Calibration of diameter standards (EURAMET.L-K4.2015)

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Main textAt its meeting in October 2014, the EURAMET TC for Length, decided upon a key comparison on the calibration of diameter gauges, named EURAMET.L-K4.2015. Twenty National Metrology Institutes and one Designated Institute from Europe, Asia and South America participated in this comparison, which was carried out in two parallel groups. Twelve laboratories from EURAMET participated in group 1, while ten laboratories from EURAMET and two laboratories from GULFMET and SIM participated in group 2. To provide the link three laboratories, CEM, INRIM and METAS, participated in both groups and in the key comparison CCL-K4.2015. Two sets of gauges consisting of two rings, two plugs and a sphere were circulated in parallel in the two groups, the circulation started in November 2016 and completed in February 2018. The reference value (KCRV) was calculated on a gauge-per-gauge basis as the weighted mean of the submitted results of the diameter, roundness and straightness measurements. With group 1, inconsistent results (En> 1) gave a number of 5 out of 60 independent results for diameter and 7 out of 77 for roundness, while with group 2 a number of 6 out of 59 for diameter. These numbers are reflected in the comparison with reference values, while it is worth noting that with the two plugs of 100 mm diameter a decrement of 2 inconsistent results is achieved by introducing an uncertainty contribution related to the apparent change of length of these gauges. Furthermore, the KCRV was calculated by linking the two groups for the diameter of all the twin gauges and for the roundness of the twin spheres. When compared to those calculated independently for each group, minor changes of the KCRVs and associated uncertainties are observed from linking the groups. Consistency checks are satisfied for most of the gauges with the exception of the plugs 100 mm, which suffer from an apparent change in length during the circulation. With the linking, inconsistent results gave a number of 12 out of 119 independent results for the diameter and 1 out of 21 for roundness of the sphere. The comparison results help to support the calibration and measurement capabilities (CMCs) of the laboratories, while recommendations and actions were agreed with those having inconsistent results.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 https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCL, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).