Consistency of the Temperature Scales above the Silver Freezing Point Realized at Four Different Spectral Bands

Above the freezing point of silver, the definition of the ITS-90 allows us to select the spectral band and the bandwidth of the radiance comparator and to choose a reference radiance blackbody from the silver, gold, and copper freezing points. We realized the ITS-90 in reference to a copper point blackbody using a radiation thermometer with four different spectral bands. The spectral characteristics of the thermometer were separately measured at each band using a spectral responsivity comparator with a silicon photodiode as a reference detector. To confirm the consistency of the scales we measured the temperature of a silver point blackbody and compared the value with that defined by the ITS-90. We also compared the scales realized at the different bands using a variable temperature blackbody from 800rfloorC to 2500rfloorC. The measured temperature of the silver point agrees with the definition within 10 mK and the realized scales agree with each other within the uncertainty of the scales