Two factors affecting temperature measurement of K-type thermocouple
1.The influence of the short-range order structure change (K state).
When the K-type thermocouple is used in the temperature range of 250℃-600℃, its microstructure changes, forming a short-range order structure. Therefore, it will affect the thermoelectric potential value. An error occurs, which is the so-called K state.
2.The influence of thermocouple wire inhomogeneity.
A. The thermocouple material itself is not homogeneous.
B. The inhomogeneity of thermocouple wire after use. For the newly made thermocouple, even the uneven thermoelectromotive force can meet the requirements. However, after repeated processing and bending, the thermocouple will be deformed and will lose its homogeneity. And When the thermocouple is in use for a long time at high temperature, the thermoelectromotive force will change due to the deterioration of the couple wire.
The failure rate of the thermocouple also increases with the increase of its length. All are affected by the inhomogeneity of the thermocouple wire.
In short, the error caused by the inhomogeneity, that is, the parasitic electromotive force, depends on the degree of inhomogeneity of the thermocouple wire itself and the size of the temperature gradient, and it is extremely difficult to quantify it.
