Maintenance of the gas detectors and the life of the sensors
Maintenance of gas detectors and sensor lifespan
Gas detector is an instrument tool for detecting gas leakage concentration, which includes portable gas detectors, handheld gas detectors, fixed gas detectors, online gas detectors, etc. Mainly using gas sensors to detect the types of gases present in the environment, gas sensors are sensors used to detect the composition and content of gases.
It is generally believed that the definition of gas sensors is based on the classification of detection targets, which means that any sensor used to detect gas composition and concentration is called a gas sensor, whether it is using physical or chemical methods. For example, sensors that detect gas flow are not considered gas sensors, but thermal conductivity gas analyzers are important gas sensors, although they sometimes use roughly the same detection principle.
classification
Semiconductor type
It is manufactured using the principle that the conductivity of some metal oxide semiconductor materials changes with the composition of environmental gases at a certain temperature. For example, an alcohol sensor is prepared using the principle that when tin dioxide encounters alcohol gas at high temperatures, its resistance will sharply decrease.
advantage
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 suitable for the needs of civilian gas detection. The following semiconductor gas sensors are successful: methane (natural gas, biogas), alcohol, carbon monoxide (city gas), hydrogen sulfide, ammonia (including amines and hydrazine). High quality sensors can meet the needs of industrial testing.
shortcoming
Poor stability and significant environmental impact; Especially, the selectivity of each sensor is not unique, and the output parameters cannot be determined. Therefore, it is not suitable for use in places where measurement accuracy is required.
Combustion type
This type of sensor is a high-temperature resistant catalyst layer prepared on the surface of a platinum resistor. At a certain temperature, combustible gases catalyze combustion on its surface. Combustion is a function of the concentration of combustible gases as the platinum resistor temperature increases and the resistance changes.
Thermal conductivity pool type
Each gas has its own specific thermal conductivity. When there is a significant difference in thermal conductivity between two or more gases, a thermal conductivity element can be used to distinguish the content of one component. This type of sensor has been widely used for detecting hydrogen, carbon dioxide, and high concentration methane.
This type of gas sensor has a narrow application range and many limiting factors.
Electrochemical formula
A considerable portion of its flammable, toxic and harmful gases 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. There are many subcategories of electrochemical gas sensors:
(1) The principle of primary cell type gas sensors (also known as Gavoni cell type gas sensors, fuel cell type gas sensors, and spontaneous cell type gas sensors) is similar to that of dry batteries we use, except that the carbon manganese electrode of the battery is replaced by a gas electrode. For example, in an oxygen sensor, 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 type of sensor can effectively detect oxygen, sulfur dioxide, chlorine gas, etc.
(2) The constant potential electrolytic cell type gas sensor is very effective in detecting reducing gases. Its principle is different from that of original battery type sensors. Its electrochemical reaction occurs under the force of current, 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, etc. It is currently the mainstream sensor for detecting toxic and harmful gases.
(3) Concentration battery type gas sensors, with electrochemically active gases on both sides of the electrochemical cell, will spontaneously form concentration electromotive force. The magnitude of the electromotive force is related to the concentration of the gas. Successful examples of such sensors are oxygen sensors for automobiles and solid electrolyte type carbon dioxide sensors.
(4) A limit current gas sensor is a type of sensor that measures oxygen concentration. It utilizes the principle that the limit current in an electrochemical cell is related to the carrier concentration to prepare an oxygen (gas) concentration sensor, which is used for oxygen detection in automobiles and for detecting oxygen concentration in molten steel.
