Armoured thermocouple calibration is not stable, what are the factors release date: 2019 - 05 - 15 read number: zero

Armoured thermocouple with wide temperature range, fast response and dynamic error is small, flexible installation, high mechanical strength, good pressure resistance. Gas, liquid and vapor and solid surface or internal temperature can be in the range of 0-1300 ℃. Armoured thermocouple of electrodes by the two different conductor material composition. When measuring reference terminal temperature difference between the client and, produce thermoelectric potential, and temperature of the instrument shows that corresponds to the thermoelectric potential. Thermal hysteresis is the important factor of instability in the calibration. Lag is a short-term order/disorder phenomenon, when nickel-chromium alloy ( Such as K type) Between 200 ° C and 600 ° C ( The most common is 400 ° C) At the right time. Performance is when the temperature of the thermocouple is periodic change in the temperature range, the calibration will also change a few degrees. When heated or cooled to 200 ° C and 1000 ° C ( The most common is 750 ° C) When the N type thermocouple may lag 5 ° C. Lag under 900 ℃ for 2 ℃ and 3 ℃. For example, if use K type thermocouple under 500 ℃, can through the night under the 450 ℃ annealing treatment to reduce lag. Oxidation is another might affect the calibration of the phenomenon. Ni - because of the oxidation phenomenon Cr- Al alloy ( Such as nickel - Chrome *) In the 500 ℃ or higher air environment has a limited life span. A special form of oxidation is known as the 'green rot', it refers to the selective chromium oxide in the environment of the low oxygen content, such as restrictions in the air and the circulation in the jacket. Nickel - Chromium - Silicon oxidation temperature up to 1250 ℃ ( 2300̊F） And there is no chrome line. The third factor which influence the stability of the calibration is pollution. Mineral insulated, integration design, the concept is behind the metal sheathed thermocouples, covers the thermocouple wire and populate the sheath of extremely fine mineral oxides ( Usually a magnesium oxide) Insulators uniform compression seal internal space and eliminate the pollution. By forging, rolling, or about 85% of tensile compression of insulator is a solid material. This is useful, because the pipe can be bent and can make smaller the diameter of the parts. Do occur, however, the gas ( Such as water vapor or air) Intrusion. The components that make up the thermocouple wire or sheath can also occur in the diffusion of steam. Bentley and Morgan came to the conclusion that transistor by magnesium oxide manganese by gas diffusion effect on the thermocouple calibration is the largest.