A gas detector is an instrument and instrument used to detect gas leak concentrations, mainly referring to portable/handheld gas detectors.…
A gas detector is an instrument and instrument used to detect gas leak concentrations, mainly referring to portable/handheld gas detectors. Gas sensors are mainly used to detect the types of gases present in the environment. Gas sensors are used to detect the composition and content of gases. It is generally believed that the definition of gas sensors is based on the detection target. In other words, any sensor used to detect gas composition and concentration is called a gas sensor, whether using physical or chemical methods. For example, sensors that detect gas flow are not considered gas sensors, but thermal conductive gas analyzers are important gas sensors, although they sometimes use generally identical detection principles.
As early as the 1970s, gas sensors had already become a major branch in the sensor field, belonging to the chemical sensor sector.
Currently, the popular types of gas sensors on the market are roughly as follows:
1. Semiconductor-type gas sensors
It is manufactured using the principle that certain metal-oxide semiconductor materials change their conductivity at certain temperatures as the composition of the ambient gas changes. For example, alcohol sensors are made based on the principle that tin dioxide drops sharply when exposed to alcohol gas at high temperatures.
Semiconductor gas sensors can be effectively used for detecting many gases, including methane, ethane, propane, butane, alcohol, formaldehyde, carbon monoxide, carbon dioxide, ethylene, acetylene, vinyl chloride, styrene, acrylic acid, and many other gases. In particular, these sensors are low-cost and suitable for civilian gas detection needs.
The following types of semiconductor gas sensors are successful: methane (natural gas, biogas), alcohol, carbon monoxide (city gas), hydrogen sulfide, ammonia (including amines and hydrazines). High-quality sensors can meet the needs of industrial inspection.
Disadvantages: Poor stability and greater environmental influence; In particular, each sensor is not uniquely selective, and output parameters cannot be determined. Therefore, it is not suitable for locations requiring accurate measurement.
Currently, the main supplier of this sensor is Japan (the inventor), followed by China. Recently, South Korea has joined the industry, and other countries like the United States have made considerable efforts in this area, but they have never entered the mainstream! China's manpower and time invested in this field are no less than Japan's. However, due to years of national policy guidance and social information isolation, the performance and quality of semiconductor gas sensors popular in China are far inferior to Japanese products. It is believed that with market progress and the further rise of private capital, Chinese-made semiconductor gas sensors will reach or surpass Japan's level within reach
2. Catalytic combustion gas sensor
This type of sensor forms a high-temperature resistant catalyst layer on the surface of a platinum resistor. At a certain temperature, the combustible gas on its surface is catalytically burned. Combustion occurs when the temperature of the platinum resistor rises and the resistance changes; the change is a function of the concentration of the combustible gas.
Catalytic combustion gas sensors selectively detect flammable gases: anything that can be burned can be detected; Anything that cannot be burned has no response from the sensor. Of course, there are many exceptions to the phrase 'anything that can burn can be tested,' but overall, the above selectivity holds.
Catalytic combustion gas sensors provide accurate measurement, fast response, and long service life. The sensor's output is directly related to the explosion hazard in the environment and holds a dominant position in the field of safety detection.
Disadvantages: Within the range of flammable gases, there is no selectivity. Working with dark fires carries the risk of ignition and explosion. Most elemental organic vapors can be toxic to sensors.
Currently, the main suppliers of this sensor are China, Japan, and the UK (the country of origin)! China is currently the largest user of this sensor (coal mine) and possesses the best sensor manufacturing technology. Although various agents constantly promote and disrupt public awareness of this sensor, the mainstream manufacturers of catalytic combustion gas sensors are domestically.
3. Thermal Conduction Cell-type Gas Sensor
Each gas has its own specific thermal conductivity. When there is a large difference in conductivity between two or multiple gases, thermal conductive elements can be used to distinguish the content of one component. This sensor has already been used for detecting hydrogen, carbon dioxide, and high concentrations of methane.
This type of gas sensor has a narrow range of applications and many limiting factors.
This is an old-fashioned product, with manufacturers all over the world. Product quality is largely similar worldwide.
4. Electrochemical gas sensor
A considerable portion of its flammable, toxic, and harmful gases is electrochemically active and can be electrochemically oxidized or reduced. These reactions enable identification of gas components and detection of gas concentrations. Electrochemical gas sensors are divided into many subcategories:
(1) Galvania-type gas sensors (also known as Gavoni battery-type gas sensors, also known as fuel cell-type gas sensors, or self-generating battery-type gas sensors) operate on the same principle as the dry batteries we use, except the carbon-manganese electrodes in the batteries are replaced by gas electrodes. Take oxygen sensors as an example: oxygen is reduced at the cathode, 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 type of sensor can effectively detect oxygen, sulfur dioxide, chlorine, and other gases.
(2) Constant potential electrolyzer type gas sensors: This sensor is very effective at detecting reducing gases. Its principle differs from that of battery sensors; its electrochemical reaction occurs under current force, making it a true sensor for coulomb analysis. This type of sensor has been successfully used in the detection of gases such as carbon monoxide, hydrogen sulfide, hydrogen, ammonia, hydrazine, and more, and is currently the mainstream sensor for detecting toxic and hazardous gases.
(3) Concentration difference battery-type gas sensors: Electrochemically active gases spontaneously generate concentration electromotive force on both sides of the electrochemical battery, and the magnitude of this electromotive force depends on the concentration of the gas. A successful example of this type of sensor is the automotive oxygen sensor
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