Title: Scaling of thermoelectric inhomogeneities with temperature in platinum–rhodium alloyed thermocouples
Abstract:Abstract Thermoelectric inhomogeneities of type S, type R and Pt-20%Rh/Pt thermocouples were determined in the temperature range between 200 °C and 1000 °C in temperature steps of 50 °C. Immersion pro...Abstract Thermoelectric inhomogeneities of type S, type R and Pt-20%Rh/Pt thermocouples were determined in the temperature range between 200 °C and 1000 °C in temperature steps of 50 °C. Immersion profiles with each thermocouple at each of the 16 scanning temperatures were measured. From the measured temperature dependencies of the inhomogeneities, methods were derived how thermoelectric inhomogeneities measured at only one or two scanning temperatures are quantitatively transferred to other temperatures or temperature ranges. For this purpose, thermoelectric inhomogeneities were classified as irreversible and reversible inhomogeneities, as they must be treated differently. Irreversible thermoelectric inhomogeneities can be extrapolated linearly with temperature or electromotive force from only one immersion profile measurement at an arbitrary temperature to other temperatures in the temperature range investigated. Reversible inhomogeneities in Pt/Rh alloyed thermocouples must be taken as a kind of unavoidable background inhomogeneity (noise) whose amplitude essentially depends on the alloy composition. The distinction between reversible and irreversible inhomogeneities is made by measuring immersion profiles at two scanning temperatures: first at a temperature between 400 °C and 450 °C, where reversible inhomogeneities have a maximum value and at a temperature between 600 °C and 700 °C, where reversible inhomogeneities have a minimum in contrast to irreversible inhomogeneities.Read More