Classification of sensors

1. According to the input amount, the different points of the measurement object：

If the input is: temperature, pressure, displacement, speed, humidity, light, gas and other non-electricity, the corresponding sensors are called temperature sensors, pressure sensors, load cells, etc.

This classification method clearly explains the purpose of the sensor, provides convenience to the user, and is easy to select the required sensor according to the measurement object. The disadvantage is that this classification method classifies sensors with different principles into one category. It is difficult to find out what are the commonalities and differences in the conversion mechanism of each sensor. Therefore, it is not good for mastering some basic principles and analysis methods of sensors. Because the same type of sensor, such as a piezoelectric sensor, can be used to measure acceleration, velocity, and amplitude in mechanical vibration, as well as impact and force, but the working principle is the same.

This classification method divides the most diverse physical quantities into two categories: basic quantities and derived quantities. For example, force can be regarded as a basic physical quantity, from which pressure, weight, stress, moment and other physical quantities can be derived. When we need to measure the above-mentioned physical quantities, just use a force sensor. Therefore, understanding the relationship between basic physical quantities and derived physical quantities is very helpful for which sensors are used in the system.

2. Classified by work (detection) principle：

The detection principle refers to the physical effect, chemical effect and biological effect mechanism on which the sensor works. There are resistive, capacitive, inductive, piezoelectric, electromagnetic, magnetoresistive, photoelectric, piezoresistive, pyroelectric, nuclear radiation, semiconductor sensors, etc.

According to the principle of variable resistance, the corresponding sensors include potentiometer, strain gauge, and piezoresistive sensors; according to the principle of electromagnetic induction, the corresponding sensors include inductive, differential pressure transmitter, eddy current, electromagnetic, and magnetic resistance. According to the relevant semiconductor theory, there are corresponding solid-state sensors such as semiconductor force-sensitive, thermal-sensitive, photosensitive, gas-sensitive, and magnetic-sensitive.

The advantage of this classification method is that it is convenient for sensor professionals to conduct inductive analysis and research on the principle and design, and avoid too many names of sensors, so it is most often used. The disadvantage is that users will feel inconvenient when choosing sensors.

Sometimes it is often named by combining the use and principle, such as inductive displacement sensors, piezoelectric force sensors, etc., to avoid too many sensor names.

3. According to whether the structural parameters of the sensor change during the signal conversion process, it can be divided into:

a. Physical property sensor: In the process of realizing signal transformation, the structural parameters are basically unchanged, but the change of physical or chemical properties of certain materials (sensing elements) is used to realize signal transformation.

This kind of sensor generally has no movable structural parts and is easy to be miniaturized, so it is also called a solid-state sensor. It is a solid-state device with semiconductors, dielectrics, ferroelectrics, etc. as sensitive materials. Such as: thermocouple, piezoelectric quartz crystal, thermal resistance, and various semiconductor sensors such as force sensitive, thermal sensitive, humidity sensitive, gas sensitive, photosensitive element, etc. 　

b. Structural sensors: relying on changes in the geometrical shape or size of the sensor’s mechanical structure (ie, structural parameters) to convert the external measured parameters into corresponding changes in physical quantities such as resistance, inductance, and capacitance to achieve signal conversion, thereby detecting the Test signal.

Such as: capacitive, inductive, strain gauge, potentiometer, etc.

4. According to the energy relationship between the sensitive element and the measured object (or according to whether additional energy is required):

a. Energy conversion type (active type, self-source type, power generation type): no additional energy is required for signal conversion, energy is directly input from the measured object, and the input signal energy is converted into another form of energy output Make it work. The active sensor is similar to a miniature generator, it can convert the input non-electric energy into electric output, the sensor itself does not need an external power source, the signal energy is directly obtained from the measured object. So as long as it is equipped with the necessary amplifier, the display and recording instrument can be promoted.

Such as: piezoelectric, piezomagnetic, electromagnetic, electric, thermocouple, photocell, Hall element, magnetostrictive, electrostrictive, electrostatic and other sensors.

In this type of sensor, part of the energy conversion is reversible, and electrical energy can also be converted into mechanical energy or other non-electricity. Such as piezoelectric, piezomagnetic, electric sensors, etc.　

b. Energy control type (passive type, other source type, parametric type): When performing signal conversion, it is necessary to supply energy first, that is, supply auxiliary energy from the outside to make the sensor work, and the change of external energy supply is controlled by the measured . For passive sensors, the measured non-electricity only controls or modulates the energy in the sensor. It must be converted into voltage or current through a measuring circuit, and then converted and amplified to drive the indicating or recording meter. The measuring circuit is usually a bridge circuit or a resonant circuit.

Such as: resistance type, capacitive type, inductive type, differential transformer type, eddy current type, thermistor, photoelectric tube, photoresistor, humidity sensitive resistor, magnetoresistor, etc.

5. According to the nature of the output signal:

Analog sensor: Convert the measured non-electricity into a continuously changing voltage or current. If required to cooperate with a digital display or digital computer, an analog/digital (A/D) conversion device is required.

The sensors mentioned above are basically analog sensors. 　

b. Digital sensor: It can directly convert non-electricity into digital quantity, can be directly used for digital display and calculation, can directly cooperate with computer, has the advantages of strong anti-interference ability and suitable for distance transmission.

At present, these sensors can be divided into three categories: pulse, frequency and digital output. Such as grating sensors.

6. According to the method of association between the sensor and the measured object (whether it is in contact), it can be divided into:

a. Contact type: such as: potentiometer type, strain type, capacitive type, inductive type, etc.;

b. Non-contact type: The advantage of the contact type is that the sensor and the measured object are regarded as one body, and the calibration of the sensor does not need to be carried out at the use site. The disadvantage is that the contact between the sensor and the measured object will inevitably produce the state or characteristics of the measured object More or less impact. Non-contact type has no such effect;

Non-contact measurement can eliminate the influence of the sensor's intervention on the measured, improve the accuracy of the measurement, and increase the service life of the sensor. However, the output of non-contact sensors will be affected by the medium or environment between the measured object and the sensor. Therefore, the sensor calibration must be carried out on site.

7. Divided by sensor composition:

a. Basic sensor: It is the most basic single conversion device.

b. Combined sensor: It is a sensor composed of different single conversion devices.

c. Application sensor: a sensor composed of a basic sensor or a combination sensor and other mechanisms.

For example, a thermocouple is a basic sensor. Combine it with a heat absorber that converts infrared radiation into heat to form an infrared radiation sensor, which is a combination sensor; applying this combination sensor to infrared scanning equipment is an application type sensor.