Bilateral comparison of 1 V and 10 V standards between the INM (Romania) and the BIPM, August to October 2013 (part of the ongoing BIPM key comparison BIPM.EM-K11.a and b)

A comparison of the 1 V and 10 V voltage reference standards of the BIPM and the Institut National de Metrologie (INM), Bucharest, Romania, was carried out from August to October 2013. At the BIPM, the travelling standards were calibrated, before and after the measurements at INM, 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 EMF at each output terminal of the travelling standard is connected in series opposition to a commercial Josephson Voltage Standard that includes a low thermal EMF scanner with three different channels. The same two channels were used for the 10 V and 1 V outputs of the Zeners. The EMF differences are measured 8 times every day using a digital nanovoltmeter and the simple mean value is considered as the result of the day. The relative value of the voltage noise floor due to flicker noise is about 1 part in 108 and represents the ultimate limit of the stability of Zener voltage standards. The comparison results show that the voltage standards maintained by INM and the BIPM were equivalent, within the comparison uncertainty, on the mean date of the comparison.