How to choose a thermocouple?

    Thermocouple is the most common contact type temperature measuring element, which occupies a very important position in the field of temperature measurement. In order to cope with various temperature measurement environments, many types have been produced. The national standard lists 7 types, and the index numbers are: S, B, R, E, K, J, T, of which S, R, and B belong to precious metal thermocouples. K, E, J, and T are low-cost metal thermocouples. The national standard stipulates the relationship between the thermoelectric potential and the temperature, the allowable error, and the thermocouple with a unified standard graduation table. It has a matching display instrument for selection. Non-standardized thermocouples are inferior to standardized thermocouples in the scope of use or order of magnitude, and there is generally no unified indexing table, which is mainly used for measurement in some special occasions.

    In different temperature measurement environments, we have to use different thermocouple types to ensure the accuracy of the temperature signal and the safety of the equipment. The selection of thermocouple should be based on comprehensive considerations such as the use temperature range, the required accuracy, the use atmosphere, the performance of the measurement object, the response time and the economic benefits.

    S-type, B-type, and K-type thermocouples are suitable for use in strong oxidizing and weak reducing atmospheres, and J-type and T-type thermocouples are suitable for weak oxidizing and reducing atmospheres. If a protective tube with better airtightness is used, the requirements for the atmosphere are not too strict.

    For durability, choose a thermocouple with a larger wire diameter, but the response is slower. For thermocouples with large heat capacity, the response is slow. When measuring a temperature with a large gradient, in the case of temperature control, the temperature control is poor. It requires a fast response time and a certain degree of durability, so it is more appropriate to choose an armored couple.

    The temperature measurement of moving objects, vibrating objects, and high-pressure vessels requires high mechanical strength. Chemically polluted atmospheres require protective tubes. In the case of electrical interference, higher insulation is required.

(Huiputech)