Selection of thermocouple thermometer

The fundamental characteristics of thermocouple thermometers have been grasped by many, so how should thermocouple thermometers stop making choices?

The characteristic of the S division mark is its strong antioxidant function, which is suitable for continuous application in an oxidizing and inert atmosphere, with a temporary application temperature of 1400 ℃ and a short-term application temperature of 1600 ℃. Among all thermocouples, the S scale has the highest accuracy grade and is commonly used as a scale thermocouple;

Compared to the S scale, the R scale has a 15% higher thermoelectric potential, but its other functions are almost identical;

The B division mark has a very small thermoelectric potential at room temperature, so there is no need to compensate for wires when measuring. Its temporary application temperature is 1600 ℃, short-term 1800 ℃. It can be applied in oxidizing or neutral atmospheres, as well as for short-term use under real conditions;

The characteristics of the N division mark are strong low-temperature oxidation resistance at 1300 ℃, good temporary stability of thermoelectric potential and reproducibility of short-term thermal cycles, good resistance to nuclear irradiation and high temperature, and the ability to replace the S division mark thermocouple;

The characteristic of K scale is its strong antioxidant function, which is suitable for continuous application in an oxidizing and inert atmosphere. The temporary application temperature is 1000 ℃, and the short-term application temperature is 1200 ℃. It is widely used in all thermocouples;

The characteristic of the E-scale is that it has the highest thermoelectric potential and sensitivity among commonly used thermocouples. It should be continuously applied in an oxidizing and inert atmosphere at a temperature of 0-800 ℃;

The characteristic of the J division mark is that it can be used in both oxidizing atmospheres (with a lower temperature limit of 750 ℃) and restorative atmospheres (with a lower temperature limit of 950 ℃), and is resistant to H2 and CO gas corrosion. It is commonly used in refining and chemical industries;

The characteristic of the T-scale is that it has the highest accuracy grade among all low-cost metal thermocouples, and is commonly used to measure temperatures below 300 ℃;

Because the data of thermocouples are relatively precious (especially when using precious metals), and the distance between the temperature measuring point and the instrument is far, in order to save thermocouple data and reduce costs, we usually use compensating wires to extend the cold end (free end) of the thermocouple to a temperature stable control room and connect it to the instrument terminal.

It must be pointed out that the effect of thermocouples on compensating wires only extends the thermoelectric electrode, causing the cold end of the thermocouple to move to the instrument terminal in the control room. It cannot eliminate the impact of temperature changes at the cold end on temperature measurement and cannot provide compensation. Therefore, other modification methods need to be taken to compensate for the impact of the cold end temperature t0 ≠ 0 ℃ on temperature measurement.