1. Catalytic combustion gas sensor
The sensor is prepared on the surface of the platinum resistance to form a high temperature resistant catalyst layer. At a certain temperature, the flammable gas is catalytically burned on the surface thereof, and the combustion is the temperature rise of the platinum resistance, the resistance changes, and the change value is the flammable gas concentration. function.
Catalytic combustion gas sensors selectively detect flammable gases: any that can be burned can be detected; if it is not combustible, the sensor does not respond. Of course, there are many exceptions to the phrase "everything that can be burned," but in general, the above selectivity is true.
The catalytic combustion gas sensor is 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: no selectivity in the range of flammable gases. Working in a dark fire, there is a danger of igniting an explosion. Most of the elemental organic vapors are toxic to the sensor.
At present, the main suppliers of such sensors are in China, Japan, and the United Kingdom (inventor countries)! Currently China is the largest user of such sensors (coal mines), and also has sensor production technology, despite the constant presence of various agents. Propaganda interferes with society's understanding of this sensor, but after all, mainstream manufacturers of catalytic combustion gas sensors are at home.
2, thermal conductivity pool type gas sensor
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. This is an old-fashioned product with manufacturers all over the world. Product quality is similar all over the world.
3. Electrochemical gas sensor
A considerable part of its flammable, toxic and harmful gases are electrochemically active and can be electrochemically oxidized or reduced. By using these reactions, gas components and gas concentration can be distinguished. Electrochemical gas sensors are divided into many subclasses:
(1), galvanic 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 the force of current. It is a A true Coulomb analysis sensor. This kind of sensor has been successfully used in the detection of carbon monoxide, hydrogen sulfide, hydrogen, ammonia, helium, etc., and is currently the mainstream sensor for the detection of 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.
Semiconductor gas sensor
[1] 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.
advantage
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. Industrial Scientific, US Gas Sensor
1. Gas sensors can be divided into three main categories in principle:
A) Gas sensors using physicochemical properties: semiconductor type (surface control type, volume control type, surface potential type), catalytic combustion type, solid thermal conductivity type, and the like.
B) Gas sensors that utilize physical properties: such as thermal conduction, optical interference, infrared absorption, and the like.
C) Gas sensors using electrochemical properties: such as constant potential electrolysis, Gavny battery, diaphragm ion electrode, fixed electrolyte, etc.
2. Toxic and harmful gases are divided into two categories: flammable gas and toxic gas.
At present, gas detectors generally have five working principles, namely electrochemical technology, catalytic combustion technology, PID technology (photoelectric ion technology), infrared technology, and semiconductor technology.
How do the sensors of various technical principles work?
Electrochemical technology principle sensor
Principle: Using the active chemical properties of the gas to be tested, it has reducing or oxidizing properties. During the process of participating in the chemical reaction, electrons are released or absorbed. A large amount of electrons form a current. The magnitude of the current is proportional to the gas concentration. The concentration of the gas to be tested is obtained.
Advantages: The performance is relatively stable, and most of the toxic and harmful gases can be measured by electrochemical sensors, and the measurement linearity is very good.
Insufficient: Electrochemical sensors are consumables, have a short service life, and have a life of 1-2 years in a general environment. They need to be replaced in a harsh environment for 3-6 months, and the maintenance cost is relatively high.
Uses: Mainly used for the detection of toxic and harmful gases.
Catalytic combustion technology principle sensor
Principle: The principle of the heat released by the combustion reaction of the surface combustible gas is used, that is, the temperature of the platinum wire coil is increased by the combustion, and the resistance value of the coil is increased. By measuring the change in the resistance value of the platinum wire, the concentration of the combustible gas can be known, and it is suitable for measuring the low concentration combustible gas.
Advantages: The performance is relatively stable. Most of the combustible gases can be measured by catalytic combustion sensors. The measurement linearity is very good and the cost is lower than that of the electrochemical sensor.
Insufficient: It is a combustion sensor and cannot be used in explosive places, such as mines, otherwise it will cause serious consequences.
Uses: Mainly used to detect more flammable gases.
PID sensor photoionization detector
Principle: The high-energy ultraviolet light is used to ionize the organic gas, and then the current formed by the charged ions on the plate is amplified to measure the magnitude of the gas.
Advantages: High sensitivity, ability to measure VOC at ppb level, fast response, fast response time, and measurement of most VOCs.
Insufficient: The cost of the sensor is high.
Uses: Mainly used to detect more volatile gases.
Infrared sensor
Principle: Different flammable gases absorb different infrared rays. By measuring the current on the infrared photosensor, the concentration of combustible gas can be measured.
Advantages: The optical principle is applicable to all places, especially the explosive area; the sensor has a long service life, generally 3-5 years, and the maintenance amount is small in the later stage.
Insufficient: The measurement accuracy is not very high, only high concentration combustible gas can be measured.
Uses: Mainly used for more common gases.
Semiconductor sensor
Principle: The adsorption of gas by a semiconductor material is used to change the resistance of the gas-sensitive resistor to determine the presence or absence of gas.
Advantages: low cost.
Insufficient: It is greatly affected by changes in the external environment. There is no linearity. Only gas can be measured and the gas concentration cannot be quantitatively measured.
Uses: Many applications in home alarms, not suitable for industrial gas detectors.
Gas sensor use instructions
Such as electrochemical sensor: the sensor can not be used for a long time, otherwise it will cause sensor poisoning and form irreparable damage.
Oxygen-detecting sensor: When the oxygen sensor is used in extremely low or extremely high concentrations, the life is greatly reduced.
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