Uncertainty budgets for realization of ITS-90 by radiation thermometry

Recent international comparisons [1,2] and key comparisons have shown that the realization of the International Temperature Scale of 1990 (ITS-90) above the freezing point of silver and its dissemination is more difficult than expected. In many cases, the deviations of the local scale realizations were larger than the combined estimated uncertainties could reasonably justify. On the other hand, it must be considered that the realization of the ITS-90 by radiation thermometry is a complex exercise involving a large number of operations with many influencing parameters. Furthermore, the key comparisons need a unified approach to the treatment of uncertainties. Consequently, a rigorous standard approach for the calculation of uncertainties is necessary. In this paper three different operational schemes have been identified for realizing the ITS-90 by radiation thermometry. For all three schemes an analysis is presented of the baseline parameters underlying the scale realization above the freezing point of silver with respect to their contribution to the uncertainty budget. The paper is a joint effort of the working group on radiation thermometry of the Consultative Committee for Thermometry (CCT) summarizing the knowledge and experience of all experts in this field.