The temperature sensor of a thermocouple utilizes the principle that when a closed circuit is formed with two different kinds of metals, an electromotive force (voltage) is generated if a temperature difference occurs between two junctions. Because the electromotive force is determined by the temperature at each junction, not by the temperature difference between the junctions, however, the temperature at the junction cannot be determined only by the electromotive force.
For your information, the junction brought into contact with or closer to the object whose temperature you want to measure is called a hot junction (or a temperature measuring junction) and the other one a reference junction.
