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Classification of Gas Analyzers and Their Advantages and Disadvantages

Gas analyzer semiconductor type: It is manufactured using the principle that some metal oxide semiconductor materials, at a certain temperature, the conductivity changes with the change of the composition of the ambient gas. 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.

Advantages: The semiconductor-type gas sensor can be effectively used to detect many gases such as methane, ethane, propane, butane, alcohol, formaldehyde, carbon monoxide, carbon dioxide, ethylene, acetylene, vinyl chloride, styrene, acrylic acid and the like. In particular, this kind of sensor has low cost and is suitable for the demand of civil gas detection. The following semiconductor-based gas sensors were successful: methane (natural gas, biogas), alcohol, carbon monoxide (city gas), hydrogen sulfide, and ammonia (including amines and hydrazines). High-quality sensors can meet the needs of industrial inspection.

Gas Sensor

Disadvantages: Poor stability and greater environmental impact; in particular, the selectivity of each sensor is not accurate and the output parameters cannot be determined. Therefore, it should not be used in places where accurate measurement is required.

Gas analyzer combustion

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.

Advantages: The catalytic combustion gas sensor selectively detects flammable gases: The sensor does not respond to anything that cannot be burned. 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, and is a dominant type of 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 elements are organic and have poisoning effects on the sensor.

Gas analyzer thermal conductivity type

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.

Gas analyzer electrochemical

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 sensors (also called: Gavoni battery type gas sensors, also called fuel cell type gas sensors, also called spontaneous battery type gas sensors), their principle is the same as the dry batteries we use, but, The carbon manganese electrode of the battery is replaced by a gas electrode already. 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 that of the original battery type sensor. Its electrochemical reaction occurs under the force of current. A true Coulomb sensor. This sensor has been successfully used in the detection of carbon monoxide, hydrogen sulfide, hydrogen, ammonia, hydrazine, and other gases, and it is the mainstream sensor for the detection of existing poisonous 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 use. Oxygen sensor, solid electrolyte carbon dioxide sensor.

(4) Limiting current type gas sensor. There is a sensor for measuring oxygen concentration. The principle of limiting current in the electrochemical cell and the carrier concentration is used to prepare an oxygen (gas) concentration sensor for oxygen detection in automobiles and molten steel. Oxygen concentration detection.

Gas analyzer infrared

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 gas analysis instrument, but in recent years, with the development of the sensor industry based on MEMS technology, the volume of this type of sensor has been reduced from 10 liters and 45 kg to the giant 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.

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