The International Temperature Scale of 1990 (ITS-90), for temperatures above the freezing temperature of silver, is defined with pyrometers which rely upon spectral radiance ratios to one of the silver, gold or copper freezing temperature blackbodies and the use of the Planck radiance law. However, due to the use of spectral radiance ratios, the temperature uncertainties of ITS-90 increase as the square of the temperature ratios. Such increases in the temperature uncertainties can be reduced by using absolute radiometry traceable to cryogenic radiometers, and the resulting temperature uncertainties can be smaller than those measured using the ITS-90 techniques. We describe the development and the characterization of an absolute pyrometer (AP1) constructed at NIST and calibrated using absolute radiance responsivity. The calibrations are performed with the pyrometer as a single unit and thus separate measurements of the lens transmittance and the spectral responsivities of the filters and detectors are not necessary. The temperature measurement capabilities of the AP1 are shown using the melt and freeze cycle of the gold-point blackbody.
Proceedings Title: Temperature, International Symposium | Eighth | Temperature: Its Measurement and Control in Science and Industry; Volume Seven | AIP
Issue: No. 1
Conference Dates: October 21-24, 2002
Conference Title: AIP Conference Proceedings
Pub Type: Conferences
absolute radiometry, gold freezing temperature, radiance responsivity, thermodynamic temperature