For high temperature measurement, thermocouple sensors are recommended. Dietmar introduces the working principle of TCs, their applications, and the importance of regular sensor replacement especially in critical applications to avoid sensor drift.
VideoMultiple industries03.12.2024
Thermocouples (TCs) work by connecting two different metals or alloys. Due to differences in heat conductivity and electron movement, a small voltage is produced relative to the temperature difference between measuring junction and reference junction, known as the thermoelectric or Seebeck effect. The measurement or hot junction is where the metals are welded together and the reference or cold junction is where the voltage is measured. As the measurement is differential, the cold junction’s temperature must be known to determine the actual temperature.
The voltage produced by thermocouples is very small, requiring precise electronics in the temperature transmitter. Standardized thermocouple pairs include type K (Chromel and Alumel), which is popular and produces a 45 mV signal at a 1000 °C (1832 °F) difference. For higher temperatures, noble thermocouples like type S (Platinum and Platinum-Rhodium) are used, producing a 15 mV signal at 1500 °C (2732 °F).
Studies show that thermocouples can drift 3-6 % per year. This drift occurs because the Seebeck voltage, produced by the difference between two alloys, decreases over time as the materials mix. This can happen through gas phase or diffusion, affecting the accuracy of the measurement. The only solution for maintaining temperature measurement accuracy is to regularly replace TC sensors in critical applications.
At the end of the course you will know about the features of the PROFINET technology and the PA profiles, network design of 100BaseTX and Ethernet-APL.
