The application of White Rabbit precision time protocol (WR-PTP) in long-distance optical fiber links has been investigated. WR-PTP is an implementation of PTP in synchronous Ethernet optical fiber networks, originally intended for synchronization of equipment within a range of 10 km. This paper discusses the results and limitations of two implementations of WR-PTP in the existing communication fiber networks. A 950-km WR-PTP link was realized using unidirectional paths in a fiber pair between Espoo and Kajaani, Finland. The time transfer on this link was compared (after initial calibration) against a clock comparison by GPS precise point positioning (PPP). The agreement between the two methods remained within [Formula: see text] over three months of measurements. Another WR-PTP implementation was realized between Delft and Amsterdam, the Netherlands, by cascading two links of 137 km each. In this case, the WR links were realized as bidirectional paths in single fibers. The measured time offset between the starting and end points of the link was within 5 ns with an uncertainty of 8 ns, mainly due to the estimated delay asymmetry caused by chromatic dispersion.

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Within the framework of EURAMET, a comparison has been organized of measurements of self-inductance at 100 mH and 1 kHz. The comparison is identified as EUROMET.EM-S26. Two 100 mH inductance standards, encased in a thermostatic controlled enclosure, were circulated among the participants. The results from 10 out of 16 participants are in agreement with the reference values. A majority of the results agrees within ±50 µH/H. The participants reported four different methods to realize the traceability of the unit of inductance. The results from these different methods are in good agreement within the reported uncertainties. The results of this comparison have been linked to the results of the comparison EUROMET.EM-S20. The organization of this comparison has been a successful exercise of sharing the workload among four different institutes and can be an example to future comparisons.Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by EUROMET, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

In 2008, seven European institutes participated in a TWSTFT calibration campaign to determine the internal signal delays of their ground stations relative to the portable reference station of Joanneum Research, Graz. In a second step, the calibration values and their uncertainties for time comparisons of 21 links involving the participating institutes were determined. The following results were obtained. The common clock differences between the two TUG stations measured in agreed within 0.5 ns, proving the suitability of the traveling station as a reliable and stable traveling reference. After substantial changes in the hardware, the links connecting to NPL and VSL were calibrated with uncertainties slightly exceeding 1 ns and 2 ns, respectively. The so-called TAI links OP-PTB, INRIM-PTB, and METAS-PTB were recalibrated. Despite hardware changes and a change of the satellite in use in early 2008, the calibration values measured this time agreed with the values determined in 2005 and 2006 well within the calibration uncertainty of slightly above 1 ns.

Within the framework of the supplementary comparison EURAMET.EM-S31, 'Comparison of capacitance and capacitance ratio', five participants (the BIPM, METAS, LNE, PTB, and VSL) inter-compared their capacitance realisations traced to the quantum Hall resistance measured at either ac or dc. The measurands were the capacitance values of three 10 pF standards and one 100 pF standard, and optionally their voltage and frequency dependences. Because the results were not fully satisfying, the circulation was repeated, augmented by a link to the NMIA calculable capacitor. Also two ac-dc resistors were circulated and their frequency dependences were measured in terms of the ac-dc resistance standards involved in the particular capacitance realisations, to allow inter-comparison of these resistance standards. At the end and in any case, a good agreement is achieved within the expanded uncertainties at coverage factor k = 2. Furthermore, the comparison led to new insight regarding the stability and travelling behaviour of the capacitance standards and, by virtue of the link to the NMIA calculable capacitor, to a determination of the von Klitzing constant in agreement with the 2014 CODATA value. Main text To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).