Spatial dependence of thermoelectric voltages and reversible heats

Abstract

Thermocouples are probably the most widely used temperature sensors in science and industry but perhaps also the most often misunderstood. The basic distinction between an ordinary resistance thermometer, in which the sensing element is localized, and a thermocouple circuit, in which potentials vary along the wires themselves, is most clearly shown by a treatment in which the spatial dependences of the phenomena are explicitly invoked. Such treatment is essential to analysis of measurement errors in thermocouple circuits. In this article, the basic equations of thermoelectricity are reviewed and their physical meanings discussed. The profile of the electrochemical potential for an illustrative example is then calculated from published data. Finally, the problem of a thermocouple in a static magnetic field is discussed.