Temperature sensitivity coefficients of the BIPM secondary voltage standards

The BIPM bilateral comparison program using secondary voltage standards as travelling references, identified as BIPM.EM-K11 in the CIPM-MRA framework, has been on-going for more than 20 years. As this comparison is not very demanding on workload and is very easy to realise, NMIs still participate at a rate of 2 to 3 participants a year for different objectives: to validate a change of technical staff or a technical improvement in the labs, but also, most importantly, for the preparation of an on-site comparison of the primary realization of the volt, using Josephson voltage standards. The output voltages of the BIPM travelling Zener standards are corrected for their dependence on temperature changes in the enclosure of the Zener voltage reference. No re-evaluation of the sensitivity coefficients has been performed since the original measurements between 1998 and 2002. We have reasons to believe that these coefficients have changed over the past 10 years and we need to confirm this assumption. A new measurement chain has been set up to perform this study, using the same methodology operated for the initial determination of the coefficients.