Why should the gas resistor be heated during work
Published time: 2019-11-27
Why does the gas resistor work when heated?
Commonly used are contact combustion gas sensors, electrochemical gas sensors and semiconductor gas sensors. The detection element of a contact combustion gas sensor is generally a platinum metal wire (a rare metal catalyst layer such as platinum or palladium can also be coated on the surface). When in use, a current is passed to the platinum wire to maintain a high temperature of 300 ° C to 400 ° C. When the flammable gas comes into contact, the flammable gas will burn on the rare metal catalyst layer. Therefore, the temperature of the platinum wire will rise, and the resistance value of the platinum wire will also rise. By measuring the change in the resistance value of the platinum wire, the flammability is known. The concentration of the gas. Electrochemical gas-sensitive sensors generally use liquid (or solid, organic gel, etc.) electrolytes, and their output can be the current generated by direct oxidation or reduction of a gas, or the electromotive force generated by an ion acting on an ion electrode. Semiconductor gas sensors have the characteristics of high sensitivity, fast response, good stability, simple use, and are widely used; semiconductor gas sensors have N-type and P-type. N-type resistance decreases with increasing gas concentration during detection; P-type resistance increases with increasing gas concentration. Like SnO2 metal oxide semiconductor gas-sensitive materials, they are N-type semiconductors.
At the temperature of 200-300 ° C, it adsorbs oxygen in the air, forming negative ion adsorption of oxygen, reducing the electron density in the semiconductor, thereby increasing its resistance value. When a flammable gas (such as CO, etc.) capable of supplying electrons is encountered, the originally adsorbed oxygen is desorbed, and the flammable gas is adsorbed on the surface of the metal oxide semiconductor in a positive ion state; the oxygen desorption releases electrons, and the combustible gas can Electrons in the positive ion state also emit electrons, which increases the electron density of the oxide semiconductor conduction band and decreases the resistance value. The flammable gas is no longer present, and the metal oxide semiconductor will automatically resume the adsorption of negative ions of oxygen, which will increase the resistance value to the initial state. This is the basic principle of semi-conductor gas sensor for detecting combustible gas.
Gas resistance heating method
Gas thermistor is a kind of semiconductor sensitive device. It uses the mechanism of gas to change the conductivity of the semiconductor to detect it. It has been found that certain oxide semiconductor materials such as SnO2, ZnO, Fe2O3, MgO, NiO, BaTiO3, etc. all have gas-sensitive effects.
Gas thermistor can be divided into two types of direct heating type and indirect heating type according to the heating method. The direct heating type consumes large power and has poor stability, so its application is gradually reduced. The indirect heating type has stable performance and low power consumption. Its structure is often equipped with a double-layer sealed stainless steel wire mesh for explosion protection, so it is safe and reliable and has a wide range of applications.
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