Oxygen-free Lift On-off
Oxygen-free Lift On-off working principle A gas-sensitive resistor is a semiconductor-sensing device that detects a mechanism in which the conductivity of a semiconductor itself is changed by adsorption of a gas. It has been found that certain oxide semiconductor materials such as SnO2, ZnO,...
Oxygen-free Lift On-off
A gas-sensitive resistor is a semiconductor-sensing device that detects a mechanism in which the conductivity of a semiconductor itself is changed by adsorption of a gas. It has been found that certain oxide semiconductor materials such as SnO2, ZnO, Fe2O3, MgO, NiO, BaTiO3, etc. have gas sensing effects.
Commonly used are contact combustion gas sensors, electrochemical gas sensors and semiconductor gas sensors. The detection element of the contact combustion gas sensor is generally a platinum wire (also coated with a rare metal catalyst layer such as platinum or palladium), and the current is applied to the platinum wire during use, and the temperature is maintained at a temperature of 300 ° C to 400 ° C. When the flammable gas is in contact, the flammable gas is burned on the rare metal catalyst layer. Therefore, the temperature of the platinum wire rises and the resistance value of the platinum wire also rises. By measuring the change in the resistance value of the platinum wire, the flammability is known. The concentration of the gas. Electrochemical gas sensors generally use a liquid (or solid, organogel, etc.) electrolyte, and the output form may be a current generated by direct oxidation or reduction of a gas, or an electromotive force generated by ions acting on an ion electrode. The semiconductor gas sensor has the characteristics of high sensitivity, fast response, good stability and simple use, and is widely used; the semiconductor gas sensor has N-type and P-type.
The resistance of the N-type decreases with the increase of the gas concentration during the detection; the P-type resistance increases with the increase of the gas concentration. Like the SnO2 metal oxide semiconductor gas sensing material, it belongs to the N-type semiconductor. It absorbs oxygen in the air at a temperature of 200-300 ° C, and forms negative ions of oxygen to reduce the electron density in the semiconductor, thereby increasing the resistance value. When a combustible gas (such as CO) capable of supplying electrons is encountered, the originally adsorbed oxygen is desorbed, and the combustible gas is adsorbed on the surface of the metal oxide semiconductor in a positive ion state; the oxygen is desorbed to emit electrons, and the combustible gas is In the positive ion state adsorption, electrons are also emitted, so that the electron density of the oxide semiconductor conduction band is increased, and the resistance value is lowered. The flammable gas does not exist, and the metal oxide semiconductor automatically restores the negative ion adsorption of oxygen, so that the resistance value is raised to the initial state. This is the basic principle of the detection of combustible gases by semiconductor gas sensors.