Commonly used sensors in gas detectorsCommonly used sensors in gas detectors
The core part of the gas detector is the gas sensor, according to different gas detection principles are not the same, common gas sensors include: PID photo ionisation sensor, infrared sensor, electrochemical sensor, catalytic combustion sensor and semiconductor sensor. The following Honeywell AIG technology for you to introduce the working principle of each sensor and the advantages and disadvantages.
First, the gas detector of the infrared principle
Principle: non-discriminatory infrared principle NDIR sensor is the use of Beer-Lambert infrared absorption law, that is, different gases have absorption of specific wavelengths of light, the intensity of the absorption and the concentration of the gas is proportional to achieve detection. It applies a filter to divide the infrared light into a very small band of spectral lines required, and the gas to be detected absorbs this very small band of spectral lines.
Advantages: high reliability, good selectivity, high accuracy, non-toxic, less interference by the environment, long life, no dependence on oxygen.
Disadvantages: affected by humidity, limited detection of gas species, currently the most important application of methane, carbon dioxide, carbon monoxide, sulphur hexafluoride, sulphur dioxide, hydrocarbons and other gases.
Second, the semiconductor principle of gas detector
Principle: semiconductor gas sensor is the use of some metal oxide semiconductor materials, a certain temperature, resistance changes with the environmental composition of the gas and change the principle of manufacturing. For example, alcohol sensors, is the use of tin dioxide at high temperatures when encountering alcohol gas, resistance will sharply reduce the principle of preparation.
Advantages: low cost, simple manufacturing, high sensitivity, fast response time, long life, low sensitivity to humidity and simple circuit and other advantages.
Disadvantages: poor stability, affected by the environment, especially the selectivity of each sensor is not unique, the output parameters can not be determined. Therefore, it is not suitable for application in the measurement of accurate requirements of the place, mainly for civilian use.
Third, the catalytic combustion principle of gas detector
Principle: catalytic combustion sensor is in the platinum resistance surface preparation of high-temperature resistant catalyst layer, a certain temperature, combustible gases in the surface of catalytic combustion, combustion so that the platinum resistance temperature rises, resistance changes, changes in the value of the combustible gas concentration function.
Advantages: Catalytic combustion gas sensors selectively detect flammable gases: whatever cannot be burned, the sensor has no response. Fast response, long life, little affected by temperature, humidity and pressure. The output of the sensor is directly related to the explosion hazard of the environment and is a dominant class of sensor in the field of safety detection.
Disadvantages: non-selective in the range of flammable gases. The sensor is susceptible to poisoning, and most elemental organic vapours are toxic to the sensor.
Note: Catalytic combustion detection can be realised conditionally, it must be ensured that the detection environment contains enough oxygen, in the absence of oxygen environment this detection method may not detect any combustible gas. Some lead compounds (especially tetraethyl lead), sulfur compounds, silicones, phosphorus compounds, hydrogen sulfide and halogenated hydrocarbons may make the sensor poisoning or inhibition.
Fourth, the gas detector PID principle
Principle: PID by the ultraviolet light source and ion chamber and other major parts of the composition of the ion chamber has a positive and negative electrodes, the formation of an electric field, the gas to be measured in the irradiation of the ultraviolet light, ionisation, the generation of positive and negative ions, the formation of electric current between the electrodes, the amplified output signal
Advantages: high sensitivity, no poisoning problems.
Disadvantages: no selectivity, affected by humidity, short life of the ultraviolet lamp, expensive.
Fifth, the gas detector electrochemical principle
Principle: through the electrolyte inside the sensor and the target gas reaction and produce and gas concentration proportional to the electrical signal to work.
Advantages: large operating temperature range, range, high sensitivity, linear output, good selectivity.
Disadvantages: short life span, limited storage period, short life span in extremely dry or highly concentrated gas environments, non-specific, susceptible to interference, humidity has an impact on accuracy.
Note: Most toxic gas sensors require a small amount of oxygen to function properly. There is a vent on the back of the sensor for this purpose. High humidity and high drought can affect sensor life. Momentary pressure changes may produce a transient sensor output and may also reach a false alarm condition.
