Provisional Low Temperature Scale of 2000
The Provisional Low Temperature Scale of 2000 is an equipment calibration standard for making measurements of very low temperatures, in the range of 0.9 mK to 1 K, adopted by the International Committee for Weights and Measures in October, 2000. It is based on the melting pressure of solidified helium-3.
At these low temperatures, the melting pressure of helium-3 varies from about 2.9 MPa to nearly 4.0 MPa. At the temperature of approximately 315 mK, a minimum of pressure occurs. Although this gives a disadvantage of non-monotonicity, in that two different temperatures can give the same pressure, the scale is otherwise robust since the melting pressure of helium-3 is insensitive to many experimental factors.
