Bilateral comparison of 10 V standards between the NSAI-NML (Ireland) and the BIPM

As part of the ongoing BIPM key comparison BIPM.EM-K11.b, a comparison of the 10 V voltage reference standards of the BIPM and the National Standards Authority of Ireland National Metrology Laboratory (NSAI - NML), Dublin, Ireland, was carried out in May and June 2018. Two BIPM Zener diode-based travelling standards (Fluke 732B), BIPM _E (ZE) and BIPM F (ZF), were transported by freight to NSAI-NML. At NSAI-NML, the reference standard for DC voltage at the 10 V level consists of a group of characterized Zener diode-based electronic voltage standards. The output ElVIF (Electromotive Force) of each travelling standard was measured by direct comparison with the group standard. At the BIPM the travelling standards were calibrated, before and after the measurements at NSAI-NML, with the Josephson Voltage Standard. Results of all measurements were corrected for the dependence of the output voltages of the Zener standards on internal temperature and ambient atmospheric pressure. The final result of the comparison is presented as the difference between the value assigned to DC voltage standard by NSAI-NML, at the level of 10 V, at NSAI-NML, U-NML, and that assigned by the BIPM, at the BIPM, U-BIPM, at the reference dates of 20 May 2018. U-NML - U-BIPM = - 1.21 mu V, u(e) = 1.38 mu V, at 10 V where ue is the combined standard uncertainty associated with the measured difference, including the uncertainty of the representation of the volt at the BIPM, at NSAI-NML, and the uncertainty related to the comparison. The comparison result is within the claimed uncertainties despite the fact that one of the NSAI NML results (for standard ZF) differed from the BIPM value by-1.66 mu V. The voltage standards maintained by NSAI-NML and the BIPM were equivalent, within their stated standard uncertainties, on the mean date of the comparison.