COMBUSTION MONITORING SENSOR USING TIN DIOXIDE SEMICONDUCTOR

An attempt has been made to develop tin dioxide semiconductor gas sensors which detect carbon monoxide and other reducing molecules present in combustion exhaust gases due to incomplete burning in combustion equipment. The sensors are placed in the exhaust gases and are operated by an intermittent periodic heating cycle between 400 and 150-degrees-C. It is found that the sensor resistance at 150-degrees-C changes considerably with an increasing amount of reducing molecules. When exposed to a highly reducing atmosphere, the sensors show hysteresis in their characteristic dependence of resistance on the reducing molecule concentration. However, the hysteresis phenomenon disappears when no catalyst is added to the sensors. Actual tests for trial sensors in the exhaust gases of a commercial gas hot water heater confirm that the sensing characteristics are quite stable for a long period of time.