Solution When The Thermocouple Is Not Constant
Most of the thermocouples are used for temperature measurement. In many industrial productions, the use of thermocouples is inseparable, but many people still don’t understand the knowledge of the use of thermocouples, so let’s do it for you. A specific introduction to this knowledge.
For thermocouples used as reference and standard, it is best to perform annealing after each indexing point when indexing. For precious metal thermocouples, the annealing procedure is very important. In the verification procedure of standard thermocouples, it is stipulated that standard thermocouples must be cleaned and annealed before verification to eliminate the contamination and stress of thermocouples, thereby improving the metallographic structure of the wire material and improving measurement stability.
In the process of production and processing of thermocouples, the surface of the couple wire is always contaminated after multiple reductions and stretching. At the same time, judging from the internal structure of the even wire. There is inevitably stress and lattice inhomogeneity. The inconsistency of these physical states affects the Seebeck coefficient of the couple wire and affects the instability of the thermocouple's indicated value. Therefore, a thermocouple that is unqualified for annealing cannot be used for accurate temperature measurement.
The stress introduced by quenching or cold working can be basically eliminated by annealing. The indication error caused by unqualified annealing can vary from a few tenths of a degree to a few degrees. It is related to the temperature to be measured and the temperature gradient on the thermocouple electrode. Cheap metal thermocouple wires are usually delivered in an "annealed" state. If you need to anneal cheap metal thermocouples for high temperature use, the annealing temperature should be higher than the upper limit of the use temperature, and the insertion depth should be greater than the actual use depth.
The above analysis has analyzed the reasons for the instability of thermocouples and the various effects that may be caused by this. It can be seen that the interference of electrical characteristics on thermocouples is extremely important, and the normal use of products can only be ensured by maintaining stability.
