CIPM MRA COMPARISON REPORTS

As part of the ongoing BIPM key comparison BIPM.EM-K11.a and b, a comparison of the 1.018 V and 10 V voltage reference standards of the BIPM and the State Research Institute, Center for Physical Sciences and Technology (FTMC), Vilnius, Lithuania, was carried out from October to December 2025. Two BIPM Zener diode-based travelling standards (Fluke 732B), BIPM_8 (Z8) and BIPM_E (ZE), were transported to FTMC and back to BIPM by freight. In order to keep the Zeners powered during their transportation and during long measurement series, a dedicated auxiliary battery supply was designed and connected in parallel to the internal battery.

At FTMC, the reference standard for DC voltage is a Josephson Voltage Standard (JVS). The output electromotive force (EMF) of each travelling standard was measured by direct comparison with the primary standard.

At the BIPM, the output EMF of each travelling standard was calibrated before and after the measurements at FTMC against the PJVS developed at the BIPM around a PTB programmable SNS (Superconductor/Normal Metal/Superconductor) array.

Results of all measurements were corrected by the BIPM 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 values assigned to DC voltage standards by FTMC, at the level of 1.018 V and 10 V, at FTMC, U _FTMC, and those assigned by the BIPM, at the BIPM, U _BIPM, at the reference date of the 27 November 2025.

U _FTMC – U _BIPM = 0.011 μV; u _c = 0.012 μV, at 1.018 V

U _FTMC – U _BIPM = 0.10 μV; u _c = 0.18 μV, at 10 V

where u _c is the combined standard uncertainty associated with the measured difference, including the uncertainty of the realization of the volt at the BIPM and at FTMC, and the uncertainty related to the comparison.

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 CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).