Detection principles of several gas detection sensors

The concentration of the detected gas depends on the gas detection transmitter, and the sensor is its core part. According to the different detection principles, it is mainly divided into metal oxide semiconductor sensors, catalytic combustion sensors, constant potential electrolytic gas sensors, galvanic cell oxygen sensors, infrared sensors, PID photoionization sensors, etc. The following briefly describes the principles and characteristics of various sensors. Metal oxide semiconductor sensors Metal oxide semiconductor sensors use the adsorption of the measured gas to change the conductivity of the semiconductor, and stimulate the alarm circuit by comparing the current change. Since semiconductor sensors are greatly affected by the environment during measurement, the output line shape is unstable. Metal oxide semiconductor sensors are currently widely used in the field of measuring gas micro-leakage due to their very sensitive response. Catalytic combustion sensor The principle of catalytic combustion sensor is one of the most widely used principles for detecting combustible gases. It has the characteristics of good output signal linearity, reliable index, low price, and no cross interference with other non-combustible gases. The catalytic combustion sensor adopts the Wheatstone bridge principle. The inductive resistor and the combustible gas in the environment undergo flameless combustion, so that the temperature changes the resistance of the inductive resistor, breaks the balance of the bridge, and outputs a stable current signal. After amplification, stabilization and processing by the later circuit, it finally displays a reliable value. Constant potential electrolytic gas sensor Constant potential electrolytic sensor is currently the most widely used technology in the field of poison detection. Foreign technology is leading in this regard, so most of these sensors rely on imports. The structure of the constant potential electrolytic gas sensor: In a cylindrical cell made of plastic, the working electrode, the counter electrode and the reference electrode are installed, the electrolyte is filled between the electrodes, and the diaphragm made of porous tetrafluoroethylene is encapsulated on the top. The connection between the preamplifier and the sensor electrode applies a certain potential between the electrodes to put the sensor in a working state. The gas undergoes oxidation or reduction reaction with the working electrode in the electrolyte, and reduction or oxidation reaction occurs at the counter electrode. The equilibrium potential of the electrode changes, and the change value is proportional to the gas concentration. Galvanic cell oxygen sensor The structure of the diaphragm Galvanic cell oxygen sensor: a polytetrafluoroethylene breathable membrane with good oxygen permeability and thickness of 10~30μm is installed on one side of the plastic container, and a precious metal (platinum, gold, silver, etc.) cathode electrode is tightly adhered to the inside of the container, and an anode (metals with high ionization tendency such as lead and cadmium) is formed on the inside of the other side of the container or the empty part of the container. Potassium hydroxide is used. When oxygen passes through the electrolyte, an oxidation-reduction reaction occurs at the cathode and cathode, ionizing the anode metal and releasing electrons. The magnitude of the current is proportional to the amount of oxygen. Since the anode metal is consumed in the entire reaction, the sensor needs to be replaced regularly. At present, domestic technology has become increasingly mature, and such sensors can be domestically produced. Infrared sensor Infrared sensors use the absorption principle of various elements to a certain wavelength. They have good anti-poisoning properties, are sensitive to reactions, and react to most hydrocarbons. However, the structure is complex and the cost is high. PID photoionization gas sensor PID is composed of UV light source and ion chamber. There are positive and negative electrodes in the ion chamber to form an electric field. The gas to be measured is ionized under the irradiation of UV light to generate positive and negative ions, forming a current between the electrodes, and the output signal is amplified. PID has the advantages of high sensitivity, no poisoning problem, safety and reliability.