The sensor is an important technological foundation for the new technology revolution and the information society. It is an extremely important high technology in the world today. Almost all modern instruments and equipment are inseparable from sensors. It is a modern sensor technology that is booming. It is a comprehensive science that covers micro-mechanics and microelectronics, computer technology, signal processing technology, circuits and systems, sensor technology, neural network technology, and fuzzy control theory. Technology, which is also widely used in military, space exploration, smart home, agriculture, medical and other fields. This article mainly introduces the classification and application of sensors.

First, the definition of the sensor:

“A device or device that can sense the specified measured and converted to usable signals according to a certain rule, usually consisting of sensitive elements and conversion elements.” The sensor is a detection device that can sense the information being measured and can transform the information sensed by the detection into electrical signals or other required forms of information output in accordance with certain laws to meet the transmission, processing and storage of information. Requirements for display, recording and control. It is the first link to achieve automatic detection and automatic control.

Second, the sensor’s classification:

There are many classification methods for sensors, but there are two commonly used classification methods, one is to divide the measured physical quantity; the other is divided according to the working principle of the sensor.

According to the measured physical quantity, the common sensors include temperature sensor, humidity sensor, pressure sensor, displacement sensor, flow sensor, liquid level sensor, force sensor, acceleration sensor, and torque sensor.

According to the working principle can be divided into:

1. Electric sensor
The electric sensor is a kind of sensor that has a wide range of applications in the non-electricity electricity measurement technology. Resistive sensors, capacitive sensors, inductive sensors, magnetoelectric sensors, and eddy current sensors are commonly used.
Resistive sensors use varistors to convert measured non-electrical quantities into resistive signals. Resistive sensors are generally potentiometer-type, contact resistance resistance, resistance strain gauges and piezoresistive sensors. Resistive sensors are mainly used for the measurement of parameters such as displacement, pressure, force, strain, torque, airflow velocity, liquid level and liquid flow.

Capacitive sensors are made using the principle of changing the capacitance of the capacitor or changing the nature and content of the medium so that the capacitance changes. It is mainly used for measuring pressure, displacement, liquid level, thickness, moisture content and other parameters.

The inductive sensor is made by changing the magnetic circuit geometry, the position of the magnet to change the inductance or mutual inductance or magnetic pressure effect principle. It is mainly used for measuring parameters such as displacement, pressure, force, vibration and acceleration.
Magnetoelectric sensors use the principle of electromagnetic induction to convert non-quantity measured into electricity. It is mainly used for the measurement of parameters such as flow rate, rotation speed and displacement.

The eddy current sensor is made by using the principle that gold shavings move in the magnetic field to cut magnetic lines and form eddy currents in the metal. It is mainly used for measuring parameters such as displacement and thickness.

2. Magnetic sensor
Magnetic sensor is made of some physical effects of ferromagnetic materials, mainly used for the measurement of displacement, torque and other parameters.

3. Photoelectric sensor

Photoelectric sensors occupy an important position in non-electricity measurement and automatic control technologies. It is made by using photoelectric effect and optical principle of optoelectronic devices, and is mainly used for measuring parameters such as light intensity, luminous flux, displacement, and concentration.

4. Potential sensor

Potential sensors are made using thermoelectric effect, photoelectric effect, Hall effect and other principles. They are mainly used for measuring parameters such as temperature, magnetic flux, current, speed, light intensity, and heat radiation.

5. Charge sensor

The charge sensor is made using the principle of piezoelectric effect and is mainly used for the measurement of force and acceleration.

6. Semiconductor sensor

The semiconductor sensor is made of semiconductor piezoresistive effect, internal photoelectric effect, magnetoelectric effect, semiconductor and gas contact to produce material changes and other principles, mainly used for temperature, humidity, pressure, acceleration, magnetic field and harmful gas measurement.

7. Resonance sensor

Resonant sensors are made using the principle of changing electrical or mechanical parameters to change the resonant frequency. They are mainly used to measure pressure.

8. Electrochemical sensor

Electrochemical sensors are based on ion conduction. According to their different electrical characteristics, electrochemical sensors can be classified into potential sensors, conductance sensors, power sensors, polarographic sensors, and electrolytic sensors. Electrochemical sensors are mainly used for the analysis of gas, liquid or solid components dissolved in liquids, the pH, conductivity, and oxidation-reduction potential of liquids.

In addition, according to the detection and conversion process of the sensor on the signal, the sensor can be divided into two categories: a direct conversion sensor and an indirect conversion sensor. The former converts the non-electrical energy input to the sensor to electrical signal output. If the photoresistor is exposed to light, the resistance value will change, and the optical signal will be directly converted into an electrical signal output; the latter will be input to the sensor. The non-electricity is first converted into another non-electricity, and then converted into an electrical signal output. For example, a pressure sensor made of a spring tube sensor belongs to this type. When a pressure is applied to the spring tube, the spring tube deforms. The sensor then converts the deformation into an electrical signal output.

Third, the application of sensors

Resistance sensor

The basic principle of a resistive sensor is to convert the measured change into a change in the resistance value of the sensing element and then to become an electrical signal output through the conversion circuit. Applications:1. Strain resistance sensor for measuring tensile and compressive stress, and other physical quantities based on it; Thermistor sensor for measuring temperature; Slide arm type resistance sensor for measuring geometric position (angle, displacement); Magnetic Sensitive resistance sensor, used to measure the magnetic field. Photoresistance sensor for measuring the intensity of light; moisture-absorbing medium resistance sensor for measuring humidity; liquid resistivity sensor for measuring water-soluble ion concentration.

2. Capacitive sensor

Piezoelectric micro-displacement, vibration table, electron microscope fine-tuning, astronomical telescope lens fine-tuning, precision micro-displacement measurement, measurement of liquid level, humidity, and material composition.

Inductive sensor

Detect the attenuation of the distance. Slippery is iron, suitable for inductive sensor detection; and the size of the warped measured part is slightly smaller than the standard test object size (standard test object size is 3 times the rated detection distance, in this application, the standard size should be 120*120mm ) In this case, there will be a certain degree of attenuation; on-site anti-jamming capability. This is a problem that can not be ignored. Common inductive sensors are easily disturbed by motors or inverters. Many technicians only choose sensors with strong anti-electromagnetic interference for applications in this area. However, in the automotive workshop, the factory building is large, and the on-site technicians are accustomed to using the walkie-talkie to communicate, especially when talking on the walkie-talkie while walking. They will inadvertently approach the sensor and cause temporary failure. With the popularization of inductive sensors, sensors have not only improved in electrical performance, their mechanical design has become more humane. To achieve the greatest degree of user-friendly installation. It reduces the stocking of multiple similar products and reduces the time for installation and maintenance; the guarantee for stable operation. In the use of the depot, we must eliminate any erosion of oil and dust. In addition, the vibration is a long-term existence when the gliding passes through the track, and the excellent anti-vibration also plays an important role.

4. Magnetoelectric sensor

Magnetoelectric sensors are mainly used for vibration measurement. The inertial sensor does not require a stationary base as a reference, it is mounted directly on the vibrating body for measurement, and thus has been widely used in ground vibration measurement and airborne vibration monitoring systems. Commonly used vibration measuring sensors include moving iron type vibration sensors and ring type vibration speed sensors.

5. Eddy current sensor

The eddy current sensor can be used to measure parameters such as vibration, displacement, thickness, rotation, temperature, hardness, etc. It can also be used for nondestructive testing. The application of KD2306 eddy current sensor in displacement can be used to detect axial displacement and differential expansion of rotating machine.

6. Potential sensor

Inductive sensors have outstanding advantages such as simple structure, fast dynamic response and easy non-contact measurement. They are particularly suitable for use in acids, alkalis, chlorides, organic solvents, liquid CO2, ammonia, PVC powder, ash, oil and water. Interface and other liquid level measurements are widely used in metallurgy, petroleum, chemical, coal, cement, and grain industries.

7. Semiconductor sensors

The main application areas of semiconductor sensors are industrial automation, telemetry, industrial robots, household appliances, environmental pollution monitoring, healthcare, pharmaceutical engineering, and bioengineering. Semiconductor sensors are divided into physical, chemical, and bio-sensitive semiconductor sensors according to input information.

8. Resonance sensor

Resonant sensors have the advantages of small size, light weight, compact structure, high resolution, high accuracy, and ease of data transmission, processing, and storage. It is mainly used to measure pressure, but also to measure torque, density, acceleration and temperature.

9. Electrochemical sensor

The application of chemical sensors in environmental and sanitation monitoring: In environmental and sanitation monitoring, it is commonly used in wet-bulb temperature and humidity meters, hand-operated wet thermometers, and ventilated and wet thermometers to measure air humidity. The application of electrochemical biosensors in the early diagnosis of diseases: DNA electrochemical biosensors are a new class of biosensors that have been researched internationally in recent years. They have the characteristics of strong specificity, high sensitivity, rapid detection, simple and economical characteristics. Early diagnosis of major diseases such as cancer has important implications.

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