high sensitivity and response and precision and not influencing the air flow are important. This research aims to improve of sensitivity and reduce the influence on the air flow by the miniaturization. When concentration changes, thermal conductivity of the gas composed of two kinds of gases is changing. The thermal conductivity changes depending on the concentration and the velocity, though the velocity is kept constant with the sonic nozzle. Heating current flows from Wheatstone bridge to keep constant temperature. The supplied current changes, too, when the thermal conductivity changes. The concentration is indirectly measured by measuring the supply current.
