Thermocouple temperature sensor is a commonly used temperature measurement equipment, its working principle and structural characteristics can be summarized as follows:
. Working principle
The working principle of thermocouple temperature sensors is based on the thermoelectric effect, specifically the Seebeck effect. When two different metals or alloy materials are connected together and there is a temperature difference at the connection point, an electromotive force is generated in the circuit, which is proportional to the temperature difference and can be used to measure temperature.
The specific process is as follows:
- Thermoelectric effect
Thermoelectric effect: Because the thermoelectric potential coefficients of two metals or alloy materials are different, when they are connected together and at different temperatures, an electromotive force is generated in the circuit.
- Measure the temperature
By measuring the size of this electromotive force, it is possible to determine the temperature difference at the point where the two metals join, and then infer the temperature of the other metal (i.e. the temperature of the hot end) from the known temperature of one metal.
. Two-structure feature
Thermocouple temperature sensor mainly consists of the following parts:
- Thermal element
The thermal element is the core part of the thermocouple sensor, usually made of two different metal alloy wires or wires welded together. Common metal materials are copper, iron, nickel, chromium and so on. The solder joints of these two metal wires form a measuring point, called the cold end contact of the thermocouple (also called the compensation end), while the other end is the hot end (also called the measurement end). When the thermal element is subjected to a change in temperature, a thermoelectric effect occurs between the two metals, resulting in a weak potential difference.
- Protect the shell
Protective housing: In order to protect the thermosensitive element from environmental effects such as mechanical damage and corrosion, thermocouple sensors usually come with a protective housing. This shell is usually made of metal or ceramic material, which has good insulation and high temperature resistance. It can prevent the sensor from being interfered by external physical and chemical factors, and ensure the accuracy and stability of the measurement results.
- Lead wires
Leads: Thermocouple sensors use leads to connect the thermal element to a reading meter or control system. The leads are usually made of metal wires of the same material as the thermocouple to ensure continuity and reliability of the measurement signal. The length and material of the lead should be selected according to the specific application requirements to avoid signal attenuation and interference.
. Three types
According to the different structural forms and materials, thermocouple sensors can be divided into many types, such as ordinary thermocouples, armored thermocouples and thin film thermocouples. Among them:
- Ordinary thermocouple
Widely used in industry, it is generally composed of a thermal electrode, an insulating sleeve, a protective tube and a junction box. Ordinary thermocouples can be divided into fixed thread connection mode, fixed flange connection mode, movable flange connection mode, no fixed device and other forms according to the connection form of its installation.
- Armored thermocouple
Also known as the sleeve thermocouple, by the thermal electrode, insulation material and metal sleeve three tensile processing of a solid combination. It is characterized by the fact that it can be made thin and long, and can be bent arbitrarily when used according to needs. The main advantages of armored thermocouples are small thermal inertia at the temperature measuring end, fast dynamic response, high mechanical strength, long life, can be installed on the complex structure of the device, is widely used in various industrial production.
- Film thermocouple
Using vacuum evaporation, chemical coating and other processes, the thermocouple material is deposited on the insulating substrate to form a very thin metal film. The measuring end of the thermocouple is very thin, so its thermal inertia is small, the reaction speed is fast, and it is often used to measure the instantaneous change of the surface temperature and the temperature change on the small area. Its temperature range is -200~300℃.
Thermocouple temperature sensor has the advantages of simple structure, wide measuring range, fast response speed, good stability, etc., and has been widely used in industry, scientific research, medical treatment and other fields.