How does a thermocouple measure temperature?

A thermocouple works on the Seebeck effect - when two dissimilar metals are joined at one end (hot junction) and exposed to different temperatures at the other end (cold/reference junction), a voltage proportional to temperature difference is generated. Common types include Type K (Chromel-Alumel, -200 to 1260 degrees C), Type J (Iron-Constantan), and Type T (Copper-Constantan). They are rugged, self-powered, and suitable for high-temperature applications.