Principles, advantages and disadvantages of common sensors of gas detectors
The core part of the gas detector is the gas sensor, and the principle of gas detection is different according to different. Common gas sensors include: PID photoion sensor, infrared sensor, electrochemical sensor, catalytic combustion sensor, and semiconductor sensor. AIYI Technologies introduces the working principle, advantages and disadvantages of each sensor in detail below.
1. Infrared principle of gas detector
Principle: The non-split infrared principle NDIR sensor uses the Beer-Lambert infrared absorption law, that is, different gases absorb light at a specific wavelength, and the intensity of absorption is proportional to the concentration of the gas to achieve detection. It uses an optical filter to divide the infrared light into a required spectral line of a very small wavelength band, and the detected gas absorbs the spectral line of this very small wavelength band.
Advantages: high reliability, good selectivity, high accuracy, no toxicity, less environmental interference, long life, and no dependence on oxygen.
Disadvantages: It is greatly affected by humidity, and the types of detection gases are limited. At present, it is mainly used in methane, carbon dioxide, carbon monoxide, sulfur hexafluoride, sulfur dioxide, hydrocarbons and other gases.
2. The semiconductor principle of the gas detector
Principle: The semiconductor gas sensor is made by using some metal oxide semiconductor materials. At a certain temperature, the resistance changes with the change of the ambient gas composition. For example, the alcohol sensor is prepared by using the principle that when tin dioxide encounters alcohol gas at high temperature, the resistance will decrease sharply.
Advantages: low cost, simple manufacturing, high sensitivity, fast response speed, long life, low sensitivity to humidity and simple circuit.
Disadvantages: poor stability and greater environmental impact, especially the selectivity of each sensor is not unique, and the output parameters can not be determined. Therefore, it should not be used in places where measurement accuracy is required, mainly for civilian use.
3. The catalytic combustion principle of the gas detector
Principle: The catalytic combustion sensor is to prepare a high temperature resistant catalyst layer on the surface of the platinum resistance. At a certain temperature, the flammable gas catalyzes combustion on its surface. The combustion causes the platinum resistance temperature to rise, and the resistance changes. The change value is a function of the flammable gas concentration.
Advantages: Catalytic combustion gas sensor selectively detects flammable gas: the sensor does not respond to anything that cannot be burned. The response is fast, the service life is longer, and it is less affected by temperature, humidity and pressure. The output of the sensor is directly related to the explosion hazard of the environment, and it is a leading sensor in the field of safety detection.
Disadvantages: within the flammable gas range, no selectivity. The sensor is susceptible to poisoning, and most elemental organic vapors have a poisoning effect on the sensor.
Note: Catalytic combustion detection is conditional. It must be ensured that the detection environment contains sufficient oxygen. This detection method may not detect any flammable gas in an oxygen-free environment. Certain lead compounds (especially tetraethyl lead), sulfur compounds, silicon compounds, phosphorus compounds, hydrogen sulfide, and halogenated hydrocarbons may poison or inhibit the sensor.
4. PID principle of gas detector
Principle: PID is composed of ultraviolet lamp light source and ion chamber. The ion chamber has positive and negative electrodes to form an electric field. Under the irradiation of the ultraviolet lamp, the gas to be measured is ionized to generate positive and negative ions. Amplify the output signal
Advantages: high sensitivity, no poisoning problems.
Disadvantages: non-selective, greatly affected by humidity, short life of UV lamp, and expensive.
5. The electrochemical principle of the gas detector
Principle: The electrolyte inside the sensor reacts with the target gas and generates an electric signal proportional to the gas concentration to work.
Advantages: wide operating temperature range, multiple ranges, high sensitivity, linear output, good selectivit
Disadvantages: short life, limited storage period, short life in extremely dry or high-concentration gas environment, non-specific type, easy to interference, and humidity affects accuracy.
Note: Most toxic gas sensors require a small amount of oxygen to maintain proper function. There is a vent on the back of the sensor for this purpose. High humidity and high drought will affect the service life of the sensor. Instantaneous pressure changes may produce a transient sensor output, or it may reach a false alarm state.
With the above information, you could find the most suitable sensor you need. There are many gas detectors with different sensors in AIYI Technologies for your choice, welcome to your support.