Subtract the types of gas sensors used in the safety field
Gas sensors are mainly used for detecting a specific gas, measuring whether the gas exists near the sensor or the content of the air near the sensor. Therefore, gas sensors are usually very important in safety systems. These sensors can provide information on combustible, flammable, and toxic gases for the safety system, as well as the consumption of oxygen and the proportion of carbon dioxide in the area.
Common gas sensors include electrochemical gas sensors, catalytic combustion gas sensors, semiconductor gas sensors, infrared gas sensors, etc. Due to different principles and structures, different types of sensors have different performance, usage methods, applicable gases, and applicable occasions. Today, I will list common types of gas sensors for everyone, hoping to be helpful.
Electrochemical gas sensor
A considerable portion of flammable, toxic and harmful gases, such as hydrogen sulfide, nitric oxide, nitrogen dioxide, sulfur dioxide, carbon monoxide, etc., have electrochemical activity and can be electrochemically oxidized or reduced. By utilizing these reactions, gas composition can be distinguished and gas concentration can be detected. Electrochemical sensors are based on this principle.
Electrochemical sensors have many subcategories:
Primary battery type gas sensor
This type of sensor is also known as a Gavoni cell type gas sensor, or a fuel cell type gas sensor or a spontaneous cell type gas sensor. Their principle is the same as the dry batteries we use daily, except that the carbon manganese electrode of the battery has been replaced by a gas electrode. Taking an oxygen sensor as an example, the oxygen cathode is reduced, and the electronic ammeter flows to the anode, where the lead metal is oxidized. Therefore, the magnitude of the current is directly related to the oxygen concentration. This sensor can effectively detect gases such as oxygen, sulfur dioxide, chlorine, etc.
Constant potential electrolytic cell type gas sensor
This type of sensor is very effective in detecting reducing gases, and its principle is different from that of a primary battery type sensor. Electrochemical reactions occur under current forcing, making it a true Coulomb analysis sensor. This sensor has been successfully used in the detection of gases such as carbon monoxide, hydrogen sulfide, hydrogen, ammonia, hydrazine, and is currently the mainstream sensor for detecting toxic and harmful gases.
Note: Coulomb analysis refers to the method of determining the content of the measured substance based on Faraday's law, based on the amount of electricity consumed during the electrolysis process.
Concentration battery type gas sensor
This type of sensor has electrochemical activity, and the gas on both sides of the electrochemical battery will spontaneously form a concentration difference electromotive force. The magnitude of the electromotive force is related to the concentration of the gas. Successful examples of this type of sensor are oxygen sensors for automobiles and solid electrolyte type carbon dioxide detectors.
Extreme current type gas sensor
This is a sensor for measuring oxygen concentration, and its working principle is based on the oxygen pump effect of a stable zinc oxide solid electrolyte. The limiting current is obtained by controlling the oxygen supplied to the cathode through gas diffusion. This type of sensor is currently mainly used for combustion control in boilers, detection of oxygen concentration in molten steel, and oxygen detection in automobiles.
Semiconductor gas sensor
Semiconductor gas sensors utilize the oxidation and reduction reactions of gas on the surface of semiconductors, resulting in changes in the resistance of sensitive components:
Oxygen and other gases with a tendency to adsorb negative ions are called oxidizing gases - electron receiving gases;
Gases with a positive ion adsorption tendency, such as hydrogen, carbon oxides, and alcohols, are called reduced gases - electron supplied gases.
When oxidizing (reducing) gases are adsorbed onto N (P) type semiconductors, the charge carriers of the semiconductors decrease (increase) and the resistivity increases (decrease); Adsorbed onto P (N) type semiconductors, the charge carriers of the semiconductors increase (decrease) and the resistivity decreases (increase). (It can be seen that oxidizing and reducing semiconductors are completely opposite.) Therefore, these properties can effectively detect the corresponding gas.
Semiconductor gas sensors can be effectively used for detecting many gases such as methane, ethane, propane, butane, alcohol, formaldehyde, carbon monoxide, carbon dioxide, ethylene, acetylene, vinyl chloride, styrene, acrylic acid, etc. Especially, this type of sensor is low-cost and can meet both industrial and civilian needs.
Disadvantages: Poor stability, significant environmental impact, and unsuitable for use in locations with accurate measurement requirements.
