A Concerted IInternational Project to Establish High-Temperature Fixed Points for Primary Thermometry

Research into high-temperature fixed points above 1,100◦C has made significant progress since they were first reported in 1999. In particular, it has been established that single cells are repeatable at the sub-50mK level, and intra-cell reproducibility at the 100mK level has been demonstrated even at temperatures as high as 2,500◦C. The fixed points have been used to compare temperature and radiometry scales over a wide temperature range, and are being developed and established as secondary references for thermocouple calibrations. However, before they can be fully accepted as primary temperature references, much work remains to be done, namely: (1) Establishment of long-term stability of the fixed-point temperature; (2) Development of robust procedures for the reliable construction of the fixed-point cells (to ensure routine intra-cell reproducibility of 100mK); (3) Demonstration of long-term robustness of the fixed-point cells; (4) Assignment of thermodynamic temperatures to a selected set of fixed points; (5) Agreement and acceptance of these temperature values by the CCT; (6) Agreed methods on how to take full utility of these new fixed points into any future IInternational Temperature Scale (ITS)—or the current ITS-90