Sensors that are commonly used in gas detectors
The most crucial part of a gas detector is the gas sensor, which varies according to different gas detection principles. Common gas sensors include PID photoionization sensors, infrared sensors, electrochemical sensors, catalytic combustion sensors, and semiconductor sensors. Below, Honeyegg Technology will provide you with a detailed introduction to the working principles and advantages and disadvantages of each sensor.
1, The Infrared Principle of Gas Detectors
Principle: Non dispersive infrared principle: NDIR sensors use the Beer Lambert infrared absorption law, which means that different gases absorb light of a specific wavelength, and the intensity of absorption is directly proportional to the concentration of the gas to achieve detection. It is the application of a filter to divide infrared light into a small band of spectral lines required, and the detected gas absorbs this small band of spectral lines.
Advantages: High reliability, good selectivity, high accuracy, no toxicity, less environmental interference, long lifespan, and no dependence on oxygen.
Disadvantages: It is greatly affected by humidity and has limited detection gas types. Currently, it is mainly used for gases such as methane, carbon dioxide, carbon monoxide, sulfur hexafluoride, sulfur dioxide, and hydrocarbons.
2, Semiconductor Principles of Gas Detectors
Principle: Semiconductor gas sensors are manufactured using the principle that the resistance of some metal oxide semiconductor materials changes with the composition of the environmental gas at a certain temperature. For example, an alcohol sensor is prepared using the principle that when tin dioxide encounters alcohol gas at high temperatures, its resistance will sharply decrease.
Advantages: It has the advantages of low cost, simple manufacturing, high sensitivity, fast response speed, long service life, low sensitivity to humidity, and simple circuit.
Disadvantages: Poor stability, greatly affected by environmental factors, especially the selectivity of each sensor is not unique, and the output parameters cannot be determined. Therefore, it is not suitable for use in places where measurement accuracy is required, but mainly for civilian use.
3, The principle of catalytic combustion in gas detectors
Principle: A catalytic combustion sensor is a high-temperature resistant catalyst layer prepared on the surface of a platinum resistor. At a certain temperature, combustible gases catalyze combustion on its surface, causing the platinum resistor temperature to increase and the resistance to change. The change in resistance is a function of the concentration of combustible gases.
Advantages: The catalytic combustion gas sensor selectively detects combustible gases: anything that cannot be burned has no response from the sensor. Fast response, long lifespan, and less affected by temperature, humidity, and pressure. The output of sensors is directly related to the explosion hazard of the environment, and they are a dominant type of sensor in the field of safety detection.
Disadvantage: Within the range of combustible gases, there is no selectivity. Sensors are prone to poisoning, and most organic vapors can have toxic effects on sensors.
4, The PID principle of gas detectors
Principle: PID consists of a UV lamp light source and an ion chamber, which have positive and negative electrodes to form an electric field. Under the irradiation of the UV lamp, the gas to be measured ionizes to generate positive and negative ions, which then form a current between the electrodes. The amplified output signal
Advantages: High sensitivity, no poisoning issues.
Disadvantages: No selectivity, greatly affected by humidity, short lifespan of UV lamps, and high price.
5, Electrochemical principles of gas detectors
Principle: It works by reacting with the target gas through the electrolyte inside the sensor and generating an electrical signal proportional to the gas concentration.
Advantages: Wide working temperature range, multiple range, high sensitivity, linear output, good selectivity
Disadvantages: Short lifespan, limited storage period, short lifespan in extremely dry or high concentration gas environments, non-specific, easily disturbed, humidity affecting accuracy.
