Read the knowledge of gas detectors in one article

Semiconductor type :

It is made by using some metal oxide semiconductor materials, and the conductivity changes with the change of the composition of the ambient gas at a certain temperature. For example, an alcohol sensor is prepared by the principle that the resistance of the tin dioxide is drastically reduced when it encounters alcohol gas at a high temperature.

Advantages :

The semiconductor gas sensor 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 the like. In particular, such sensors are inexpensive and suitable for the needs of civil gas detection. The following semiconductor gas sensors have been successful: methane (natural gas, biogas), alcohol, carbon monoxide (city gas), hydrogen sulfide, ammonia (including amines, terpenoids). High quality sensors meet the needs of industrial inspection.

Disadvantages :

The stability is poor and is greatly affected by the environment; 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:

The sensor is prepared on the surface of a platinum resistor to form a high temperature resistant catalyst layer. At a certain temperature, the combustible gas is catalytically burned on the surface thereof, and the combustion is a rise in the temperature of the platinum resistance, the resistance changes, and the change value is the concentration of the combustible gas. function.

Advantages :

Catalytic combustion gas sensors selectively detect flammable gases: the sensor does not respond to any failure to burn. Catalytic combustion gas sensors are accurate in measurement, fast in response, and long in 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 :

In the range of flammable gases, there is no selectivity. Working in a dark fire, there is a danger of igniting an explosion. Most of the elemental organic vapors are toxic to the sensor.

Thermal conductivity :

Each gas has its own specific thermal conductivity. When the thermal conductivity of two or more gases is different, the thermal conductivity element can be used to distinguish the content of one of the components. Such sensors have been used for the detection of hydrogen, the detection of carbon dioxide, and the detection of high concentrations of methane.

This gas sensor has a narrow application range and many limiting factors.

Electrochemistry :

A considerable part of its flammable, toxic and harmful gases are electrochemically active and can be electrochemically oxidized or reduced. Using these reactions, gas components and gas concentrations can be resolved. Electrochemical gas sensors are divided into many subclasses:

(1), galvanic type gas sensor (also known as: Gaffney battery 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 our dry battery, just, The carbon-manganese electrode of the battery 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, and the like.

(2) Constant-potential electrolytic cell type gas sensor, which is very effective for detecting reducing gas. Its principle is different from that of galvanic sensor. Its electrochemical reaction occurs under current forcing. A true Coulomb analysis sensor. Such sensors have been successfully used in the detection of gases such as carbon monoxide, hydrogen sulfide, hydrogen, ammonia, helium, etc., and are the mainstream sensors for the detection of existing toxic and harmful gases.

(3) Concentrated battery type gas sensor, electrochemically active gas on both sides of the electrochemical cell will spontaneously form a concentrated electromotive force, and the magnitude of the electromotive force is related to the concentration of the gas. A successful example of such a sensor is for automobiles. Oxygen sensor, solid electrolyte type carbon dioxide sensor.

(4) Limit current type gas sensor, there is a sensor for measuring oxygen concentration. The oxygen (gas) concentration sensor is prepared by using the principle that the limiting current in the electrochemical cell is related to the carrier concentration, and is used for oxygen detection of the automobile, and molten steel. Oxygen concentration detection.

Infrared;

Most of the gases have characteristic absorption peaks in the mid-infrared region, and the concentration of a certain gas can be determined by detecting the absorption of the characteristic absorption peak position.

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 MEMS technology, the size of this sensor has been reduced from 10 liters to 45 kilograms of giants to 2 ML (thumb size) or so. The use of an infrared detector that does not require a modulating source makes the instrument completely free of mechanical moving parts, completely maintenance-free. The infrared gas sensor can effectively distinguish the type of gas and accurately determine the gas concentration.

This sensor has been successfully used for the detection of carbon dioxide and methane.

Magnetic oxygen editing

This is the core of the magnetic oxygen analyzer, but the "sensorization" process has also been implemented.

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

This kind of sensor can only be used for the detection of oxygen. Only nitrogen oxides can have a slight influence in the atmospheric environment. However, since the content of these interfering gases is often small, the selectivity of magnetic oxygen analysis technology is almost!