Technical principle of gas detector
The gas detector is an instrument specially designed to detect the safe concentration of gas. Its working principle is mainly to convert the physical or chemical non-electrical signals collected by the gas sensor into electrical signals, and then rectify and filter the above electrical signals through external circuits, and control the corresponding modules through these processed signals to realize gas detection. However, the core of the gas detector is the built-in sensor component. According to the different gases to be detected, the detection technical principles are different. For example, the common technical principles of the gas detector include catalytic combustion, electrochemistry, infrared, PID, heat conduction, optical waveguide and so on. Can the friends know what functional characteristics are different between them?
1. Principle of catalytic combustion technology
The technical principle of catalytic combustion gas detector is that it adopts the principle of Wheatstone bridge, and the detection element and compensation element are paired to form one arm of the bridge. When combustible gas is encountered, flameless combustion occurs on the surface of the sensitive body of the detection element, the temperature of the sensitive body increases, the resistance of the temperature-sensitive material increases, and the output voltage of the bridge increases, which increases in direct proportion with the increase of gas concentration. The concentration of the detection gas can be determined according to the change of the output signal of the detection bridge.
2. Principles of semiconductor technology
The technical principle of the semiconductor gas detector is that it changes the conductivity of the semiconductor by the adsorption of the gas to be measured, and excites the alarm circuit by comparing the current changes. The semiconductor sensor is greatly influenced by the environment when measuring, so the output linearity is unstable. Because of its sensitive response, semiconductor sensors are widely used in measuring micro-leakage of gas.
3. Principle of electrochemical technology
The electrochemical gas detector works by the sensor reacting with the gas to be measured and generating an electrical signal proportional to the gas concentration. The gas to be measured first reacts with the sensor through the tiny capillary opening, then it is a hydrophobic barrier, and finally it reaches the electrode surface. Secondly, an appropriate amount of gas is allowed to react with the sensing electrode to form a sufficient electrical signal, while preventing electrolyte from leaking out of the sensor. The gas diffused through the barrier reacts with the sensing electrode, which can adopt oxidation mechanism or reduction mechanism.
4. The principle of infrared technology
The technical principle of infrared gas detector is based on Lambert-Beer law, and its physical law is that when a beam of parallel monochromatic light passes vertically through a uniform and non-scattering light-absorbing substance, its absorbance is directly proportional to the concentration of light-absorbing substance and the thickness of absorption layer. The commonly used infrared wavelength of infrared gas detector is 2 ~ 12 μ m. Simply put, the principle of infrared gas detector is that the gas to be measured continuously passes through a container with a certain length and volume, and a beam of infrared light is injected from one of the two light-permeable end faces of the container, and then the radiation intensity of infrared light is measured at the other end face. Finally, the concentration of the gas to be measured can be known according to the direct ratio between the absorption of infrared light and the concentration of light-absorbing substances.
5.PID technology principle
The technical principle of photo-ion PID gas detector is that it can be easily detected by a detector through an ultraviolet light source, and positive and negative ions generated by chemical substances under its excitation. Ionization occurs when molecules absorb high-energy ultraviolet rays. Under this excitation, molecules generate negative electrons and form positive ions. The current generated by these ionized particles can be amplified by the detector, and the concentration of ppm can be displayed on the outside. After passing through the electrode, these ions quickly recombine and become the original organic molecules together. Molecules will not be damaged in this process.
6. Principle of heat conduction technology
The heat conduction gas detector is a new detection principle for measuring combustible gas, which mainly analyzes the concentration of the measured gas by measuring the change of thermal conductivity of mixed gas. Usually, the difference of thermal conductivity of thermal conductivity gas sensor is converted into the change of resistance through circuit. The traditional detection method is to send the gas to be measured into a gas chamber, and the center of the gas chamber is a thermistor, such as a thermistor, platinum wire or tungsten wire, which is heated to a certain temperature to convert the change of thermal conductivity of the mixed gas into the change of resistance of the thermistor, and the change of resistance can be easily and accurately measured.
