Gas detector types and related features

There are about the following types of gas sensors that are currently on the market:

1. Semiconductor type gas sensor It is made of some metal oxide semiconductor materials, and the principle of conductivity changes with the change of the atmospheric gas composition at a certain temperature. For example, the alcohol sensor is made by using the principle that when tin dioxide is exposed to alcohol gas at a high temperature, the resistance decreases sharply.

The semiconductor gas sensor can be effectively used to detect methane, ethane, propane, butane, alcohol, formaldehyde, carbon monoxide, carbon dioxide, ethylene, acetylene, vinyl chloride, styrene, acrylic acid, and the like. In particular, this sensor is inexpensive and suitable for the needs of civil gas detectors.

The following types of semiconductor gas sensors are successful: methane (natural gas, methane), alcohol, carbon monoxide (city gas), hydrogen sulfide, ammonia (including amines, arsines). High-quality sensors can meet the needs of industrial inspections.

Disadvantages: poor chaos, a greater impact on the environment; in particular, the selectivity of each sensor is not unique, the output parameters can not be determined. Therefore, it should not be used to measure the correct requirements of the place.

At present, the main suppliers of such sensors are in Japan (inventors), followed by China, and recently they have newly joined South Korea. Other countries such as the United States also have comparable work in this respect, but they have not yet entered the mainstream. China has invested more manpower and time in this field than Japan, but because of many reasons such as the orientation of national policies and the omission of social information, the quality of semiconductor-type gas sensors that are popular in the market in China is far inferior to that of Japanese products. I believe that follows. With the increase of the market and the further rise of private capital, the semiconductor-type gas sensors made in China have reached and exceeded Japan's level, which is just around the corner.

2, catalytic combustion type gas sensor This sensor is prepared on the surface of the platinum resistance high temperature catalyst layer, at a certain temperature, the flammable gas catalytic combustion on the surface, the combustion is platinum resistance temperature increases, changes in resistance, change The value is a function of the flammable gas concentration.

Catalytically combustible gas sensors selectively detect flammable gases: they can be detected if they can be combusted, and sensors that do not combust have no response. Of course, there are many exceptions to the phrase "everything that can be burned, and it can be detected." However, in general, the above-mentioned selectivity is true.

Catalyzed combustion gas sensors measure correctly, respond quickly, and have a long life. The output of the sensor is directly related to the explosion hazard of the environment, and is a dominant sensor in the field of safety inspection.

Disadvantages: No selectivity in the flammable gas range. Under fire, there is a danger of igniting the explosion. Elemental organic vapors in most departments have toxic effects on the sensors.

At present, the main suppliers of such sensors are in China, Japan and the United Kingdom (inventor countries)! At present, China's largest user of such sensors (coal mines) also has the best sensor production technology. Despite the fact that there are various types of agent agencies who are constantly advocating to interfere with society's familiarity with this type of sensor, in fact, catalytic combustion The mainstream manufacturer of gas sensors is at home.

3. Each gas of the thermal conductivity type gas sensor has its own specific thermal conductivity. When the thermal conductivity of two or more gases differs greatly, the thermal conductivity element can be used to distinguish one of the components. content. This type of sensor has been used in sensors for the detection of hydrogen, the detection of carbon dioxide, and the detection of high concentrations of methane.

This type of gas sensor has a narrow range of applications and many limitations.

This is an old-fashioned product with manufacturers all over the world. The quality of products in the world is very much the same.

4, electrochemical gas sensor It is commensurate with a department of flammable, toxic and hazardous gases are electrochemically active, can be electrochemical oxidation or reduction. Using these reactions, gas components can be distinguished and gas concentrations can be detected. Electrochemical gas sensor is divided into many sub-categories:

1) Primary battery type gas sensor (also known as: gas sensor type gas sensor, also known as fuel cell type gas sensor, also known as spontaneous battery type gas sensor), their principle is the same as we use the dry battery, only, the battery's 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 size 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 type gas sensor, this kind of 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 the current, it is a real Coulomb analysis of the sensor. This sensor has been successfully used in the detection of carbon monoxide, hydrogen sulfide, hydrogen, ammonia, helium, and other gases, and is currently the mainstream sensor for the detection of toxic and harmful gases.

3) Concentrated cell type gas sensor, with electrochemically active gas, on both sides of the electrochemical cell, it will spontaneously form a concentrated electromotive force. The magnitude of the electromotive force is related to the concentration of gas. A successful example of such a sensor is an automotive oxygen sensor. Solid electrolyte type carbon dioxide sensor.

4) Limiting-current type gas sensor, there is a sensor for measuring oxygen concentration. The oxygen (gas) concentration sensor is prepared by using the principle of limiting current in the electrochemical cell and carrier concentration, which is used for oxygen detection in automobiles, and oxygen concentration in molten steel. Testing.

At present, the main suppliers of such sensors are all over the world, mainly in Germany, Japan and the United States. Recently, they have newly joined several European suppliers: the United Kingdom and Switzerland. China started very early in this field, but the industrialization process was ineffective.

5. The gas in most parts of the infrared gas sensor has characteristic absorption peaks in the mid-infrared region. The absorption of the characteristic absorption peak position can be detected to determine the concentration of a certain gas.

These sensors used to be large-scale analytical instruments, but in recent years, following the development of the MEMS-based sensor industry, the size of this sensor has exceeded 10 liters and the size of the 45-kilowatt giant has been reduced to 2 milliliters. (thumb size) left and right. The use of an infrared detector that does not require modulation of the light source makes the instrument completely free of mechanical moving parts and is fully 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.

The current supplier of "sensors" is in Europe! China is currently a "half" vacancy in this area!

6. Magnetic Oxygen Sensor This is the core of the magnetic oxygen analyzer, but the process of “sensorization” has also been implemented.

It is based on the principle that oxygen in the air can be attracted by a strong magnetic field.

This sensor can only be used for oxygen detection with excellent selectivity. Only nitrogen oxides in the atmosphere can have a slight effect, but because these interfering gases are often very small, the selectivity of magnetic oxygen analysis technology is almost unique!

Old-brand industrial products, manufacturers all over the world.

7. Others In recent years, with the continuous emergence of new technologies, gas sensor technology has also undergone a corresponding revolution. The types of gas sensors are also adding new ones.

However, whether or not some sensors should be listed in the name of gas sensors is controversial, such as: PID detectors, although also used for gas detection, although the size is as small, but because it can not really achieve maintenance-free, so this equipment No matter how small the volume is, it should be listed in the name of "testing equipment."