An active temperature modulation of gas sensor based on a self-adaptive strategy

The sensitivity and the selectivity of metal-oxide gas sensors are largely dependent on the operating temperature. These sensors are usually operated either at a fixed temperature value or using a pattern of multiple temperatures. In either case, the temperature value and its profile have a predetermined unchangeable pattern. In this paper we propose an active temperature modulation methodology that gives rise to a self-adapted temperature pattern that can be used as a representative feature of the sensor response. For this purpose, we designed a closed-loop circuit, connecting the sensor resistance to the sensor heater. With this circuit topology deviations in sensor resistance value are mirrored into changes of operating temperature. Herewith, the method is implemented with an astable multivibrator, so with a steady resistance values the temperature modulation signal converges to a periodic pattern of pulses that is characteristic of the sensor state.