Classification and principle of carbon dioxide sensor

Classification and principle of carbon dioxide sensor

Carbon dioxide is a colorless and odorless gas, and it is one of the important components of the atmosphere. As the main reactant of photosynthesis, the concentration of carbon dioxide is directly related to the photosynthetic efficiency of crops, and determines the growth and development, maturity, stress resistance, quality, and yield of crops. However, its excessively high content will not only produce various effects such as the greenhouse effect, but also endanger human health. People will experience obvious headaches when the concentration reaches 0.3%, and dizziness when it reaches 4%-5%. The indoor environment, especially in air-conditioned rooms, is relatively sealed. If there is no ventilation for a long time, the carbon dioxide concentration will gradually increase, which is harmful to human health. According to the indoor air quality standard implemented in 2003, the daily average carbon dioxide content volume fraction standard value Not more than 0.1%.With the continuous development of science and technology, the improvement of people’s living standards, and people’s increasing emphasis on environmental protection, quantitative monitoring and control of carbon dioxide gas has become Growing demand.Carbon dioxide sensors have a wide range of applications in many fields such as industry, agriculture, national defense, medical and health, environmental protection, and aerospace.

Let me introduce to you the working principle of the carbon dioxide sensor. Any substance has its characteristic bright-line spectrum, and the corresponding absorption spectrum, as well as carbon dioxide gas molecules. The vibration of the crystal lattice of the ceramic material has an obstructive effect on the movement of electrons. As the temperature rises, the lattice vibration strengthens and the amplitude increases, which hinder the enhancement of the electron action. According to the gas selective absorption theory, when the emission wavelength of the light source coincides with the absorption wavelength of the gas, resonant absorption occurs, and the absorption intensity is related to the concentration of the gas. The gas concentration can be measured by measuring the absorption intensity of light. At present, there are many types of carbon dioxide sensors. Based on their principles, they are divided into thermal conductivity, density meter, radiation absorption, conductivity, chemical absorption, electrochemistry, chromatography, mass spectrometry, and infrared. Optical type and so on.The infrared absorption carbon dioxide gas sensor is made based on the principle that the absorption spectrum of the gas varies with different substances. The carbon dioxide sensor element controls the internal infrared lamp to emit infrared light of a fixed wavelength through the drive circuit. After the absorption of the gas to be measured, the amplitude of the infrared light changes, and then the concentration of the gas to be measured is calculated by detecting the change, that is, the output of the sensor element The signal is filtered, amplified, and ADC collected and converted, and then input to the microprocessor. The microprocessor system performs corresponding temperature and pressure compensation processing according to the collected temperature and pressure and finally calculates the carbon dioxide concentration value to be measured and outputs it to the display Equipment. There are mainly tunable diode laser absorption spectroscopy, photoacoustic spectroscopy technology, cavity enhanced spectroscopy technology and non-dispersive infrared spectroscopy technology. Infrared absorption sensors have many advantages, such as high sensitivity, fast analysis speed, and good stability.

The electrochemical carbon dioxide gas sensor is a type of chemical sensor that converts the concentration (or partial pressure) of carbon dioxide into an electrical signal through an electrochemical reaction. According to the detected electrical signal, the electrochemical type is divided into potential type, current type and capacitive type. According to the electrolyte form, there are liquid electrolytes and solid electrolytes. Since the 1970s until now, solid electrolyte carbon dioxide sensors have been receiving the attention of the majority of scientific researchers. The principle of the solid electrolyte carbon dioxide sensor is that the gas-sensitive material generates ions when passing through the gas, thereby forming an electromotive force, and measuring the electromotive force to measure the gas volume fraction.The use of carbon dioxide and other gases to make a thermal conductivity type carbon dioxide gas sensor is also the first sensor to detect carbon dioxide. But its sensitivity is low.The surface acoustic wave gas sensor coats a piezoelectric crystal with a gas-sensitive film that selectively adsorbs a certain gas. When the gas-sensitive film interacts with the gas to be measured, the film quality and adhesion of the gas-sensitive film Changes in properties such as elasticity and electrical conductivity cause the frequency of the surface acoustic wave of the piezoelectric crystal to drift, thereby detecting the gas concentration. The surface acoustic wave gas sensor is a kind of mass-sensitive sensor. In addition, the quartz crystal microbalance gas sensor has a similar working principle to the surface acoustic wave sensor, and it is also a mass-sensitive sensor. The mass-sensitive sensor itself does not have selectivity to gas or vapor, and its selectivity as a chemical sensor only depends on the nature of the surface coating material. Semiconductor carbon dioxide gas sensors use semiconductor gas sensors as the gas sensors. Metal oxide semiconductor carbon dioxide gas sensors are characterized by fast response, strong environmental resistance, and stable structure.

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