Indoor air quality detection and application of sensors The advantages and disadvantages of current gas sensors, as well as the development trend and prospects of gas sensors.
The importance of air to people
People are inseparable from oxygen at all times, and they obtain oxygen by inhaling air. An adult needs to inhale up to 6500 liters of air every day to get enough oxygen, so polluted air has a direct impact on human health. More than 90% of people's life is spent indoors. It can be seen that the impact of indoor air quality on people is even more crucial.
2. Background of indoor environmental pollution
Today, human beings are facing "soot pollution" and "photochemical smog pollution", and then there is the third environmental pollution, mainly "indoor air pollution". American experts have 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 major hazards are: radon, formaldehyde, benzene, ammonia, esters, trichloroethylene, etc. A large number of shocking facts have confirmed that indoor air pollution has become an "invisible killer" that endangers human health, and it has also become a common concern of all countries in the world. According to statistics, nearly half of the world's people are exposed to indoor air pollution, and indoor environmental pollution has caused 35.7% of respiratory diseases, 22% of chronic lung diseases and 15% of bronchitis, bronchitis and lung cancer.
3. Some ideas about developing indoor air quality service
1. Start to investigate the basic situation of air quality in domestic households and offices.
2. Understand and start to introduce indoor air quality testing equipment.
3. To carry out large-scale publicity activities, first of all, the meteorological department and the environmental protection department should jointly establish a management mechanism for indoor air quality problems.
4. Conduct special investigation and research on the regulations, technical standards, indoor pollution measurement methods and measurement instruments of international environmental protection departments related to indoor air quality.
Fourth, the powerful weapon of the air detector - the sensor
Detection technology is an indispensable and important technical means for people to understand and transform the world. The sensor is an important tool for the development, acquisition, transmission and processing of information resources in scientific experiments and industrial production activities. Below are six types of sensors that play an important role in air quality detection.
1. Metal oxide semiconductor sensor. The metal oxide semiconductor sensor uses the adsorption of the gas to be measured to change the conductivity of the semiconductor, and activates the alarm circuit through the comparison of the current change. Since the semiconductor sensor is greatly affected by the environment during measurement, the output line shape is unstable. Metal-oxide-semiconductor sensor, because of its very sensitive response, is widely used in the field of measuring the micro-leakage phenomenon of gas.2. Catalytic combustion sensor. The principle of catalytic combustion sensor is one of the most widely used principles for detecting combustible gas. The catalytic combustion sensor adopts the principle of Wheatstone bridge. The induction resistance and the combustible gas in the environment burn without flame. It is the temperature that changes the resistance of the induction resistance, breaks the balance of the bridge, and makes it output a stable current signal. Amplification, stabilization and processing of the later circuits finally show reliable values.
3. Constant potential electrolytic sensor. The constant potential electrolytic sensor is currently the most widely used technology in the field of drug testing, and foreign technology is leading in this aspect, so most of these sensors rely on imports. The structure of the constant potential electrolytic gas sensor: in a cylindrical cell body made of plastic, the working electrode, the counter electrode and the reference electrode are installed, and the electrolyte is filled between the electrodes, and the diaphragm is made of porous tetrafluoroethylene. top package. The connection between the preamplifier and the sensor electrodes applies a certain potential between the electrodes to make the sensor work. The gas reacts with the working electrode in the electrolyte, and the reduction or oxidation reaction occurs at the counter electrode. The equilibrium potential of the electrode changes, and the change value is proportional to the gas concentration.
4. Galvani battery oxygen sensor. The structure of Galvani battery type oxygen sensor: one side of the plastic container is equipped with a 10-30μm thick polytetrafluoroethylene gas permeable membrane with good oxygen permeability, and precious metals (platinum, gold, silver, etc.) are tightly adhered to the inside of the container. etc.) cathode electrode, form anode (with lead, cadmium and other metals with high ionization tendency) on the inner side of the other side of the container or in the empty part of the container. with potassium hydroxide. When oxygen passes through the electrolyte, a redox reaction occurs at the cathode and anode, which ionizes the anode metal and releases electrons. The magnitude of the current is proportional to the amount of oxygen. Since the anode metal is consumed in the whole reaction, the sensor needs to be replaced regularly. At present, domestic technology has become more and more mature, and it is completely possible to localize such sensors. 5. Infrared sensors. Infrared sensor utilizes the absorption principle of various elements to a certain wavelength, has good anti-toxicity, sensitive response, and responds to most hydrocarbons. But the structure is complex and the cost is high.
6. PID photoionization gas sensor. PID is composed of main parts such as ultraviolet light source and ion chamber. There are positive and negative electrodes in the ion chamber to form an electric field. Under the irradiation of the ultraviolet lamp, the gas to be tested is ionized to generate positive and negative ions, and a current is formed between the electrodes, which is amplified and output. Signal. PID has the advantages of high sensitivity, no poisoning problem, safety and reliability.