Room-temperature dosimeter-type gas sensors with periodic reset

NO2 sensing tests have been performed on room-temperature-operated SnO2 gas sensors. Due to elongated response and recovery time constants these sensors exhibited a dosimeter rather than a conventional concentration-dependent NO2 response. In order to enable continuous monitoring such sensors need to be subjected to periodically repeated sense & reset operations. Reset procedures which proved to be effective in restoring baseline conductance again are low-temperature annealing (T ∼ 120 °C), ultraviolet (UV) light exposure, and exposure to humidified synthetic air (T ∼ 300 K, r.h. ∼ 80%). Unlike high-temperature gas sensors, room-temperature operated sensors exhibit very little intrinsic sensor drift. Severe levels of sensor drift, however, can arise from contamination-induced effects in the sensor periphery. It is demonstrated that such contamination-induced sensor drifts can be effectively compensated by exploiting the knowledge about the timing of the sense & reset operations.