Temperature Sensors: Principle of Operation and Construction

Temperature sensors are an important and familiar device in many different fields. Not only do they ensure the safety of goods, but they also help maintain product quality and value throughout the transportation process. So how do temperature sensors work and how do they work? In this article, join RX Tradex to explore the working principle and structure of popular temperature sensors, thereby better understanding their essential role in modern life and manufacturing.

1. What is a temperature sensor?

A temperature sensor is a device that can measure and record all information about the temperature of the surrounding environment or a specific object. They are widely used in many fields, from industry, healthcare, environment to transportation. Temperature sensors work based on changes in physical or chemical properties when there is a change in temperature.

Temperature sensors often use a variety of elements to measure, such as changes in electrical impedance, gas pressure, or material deformation. When the temperature changes, these changes affect the internal components of the sensor, which in turn generates electrical or other signals, which are recorded and converted into digital data for analysis.

2. Structure and working principle of temperature sensor

The principle of operation of the temperature sensor

The temperature sensor works on the principle that the characteristics of the heat source change when acting on external factors. When used, the sensor detects the temperature change of the object to be measured and generates a corresponding signal. This signal is then converted into an electrical signal and transmitted to the processing circuit. Here, through the signal processing unit, the electrical signal will be converted into temperature data and displayed on the screen to the user.

Structure of Temperature Sensor

Temperature sensors typically consist of two different metal leads, which are connected to the hot and cold ends. In addition, the structure of the temperature sensor also includes some other important parts as follows:

Sensor Unit: This is the core component that determines the accuracy of the sensor. This unit is placed in the protective housing after connecting to the connector.

Connection wires: The sensor can use 2, 3, or 4 wires to connect between parts. The material of the conductor depends on the usage conditions of the probe.

Ceramic Insulation Material: This part acts as an insulator, preventing short circuits and insulating between the wires connected to the protective housing.

Filler: The  filler filler, usually fine alumina powder, is dried and vibrated to fill the gaps, protecting the sensor from vibration.

Protective Housing: This protective housing protects the sensor components and internal connection wires. This part needs to be made of durable materials, suitable for the size of the sensor, and when needed can be covered with an additional layer of protection.

Connector Ends: Connector ends are typically made from insulating materials such as ceramics, which contain circuit boards that allow for resistance connections. A current converter from 4 to 20mA can be installed in place of the terminal panel if necessary.

3. Types of Temperature Sensors

Temperature sensors come in a variety of types, designed to meet different requirements and conditions of use. Here are some common types of temperature sensors:

• NTC (Negative Temperature Coefficient) Sensor: This type of sensor uses a thermistor, a material whose impedance decreases as the temperature increases. NTC sensors stand out for their high sensitivity and fast response, making them suitable for applications that require accurate measurements in narrow temperature ranges.
• PT100 and PT1000 Sensors: These are sensors based on the RTD (Resistance Temperature Detector) principle with platinum wire. The PT100 sensor has an impedance of 100 ohms at 0°C, while the PT1000 has an impedance of 1000 ohms. They are known for their high accuracy and stability over a wide temperature range.
• K-Type and J-Type Sensors: These thermocouple sensors operate on the principle of generating potential from the temperature difference between the two sensor ends. K-Type and J-Type sensors are popular and capable of measuring over a wide temperature range, commonly used in industry and science.
• Infrared (IR) Sensor: This type of sensor measures the temperature based on the infrared radiation emitted from the object. IR sensors are suitable for applications that require remote temperature measurement, such as in the food and medical industries.
• LM35 Sensor: The LM35 sensor uses the principle of variance to provide a voltage signal that corresponds to the temperature. It is easy to use and is often applied in projects and experiments.
• Thermopile Sensor: This sensor consists of an array of thermocouples, measures the amount of heat poured in and generates the corresponding voltage signal.
• These types of temperature sensors offer flexibility and versatility in meeting measurement requirements ranging from industrial applications to medical and everyday utility needs.

4. Types of Temperature Sensor Wires

There are many types of temperature sensor wires used in different applications, depending on the operating principle and application environment. Here are some common types:
Thermocouple Sensor Wire: Based on the principle of generating potential when there is a temperature difference between two ends of the wire. Types of thermocouples such as K-Type, J-Type, T-Type… capable of measuring temperature over a wide range, suitable for industrial applications.

• RTD (Resistance Temperature Detector) sensor wire: Uses platinum wire, where the impedance changes with temperature. RTD sensor wires are known for their high accuracy and stability, making them suitable for industrial and medical applications.
• NTC (Negative Temperature Coefficient) sensor wire: This type of wire uses a thermistor, with impedance decreasing as the temperature rises. NTC sensor wires are typically highly sensitive and suitable for applications that require accurate measurements in narrow temperature ranges.
• Thermopile Sensor Wire: Consisting of an array of thermocouples, this wire is capable of collecting heat and converting it into a corresponding voltage signal.
• Infrared (IR) Sensor Wire: Operating based on measuring the infrared radiation emitted from an object to determine temperature, IR sensor wire is often used to measure temperature remotely.
• Current Loop: Based on the principle of temperature-varying current, this type of wire transmits temperature data through current and is read by a specialized device.

These types of temperature sensor wires offer a wide range of versatility and applicability in a wide range of fields, from industrial and medical to environmental and transportation.

5. Parameter of Temperature Sensor

Temperature Scale: This is one of the important parameters that users need to pay attention to when choosing a temperature sensor. Sensor types typically have a measurement range of -100°C to 600°C, or possibly even wider.

Error: Current temperature sensors often have error standards such as 0.1 C, 0.15 C, and 0.3 C. In which, an error of 0.3 C is the most common in Vietnam.

Sensor Length: Temperature sensors come in a variety of lengths, with common sizes such as 50mm, 100mm, 200mm, 300mm, and can be up to 1000mm depending on the usage needs.

Connection threads: Temperature sensors typically have common connection thread styles including:

• External thread connection G 1/8
• External thread connection G 1/4
• External thread connection G 1/2
• Connection Clamp, commonly used in the food industry
• High-pressure flanged connections
• Threaded connection in G 1/4
• Threaded connection in G 1/2

Sensor diameter: Temperature sensors are usually compact in size, with common diameters of 6mm, 8mm, and 10mm depending on the type.

6. Application of Thermal Sensor

The temperature sensor has the function of measuring temperature, which is used in a variety of fields, increasing the efficiency of accurate measurement.

Measure the temperature in appliances such as in kettles, furnaces, drying ovens, storage warehouses,…

Thermistor sensors with metal oxide material are often used for measurement in refrigeration systems.

In agriculture, electronic temperature sensors are quite commonly used.

Thermal sensors such as PT100, K, R, S, B, T are commonly used in chemical production, material processing, and mechanical processing,…

Electronic thermometers are used to measure the temperature inside cars, trucks, motorcycles, etc.

7. Some precautions when using and storing

Before choosing to buy a temperature sensor, users need to consider the nature of the work and the environment of use to choose the type of sensor with the right specifications.

Temperature sensors are often used to measure high temperature values. During use, attention should be paid to ambient factors such as light, measurement angle, and vibration of the handle, as they may affect the accuracy of the device.

Choosing the right type of industrial temperature sensor to meet technical requirements, quality, and price can be challenging for many people. Therefore, it is advisable to look for a reputable and professional supplier.

8. Conclusion

Above is useful information about the types of temperature sensors, along with factors to consider when buying and using this device. Understanding the operating principle, structure and specifications of temperature sensors will help you choose the right product for your needs, ensuring measurement efficiency and safety in practical applications. In addition, if you want to stay up-to-date with the latest advanced technologies and market trends, join NEPCON 2024 – Vietnam’s leading exhibition on SMT, inspection technology, equipment, and electronics manufacturing supporting industry organized by RX Tradex Vietnam. Register now for exhibitors or visitors.