Abstract
0.65μm radiation thermometers are used as the standard thermometers at high temperatures. The spectral stability of these thermometers influences largely on the calibration uncertainty. Little information is available about the spectral stability. Therefore, we studied the long-term spectral stability of ten 0.65μm radiation thermometers. Most radiation thermometers had the tendency that the effective wavelengths moved to longer wavelengths in course of time. Some thermometers showed that their effective wavelengths moved at a rate about 0.1 nm/year. Interference filters with hard coating showed very stable effective wavelengths. Three radiation thermometers showed large changes in effective wavelengths and once the effective wavelengths started to move, they did not stop. Thermometers with their effective wavelengths moving more than 0.2 nm/year need to be repaired with the filter. The scale of standard radiation thermometers should be managed on the base of this knowledge.
