A thermocouple consists of two dissimilar metals, joined together at one end, and produce a small unique voltage at a given temperature. This voltage is measured and interpreted by a thermocouple thermometer.

The thermoelectric voltage resulting from the temperature difference from one end of the wire to the other is actually the sum of all the voltage differences along the wire from end to end

Thermocouples can be made from a variety of metals and cover a temperature range 200 oC to 2,600 oC.