[Keywords:] air quality gas sensor indoor environmental pollution
First of all, the importance of air to people
People can't live without oxygen all the time. They get oxygen by inhaling air. An adult needs to inhale 6500 liters of air every day to get enough oxygen. Therefore, polluted air has a direct impact on human health. People spend more than 90% of their life indoors, so the influence of indoor air quality on people is more important.
Second, the indoor environmental pollution background
Now human beings are faced with "soot pollution" and "photochemical smog pollution", and then the third environmental pollution is "indoor air pollution". American experts found that there are more than 500 kinds of volatile organic compounds in indoor air, including more than 20 kinds of carcinogens and more than 200 kinds of pathogenic viruses. The main hazards are radon, formaldehyde, benzene, ammonia, esters and trichloroethylene. A large number of shocking facts have confirmed that indoor air pollution has become an "invisible killer" that harms human health, and it has also become a common concern of all countries in the world. According to statistics, nearly half of the people in the world are exposed to indoor air pollution. Indoor environmental pollution has caused 35.7% respiratory diseases, 22% chronic lung diseases and 65,438+05% tracheitis, bronchitis and lung cancer.
Three, some ideas about developing indoor air quality service
1. Investigate the basic situation of air quality in homes and offices in China.
2. Understand and start to introduce indoor air quality testing equipment.
3. To carry out large-scale publicity activities, first of all, the competent meteorological department and the competent environmental protection department should jointly establish a management mechanism for indoor air quality problems.
4. Conduct special research on the laws and regulations, technical standards, indoor pollution measurement methods and measuring instruments of international environmental protection departments.
Four, the powerful weapon of air detector-sensor
Detection technology is an indispensable and important technical means for people to understand and transform the world. Sensors are important tools for developing, acquiring, transmitting and processing information resources in scientific experiments and industrial production. The following will introduce six kinds of sensors that play an important role in air quality detection.
1. metal oxide semiconductor sensor. The metal oxide semiconductor sensor changes the conductivity of the semiconductor by the adsorption of the measured gas, and excites the alarm circuit by comparing the change of current. Because the semiconductor sensor is greatly influenced by the environment during measurement, the output line shape is unstable. Metal oxide semiconductor sensor is widely used in the field of measuring gas micro-leakage because of its very sensitive response.
2. Catalytic combustion sensor. The principle of catalytic combustion sensor is one of the most widely used combustible gas detection principles at present, which has the characteristics of good linear output signal, reliable index, low price and no cross interference with other nonflammable gases. The catalytic combustion sensor adopts the principle of Wheatstone bridge, and the inductive resistor and combustible gas in the environment produce flameless combustion. It is the temperature that changes the resistance of the inductance and resistance, breaks the balance of the bridge, and makes it output a stable current signal, which is amplified, stabilized and processed by the later circuit, and finally shows a reliable value.
3. Constant potential electrolytic sensor. At present, potentiostatic electrolytic sensor is the most widely used technology in the field of poison detection. Foreign technology is leading in this field, so most of these sensors rely on imports. Structure of constant potential electrolytic gas sensor: In a cylindrical battery made of plastic, a working electrode, a counter electrode and a reference electrode are installed, electrolyte is filled between the electrodes, and a diaphragm made of porous tetrafluoroethylene is encapsulated at the top. The connection between the preamplifier and the sensor electrode applies a certain potential between the electrodes, which makes the sensor in working state. The gas reacts with the working electrode in the electrolyte, reducing or oxidizing the electrode, and the equilibrium potential of the electrode changes, which is proportional to the gas concentration.
4. galvani battery oxygen sensor. The structure of galvani battery oxygen sensor: A layer of PTFE gas permeable membrane with good oxygen permeability and thickness of 10-30μm, precious metals (platinum, gold, silver, etc.) is installed on one side of a plastic container. The cathode electrode is closely attached to the inside of the container, and the anode (a metal with strong tendency to generate plasma with lead and cadmium) is formed on the other side of the container or the spare part of the container. Use potassium hydroxide. When oxygen passes through the electrolyte, the anode and cathode undergo redox reaction, which ionizes the anode metal and releases electrons. The current is proportional to the amount of oxygen. Because the anode metal is consumed in the whole reaction, the sensor needs to be replaced regularly. At present, the domestic technology has become increasingly mature, and this sensor can be completely localized. 5. Infrared sensor. Infrared sensor uses the absorption principle of various elements to specific wavelengths, which has good anti-toxicity, sensitive response and reaction to most hydrocarbons. But the structure is complex and the cost is high.
6. Photoionization gas sensor. PID is mainly composed of ultraviolet light source and ionization chamber. There are positive and negative electrodes in the ion chamber to form an electric field. Under the irradiation of ultraviolet light, the gas to be measured is ionized to produce positive and negative ions, and a current is formed between the electrodes, and the signal is amplified. PID has the advantages of high sensitivity, no poisoning problem, safety and reliability.
Verb (abbreviation of verb) deeply analyzes the development status of gas detection instrument industry
In recent years, with the rapid development of China's economy, the instrument industry has also developed rapidly. Since 2004, production and sales have exceeded 1000 billion yuan for the first time, and the industry has entered the fast lane. In 2006, the total output value of the industry exceeded 200 billion yuan. In 2007, the total output value of instrument industry reached 307.8 billion yuan, with a growth rate of 28.5%. According to the statistics of instrument industry association, the total output value of instrument industry in the first half of 2008 reached1755.9 billion yuan, up 23.8% year-on-year, among which the growth rate of analytical instruments and environmental monitoring instruments was as high as 32%.
The progress of science and technology provides conditions for the development of gas detection instrument industry. The promotion of market and government policies, the improvement of people's safety awareness and the improvement of relevant laws and regulations are the core driving forces for the development of gas detection instrument industry, which makes the gas detection instrument industry in a period of rapid industrial growth.
From the perspective of technical development, according to the different principles of using sensors, common gas detection instruments have their own applicable gas and application fields, and new technologies and products are becoming the mainstream of gas detection instruments in the future.
6. Prospect of future air quality testing.
With the continuous improvement of people's living standards and increasing attention to environmental protection, the detection of various toxic and harmful gases, air pollution, industrial waste gas monitoring and the detection of food and living environment quality all put forward higher requirements for gas sensors. The successful application of new material development technologies, such as nano and thin film technology, provides a good prerequisite for the integration and intelligence of gas sensors. Gas sensors will be developed on the basis of making full use of micromechanics and microelectronics, computer technology, signal processing technology, sensing technology, fault diagnosis technology and intelligent technology. It will be an important research direction in this field to develop a fully automatic digital intelligent gas sensor that can simultaneously monitor multiple gases.
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