The gas sensor is a commonly used gas measuring instrument, which can convert a certain gas volume fraction into a converter corresponding to an electric signal, and has the advantages of stable performance, flexible use, high reliability, and easy maintenance. What types of gas sensors are there? The following small series will specifically introduce the classification of gas sensors, I hope to help everyone.
Classification of gas sensorsSemiconductor sensor
This type of sensor accounts for about 60% of the gas sensor, and is classified into an electrically conductive type and a non-conducting type according to the mechanism thereof. The electric conductivity type is further divided into a surface type and a volume control type, and Table 1 shows various semiconductor sensors.
(1) SnO2 semiconductor is a typical surface type gas sensor, and its sensing principle is that SnO2 is an n-type semiconductor material. When a voltage is applied, the temperature of the semiconductor material increases, and the adsorbed oxygen receives electrons in the semiconductor to form an O2- or O2-progenitor gas H2, CO, and CH4, causing the surface resistance of the semiconductor to decrease, the conductance to rise, and the conductance. The change is proportional to the gas concentration. NIO is a p-semiconductor, and oxidizing gases cause a decrease in conductance and are sensitive to O2. ZnO semiconductor sensors are also of this type.
Semiconductor gas sensor
The conductivity type sensor components are classified into surface sensitive type and volume control type, and the surface sensitive type sensing materials are SnO2 + Pd, ZnO ten Pt, AgO, V 2 05, metal indigo, and P-SnO2.
The surface sensitive gas sensor detects gases as various flammable gases C0, NO2 Freon. . Sensing material Pt—SnO2
The gas sensor detects gases as flammable gases CO, H2, and CH4.
b. Volume-controlled sensing materials are Fe2O8, la1-SSrx COO8 and TIO2, CoO-M gO-SnO2 body sensors can detect gases for various flammable gases C0, NO2 Freon. . Sensing material Pt—SnO2
The volume control type semiconductor gas sensor can detect gas as liquefied petroleum gas, alcohol, air-fuel ratio control, and combustion furnace gas exhaust.
The volume control type is a change in lattice defect leading to a change in electrical pregnancy rate, and the change in conductance is proportional to the gas concentration.
Fe2O8 and TI O2 belong to this category and are sensitive to flammable gases.
The thermal linear sensor is a semiconductor sensor that utilizes a change in thermal conductivity, also known as a thermal linear semiconductor sensor. The SnO2 layer is coated on the Pt wire coil, and the Pt wire has a function of detecting temperature changes in addition to heating. When the applied voltage semiconductor heats up, the surface absorbs oxygen, and the concentration of free electrons decreases. When the flammable gas is present, the concentration of free electrons in the oxygen consumption increases, the thermal conductivity increases as the concentration of free electrons increases, and the heat dissipation rate increases accordingly. The Pt wire temperature drops, the resistance decreases, and the P t wire resistance change is linear with the gas concentration.
This type of sensor is small, stable, and resistant to poisons. It can detect low-concentration gases and plays an important role in the detection of combustible gases.
Non-conducting FET field effect transistor gas sensor, Pd-FET. Field effect transistor sensor, uses Pd to absorb H z and diffuse to reach the interface of semiconductors si and P d, reducing the work function of Pd, which is sensitive to H2 and CO. The non-conducting FET field effect transistor gas sensor is small in size, easy to integrate, and multifunctional, and is a promising gas sensor.
Solid electrolyte gas sensor
The sensor element is an ion-to-solid electrolyte membrane, called an electrochemical cell, which is divided into a cation conduction and an anion conduction. It is a highly selective sensor. The research is more practical and the zirconia solid electrolyte sensor is used. The mechanism is The potential difference between the two cells on both sides of the diaphragm is equal to the potential of the concentration cell. The stable chromium oxide solid electrolyte sensor has been successfully applied to the determination of oxygen in molten steel and the measurement of engine air-fuel ratio components.
In order to compensate for the lack of conductivity of solid electrolytes, in recent years, the gas is coated with a gas sensitive membrane on the solid electrolyte to correlate the amount of gas molecules present in the surrounding environment with the number of movable particles in the medium.
Contact combustion sensor
The contact combustion sensor is suitable for the detection of flammable gases H2, CO and CH4. Combustible gas contact surface catalyst
When Pt and Pd are burned and broken, the heat of combustion is related to the richness of gas. These sensors have wide application, small size, simple structure and good stability. The disadvantage is poor selectivity.
Electrochemical sensors
Electrochemical gas sensors are commonly used in two types.
Constant potential electrolytic sensor
The gas to be measured is ionized under a specific electric field, and the concentration of the gas is measured by the electrolysis current flowing through. The sensitivity of the sensor is high, and the potential for detecting the gas is changed, which plays an important role in the detection of toxic gas.
Primary battery gas sensor
In the KOH electrolyte solution, the pt-Pb or Ag-Pb electrode constitutes a battery, which has been successfully used for detecting O2, and its sensitivity is high, and the disadvantage is that the water is permeable to moisture and the electrode is easily poisoned.
Optical gas sensing
Direct absorption gas sensor
The infrared gas sensor is a typical absorption optical gas sensor. The gas component is detected by the respective spectral absorption spectra of the gas, and the non-dispersive infrared absorption spectrum has high sensitivity to gases such as SO2, CO, C O2 , and NO.
In addition, ultraviolet absorption, non-dispersive ultraviolet absorption, correlated spectroscopic, second derivative, and self-modulating light absorption methods have high sensitivity to gases such as NO, N O2 SO2, and CH(CH4).
Photoreactive gas sensor
It is a change in optical characteristics such as light intensity absorption caused by a gas reaction, and the sensing element is ideal, but the change in gas light perception is limited, and the degree of freedom of the sensor is small.
New sensor for gas optical properties
The optical fiber temperature sensor is of this type, and the catalyst is applied to the tip of the optical fiber to react with the gas and generate heat. The temperature changes, causing the fiber temperature to change. The use of optical fiber temperature measurement has reached a practical level, and the detection of gas is also successful.
In addition, sensors that measure gas components using other physical quantity changes are being developed, such as surface acoustic wave sensors for detecting SO2, N O2 , H 2 S, NH 3 , H 2 , etc., which also have higher sensitivity.
Gas sensor circuit diagram analysisSome semiconductors have such a characteristic that the resistance value of the surrounding air filled with a certain gas sharply decreases with an increase in temperature. This effect can also be expressed as a function of the material's properties as the gas concentration reaches a certain level. A gas sensor can be fabricated using such a semiconductor material. Among these materials are iron trioxide, tin oxide and zinc oxide. They react to gases or vapors such as methane, butane, ethanol and benzene.
A typical sensor resistance R versus gas concentration P is shown in FIG.
According to the above principle, a gas sensor of type 822418200031 is constructed, which consists of a millimeter-sized ceramic piece heating lamp ratio and an opposite electrode, and operates at a temperature of 300 ° C, through which a direct current or an alternating current is passed.
Figure 2 shows a simple gas alarm circuit. When the 1KΩ potentiometer sliding contact potentiometer exceeds a certain value, the thyristor is triggered to conduct, the relay acts to send a signal or the control actuator is disconnected until the stop button S is pressed, and the relay is powered off again.
Some semiconductors have such a characteristic that the resistance value of the surrounding air filled with a certain gas sharply decreases with an increase in temperature. This effect can also be expressed as a function of the material's properties as the gas concentration reaches a certain level. A gas sensor can be fabricated using such a semiconductor material. Among these materials are iron trioxide, tin oxide and zinc oxide. They react to gases or vapors such as methane, butane, ethanol and benzene.
A typical sensor resistance R versus gas concentration P is shown in FIG.
According to the above principle, a gas sensor of type 822418200031 is constructed, which consists of a millimeter-sized ceramic piece heating lamp ratio and an opposite electrode, and operates at a temperature of 300 ° C, through which a direct current or an alternating current is passed.
Figure 2 shows a simple gas alarm circuit. When the 1KΩ potentiometer sliding contact potentiometer exceeds a certain value, the thyristor is triggered to conduct, the relay acts to send a signal or the control actuator is disconnected until the stop button S is pressed, and the relay is powered off again.
Android Wi-Fi Tablet,Tablet Computer,Pcs Tablets,Tablet Pc Android
C&Q Technology (Guangzhou) Co.,Ltd. , https://www.gzcqteq.com