The gas sensor is a sensor used to detect the composition and content of the gas. The gas detector is an instrument and instrument for detecting the concentration of gas leakage. It mainly refers to a portable / hand-held gas detector. Gas sensors are mainly used to detect the types of gases present in the environment.
First, the semiconductor type gas sensor
It is manufactured using the principle that some metal oxide semiconductor materials change the electrical conductivity with the change of the composition of the ambient gas at a certain temperature. For example, an alcohol sensor is manufactured using the principle that when the tin dioxide encounters alcohol gas at high temperature, the resistance will decrease sharply.
Semiconductor gas sensors can be effectively used for the detection of many gases such as methane, ethane, propane, butane, alcohol, formaldehyde, carbon monoxide, carbon dioxide, ethylene, acetylene, vinyl chloride, styrene, acrylic acid and so on. In particular, this kind of sensor has low cost and is suitable for the demand of civil gas detection.
Disadvantages: Poor stability and greater environmental impact; in particular, the selectivity of each sensor is not * and the output parameters cannot be determined. Therefore, it should not be used in places where accurate measurement is required.
Catalytic Combustion Gas Sensor
This sensor prepares a high-temperature-resistant catalyst layer on the surface of platinum resistors. At a certain temperature, flammable gas catalyzes combustion on its surface. Combustion is the temperature rise of platinum resistors, the resistance changes, and the change value is the concentration of flammable gas function. Catalytic combustion gas sensors selectively detect flammable gases.
Advantages: The catalytic combustion gas sensor has accurate measurement, fast response and long life. The output of the sensor is directly related to the explosion hazard of the environment. It is a leading sensor in the field of safety detection.
Disadvantages: non-selective in the flammable gas range. Under fire, there is a danger of igniting an explosion. Most elemental organic vapors are toxic to the sensor.
Third, the thermal conductivity type gas sensor
Each gas has its own specific thermal conductivity. When the thermal conductivity of two or more gases differs greatly, a thermal conductivity element can be used to distinguish the content of one of the components. This sensor has been used sensorily for the detection of hydrogen, carbon dioxide, and high-concentration methane.
This kind of gas sensor has a narrow application range and many limiting factors.
This is an old fashioned product with manufacturers all over the world. Product quality is similar in the world.
Fourth, the electrochemical gas sensor
A considerable part of its flammable, toxic and harmful gases are electrochemically active and can be electrochemically oxidized or reduced. Using these reactions, you can distinguish gas components and detect gas concentrations. Electrochemical gas sensors are divided into many sub-categories:
(1) Primary battery type gas sensor (also called: Gavoni battery type gas sensor, also called fuel cell type gas sensor, and also called spontaneous battery type gas sensor), their principle is the same as the dry battery we use, except that The carbon-manganese electrode was replaced by a gas electrode. Taking an oxygen sensor as an example, oxygen is reduced at the cathode, and electrons flow through the ammeter to the anode, where the 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 and so on.
(2) Constant potential electrolytic cell gas sensor. This sensor is very effective for detecting reducing gas. Its principle is different from the original battery type sensor. Its electrochemical reaction occurs under the force of current. It is a kind of Sensor for true Coulomb analysis. This sensor has been successfully used in the detection of carbon monoxide, hydrogen sulfide, hydrogen, ammonia, hydrazine, and other gases. It is currently the mainstream sensor for the detection of toxic and harmful gases.
(3) Concentration battery type gas sensors. Gases with electrochemical activity on both sides of the electrochemical cell will spontaneously form a concentration difference electromotive force. The magnitude of the electromotive force is related to the concentration of the gas. A successful example of this type of sensor is automotive oxygen. Sensor, solid electrolyte carbon dioxide sensor.
(4) The limit current type gas sensor, there is a sensor for measuring the oxygen concentration. The principle that the limit current in the electrochemical cell is related to the carrier concentration is used to prepare an oxygen (gas) concentration sensor for oxygen detection in automobiles and oxygen in molten steel. Concentration detection.
Five, infrared gas sensor
Most gases have characteristic absorption peaks in the mid-infrared region. By detecting the absorption at the position of the characteristic absorption peak, the concentration of a certain gas can be determined.
This type of sensor used to be a large-scale analytical instrument, but in recent years, with the development of the sensor industry based on FTIR / MEMS technology, the volume of this type of sensor has been reduced from a 10-liter, 45-kilogram giant. To about 2 ml (thumb size). The use of an infrared detector without a modulated light source makes the instrument completely free of mechanical moving parts, and is completely maintenance-free.
The infrared gas sensor can effectively distinguish the type of gas and accurately measure the gas concentration. This sensor has been successfully used for the detection of carbon dioxide and methane.
Six, magnetic oxygen sensor
This is the core of the magnetic oxygen analyzer, but the “sensorization” process has also been implemented.
It is prepared using the principle that oxygen in the air can be attracted by a strong magnetic field. This type of sensor can only be used for the detection of oxygen and has excellent selectivity. Only nitrogen oxides in the atmospheric environment can have a small effect, but because the content of these interfering gases is often small, the selectivity of magnetic oxygen analysis technology is almost *!
In recent years, with the continuous emergence of new technologies, gas sensor technology has also undergone a corresponding revolution. New types of gas sensors are also being added. However, it is quite controversial whether some sensors should be listed under the name of gas sensors. For example: the principle of laser, although it is also used for gas detection, although it is as small as it is, this equipment is not truly maintenance-free. No matter how small the volume, it should be listed under the name of “Inspection Instrument”.