How to control the stability of the thermocouple
Thermocouple is one of the most accurate and economical products in the development of measuring sensors, so it has become one of the most widely used types of temperature measuring elements. It directly measures temperature. The appearance of various thermocouples is often very different due to their needs, but their basic structure is generally the same. They are usually composed of main parts such as thermal electrodes, insulation protection tubes and junction boxes, and are usually associated with display instruments, recording instruments and electronic regulators Supporting the use of. Thermocouples measure the temperature difference between their hot and cold ends. In order to obtain the absolute temperature of the hot-end sensing point, the cold-end temperature must be measured and the thermocouple output adjusted accordingly. Now, the cold junction at the input end of the thermocouple signal processing unit is at the same temperature, usually maintained by a sheet of material with high thermal conductivity. Copper with a thermal conductivity of 381 W / mK is an ideal material. The input connections must be electrically isolated and thermally connected to the chip. The entire signal processing unit should ideally be in this isothermal environment.
The stability of the thermocouple depends on the temperature and the climate. How can the stability of the thermocouple be controlled? For the same sensor, for example, the maximum use temperature of a K-type thermocouple also changes due to different diameters. K-type thermocouples with the same diameter also have different stability due to different structures. When selecting a thermocouple, you must Considering the use conditions: common temperature and maximum use temperature; redox atmosphere, etc .; anti-vibration performance. For assembled thermocouples, the influence of the atmosphere depends first on the material of the protection tube and the structure of the thermocouple. It is necessary to protect the physical and chemical properties of the tube material. For example, in the powder metallurgy industry, molybdenum tubes are often used as thermocouple protection tubes. Under the H2 atmosphere of 1600 degrees Celsius, the effect is better, but the molybdenum tube is oxidizing. In the atmosphere, it is damaged by oxidation in a short time.