Use of primary frequency standards for estimating the duration of the scale unit of Tai

摘要

The accuracy of International Atomic Time TAI is based on a small number of primary freqency standards (PFS) that aim at realizing the SI second, the unit of proper time. Following the 14~th meeting of the consultative Committee for Time and Frequency (april 1999)_, the BIPM time section is reconsidering how the PFS comparisons are used for evalauting the duration of the scale unit of TAI, u_TAI' and how they are reported in Circular T and other BIPM publications. In the new procedure, it is proposed to break down the estimation of the uncertainty of the comparison in several elementary components and to report all of them in the BIPMpublications in order to make the uncertaitny evalaution more tansparent and traceable. The BIPM also regularly computes an estimation of the duration of the scale unit of TAI using an accuracy algorithm combining the data of all PFS. The parameters used in this algorithm are re-evalauted and a new estimation of u_TAI has been carried out over the recent years. The standard uncertainty on this value is now estimated to be 3x10~(-15).