An interesting question about thermocouples; feel free to discuss it

I’ll grab the sofa first; I’m just mentioning it casually for now. The thermocouple on the left is the most conventional design, while the one on the right is twisted into a spiral shape. Assumption 1: If the twisted region is not short-circuited, will the temperature measurement be consistent with that in the left diagram? ； Assumption 2: If the twisted regions come into contact, the temperature measurement point should theoretically move downward ； Assumption 3: If the twisted region is not short-circuited, but becomes short-circuited due to thermal expansion after heating to a certain temperature, does the temperature measurement point also move downward? Can we assume some interesting things for later on, such as a higher temperature in the upper part and a lower temperature in the spiral-shaped area? Will the temperature rise and fall from time to time?

The temperature measurement of a thermocouple is based on the different electromotive forces generated by the material at its sensing end at various temperatures; this sensing end consists of just a small portion of material, which is usually made from precious metals. In the picture behind, if the wires are shorted, that means the thermocouple has failed

Maybe I didn’t explain it clearly; it’s not that the wires are shorted, but rather all the elements in the diagram are thermocouple wires, for example, all of them are of the K-type or S-type.

The question raised by the original poster is really good, but the issue with thermocouples is truly confusing for ordinary people!

Generally, the wire of precious metal thermocouples is made using the two methods mentioned by the original poster for forming the hot junction: the R/S/B type platinum-rhodium thermocouples usually employ the first welding method, probably because the platinum-rhodium wire is relatively flexible, allowing the small ball-shaped junction to remain intact for an extended period of time； Tungsten-rhenium thermocouple wires designed for higher temperatures are relatively rigid; only a small ball junction is welded at their end. At ultra-high temperatures (1700°C), these wires may break, preventing the formation of a complete circuit. Therefore, it is necessary to wrap and secure additional tungsten-rhenium wire around the thermocouple junction to extend its lifespan. Attached are a few photos that people usually don’t see:

Occasionally, the thermocouple breaks; if there is a spare thermocouple available, simply twist the ends of its wires into a twist shape, and temperature measurement will not be affected.

There are two conditions required for a thermocouple to generate a temperature difference: a temperature gradient and two metals of different materials; nothing else matters, as the temperature will remain the same even if a hundred knots are made.