| Popis: |
EMF drift and changes in Seebeck coefficient were examined in metal-sheathed Ni-based thermocouples held at temperatures in the range 500-1100 degrees C for up to 1000 h. In 200 h, EMF drifts of up to the equivalent of 10 degrees C were observed and a subsequent reduction in immersion caused a drop of 80 degrees C. The analysis of X-ray spectra showed the presence and migration of Mn to be the main contributor to instability. The most stable configuration examined was the Inconel-sheathed Nicrosil/Nisil thermocouple. It is suggested that the optimum Ni-based thermocouple is one having Nicrosil and Nisil thermoelements and a Nicrosil sheath. |
