Methods of formation of Hot junction
To form the hot junction, a suitable method has to be adopted to obtain a good electrical contact between the thermocouple wires.
For Chromal/Alumal and other combinations, for use in high temperature measurements, welding is the only method to obtain a suitable joint. For this purpose Tig welding & Laser beam welding is mostly used.
Tig welding
Gas tungsten arc welding (GTAW), also known as tungsten inert gas (TIG) welding, is an arc welding process that uses a non-consumable tungsten electrode to produce the weld. The weld area is protected from atmospheric contamination by a shielding gas.
Laser beam welding
Laser beam welding (LBW) is a welding technique used to join multiple pieces of metal through the use of a laser.
The beam provides a concentrated heat source, allowing for narrow, deep welds and high welding rates. LBW is a versatile process, capable of welding carbon steels, HSLA steels, stainless steel, aluminum and titanium. The speed of welding is proportional to the amount of power supplied but also depends on the type and thickness of the workpieces.