One of the most frequently used temperature transducers is the thermocouple. Thermocouples are very rugged and inexpensive and can operate over a wide temperature range.
A thermocouple is created whenever two dissimilar metals touch and the contact point produces a small open-circuit voltage as a function of temperature.
This thermoelectric voltage is known as the Seebeck voltage, named after Thomas Seebeck, who discovered it in 1821. The voltage is nonlinear with respect to temperature.
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