Temperature Measurement
Thermocouples, RTDs, wire configurations, cold junction compensation, thermowells, Seebeck effect, and sensor selection.
- Identify common thermocouple types and their temperature ranges
- Explain the Seebeck effect and cold junction compensation
- Describe RTD operating principles and wire configurations
- Select the appropriate temperature sensor for a given application
Leçon 1
Thermocouple Types, Materials & Accuracy
How Thermocouples Work
A thermocouple generates a small voltage (millivolts) when two dissimilar metals are joined at a junction and exposed to a temperature difference. This is called the Seebeck effect. The voltage produced is proportional to the temperature difference between the measurement junction (hot junction) and the reference junction (cold junction).
The most commonly used thermocouple for general industrial applications up to 1200 degrees C is the Type K thermocouple, made from chromel and alumel. This is a key exam fact.
| Type | Materials | Range | Accuracy | Common Use |
|---|---|---|---|---|
| K | Chromel/Alumel | -200 to 1200 C | Good | General industrial |
| J | Iron/Constantan | -40 to 760 C | Good | Lower temps, non-oxidizing |
| T | Copper/Constantan | -200 to 370 C | Best at low temps | Cryogenic, food |
| S | Pt/Pt-Rh | 0 to 1600 C | High | Laboratory, high temp |
Type K is the most commonly used thermocouple for general industrial applications. Thermocouples generate millivolt signals based on the Seebeck effect - the voltage from two dissimilar metals at different temperatures.