Final report on the CIPM key comparisons for compressed air and nitrogenconducted in November 2004/June 2005: CCM.FF-5.b

Abstract

The calibration of gas meters for flow rate measurements of natural gas at high pressure is of critical importance for gas importers, gas distributors and international trade. It is recommended to calibrate gas meters actually with natural gas at high pressure; however, some countries apply compressed air or nitrogen as a surrogate fluid.Key comparisons (KCs) have been organized among all national metrology organizations (NMIs) worldwide that maintain national standards and take care of compressed air/nitrogen flow metrology. It turned out that, for the time being, only four NMIs were ready to participate, as no other NMIs or countries maintain national standards. These four NMIs are LNE in Paris, NEL in Great Britain, CMS/ITRI in Chinese Taipei, and KRISS in Korea. PTB-pigsar in Germany has been used as the pilot lab for the initial calibration of the transfer standard.All existing facilities in the world were invited to participate, but they all refrained from participation, as they are not yet ready, e.g. CEESI, SwRI, NIST. Russia does not maintain a calibration facility for this type of fluid flow so far. For more details we refer to the full report.The KC for compressed air was conducted during November 2004/June 2005 successfully at flow rates over a wide overlapping range of flow rate and pressure using a set of turbine meters. The transfer package comprises of two turbine meters put in series. Flow rates between 65 m3/h and 1000 m3/h and pressures between 5 bar and 40 bar have been applied.It shall be mentioned here that the weighted average for the KCRV according to a BIPM recommendation for KCs has been used as the first choice. The final report presents the degree of equivalence among the participants as well as the degree of equivalence to the KCRV and confirms all claimed uncertainties of the national calibration facilities of France, Great Britain, Korea and Chinese Taipei. In addition, a link to CCM.FF-K5a for natural gas can be made. Quantitative En values for the degree of equivalence of all participants referred to the KCRV as well as the degree of equivalence among the participating NMIs have been reported too.It turned out that all claimed uncertainties of the calibration and measuring capabilities of the participating facilities could be confirmed.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 CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).