Comparison of the benefits and drawbacks of several gas detector sensor operating theories
Gas sensors are the main devices used to check gas composition and concentration. The working principles of gas sensors include semiconductors, catalytic combustion, thermal conductivity, electrochemistry, infrared, and photoionization. The various working principles of gas sensors are introduced as follows:
1、 Semiconductor gas sensor
It is made using some metal oxide semiconductor materials and the principle that the conductivity changes with the composition of the environmental gas at a certain temperature.
2、 Catalytic combustion gas sensor
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
3、 Thermal conductivity gas sensor
Each gas has its own specific thermal conductivity. When the thermal conductivity of two or more gases differs significantly, a thermal conductivity element can be used to distinguish the content of one component between them.
4、 Electrochemical gas sensor
A portion of its flammable, toxic, and harmful gases have electrochemical activity and can be electrochemically oxidized or restored. By using these reactions, it is possible to distinguish gas components and check gas concentration. Electrochemical gas sensors are divided into many subcategories
(1) The principle of primary cell type gas sensors (also known as Gavoni cell type gas sensors, fuel cell type gas sensors, and self sensing cell type gas sensors) is similar to that of dry batteries, except that the carbon manganese electrode of the battery is replaced by a gas electrode. This type of gas sensor has a narrow application range and many constraints.
(2) The stable potential electrolytic cell type gas sensor is very effective in detecting restorative gases. Its principle is different from the original battery type sensor, and its electrochemical response is triggered by the force of current, making it a true Coulomb analysis sensor. This type of sensor is currently the mainstream sensor for detecting toxic and harmful gases.
(3) The concentration difference battery type gas sensor, with electrochemical active gas on both sides of the electrochemical battery, will consciously form a concentration difference electromotive force. The size of the electromotive force is related to the concentration of the gas. Successful examples of this type of sensor are oxygen sensors for cars and solid electrolyte type carbon dioxide sensors.
(4) Extreme current type gas sensor, there is a sensor that measures oxygen concentration. The oxygen concentration sensor is prepared based on the principle that the extreme current in the electrochemical pool is related to the carrier concentration, and is used for oxygen inspection in sedans and oxygen concentration inspection in molten steel.
5、 Infrared sensor
It belongs to precision sensors and has good measurement specificity. Currently, it mainly detects low-carbon hydrocarbons and CO2.
6、 Photoion sensor PID
There is an ultraviolet light source that can easily detect positive and negative ions generated by chemical substances under its excitation by the detector. When molecules absorb high-energy ultraviolet radiation, ionization occurs, and under this excitation, molecules generate negative electrons and form positive ions. The current generated by these ionized particles can be amplified by the detector to display the PMM level concentration on the instrument. These ions quickly recombine into the original organic molecules after passing through the electrodes.
