Classification of Sensors – Part Two
1. Classification by Operating Principle
Classification by operating principle refers to naming sensors based on the principle of signal conversion, such as strain sensors, capacitive sensors, piezoelectric sensors, thermoelectric sensors, inductive sensors, Hall sensors, etc. This classification method clearly reflects the working principles of sensors, facilitating in-depth analysis of sensor research. The subsequent chapters of this book are organized according to the classification of sensors by their operating principles.
2. Classification by Measured Object
· Classification by the measured object of the sensor—input signal classification—conveniently represents the functions of sensors and aids users in selection. According to this classification method, sensors can be divided into temperature, pressure, flow, level, acceleration, speed, displacement, torque, humidity, viscosity, concentration, and other types of sensors. Manufacturers and users are accustomed to this classification method. Additionally, this method categorizes various physical quantities into two major categories: basic quantities and derived quantities. For example, considering “force” as a basic physical quantity, derived physical quantities such as pressure, gravity, stress, and torque can be derived. When we need to measure these derived physical quantities, we can simply use sensors for basic physical quantities. Therefore, understanding the relationship between basic and derived physical quantities is very helpful for sensor selection. Table 2.5.2 lists commonly used basic and derived physical quantities.
Table 2.5.2 Commonly Used Basic and Derived Physical Quantities
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Basic Physical Quantity |
Derived Physical Quantity |
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Displacement |
Linear Displacement |
Length, Thickness, Strain, Vibration, Wear, Flatness |
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Angular Displacement |
Rotation Angle, Deflection Angle, Angular Vibration |
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Speed |
Linear Speed |
Speed, Vibration, Flow, Momentum |
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Angular Speed |
Rotation Speed, Angular Vibration |
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Acceleration |
Linear Acceleration |
Vibration, Impact, Mass |
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Angular Acceleration |
Angular Vibration, Torque, Moment of Inertia |
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Force |
Pressure |
Gravity, Stress, Torque |
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Time |
Frequency |
Period, Count, Statistical Distribution |
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Temperature |
Heat Capacity, Gas Speed, Eddy Current |
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Light |
Light Flux and Density, Spectral Distribution |
Classifying sensors based on input physical quantities groups sensors with different principles into one category, making it difficult to identify commonalities and differences in the conversion mechanisms of each type of sensor. This hinders the understanding of some basic principles and analysis methods of sensors. For instance, temperature sensors include various types made from different materials and methods, such as thermocouple temperature sensors, thermistor temperature sensors, metal thermistor temperature sensors, P-N junction diode temperature sensors, infrared temperature sensors, etc. Typically, the naming of sensors combines their working principles with the measured parameters, stating the working mechanism first, followed by the measured parameter, such as silicon piezoresistive pressure sensor, capacitive accelerometer, piezoelectric vibration sensor, resonant mass flow sensor, etc.
Regarding sensor classification, different measurements can use the same measurement principle, and the same measurement can employ different measurement principles. Therefore, it is essential to understand the characteristics of each measurement principle when measuring different quantities.
3. Classification by Need for External Power Supply
Sensors can be classified into active sensors and passive sensors based on this criterion.
Passive sensors are characterized by their ability to convert the measured quantity into an electrical signal without requiring an external power supply. For example, photoelectric sensors can convert light rays into electrical signals, similar to solar cells; piezoelectric sensors can convert pressure into voltage signals; thermocouple sensors can directly convert the energy (thermal energy) of the measured temperature field into voltage signals.
Active sensors require auxiliary power to convert the detected signal into an electrical signal. Most sensors fall into this category.
4. Classification by Functional Materials of the Sensor
Sensors can be classified into semiconductor sensors, ceramic sensors, fiber optic sensors, polymer film sensors, etc., based on the functional materials that constitute them.
5. Classification by Naming Based on Certain High-Tech Technologies
Some sensors are named based on certain high-tech technologies, such as integrated sensors, smart sensors, robotic sensors, biomimetic sensors, etc.
It should be noted that due to the vast number of sensitive materials and sensors, the categories are very complex, with overlaps and intersections. Therefore, further elaboration is not provided here. To reveal the intrinsic connections among various sensors, Table 2.5.3 presents the classification of sensors, conversion principles, and their typical applications for reference when selecting sensors.
Table 2.5.3 Sensor Classification Table
|
Sensor Classification |
Conversion Principle |
Sensor Name |
Typical Application |
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Conversion Form |
Intermediate Parameter |
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Electrical Parameters |
Resistance |
Moving potentiometer contact changes resistance |
Potentiometer Sensor |
Displacement |
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Change in the size of resistance wire or sheet |
Resistance Strain Sensor, Semiconductor Strain Sensor |
Microstrain, Force, Load |
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Resistance |
Temperature Effect of Resistance (Resistance-Temperature Coefficient) |
Hot Wire Sensor |
Airflow Speed, Liquid Flow |
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Resistance Temperature Sensor |
Temperature, Radiant Heat |
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Thermistor Sensor |
Temperature |
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Photoresistive Effect of Resistance |
Photoresistor Sensor |
Light Intensity |
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Humidity Effect of Resistance |
Humidity Sensor |
Humidity |
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Capacitance |
Change in Geometric Size of Capacitance |
Capacitive Sensor |
Force, Pressure, Load, Displacement |
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|
Change in Dielectric Constant of Capacitance |
Liquid Level, Thickness, Moisture Content |
Table
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Sensor Classification |
Conversion Principle |
Sensor Name |
Typical Application |
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|
Conversion Form |
Intermediate Parameter |
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Electrical Parameters |
Inductance |
Change in Geometric Size of Magnetic Circuit, Position of Magnetic Conductor |
Inductive Sensor |
Displacement |
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Eddy Current Demagnetization Effect |
Eddy Current Sensor |
Displacement, Thickness, Hardness |
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Using Magnetostrictive Effect |
Magnetostrictive Sensor |
Force, Pressure |
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Change in Mutual Inductance |
Differential Transformer |
Displacement |
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Self-speed Angle Machine |
Displacement |
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Rotary Transformer |
Displacement |
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Frequency |
Change in Inherent Parameters of Resonant Circuit |
Vibrating Wire Sensor |
Pressure, Force |
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Vibrating Cylinder Sensor |
Air Pressure |
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Quartz Resonant Sensor |
Force, Temperature, etc. |
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Counting |
Moire Fringe |
Grating |
Large Angle Displacement, Large Linear Displacement |
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Change in Mutual Inductance |
Inductive Synchronizer |
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Magnetic Signal Pickup |
Magnetic Grating |
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Digital |
Digital Encoding |
Angle Encoder |
Large Angle Displacement |
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Electrical Energy |
Electromotive Force |
Thermocouple |
Temperature, Thermal Flow |
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Hall Effect |
Hall Sensor |
Magnetic Flux, Current |
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Electromagnetic Induction |
Magnetoelectric Sensor |
Speed, Acceleration |
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Photoelectric Effect |
Photoelectric Cell |
Light Intensity |
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Charge |
Radiation Ionization |
Ion Chamber |
Ion Counting, Radioactive Intensity |
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Piezoelectric Effect |
Piezoelectric Sensor |
Dynamic Force, Acceleration |