Physikalisch-Technische Bundesanstalt

The mayor tasks of the working group are fundamental primary thermometry for the new definition of the SI base unit kelvin and the realisation and dissemination of the International Temperature Scale (ITS-90) in the temperature range between 0.65 K and 273 K. For primary thermometry two methods are in use: dielectric-constant gas thermometry and constant-volume gas thermometry. For the realisation of the ITS-90, vapour-pressure thermometry and interpolating gas thermometry as well as the calibration of platinum resistance thermometers at the defining fixed points are necessary. The dissemination of the ITS-90 at low temperatures is mainly enabled by means of high-precision resistance thermometry with platinum and rhodium-iron sensors.