The International Temperature Scale of 1990 (ITS90) is defined from 0.65 K upwards to the highest temperature measurable by spectral radiation thermometry, the radiation thermometry being based on the Planck radiation law. Part I of this paper describes the realization of contact thermometry up to 1234.93K for which the ITS-90 is defined in terms of calibration of thermometers at 15 fixed points and vapor pressure/temperature relations which are phase equilibrium states of pure substances. The realization is described by the assembly of fixed-point devices using samples of highest available purity and by the construction of suitable temperature-controlled environments to achieve the defining equilibrium states to calibrate thermometers. The high quality of the temperature realization and measurements are well documented. Various research efforts are described, including research to improve the uncertainty in thermodynamic temperatures by measuring the velocity of sound in gas up to 800K, research in applying noise thermometry technique, and research on thermocouples. Thermometer calibration services and high-purity samples and devices suitable for on-site thermometer calibration that are available to the thermometry community are described. Part II of the paper describes the realization of temperature above 1234.93 K for which the ITS-90 is defined in terms of the calibration of spectroradiometers using reference blackbody sources that are at the temperature of the equilibrium liquid to solid phase transition of pure silver, gold, or copper. The realization of temperature from absolute spectral or total radiometry over the temperature range from about 60 K to 3000 K is also described. The dissemination of the temperature scales using radiation thermometry from NIST to the customer is achieved by calibration of blackbody sources, tungsten strip lamps, and pyrometers. As an example of the research efforts in absolute radiometry, which impacts the NIST spectral irradiance and radiance scales, results with filter radiometers and a high temperature blackbody are summarized.
Citation: Journal of Research (NIST JRES) -
Volume: 106 No. 1
NIST Pub Series: Journal of Research (NIST JRES)
Pub Type: NIST Pubs
acoustic thermometry, blackbody sources, gas thermometry, Johnson noise thermometry, Kelvin, pyrometers, radiation thermometry, SPRTs, thermocouples