2007 Volume 43 Issue 4 Pages 271-276
0.65μm radiation thermometers are used as the standard thermometers at high temperatures. The stability of these thermometers influences largely the calibration uncertainty. Little information is available about the longterm output stability. Therefore, we studied the long-term output stability of ten 0.65μmradiation thermometers by conducting repeated calibration with the fixed-point blackbodies. Most radiation thermometers showed the tendency that the output signal increased in course of time. Some increases were ascribed to the filter wavelength change. When the center wavelength of the filter shifted to a longer wavelength, the output signal increased. Some thermometers showed a one percent decrease in a short period. These decreases were recovered after cleaning the objective lens. Therefore it is important to be careful not to contaminate the objective lens. The long term stability of the normal thermometer output is estimated to be within2% per year including the wavelength contribution and 0.2% per year for the gain contribution.
