Thermocouples

       Thermocouples are formed by welding the metals from each of their ends to the ends of another metal that have different alloys.  If we heat the thermocouples from their welding points, they produce an mV equaled to the characteristic of the metal couple from their free ends. This value gives us the heat information. There are various mV tables belonging to any element type. According to those tables, heat information is changed to industrial state. 
Thermocouples cannot be used in processes with such states; they need carrier sheaths protecting them against external factors. These sheaths vary depending on the process in which it will work. Thermocouples can rise to higher temperatures in contrast with thermoresistances. 
- Between 200? 1800 °C: here, alloy of thermocouple and wire diameter are important and it must be selected accordingly.  Since thermocouples consist of two different alloys, they are produced with compensation wires that have the same characteristics. They have some key advantages like having resistance to process conditions and making faster measurement than thermoresistances, although they have lower linearity compared to thermoresistances.


WORKING AREAS OF THERMOCOUPLES

• Fe-Const (J type) -200- 800 °C
• NiCr-Ni (K type) -200- 1200 °C
• Chromel-Alumel (K type) -200- 1200 °C
• Pt%10Rh-Pt (S type) 0- 1600 °C
• Pt%13Rh-Pt (R type) 0-1700 °C
• Pt%30Rh-Pt%6Rh (B type) 0-1800 °C
• Cu-Const (T type) -200 -300 °C
• Pt 100 -200 -850 °C