The concentration of the detected gas depends on the gas detection transmitter. The sensor is its core part. According to the different detection principles, it is mainly divided into metal oxide semiconductor sensors, catalytic combustion sensors, constant potential electrolytic gas sensors, and galvanic batteries. Type oxygen sensor, infrared sensor, PID photoionization sensor, etc., the principle and characteristics of various sensors are briefly explained below.
Metal oxide semiconductor sensor
The metal oxide semiconductor sensor uses the adsorption of the measured gas to change the conductivity of the semiconductor, and the alarm circuit is excited by the comparison of the current change. Because the semiconductor sensor is greatly affected by the environment during measurement, the output line shape is unstable. The metal oxide semiconductor sensor has a very sensitive response, so the currently widely used field is the measurement of gas micro-leakage.
Catalytic combustion sensor
The principle of catalytic combustion sensor is one of the most widely used principles for detecting combustible gas. It has the characteristics of good output signal line shape, reliable index, low price, and no cross interference with other non-combustible gas. The catalytic combustion sensor uses the Wheatstone bridge principle. The induction resistance and the combustible gas in the environment are flameless, causing the temperature to change the resistance of the induction resistance, breaking the balance of the bridge, and outputting a stable current signal. The amplification, stabilization and processing of the later circuit finally show reliable values.
Constant potential electrolytic gas sensor
Constant potential electrolytic sensors are currently the most widely used technology in the field of poison detection. In this regard, foreign technology is leading, so most of these sensors rely on imports. The structure of a constant potential electrolytic gas sensor: in a cylindrical cell made of plastic, a working electrode, a counter electrode and a reference electrode are installed, and the electrolyte is filled between the electrodes, a membrane made of porous tetrafluoroethylene, in Top package. The connection of the preamplifier and the sensor electrode applies a certain potential between the electrodes, so that the sensor is in a working state. Oxidation or reduction reaction occurs between the working electrode in the gas and the electrolyte, and reduction or oxidation reaction occurs on the counter electrode, the equilibrium potential of the electrode changes, and the change value is proportional to the gas concentration.
Galvani battery oxygen sensor
Diaphragm battery-type oxygen sensor structure: on one side of the plastic container is equipped with a 10-30μm thick PTFE gas permeable membrane with good oxygen permeability, and precious metals (platinum, gold, (Silver, etc.) cathode electrode, and an anode (a metal with a large ionization tendency such as lead or cadmium) is formed inside the other surface of the container or in an empty part of the container. Use 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 current is proportional to the amount of oxygen. Since the anode metal is consumed throughout the reaction, the sensor needs to be replaced regularly. At present, domestic technology has matured, and such sensors can be fully domesticated.
Infrared sensor
Infrared sensors use the absorption principle of various elements to a certain wavelength, have good anti-toxicity, and are sensitive to reaction, and they can react to most hydrocarbons. But the structure is complicated and the cost is high.
PID photoionization gas sensor
The PID is composed of the main parts of the ultraviolet lamp light source and the 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 measured is ionized to generate positive and negative ions. signal. PID has the advantages of high sensitivity, no poisoning problems, safety and reliability. (Organized by China Educational Equipment Purchasing Network)
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