Thermocouples

Abstract Thermocouples are widely used in various applications in medicine and biomedical engineering. The sensors are accurate, flexible, well documented, and not too expensive. Thus they are considered to have the best cost/performance ratio for many applications. Thermocouples are based on the thermoelectric Seebeck effect, which gives an electric potential between the junctions of two dissimilar metallic conductors when the junctions are held at different temperatures. Virtually every pair of metallic conductors are possible to use, but for practical reasons standardized thermocouples with determined thermoelectric properties and temperature/potential relation are used. As all temperature sensor thermocouples are associated with various kinds of measurement errors. Some are specific for thermocouples, but the most important is based on the fact that every contact sensor only measures its own temperature. The sensor should therefore be in good thermal contact with the measuring object in order to obtain an accurate temperature at a reasonable time. Depending on, for example, the present temperature gradients and the heat flux in the probe compared to its surroundings, significant and even substantial deviations and uncertainties can easily occur. Another important source of measurement errors is electromagnetic (EM) interference, which is particular troublesome in EM induced thermal treatment applications when temperature measurement is carried out in strong fields.