What are the types of gas sensors?
Sensors are the core components of gas detection equipment. According to their detection principles, sensors can be divided into: metal oxide semiconductor sensors, electrochemical sensors, catalytic combustion sensors, infrared sensors, PID photoionization sensors, and so on.
1.Infrared sensor
The infrared sensor is based on the principle of absorption of a specific wavelength in a mid-infrared region by a gas absorption method, detects the absorption intensity of a characteristic absorption peak position, and determines the concentration and type of a certain gas. Its characteristics are good anti-toxicity, high sensitivity, but complicated structure and high cost. It reacts to most hydrocarbons, such as methane, acetylene, ammonia, carbon dioxide, etc., which can effectively distinguish the type of gas and accurately determine the gas concentration.
2.Electrochemical sensors
Electrochemical gas sensor is a kind of micro fuel cell element. It utilizes the principle of electrochemical oxidation / reduction reaction of gas. Gas reacts on working electrode and generates current between chemical reagent and electrode. The current changes with the change of gas concentration. The value of the gas concentration is obtained by detecting the magnitude of the current. This type of sensor includes primary battery type, constant potential electrolytic cell type, concentration difference battery type, limit current type and so on. The main characteristics of electrochemical sensors are high sensitivity, good selectivity, good long-term stability, slow response time, but short life. Such sensors can detect many toxic gases and oxygen, such as carbon monoxide, hydrogen sulfide, ammonia, and oxygen. Wait.
3. Catalytic combustion sensor
Catalytic combustion type gas sensor is a gas-sensing material in the state of energization, combustible gas burns under the action of a catalyst, because the combustion causes the temperature of the gas-sensing material to rise and the resistance changes. Generally, a high temperature resistant catalyst layer is prepared on the surface of a platinum resistor. At a certain temperature, a flammable gas is catalyzed and combusted on its surface. The temperature of the platinum resistor rises and the resistance changes. The change value is a function of the flammable gas concentration. The main characteristics of this type of gas sensor are high accuracy, fast response, long life, poor selectivity in the range of flammable gas, and prone to "sensor poisoning" (organic vapors will make the sensor ineffective), and there is a danger of detonating the gas.
4.Metal oxide semiconductor sensor
The metal oxide semiconductor gas sensor uses the adsorption of the measured gas at a certain temperature to change the conductivity of the semiconductor. The change rate is related to the gas composition and concentration. By detecting the change in resistance, the gas to be measured is detected. The main characteristics of semiconductor gas sensors are high sensitivity, fast response, long life, low cost, and low sensitivity to humidity, but they require high temperature heating, poor gas selectivity, large environmental factors, poor output stability, and high power consumption. Widely used for the measurement of micro leaks in gases, such as methane (natural gas, biogas), alcohol, carbon monoxide (city gas), hydrogen sulfide, ammonia (including amines, hydrazines) and other gases, but not suitable for precision measurement Gas content occasions.
5. PID photoionized gas sensor
The PID photoionization sensor is composed of the ultraviolet light source and the ion chamber. The positive and negative electrodes in the ion chamber form an electric field. Under the irradiation of the ultraviolet lamp, the test gas is ionized to generate positive and negative ions, and a current is formed between the electrodes. , Amplified output signal. PID photoionized gas sensor has high precision, good sensitivity, fast response, no poisoning problem, safe and reliable, but high cost and regular maintenance. It is mainly used for the measurement of volatile organic compounds, such as aromatic hydrocarbons, ketones and aldehydes.
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