A thermocouple consists of two wires made of different alloys. Each of these wires generates a specific voltage as soon as one end is warmer than the other. When the two wires are connected, the difference in voltage between them can be measured. This difference is called thermoelectric voltage.
How exactly is thermoelectric voltage generated?
Every electrical conductor contains free electrons. They can move within the conductor, thereby enabling, for example, an electric current to flow.
In very simplified physical terms, these free electrons occupy a certain amount of space, which increases with temperature.
In a uniformly heated copper conductor, this region is approximately the same size. This is shown schematically in Figure 1.
Now heat one end of the ladder.
This increases the range of motion of the free electrons in this region. Because like charges repel each other, the more highly energized electrons “push” the rest toward the cold end.
As a result, there is a shortage of electrons at the heated end and an excess at the cold end. This creates a voltage.
Important to know: The voltage level is mainly influenced by the chemical composition of the wire and the temperature difference!
However, the voltage from a single wire is not enough to generate a signal. Therefore, a second wire is needed. Both wires should be connected at the point with the highest temperature.
The voltage difference between the two wires serves as a signal and is defined as thermoelectric voltage.
