The concentration of the detection gas depends on the gas detection transmitter. 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 electrolysis gas sensors, and galvanic batteries. Type oxygen sensor, infrared sensor, PID photoionization sensor, etc. The principles and characteristics of various sensors are briefly explained below.

Metal oxide semiconductor sensor

The metal oxide semiconductor sensor uses the adsorption effect of the measured gas to change the conductivity of the semiconductor, and through the comparison of current changes, it activates the alarm circuit. Since the semiconductor sensor is greatly affected by the environment during measurement, the output line shape is unstable. The metal oxide semiconductor sensor has a very sensitive response, so it is currently widely used in the field of measuring the micro-leakage phenomenon of gas.

Catalytic combustion sensor

The principle of catalytic combustion sensor is one of the most widely used principles for detecting combustible gas. It has the characteristics of good output signal line shape, reliable index, low price, and no cross-interference with other non-combustible gases. The catalytic combustion sensor adopts the principle of Wheatstone bridge, the induction resistance and the combustible gas in the environment undergo flameless combustion, so that the temperature changes the resistance of the induction resistance, breaks the balance of the bridge, and makes it output a stable current signal. The amplification, stabilization and processing of the later circuit finally show a reliable value.

Constant potential electrolytic gas sensor

Constant-potential electrolytic sensors are currently the most widely used technology in the field of drug testing. In this regard, foreign technology is leading, 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 is made of porous tetrafluoroethylene. Top package. The connection between the preamplifier and the sensor electrode applies a certain potential between the electrodes to make the sensor in working condition. The gas and the working electrode in the electrolyte undergo an oxidation or reduction reaction, and a 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.

Gavari battery oxygen sensor

The structure of the diaphragm gastrointestinal oxygen sensor: On one side of the plastic container is equipped with a 10~30μm thick PTFE breathable membrane with good oxygen permeability, and the precious metal (platinum, gold, gold, etc.) is tightly adhered to the inside of the container. Silver, etc.) The cathode electrode is formed on the other side of the container or in the empty part of the container as an anode (a metal with a high tendency to ionize with lead or cadmium). Use potassium hydroxide. When oxygen passes through the electrolyte, an oxidation-reduction reaction occurs at the anode and cathode, which ionizes the anode metal and releases electrons. The current is proportional to the amount of oxygen. Because the anode metal is consumed during the entire reaction, the sensor needs to be replaced regularly. At present, the domestic technology has matured day by day, and such sensors can be made domestically.

Infrared sensor

Infrared sensors use the absorption principle of various elements to a certain wavelength, and have good anti-toxicity, sensitive response, and have a reaction to most hydrocarbons. But the structure is complicated and the cost is high.

PID photoionized gas sensor

PID is composed of main parts such as ultraviolet light source and ion chamber. There are positive and negative electrodes in the ion chamber to form an electric field. Under the irradiation of the ultraviolet lamp, the gas to be measured is ionized to generate positive and negative ions, and a current is formed between the electrodes, and the output is amplified. signal. PID has the advantages of high sensitivity, no poisoning problem, safety and reliability.