A semiconductor gas sensor is operated to determine a concentration of a detection gas by using a degree by which a resistance of a detection material such as a metal oxide, a polymer and a carbon nano tube is changed during an oxidation/reduction reaction of the detection gas and the detection material. To this end, the semiconductor gas sensor employs a dedicated heater for a smooth oxidation/reduction reaction of a detection gas and a detection material, and such a reaction is generated in a temperature section of 200 to 500 degrees Celsius.
An electrochemical gas sensor is operated to determine a concentration of a gas through a degree by which a current or an electromotive force is changed while the detection gas and a detection material such as an alkaline metal or an alkaline earth metal carbonate react each other at a high temperature to influence an ion conductivity of a solid electrolyte.
The semiconductor gas sensor or the electrochemical gas sensor employs a heater therein in terms of operation principle. The detection material used for the semiconductor gas sensor or the electrochemical gas sensor mainly includes a metal oxide, an alkaline metal carbonate, a carbon nano tube, graphene or a polymer.
However, a gas sensor according to the related art is known that sensitivity, selectivity and the like are influenced by humidity, that is, water molecules in the air (Jianwei Gong et al., Sensors and Actuators B 114(2006) 32-39). To solve this problem, a study for improving humidity stability of a gas sensor through a filter for adsorbing moisture to a gas inlet port or removing moisture from the gas inlet port while the gas sensor is packaged (U.S. Pat. No. 5,841,021). Such a filter technology helps remove moisture of a part of a gas sensor and secure stability of the gas sensor, deteriorates efficiency of the gas sensor in a situation where excessive moisture is present. And the filter has a limit in life when the filter is stored for a long time. Therefore, a process of replacing a filter after a predetermined time period is required to protect a gas sensor.