stacked semiconductor
It is manufactured by the principle that the conductivity of some metal oxide semiconductor materials changes with the change of the ambient gas composition at a certain temperature. For example, the alcohol sensor is prepared by using the principle that the resistance of tin dioxide will decrease sharply when it encounters alcohol gas at high temperature.
combustion
This kind of sensor prepares a high temperature resistant catalyst layer on the surface of the platinum resistor. At a certain temperature, the combustible gas catalyzes combustion on its surface. The combustion is caused by the temperature rise of the platinum resistor, the resistance changes, and the change value is the concentration of the combustible gas. function.
thermal conductivity pool
Each gas has its own specific thermal conductivity. When the thermal conductivity of two or more gases is quite different, the thermal conductivity element can be used to distinguish the content of one of the components. Such sensors have been sensory used for the detection of hydrogen gas, the detection of carbon dioxide, and the detection of high-concentration methane.
Electrochemical
A considerable part of its flammable, toxic and harmful gases are electrochemically active and can be electrochemically oxidized or reduced. Using these reactions, it is possible to distinguish gas components and detect gas concentrations. Electrochemical gas sensors fall into many subcategories:
(1) Primary cell type gas sensor (also called: Gavoni cell type gas sensor, also called fuel cell type gas sensor, also called spontaneous battery type gas sensor), their principle is the same as the dry cell we use, but, The carbon-manganese electrodes of the battery were replaced by gas electrodes. In the case of an oxygen sensor, oxygen is reduced at the cathode and electrons flow through the ammeter to the anode, where lead metal is oxidized. The magnitude of the current is directly related to the concentration of oxygen. This sensor can effectively detect oxygen, sulfur dioxide, chlorine, etc.
(2) Constant potential electrolytic cell type gas sensor, this sensor is very effective for detecting reducing gas, its principle is different from that of galvanic cell type sensor, its electrochemical reaction occurs under the force of current, which is a A true coulometric sensor. This sensor has been successfully used in the detection of carbon monoxide, hydrogen sulfide, hydrogen, ammonia, hydrazine, and other gases, and is the mainstream sensor for the detection of existing toxic and harmful gases.
(3) Concentration battery type gas sensor, the gas with electrochemical activity will spontaneously form a concentration electromotive force on both sides of the electrochemical cell, and the magnitude of the electromotive force is related to the concentration of the gas. Oxygen sensor, solid electrolyte carbon dioxide sensor.
(4), limiting current type gas sensor, there is a sensor for measuring oxygen concentration using the principle that the limiting current in the electrochemical cell is related to the carrier concentration to prepare an oxygen (gas) concentration sensor, which is used for oxygen detection in automobiles and molten steel. Oxygen concentration detection.
