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Jul 9 2018

Sensor Basics: Types of Sensors & Classification

I Introduction

The types of sensors are very wide, and we can use different criteria to classify them, such as their conversion principles (basic physical or chemical effects of sensor work), their uses, their output signal types, and the materials and processes that make them.

Before learning about the type of sensor, you need to know what a sensor is. The definition of "sensor" in the Webster's Dictionary is: a device that responds to a physical stimulus (such as heat, light, sound, pressure, magnetism, or a particular motion) and transmits a resulting impulse (as for measurement or operating a control).

According to this definition, the role of the sensor is to convert one energy into another energy form, so many scholars also use "Transducer" to refer to "Sensor".

Types of Sensors


I Introduction

II Introduction and Schematic of Common Sensor Types

 2.1 Common Sensor Types, Applications and Introduction

 2.2 Circuit/Schematic Diagrams of Several Common Types of Sensors

III Sensor Types Classified by Working (Detection) Principles

IV Energy Conversion&Energy Control Type Sensor 

V Sensor Types Classified by Input Quantity (Measured Physical Quantity)

VI Physical Sensor&Structural Sensor

VII Analog Sensor&Digital Sensor

VIII Contact and Non-contact Type Sensor

IX Sensor Types Classified by Composition

X Special Types of Sensors

XI Questions Related to Types of Sensors

II Introduction and Schematic of Common Sensor Types

2.1 Common Sensor Types, Applications and Introduction

Common Types of Sensors

Types of Sensors



Temperature Sensor

Digital signal output sensor

DS18B20, 18B20 digital temperature sensor, can be applied to various narrow space equipment, digital temperature measurement and control fields


Thermistor sensor

Thermistor 5K10K\temperature sensor\temperature probe


MTS102 Temperature Sensor


Ultrasonic sensor

Ultrasonic sensor TCT40-16F / S (receive / transmit)

Ultrasonic sensors are sensors that convert ultrasonic signals into other energy signals (usually electrical signals).


Ultrasonic sensor TCT40-16F/S(integrated transceiver)



Ultrasonic ranging module

Ultrasonic ranging module is a product used to measure distance. By sending and receiving ultrasonic waves, using the time difference and sound propagation speed, the distance from the module to the obstacle in front is calculated.


MMA7660 MMA7660FC ultra-small, low power consumption, three-axis acceleration sensor

Three-axis acceleration sensing can be applied to the inclination control of trolleys, robots, etc.

Gas sensor

Smoke sensor MQ-2

Can be used to detect CO, CH4 and other flammable gases


Alcohol sensor MQ-3

Semiconductor alcohol sensor MQ-3

Humidity Sensor

Humidity resistor

Humidity sensitive components, with wide range of humidity sensing, high sensitivity, small hysteresis difference and fast response speed.

Vibration sensor/Displacement sensor


Displacement sensor, also known as linear sensor, is a linear device belonging to metal induction.

Hall switch sensor

Hall switch sensor / motor speed measurement / position detection

A magnetic field sensor made according to the Hall effect.

Photoelectric sensor

Photocell, photomultiplier tube, photoresistor, photodiode, phototransistor, photocell

A photoelectric sensor is a device that converts optical signals into electrical signals.

2.2 Circuit/Schematic Diagrams of Several Common Types of Sensors

  • The Circuit of Temperature Sensor

The Circuit of Temperature Sensor

Figure1. The Circuit of Temperature Sensor

  • The Schematic of Ultrasonic Sensor

The Schematic of Ultrasonic Sensor

Figure2. The Schematic of Ultrasonic Sensor

  • The Schematic of Triaxial Acceleration Sensor

The Schematic of Triaxial Acceleration Sensor

Figure3. The Schematic of Triaxial Acceleration Sensor

  • The Schematic of Temperature Sensor&Humidity Sensor

The Schematic of Temperature Sensor&Humidity Sensor

Figure4. The Schematic of Temperature Sensor&Humidity Sensor

  • The Schematic of Hall Switch Sensor

The Schematic of Hall switch sensor

Figure5. The Schematic of Hall switch sensor

III Sensors Types Classified by Working (Detection) Principles

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

According to the principle of variable resistance, there are corresponding sensors such as potentiometer, strain gauge, and piezoresistive; if according to the principle of electromagnetic induction, there are corresponding inductive, differential pressure transmitters, eddy current, electromagnetic, and magnetic resistance Sensors, etc.; according to semiconductor related theories, there are corresponding solid-state sensors such as semiconductor force sensitive, heat sensitive, light sensitive, gas sensitive, and magnetic sensitive.

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

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

Let's take a closer look at several types of sensors with different working principles.

(1) Electrical sensor

Electrical sensors are a kind of sensors with a wide range of applications in non-electricity measurement technology. Commonly used are resistive sensors, capacitive sensors, inductive sensors, magnetoelectric sensors and eddy current sensors.

① The resistive sensor is made by using the principle of the varistor to convert the measured non-electricity quantity into a resistance signal. Resistive sensors generally include potentiometer type, contact variable resistance type, resistance strain gauge type and piezoresistive sensor. Resistance sensors are mainly used for the measurement of parameters such as displacement, pressure, force, strain, torque, air flow rate, liquid level and liquid flow.

Working Principle of Resistive Sensor

Figure6. Working Principle of Resistive Sensor

② Capacitive sensors are made using the principle of changing the geometric size of the capacitor or changing the nature and content of the medium, thereby changing the capacitance. Mainly used for the measurement of pressure, displacement, liquid level, thickness, moisture content and other parameters.

Capacitive sensors

Figure7. Capacitive sensors

③ Inductive sensors are made by the principle of inductance or piezomagnetic effect that changes the geometric size of the magnetic circuit and the position of the magnet to change the inductance or mutual inductance. Mainly used for the measurement of displacement, pressure, force, vibration, acceleration and other parameters.

④ The magnetoelectric sensor is made by using the principle of electromagnetic induction to convert the measured non-electricity into electrical energy. Mainly used for the measurement of parameters such as flow, speed and displacement.

Recommendation: A Related Article about Magnetoelectric Wheel Speed Sensor 

⑤ The eddy current sensor is made by the principle that gold chips move in the magnetic field to cut the magnetic field lines and form an eddy current in the metal. Mainly used for the measurement of parameters such as displacement and thickness.

(2) Magnetic sensor

Magnetic sensors are made using some physical effects of ferromagnetic substances, and are mainly used for the measurement of parameters such as displacement and torque.

(3) Photoelectric sensor

Photoelectric sensors play an important role in non-electricity electrical measurement and automatic control technology. It is made using the photoelectric effect and optical principle of the photoelectric device, and is mainly used for the measurement of parameters such as light intensity, luminous flux, displacement, concentration, etc.

Photoelectric sensor

Figure8. Photoelectric sensor

(4) Potential type sensor

Potential sensors are made using the principles of pyroelectric effect, photoelectric effect, and Hall effect. They are mainly used for the measurement of parameters such as temperature, magnetic flux, current, speed, light intensity, and thermal radiation.

(5) Charge sensor

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

(6) Semiconductor sensor

Semiconductor sensors are made using the principles of semiconductor piezoresistive effect, internal photoelectric effect, magnetoelectric effect, and substance change caused by the contact between semiconductor and gas. They are mainly used for temperature, humidity, pressure, acceleration, magnetic field and harmful gas measurement.

Recommendation: Articles about: Piezoelectric Pressure Sensor and Magnetoelectric Wheel Speed Sensor 

(7) Resonant sensor

The resonant sensor is made by the principle of changing the inherent parameters of electricity or machinery to change the resonant frequency, which is mainly used to measure pressure.

(8) Electrochemical sensor

Electrochemical sensors are made on the basis of ion conductivity. According to the formation of different electrical characteristics, electrochemical sensors can be divided into potentiometric sensors, conductivity sensors, electric quantity sensors, polarographic sensors, and electrolytic sensors. Electrochemical sensors are mainly used to analyze the measurement of gas, liquid or solid components dissolved in liquid, the pH of the liquid, electrical conductivity and redox potential.

Resistive Sensor and Capacitive Sensor

Figure9. Resistive Sensor and Capacitive Sensor

IV Energy Conversion&Energy Control Type Sensor 

To be more specific, the sensor can be divided into the following two types according to the energy relationship between the sensitive element and the measured object (or whether additional energy is required).

(1) Energy conversion type (active type, self-source type, power generation type): no additional energy is required when performing signal conversion, the energy is directly input from the measured object, and the input signal energy is converted into another form of energy output to make it work. The active sensor is similar to a micro-generator, which can convert the input non-electric energy into electrical energy output. The sensor itself does not need an external power supply, and the signal energy is directly obtained from the measured object. Therefore, as long as it is equipped with the necessary amplifier, it can promote the display and recording instrument.

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

Recommendation: articles about Magnetostrictive Knock Sensor&Hall Pressure Sensor

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

Piezoelectric sensors

Figure10. Piezoelectric sensors

(2) Energy control type (passive type, other source type, parametric type): when performing signal conversion, it is necessary to supply energy first, that is, to supply auxiliary energy from the outside to make the sensor work, and the change of external energy supply is controlled by the measured objects. For passive sensors, the measured non-electric quantity only controls or modulates the energy in the sensor. It must be converted into voltage or current through the measurement circuit, and then converted and amplified to promote the indication or recording instrument. The matching measurement circuit is usually a bridge circuit or a resonance circuit.

Such as: resistance type, capacitance type, inductance type, differential transformer type, eddy current type, thermistor, photocell, photoresistor, humidity sensitive resistor, magnetoresistive resistor, etc.

V Sensor Types Classified by Input Quantity (Measured Physical Quantity)

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

This classification method clearly explains the purpose of the sensor and provides convenience to the user. It 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 the commonalities and differences in the conversion mechanism of each sensor. Therefore, it is unfavorable to grasp some basic principles and analysis methods of the sensor. 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.

Methane Sensor

Figure11. Methane Sensor

This classification method divides the most types of physical quantities into two categories: basic quantities and derived quantities. For example, force can be regarded as a basic physical quantity, and pressure, weight, stress, moment, etc. can be derived from the force. When we need to measure the above physical quantities, we only need to use force sensors. So understanding the relationship between basic physical quantities and derived physical quantities is very helpful for what kind of sensors the system uses.

VI Physical Sensor&Structural Sensor

(1) Physical sensor: During the signal conversion process, the structural parameters are basically unchanged, but the change of the physical or chemical properties of some material materials (sensitive components) is used to realize the signal conversion.

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

(2) Structural sensor: Relying on the change of the geometric shape or size of the sensor mechanical structure (that is, the structural parameter) to convert the external measured parameters into corresponding changes in physical quantities such as resistance, inductance, capacitance, etc., to achieve signal conversion and thus detect Signal under test.

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

Various Sensor Shapes and Sizes

Figure12. Various Sensor Shapes and Sizes

VII Analog Sensor&Digital Sensor

According to the nature of the output sigal, sensors can be divided into the following two types:

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

The sensors mentioned above are basically analog sensors.

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

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

Difference between analog and digital sensors

Figure13. Difference between analog and digital sensors

VIII Contact and Non-contact Type Sensor

(1) Contact type: such as: potentiometer type, strain type, capacitive type, inductive type, etc..

(2) Non-contact type: The advantage of the contact type is that the sensor and the measured object are regarded as one, and the calibration of the sensor does not need to be performed on the site. The disadvantage is that the contact between the sensor and the measured object will inevitably affect the state or characteristics of the measured object. Non-contact has no such effect;

Non-contact measurement can eliminate the influence of the sensor intervention and cause the measurement to be affected, improve the accuracy of the measurement, and at the same time, can increase the service life of the sensor. However, the output of the non-contact sensor 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.

IR Sensor

Figure14. IR Sensor

IX Sensor Types Classified by Composition

(1) Basic sensor: It is a most basic single conversion device.

(2) Combined sensor: It is a sensor composed of different single conversion devices.

(3) Applied sensor: It is a sensor composed of basic sensor or combination sensor combined with other mechanisms.

For example: a thermocouple is a basic sensor. It is combined with a heat absorber that converts infrared radiation into heat to form an infrared radiation sensor, that is, a combined sensor; applying this combined sensor to infrared scanning equipment is an application sensor.

X Special Types of Sensors

The classification introduced above is the basic type of sensor, which can be divided into the following types according to particularity:

(1) According to the detection function, it can be divided into sensors that detect temperature, pressure, temperature, flowmeter, flow rate, acceleration, magnetic field, luminous flux, etc..

(2) According to the physical basis of sensor work, it can be divided into mechanical, electrical, optical, liquid, etc..

(3) According to the scope of the conversion phenomenon, it can be divided into chemical sensors, electromagnetic sensors, mechanical sensors and optical sensors.

(4) According to the material, it can be divided into metals, ceramics, organic polymer materials, semiconductor sensors, etc..

(5) According to the application field, it is divided into industrial, civil, scientific research, medical, agricultural, military and other sensors.

(6)According to functional purposes, it is divided into sensors for measurement, monitoring, inspection, diagnosis, control, analysis, etc..


Figure16. Sensors/Transducers


Sensor is a type of transducer.

a) True

b) False



Explanation: Sensor is a device which enables measurement of input value.


Type of sensor used to detect both metallic and non-metallic objects

a) Capacitive sensor

b) Inductive sensor

c) Thermocouple sensor

4) pH Sensor





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