Two conductors with different compositions (called thermocouple wires or hot electrodes) are connected at both ends to form a loop. When the junction temperature is different, electromotive force will be generated in the loop. This phenomenon is called thermoelectric effect, and this electromotive force is called thermoelectric potential. Thermocouple uses this principle to measure temperature, in which one end directly used to measure the temperature of medium is called working end (also called measuring end) and the other end is called cold end (also called compensation end); The cold end is connected with a display instrument or a supporting instrument, and the display instrument will point out the thermoelectric potential generated by the thermocouple.

Thermocouple is actually an energy converter, which converts thermal energy into electrical energy and uses the generated thermoelectric potential to measure temperature. For the thermoelectric potential of thermocouple, we should pay attention to the following problems:

1: Thermoelectric potential of thermocouple is the difference of temperature function between two ends of thermocouple working end, not the function of temperature difference between cold end and working end of thermocouple;

2. When the thermocouple material is uniform, the thermoelectric potential generated by the thermocouple has nothing to do with the length and diameter of the thermocouple, but only with the composition of the thermocouple material and the temperature difference between the two ends;

3. When the material composition of two thermocouple wires is determined, the thermoelectric potential of thermocouple is only related to the temperature difference of thermocouple; If the temperature at the cold end of the thermocouple remains unchanged, the thermoelectric potential of the thermocouple is only a single-valued function of the temperature at the working end. Weld two conductors or semiconductors A and B of different materials into a closed loop, as shown in the figure. When there is a temperature difference between the two persistent points 1 and 2 of conductors A and B, electromotive force will be generated between them, thus forming a certain amount of current in the loop. This phenomenon is called thermoelectric effect. Thermocouples work by this effect.

Features,

◆ Simple assembly and convenient replacement.

◆ Pressure spring type temperature sensing element with good seismic performance.

◆ Large measuring range

High mechanical strength and good pressure resistance.

Scope of work The commonly used graduation numbers of industrial thermocouples mainly include S, R, B, N, K, E, J, T, etc. Among them, S, R and B belong to noble metal thermocouples. N, K, E, J and T belong to cheap metal thermocouples. T and S graduation numbers are characterized by strong oxidation resistance and should be used continuously in oxidation and inert atmosphere. The long-term service temperature is 1400℃, and the short-term service temperature is 1600℃. Among all thermocouples, the S scale has the highest accuracy level and is usually used as a standard thermocouple. Compared with the S scale, the R scale has almost the same performance except that the thermal electromotive force is about 15%. The thermoelectromotive force of scale B is very small at room temperature, so it is generally unnecessary to compensate the conductor when measuring. Its long-term service temperature is 1600℃, and its short-term service temperature is 1800℃. It can be used in oxidizing or neutral atmosphere, and can also be used in vacuum for a short time. N-scale thermometer has the characteristics of strong oxidation resistance at high temperature of 1300℃, good long-term stability and short-term thermal cycle reproducibility of thermoelectromotive force, good nuclear radiation resistance and low temperature resistance, and can partially replace S-scale thermocouple. K index number is characterized by strong oxidation resistance and is suitable for continuous use in oxidizing and inert atmosphere. Long-term service temperature 1000℃, short-term service temperature 1200℃. It is widely used in all thermocouples. The characteristic of E-scale degree is that among the commonly used thermocouples, its thermoelectromotive force is the largest, that is, its sensitivity is the highest. It is suitable for continuous use in oxidation and inert atmosphere at 0-800℃; The characteristic of J-scale number is that it can be used in both oxidizing atmosphere (the upper limit of temperature is 750℃) and reducing atmosphere (the upper limit of temperature is 950℃). It is resistant to H2 and carbon monoxide gas corrosion, and is mostly used in oil refining and chemical industry. T-scale is characterized by the highest accuracy among all cheap metal thermocouples, and is usually used to measure the temperature below 300℃. 、

Thermocouples are used in almost all industrial fields, such as steel, power generation, petroleum, chemical industry, glass fiber, food, glass, pharmacy, ceramics, non-ferrous metals, heat treatment, aerospace, powder metallurgy, carbon, coking, printing and dyeing.

Manufacturer,

China's thermocouple market is small, with an annual output value of about 3 billion. Products made of precious metals such as nickel, copper, platinum and rhodium. It's not as big as 2 yuan a box of milk, and it's all loose. Because there is almost no technical and financial threshold for producing thermocouples, it is relatively easy to enter. Individual and private enterprises in Tianchang, Anhui, Xinghua, Jiangsu, and Yueqing, Zhejiang have flourished, and fierce competition has led to a mixed market.

practical application

Thermocouples are used in almost all industrial fields, such as steel, power generation, petroleum, chemical industry, glass fiber, food, glass, pharmacy, ceramics, non-ferrous metals, heat treatment, aerospace, powder metallurgy, carbon, coking, printing and dyeing.