What are the methods of gas detection?

There are many methods for gas detection. At present, gas detection in the industrial field is carried out by gas sensors, which are usually based on the following principles:

1. Catalytic combustion sensor: Generally speaking, for combustible gases, such as alkanes and alcohols, the sensor consumes a large amount of current, and its interior needs to be kept at a high temperature, and the gas is catalytically burned at high temperature, thus changing the resistance of the sensing element. The measurement accuracy can reach 65438±0% LEL (lower explosive limit).

Electrochemical principle: through the reaction between gas and electrolyte, a weak current is generated on the electrode. Generally speaking, for toxic gases such as Co \ H2S \ SO2 \ Cl2 \ NH3 \ NO \ NO2 \ cocl2 \ HCN, the gas selectivity of electrochemical sensors is not very strong, and generally there will be cross reactions. Commonly used CO/H2S sensors are relatively cheap (the price ranges from tens to hundreds of yuan). The measurement accuracy of ordinary electrochemical sensor can reach ppm level, and that of four-electrode electrochemical sensor can reach ppb level (several thousand yuan, expensive).

Infrared optics: CH4\CO2 can absorb infrared light in a certain band, and the gas concentration can be calculated according to the different absorption degree (the price of civil products is about 100 yuan, and the price of industrial products is several hundred to several thousand yuan).

4.PID method: PID uses ultraviolet lamp to ionize the sample gas to detect the concentration of VOC gas. When the sample molecules absorb high ultraviolet energy, the molecules are ionized into ions with positive and negative charges, which are sensed by the charge sensor to form a current signal. (The price of industrial products is several hundred to several thousand yuan)

5. Gas chromatography/mass spectrometry (GC/MS): The gas selectivity is good, and the price is expensive, generally tens of thousands to hundreds of thousands of yuan.

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