Hysteresis in Thermoelectric E.M.F. of Platinium vs Platinium-10% Rhodium Thermocuples

Abstract

A study on changes of hysteresis characteristic in thermoelectric e.m.f. of Pt vs Pt-Rh 10% thermocouples is described.
The hysteresis changes of thermoelectric power appear mainly on the Pt-Rh 10% element, and are determined by the heating conditions in use, such as heating temperature, heating time, and cooling rate.
Moreover characteristics of the hysteresis vary according to the degree of cold working and the annealing temperature of the element.
The e.m.f. changes caused by the hysteresis are calculated under some practical conditions, and actually confirmed by silver freezing point measurements and intercomparison tests on several thermocouples.
As a result of these trials, an e.m.f variation amounting up to±3μV is found in case of unconditional use, but it is reduced to the order of±0.5 μV by application of a constant heat treatment before every measurement.