In the process automation two measurement principles for temperature have asserted themselves as a standard:
RTD - Resistance temperature detectors: Measuring principle
The RTD sensor changes the electrical resistance with a change in temperature. They are suitable for the measurement of temperatures between -200 °C and approx. 600 °C and stand out due to high measurement accuracy and long-term stability. The sensor element most frequently used is a Pt100. As a standard, Endress+Hauser RTD sensors fulfill the IEC 60751 accuracy class A.
TC - Thermocouples: Measuring principle
A thermocouple is a component made of two different metals connected with each other at one end. An electrical potential (thermoelectric force) is caused due to the Seebeck effect at the open end if the connection and the free ends are exposed to different temperatures. With the help of the so-called thermocouples reference tables (see IEC 60584) the temperature at the connection (measuring junction) can be concluded.
Thermocouples are suitable for temperature measurement in the range of 0 °C to +1800 °C. They stand out due to the fast response time and high vibration resistance.