The Provisional Low Temperature Scale from 0.9 mK to 1 K, PLTS‐2000

The Provisional Low Temperature Scale from 0.9 mK to 1 K, PLTS‐2000, was adopted by the Comite International des Poids et Mesures in October 2000. It is defined using an equation for the melting pressure of 3He over the complete temperature range, and forms an extension of the International Temperature Scale of 1990, ITS‐90, below its lower limit of 0.65 K. An internationally‐accepted ultra‐low temperature scale is needed to provide the basis for reliable thermometry in the temperature range in which commercial dilution refrigerators operate, and at lower temperatures where experiments investigating the thermodynamic properties of 3He and other condensed matter are carried out in many research centres. This paper is a summary of a fuller publication describing the background and derivation of the scale, published in the Journal of Low Temperature Physics [1], and includes tables of values of melting pressure, pm / MPa, and temperature T2000 / K, and the derivative, dpm /dT2000 in MPa/K.