The gas sensor is the heart of a gas detection system and is usually installed in the probe head. Essentially, a gas sensor is a transducer that converts the volume fraction of a gas into a corresponding electrical signal. The probe head conditions the gas sample through the gas sensor, which typically includes filtering out impurities and interfering gases, drying or cooling treatment, sample aspiration, or even chemically treating the sample to allow for faster measurements by the chemical sensor.

There are many types of gases with different properties, and therefore many types of gas sensors. According to the nature of the gas to be detected can be divided into: for the detection of flammable and explosive gas sensors, such as hydrogen, carbon monoxide, gas, gasoline volatile gas, etc.; for the detection of toxic gases sensors, such as chlorine, hydrogen sulphide, arsine, etc.; for the detection of industrial process gases sensors, such as oxygen in the steelmaking furnace, heat treatment furnace carbon dioxide; for the detection of atmospheric pollution sensors, such as the formation of acid rain NOx, CH4, O3, household pollution such as formaldehyde and so on.

According to the structure of the gas sensor can also be divided into two categories of dry and wet; according to the output of the sensor can be divided into two categories of resistive and resistive; according to the detection of the yard can be divided into electrochemical method, electrical method, optical method, chemical method several categories.

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