Thermoelectric hysteresis in Nicrosil and Nisil

Hysteresis in the Seebeck coefficients of the thermocouple alloys Nicrosil and Nisil was studied over the temperature range, 200 to 1200 degrees C, for heating periods up to 300 h. The alloys were thermoelements in Nicrosil-sheathed mineral-insulated cable. For both alloys hysteresis peaks were found near 400 and 700 degrees C. In Nicrosil the lower temperature peak was small (<0.05 mu V K-1) and the peak near 700 degrees C increased rapidly to about 0.3 mu V K-1) for 50 h of heating and changed little thereafter. Both peaks in Nisil were about 0.2 mu V K-1 in magnitude after 100 h of heating and increased steadily with time, reaching 0.3 mu V K-1 at 300 H. The study showed that hysteresis was the main cause of instability in such thermocouples and suggested that hysteresis in Nisil could be greatly reduced during manufacture.