On the thermodynamic accuracy of the ITS-90: platinum resistance thermometry below 273 K

摘要

An analysis of the resistance-temperature relationship for six low-temperature platinum resistance thermometers is carried out to determine the thermodynamic accuracy of the ITS-90 below 273 K. The use of smooth thermodynamic functions in a model equation for platinum resistance indicates that there is a significant deviation of the ITS-90 from thermodynamic values over the range 80 K to 270 K. The deviation is consistent with recent results in acoustic and gas thermometry, namely around 10 mK at 150 K. For this reason a re-evaluation of the existing thermodynamic data on the temperature scale appears warranted.