This article will help you understand the types of sensors and the operating principles of Thermal Sensors, Optical Sensors, and Proximity Sensors. Temperature sensors are devices that help monitor and regulate temperature in industrial systems, homes, and medical devices. Optical sensors operate based on the detection and measurement of light, allowing applications in automation, energy management, and smart lighting systems. Proximity sensors are used to detect the presence of objects without contact, providing high accuracy and safety in manufacturing and automation processes. These sensors not only help improve performance in many applications, but also play an important role in optimizing production processes and ensuring safety. Hopefully, through this article, you will have a deeper insight into the types of sensors and their roles in everyday life.
1. Sensor information
Sensor concept
Sensors are devices used to detect and collect information about the states and changes in the environment. These signals are then sent to a measuring device, which can convert them into electrical signals and display them on a screen, making it easy for people to read and understand the data obtained. Sensors provide information about parameters such as temperature, pressure, humidity, light and many other variables. They are often used for measurement, monitoring and control in many different fields.
The role of sensors
Sensors play an important role in many fields such as industrial automation, healthcare, automotive, and electronics. Here are some of their prominent functions:
Data acquisition: Sensors collect information from the surrounding environment, such as light, motion, and temperature.
Measurement and monitoring: They help measure physical and chemical parameters, making it easy for users to monitor.
Adjustment: Data from sensors is used to adjust the system, ensuring the device operates efficiently and accurately.
Applications of sensors
Process control: Sensors help “sense” signals in automation systems, optimizing operations.
Measurement: Sensors measure values such as temperature, pressure, and humidity, converting physical signals into electrical signals for precise monitoring.
Safety: Sensors control equipment and machinery, preventing accidents by detecting nearby objects.
Environmental monitoring: Sensors monitor and adjust environmental conditions in systems such as HVAC and clean rooms.
Automation: Sensors are a key component in manufacturing processes and robotics, helping to improve efficiency.
Smart cars: Sensors help self-driving cars detect the environment and avoid collisions.
Healthcare technology: Sensors monitor health and diagnose diseases, such as heart rate and blood sugar sensors.
IoT (Internet of Things): Sensors collect and transmit data over networks, serving energy management and smart homes.
Scientific research: Sensors collect data in the laboratory, supporting the analysis of physical and biological phenomena.
Consumer electronics: Sensors enhance the functionality of smartphones and smartwatches, enabling heart rate measurement, location, and human-machine interaction.
Sensor Classification
According to the operating principle
Electrical sensors: Based on electrical phenomena such as the Hall effect, the capacitive effect, the thermoelectric effect, etc.
Optical sensors: Based on optical phenomena such as the photoelectric effect, the photoconductive effect, the photoluminescent effect, etc.
Magnetic sensors: Based on magnetic phenomena such as the Hall effect, the electromagnetic effect, etc.
Thermal sensors: Based on thermal phenomena such as the thermoelectric effect, thermistor effect, etc.
Force sensors: Based on force phenomena such as the piezoelectric effect, the magnetoelectric effect, etc.
Chemical sensors: Based on chemical reactions to measure the concentration and composition of chemical substances.
Biological sensors: Based on biological phenomena to measure biological parameters such as blood pressure, heart rate, etc.
According to output signal
According to operating environment
2. Common types of sensors today
Temperature Sensors: Measure the temperature of the surrounding environment and convert it into an electrical signal. Common types include thermocouples, thermistors, and infrared sensors.
Optical Sensors: Measure the intensity of light and convert it into an electrical signal. Photodiode sensors and CCD sensors are some common types.
Proximity Sensors: Often used to detect the presence of an object without physical contact. They are commonly used in a variety of applications, such as industrial automation, home appliances, and security systems.
3. Temperature Sensor
Temperature Sensor Concept
Temperature sensors are important devices used to monitor and measure temperature in factories, systems and equipment. Operating on the principle of resistance, this device is usually made of metal, with resistance varying according to the temperature level.
There are many different types of temperature sensors, but the Pt100 sensor is the most popular, accounting for about 90% of the demand in the industry. Therefore, RTD sensors are often simply called Pt100 sensors.
Temperature Sensor Structure
Currently, there are two basic types of temperature sensors: bulb-shaped temperature sensors (with a terminal block on top) and wire-shaped temperature sensors. However, they are basically the same in structure, including the following main parts:
.webp "Cấu tạo cảm biến nhiệt độ 1")
The temperature sensor has a probe made of Platinum material for extremely high accuracy.
.webp "Cấu tạo của cảm biến nhiệt độ 2")
Connection head: Usually made of aluminum, stainless steel or cast iron, has the function of protecting the connection bridge, signal wire inside. Normally, wire-type RTDs will not have this connection head.
Sensor probe: Is the part containing metal (Platium or Nickel), has the function of directly sensing the temperature value through resistance changes to transmit signals to the display or control device.
Mechanical connection: Is the connection part that helps fix the RTD temperature probe to the device/system. There are two common connection types: threaded connection or flange connection.
Principle of operation
The operating principle of the temperature sensor is quite simple, when the sensor probe comes into contact with the measuring environment, the temperature at the probe changes, causing the output resistance at the rest of the sensor to change. Each temperature change will give a resistance value, the resistance value is always proportional to the temperature value measured by the sensor.
Temperature sensor wiring diagram
2-wire Pt100 temperature sensor: This is the type of sensor with the highest error due to the influence of resistance on the 2 wires, and that is why this type is rarely used. This type is usually the lowest price of the three types of Pt100 temperature sensors.
Connecting the 2-wire Pt100 temperature sensor: With this type, we will connect the 2 wires directly to pins 3 and 6.
.webp "Sơ đồ đấu nối của cảm biến nhiệt độ")
3-wire Pt100 temperature sensor: This is the most commonly used type of Pt100 because they have relatively high accuracy, meeting most basic measurement applications. The two common wires cancel each other's resistance & the remaining wire acts as a wire that changes the resistance value when the temperature changes
Wiring a 3-wire Pt100 temperature sensor: This is the most commonly used type of Pt100 today. The reason is that it has a temperature compensation wire so it has very high accuracy. Looking at the connecting wire, we will see 3 wires, of which 2 are the same color (usually red) and 1 is a different color (usually white).
To wire, we connect 2 wires of the same color to pins 3 and 4. Then connect the 2 wires together, the remaining wire is connected to pin 6.
.webp "Sơ đồ đấu nối cảm biến nhiệt độ")
Cable Temperature Probe
Wire-type Pt100 probe is a temperature sensor with a metal tip, with an integrated output wire. The output wire can be chosen in arbitrary length and in many different types. It is often used in places where the temperature measurement area is small because it can be bent, so it can be measured in places where the bulb head cannot be inserted.
For the measuring head, we also have many types, sizes, and lengths. In wire-type Pt100, we also divide it into 2 types:
Samil PT100 temperature sensor with screw thread
Equipped with additional screw thread to help Pt100 temperature sensor can be fixed into the wall. For pressure measuring tanks, we should use the threaded type to screw in.
Samil RTD Pt100 temperature probe without thread
This type of RTD temperature sensor is often used to plug into molds, and press tightly. It can also be released freely in the environment to measure air or places without pressure. In particular, it is designed for handheld sensors. For applications like this, we use the threadless type, which is more compact and cost-effective than the screw type.
Onion-shaped Pt100 temperature sensor (Head Mounted)
With the bulb head, the temperature sensor provides us with more professional specifications. The large head of the sensor provides us with a waterproof, sturdy electrical connection. can measure higher temperatures than the wired type. In addition, it is also the place to place the Pt100 to 4-20mA signal converter.
The bulb type Pt100 thermocouple has two temperature ranges. These are the two temperature ranges that the bulb Pt100 sensor can operate:
Low temperature: -50-150℃
High temperature: -200- above 500℃
Similar to the Pt100 thread type, the bulb also has a variety of thread sizes. Especially for the bulb type, we have a thread type installed in the middle of the measuring rod. This type is commonly used for the type with integrated signal converter, to insulate the converter from getting hot.
.webp "Cảm biến nhiệt độ pt100")
Ứng dụng của cảm biến nhiệt độ
If we understand what a temperature probe is, we must have known more or less some of its basic applications in everyday life. Samil temperature probes are used in almost all industries. We often see the need in medical applications, the motorsport industry, the food and beverage industry, and even in the media industry. Some of the applications that require the use of this device are:
How to choose a temperature sensor
When choosing a temperature sensor, you need to consider two main types: RTD Pt100 and K(CA). The choice of sensor head type is also very important. Samil offers two types of sensor heads:
HEAD Mounted (onion): Suitable for high temperature environments such as hot water or hot steam, with a sturdy design and easy installation of the signal converter. The onion type is often used to measure high temperatures, installed in boilers, drying ovens, furnaces, in large pipes, with a heat resistance of up to 800 C. (If the temperature is higher, we must use a thermocouple).
Cable (wire type): Common for low temperature measurement applications below 200°C in closed areas such as cabinets or manufacturing plants. Wire type is often used for low temperatures, from -100°C to 600°C, such as in cold storage, autoclaves, or refrigerators.
Temperature Range: This is also an important factor when choosing an RTD. Although Pt100s are capable of measuring from -200°C to 850°C, not all manufacturers achieve this maximum range. Check the specifications carefully before deciding. Some common ranges include: 0 ÷ 100°C, 0 ÷ 300°C, and -50 ÷ 500°C.
4. Photoelectric Sensor
Optical Sensor Concept
Photoelectric Sensor is a device that combines photoelectric components. When exposed to light, they will change state based on the phenomenon of electron emission at the Cathode, the optical signal will be converted into an electrical signal. From there, it is possible to detect the presence of an object.
Common structure
The photoelectric sensor consists of 3 parts: the light emitter, the light receiver and the electrical signal processing board.
Light emitter: This part takes the position of the photothermal sensor, emitting pulsed light. Depending on the manufacturer, there will be a separate light frequency designed. This part supports the light receiver to distinguish the light source from the sensor and many other sources.
Light receiver: This part is the part that receives the light and then transmits the signal to the processing part.
Electrical signal processing circuit: This part receives the signal from the light receiver and converts the signal according to the transistor ratio into ON/OFF mode, this signal has a wider amplification.
Photoelectric sensor wiring diagram
3 wire type NPN or PNP
Pin 4 is the sensor output signal. When there is an obstacle, pin 4 will be activated corresponding to 24VDC (PNP) and 0V (NPN).
Most photoelectric sensors have PNP or NPN output signals. They work the same way but have different output signals. PNP signals correspond to 12~24VDC output while NPN signals have 0V output.
5-wire photoelectric sensor relay contact output type
Commonly used optical sensors
Independent Transceiver Optical Sensor
Independent photoelectric transceiver sensor (Through-Beam Sensor). The sensor consists of a light emitting device and a light receiving device placed opposite each other. This is a widely used sensor line because of its ability to detect objects at a distance of 60m, operates accurately, is not influenced by color and surface.
Working principle: When this sensor is working, there are only two states: with and without obstacles. When there are no obstacles, the two sensors, emitting light and receiving light, will work continuously with each other. When there is an obstacle, the emitting sensor will still emit light, but because there is an obstacle in between, the receiving sensor will not receive light. From there, the object is recognized.
Mirror reflective photoelectric sensor
The Retro-Reflection Sensor has both a light emitter, a light receiver and a reflective mirror. The reflective mirror acts as a special prism. Its outstanding advantage is the ability to detect objects with a opaque, transparent format with a maximum distance of about 15m, saving electrical wires and simple, quick installation. However, this sensor can be affected by strong light and interference from other sources.
Working principle: The mirror reflection sensor works when the light emitter will emit light to the mirror. If there is no obstacle, the mirror will collect all the light. If there is an obstacle or an object passes through, the frequency of the reflected light will change or the collected light will be lost.
Diffuse reflective photoelectric sensor
Diffuse Reflection Photoelectric Sensor This type of photoelectric sensor has both the transmitter and receiver mounted on the same location on the housing. This design allows light to travel from the transmitter directly to the sensing object without passing through the receiver. The light received by the receiver is reflected from the object. The increase in light intensity at the receiver helps the sensor detect the object.
Working principle: This sensor is light that is emitted and reflected back from the surface of the object, then collected by the light receiver. The advantage of the diffuse reflection photoelectric sensor is that it can detect objects in a large space and the surface of the object does not need to be a completely reflective surface. However, the sensitivity of the sensor can be adjusted by changing the impedance or distance from the light source. However, this device has a fairly limited range of about 2m. The accuracy of this sensor is also influenced by the colors and surface of the object.
Overview comparison of sensor types
| Optical sensor type | Advantage | Disadvantages |
| Transceiver | - Highest accuracy
- Largest operating range
- Most reliable | - Both transmitter and receiver need to be installed in two different locations
- Cannot detect transparent objects
- Performance depends on installation |
| Mirror reflection | - Accuracy is only slightly lower than the transceiver type
- Detection distance is larger than the diffuse type
- Very reliable | - Requires sensor and reflector prism installation at two locations
- Higher cost than diffuse type
- Detection range is smaller than transceiver type
- May not detect reflective objects well |
| Diffuse reflection | - Only need to install in one location
- Lower cost than the reflector and transceiver type | - Less accurate than transceiver and reflector
- Setup takes longer |
Applications of Photoelectric Sensors
Nowadays, in the context of the strong development of the industrial revolution, when the production system is fully automated or semi-automated, photoelectric sensors maximize their functions and uses. With their help, production output and product quality are improved while costs are reduced, and the competitiveness of enterprises will be significantly improved.
Below are some typical applications of photoelectric sensors in human activities from industry to civil use:
Check products passing through during processing and packaging
Check the path of cars, canned foods, bottled water, etc. on the conveyor belt
Determine the high level of liquids (soft drinks, coffee, etc.) in cans, boxes
Count bottles on conveyor belts moving at high speed
Detect missing labels on bottles
Ensure safety when opening and closing garage doors
Detect vehicles in parking lots
Turn on the water faucet with hand waves
Detect people and objects passing through doors
5. Proximity Sensor
Proximity sensor concept
Proximity sensor is an electronic device that detects the presence of an object in close proximity without direct contact. Also known as a “Proximity Switch” or “PROX”, this sensor responds when an object is nearby, usually just a few millimeters away.
They are often used to determine the end position of a machine part, initiate signals for other functions. In particular, proximity sensors operate effectively even in harsh environments.
The sensor converts signals about the movement of an object into electrical signals through three detection systems: electromagnetic induction, capacitance change, and magnet.
Proximity sensor characteristics
- Detects objects without contact, without impact on the object, maximum distance up to 30mm.
Stable operation, good anti-vibration and anti-shock.
Fast response speed, long life compared to limit switch.
Small sensor head can be installed in many places.
Can be used in harsh environments
Classification of proximity sensors
Capacitance type
Capacitive proximity sensors detect objects by generating an electrostatic capacitive field. Therefore, capacitive proximity sensors are capable of detecting any material whose dielectric is different from air. The sensor can detect conductive and non-conductive materials including metals, iron, stone, plastic, water, and grains.
Working principle of capacitive proximity sensor: Based on the change in capacitance when an object moves into the sensing area. When the object approaches, the dielectric increases, causing the oscillator in the sensor to detect the change and generate an output signal.
What is special is that the dielectric change is not the same between materials, depending on distance, material type and size. This allows the sensor sensitivity to be adjusted to suit each type of object and detection distance.
Advantages and disadvantages of capacitive proximity sensors
Advantages of capacitive sensors:
- Can sense conductive and non-conductive objects.
- Linearity and sensitivity are not dependent on metal materials.
- Fast operating speed.
- Long life and high stability to temperature.
- Detected objects can be liquids, non-metallic materials.
- Large sensing range.
- Small sensor head, can be installed in many places.
- It can sense small, light objects.
Disadvantages of capacitive sensors:
- Affected by humidity.
- The wire connected to the sensor must be short so that the wire capacitance does not affect the resonator of the oscillator.
Electromagnetic type
Magnetic sensors are a type of proximity sensor that works on the principle of electromagnetic induction, detecting magnetic objects, mainly iron, without contact. The detection distance is usually from a few millimeters to a few tens of millimeters.
This sensor creates a magnetic field around it, and when there is a metal object nearby, the magnetic field will detect it and send a signal to the center. Although it only detects metal, magnetic sensors are very popular in industry because of their good anti-interference ability and lower cost than capacitive sensors.
- Magnetic Induction – Shielded: The magnetic field is concentrated in front of the sensor so it is less susceptible to interference from surrounding metals, but the measuring distance is shorter.
- Magnetic Induction – Un-Shielded: There is no magnetic shielding around the sensor face so the measuring distance is longer, but it is susceptible to interference from surrounding metals.
How a magnetic sensor works: When powered, an electric current flows through a circuit containing an inductor as the magnetic field through it changes. This effect is used to detect metallic objects that interact with the magnetic field. Non-metallic substances such as liquids or dirt will not interact with the magnetic field. Therefore, magnetic sensors can work well in dusty environments or in humid conditions.
The larger the size and cross-section of the magnetic sensor, the stronger the magnetic field emitted; this means the larger the area where it can detect objects; the higher the efficiency it brings.
Advantages and disadvantages of electromagnetic proximity sensors
Advantages of electromagnetic proximity sensors:
Unaffected by humidity and dust.
No moving parts, no “blind zone” (the sensor does not detect the object even though the object is close to the sensor), no interference with electromagnetic waves, ultrasonic waves.
Not dependent on color, less dependent on the object surface than other techniques.
Non-contact detection, fast response speed.
Can be used in harsh environments, small sensor head, can be installed in many places.
Disadvantages of electromagnetic proximity sensors:
- Only detects metal objects.
Affected by strong electromagnetic fields.
Shorter operating range than other techniques.
Difference between capacitive sensor and electromagnetic sensor
Both capacitive and electromagnetic proximity sensors are similar in principle in how they work, but different in the nature of detecting objects.
The capacitive proximity sensor, as I presented above in the operating principle, clearly states that the sensor detects by changing the solvent at the sensor tip, from which the sensor is capable of detecting all types of objects, both metal and non-metal. And detects objects at a greater distance. A completely different point from the magnetic sensor, because the electromagnetic proximity sensor can only detect metal objects.
Wiring diagram for 2 and 3 wire proximity sensors
3-wire DC type
2-wire DC type
.webp "Sơ đồ đầu nối loại dc 2 dây")
AC 2 wire type
Note: When using 2-wire type sensor
When wiring a 2-wire sensor (both AC and DC) to use or check the sensor status, do not supply power directly to the sensor. Doing so will cause the sensor to short-circuit, leading to sensor damage. Therefore, we must first connect the power through an intermediate relay, then connect the intermediate relay to the sensor.
Applications of proximity sensors
- Capacitive sensor detects the amount of milk in the carton: With this application, the sensor is installed and aligned at the desired height to detect whether there is milk inside the carton or not, helping to eliminate empty cartons.
- Capacitive sensor detects oil spills and leaks: This type can be used on flat surfaces such as concrete floors, wooden floors or tank walls. When oil spills out, the sensor will detect it and send a signal to the warning light or buzzer.
6. Video exploring Amazen's temperature, optical and proximity sensors
Conclusion
In case you need to learn or need technical advice on Temperature Sensors, Optical Sensors and Proximity Sensors, please contact Amazen immediately via:
Hotline: 0934 399 068 - Sales: 0938 072 058
Email: amazen@amazen.com.vn
With a team of highly specialized technical support and sales consultants, our company is confident that we will bring our customers the best shopping experience.
Amazen commits that all inverter products we currently provide are genuine, 100% new, guaranteed quality and fully accompanied by CO/CQ and VAT certificates.