The thermocouple is a temperature sensor that provides a small millivolt
signal that ranges between 10-80 mV. Thermocouples are made by connecting
two dissimilar metals at one end to form a junction. The theory of operation
of the thermocouple can be explained by the Seebeck effect, which was discovered
by Thomas Seebeck in 1821. The amount of voltage that the thermocouple
produces depends on the two types of metal that are used to form the junction.
When Seebeck made this discovery in 1821, the thermocouple was not useful
because the small amount of voltage that was produced in the millivolt
range could not be amplified at the time.