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Thermocouples are probably the most popular temperature sensors in use today. Basic models are relatively accurate, low cost, interchangeable, and can measure a wide range of temperatures. Accurate temperature measurement is one of the most common tasks faced by professionals in modern industrial and control design. This section is intended to provide an introduction to the “laws” which govern thermocouples, and the physics behind why they work.
In 1822, a discovery by Thomas J. Seebeck paved the way for the modern thermocouple. Seebeck discovered that when two dissimilar metals are connected (junctioned) together, an electric current will flow between them when one metal is heated with respect to the other. This phenomena is known as the Seebeck Effect. This current will continue to flow as long as the two junctions, known as the “hot” junction and “cold” junction, are at different temperatures. The magnitude and direction of the current is affected by the types of metals used, and the temperature difference between the hot and cold ends. There are standard tables available which show the voltage produced by a thermocouple at any given temperature for many of the more common thermocouple types. More will be covered on the actual use of thermocouples in the next section, but for now we’ll look at the reasons behind why thermocouples work the way they do.
In 1822, a discovery by Thomas J. Seebeck paved the way for the modern thermocouple. Seebeck discovered that when two dissimilar metals are connected (junctioned) together, an electric current will flow between them when one metal is heated with respect to the other. This phenomena is known as the Seebeck Effect. This current will continue to flow as long as the two junctions, known as the “hot” junction and “cold” junction, are at different temperatures. The magnitude and direction of the current is affected by the types of metals used, and the temperature difference between the hot and cold ends. There are standard tables available which show the voltage produced by a thermocouple at any given temperature for many of the more common thermocouple types. More will be covered on the actual use of thermocouples in the next section, but for now we’ll look at the reasons behind why thermocouples work the way they do.
After much investigation of thermoelectric circuits several basic concepts have been conceived. These concepts can be summed up according to 3 fundamental “laws”.
