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At National Institute of Metrological Research (INRIM), an automated setup to calibrate dc voltage generators, mainly top-level calibrators, from 1 mV to 1 kV has been developed. The heart of the setup is an INRIM-built automated precision fixed ratios dc voltage divider. It can be interconnected to a DMM characterized in linearity, to a dc voltage standard and to a dc voltage generator under calibration to manage automatically the calibration process. Novelty of the system is the employment of the divider being such an instrument not commercially available. Main results are the improvement of the reliability and the increasing of the accuracy of the calibration process saving a lot of time. In addition, it is possible to avoid several standards (still manually operating) carrying out the whole process without changing the setup configuration and without the presence of operators. The expanded uncertainties of the system span from 6.0 × 10−7 to 1.3 × 10−4 improving the previous capabilities of the INRIM laboratory for calibration of multifunction instruments. The setup concept can be transferred to secondary high-level electrical laboratories to improve and expedite their calibrations.

At INRIM a DC Voltage precision resistive divider performing decade ratios from 10:1 to 107:1 was built. It can be automatically calibrated with a top-class calibrator and a precision multimeter calibrated in terms of deviation from linearity. It is made up of 90 kΩ, 9 kΩ, 900 Ω, 90 Ω, 9 Ω, 0.9 Ω, 90 mΩ and 10 mΩ bulk metal foil resistors connected in series, in four-terminal configuration. Peculiarities of the calibration method of the divider are: the evaluation of the DMM input impedance to correct its readings minimizing the load error and a solution to reduce the emfs effect of the relays. These operations are made during the calibration of the divider. The calibration and use uncertainties of the divider span respectively from 6.1 × 10−7 to 5.9 × 10−4 and from 6.7 × 10−7 to 6.5 × 10−4. The project is transferable to secondary laboratories in the framework of the INRIM knowledge transfer task.

At National Institute of Metrological Research (INRIM), a selectable-value transportable high dc voltage standard (THVS) operating in the range from 10 V to 100 V in steps of 10 V, was developed. This standard was built to cover the lack of high level dc voltage standards at values higher than 10 V to employ mainly as transportable standard for inter-laboratory comparisons (ILCs) or eventually as laboratory (local) high level dc voltage standard. An electronic technique was used to improve the THVS accuracy of the high values. The THVS shows lower noise, better short- term stability and accuracy than top level dc voltage and multifunction calibrators (MFCs) and satisfactory suitability to be transported. The project is extensible to 1000 V.

At the National Institute of Metrological Research (INRIM) a measuring setup able to vary, accurately and in a selective way, the temperature, humidity and pressure to detect eventual hysteretic phenomena and to evaluate their effects on electrical standards as high precision standard resistors and Zener-diode based DC Voltage standards. Main element of the setup is a pressure-tight case housing the standards and acting the stresses due to the desired parameters. By means of pressure-tight-connectors, the standards under test are connected to the measuring instruments, while the climatic conditions are acquired through inner and external sensors. Humidity is controlled by means of two conditioning containers filled respectively with water and silica-gel, which regulate the air-moisture percentage the case in a range of 10-90%. A pumping system establishes the pressure in the case from 600 hPa to 1400 hPa. The characterization vs. humidity and pressure is made at constant temperature by means of a commercial air-bath acting from 15 and 45 ° C. Preliminary results have been obtained for pressure dependence of commercial 100 Ω resistors and of an INRIM-developed 10 V Zener-diode based DC Voltage standard.

A portable temperature controlled DC Voltage and DC Resistance Reference with Switching Unit (RSU) has been developed at National Institute of Metrological Research (INRIM) to calibrate multifunction electrical instruments involving 10 V, a $\pmb{1 \Omega}$ and a $\pmb{10 \mathrm{k}\Omega}$ Standards. The resistors are made with two resistors nets while the 10 V is a low noise-drift INRIM-projected circuit. Preliminary measurement over one-month period shows standards uncertainties span from $\pmb{3.0\times 10^{-7}}$ to $\pmb{6.4\times 10^{-7},}$ suitable for artifact calibration. With a real clock calendar, the RSU can show both the RSU Standards calibration values and updated ones between two calibrations according to an internal algorithm.

Inter-laboratory comparisons (ILCs) are an effective mean to establish the compatibility of the measurements among laboratories. As consequence they are a mean to assure confidence in the competence and in the correctness of the dissemination processes from national Standards in different countries. This paper refers on a ILC between the National Institute of Metrological Research (INRIM-Italy) and the European space research and technology Centre (ESA- ESTEC), belonging to two different countries, on DC Voltage, DC Resistance and Electrical Capacitance carried out in 2016. The comparison showed a satisfactory agreement between the results of the two Laboratories.

A l’Institut national de recherche metrologique (INRIM) il a ete developpe un etalon de haute tension continue avec des valeurs selectionnables de 10 V a 100 V pour compenser le manque d'etalons de haut niveau de tension continue d'une valeur superieure a 10 V pour les comparaisons interlaboratoires de haut niveau. Il a ete utilise une nouvelle technique electronique de terre mobile. L'etalon developpe a un bruit inferieur et il a la stabilite egal a celle des calibrateurs de tension continue ou multifonction de haut niveau largement utilise dans les laboratoires d'etalonnage electriques; il a aussi une meilleure attitude a etre transporte pour les comparaisons interlaboratoires. Le projet est extensible jusqu'a 1000 V.

Circulation of the travelling standard for international comparison CCEM-K8 on DC voltage ratio was completed in June 2001. Awaiting the conclusion of the process leading to the agreed final report, the final evaluation of the behavior of the standard is given.

Key comparisons CCEM-K8 and EUROMET.EM-K8 on DC voltage ratio [1, 2] were carried out in parallel, both having IEN as the pilot laboratory. Two Datron 4902S voltage dividers were used as travelling standards, each divider being dedicated to one comparison. On these dividers the measurements of the ratios 1000 V / 10 V and 100 V / 10 V were mandatory and were used to evaluate the degrees of equivalence of the participants with respect to the reference value of their own comparison. The mandatory measurements were performed by all the 15 participants in CCEM-K8 and by 19 out of the 20 participants in EUROMET.EM-K8.

Comparison CCEM-K8.1 is a follow-up to comparison CCEM-K8 and was organized for those participants in CCEM-K8 willing to improve their results. The same travelling standard as in CCEM-K8, a Datron 4902S DC resistive divider, was used, but the trimmers of the divider were adjusted in order to change the deviation of the divider's ratios from nominal value. The comparison protocol was the same as for CCEM-K8 and requested the measurement of voltage ratios 1000?V/10?V and 100?V/10?V, the measurement of other ratios being optional. Two laboratories participated, but one of them withdrew before the draft?A report was released. In the comparison's final report the results of the other laboratory, CEM from Spain, are linked to those of comparison CCEM-K8 through the measurements of IEN, which was the pilot laboratory of both comparisons. Main text. 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 kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCEM, according to the provisions of the Mutual Recognition Arrangement (MRA).

The purpose of the regional comparison EUROMET.EM-K8 was to compare the scaling capabilities up to 1000 V DC of the European national metrology institutes, thus extending to Europe the evaluation of equivalence of voltage ratio measurements obtained by the comparison CCEM-K8. Twenty laboratories participated, with the Istituto Elettrotecnico Nazionale Galileo Ferraris (Torino, Italy) acting as pilot laboratory. The circulation of the travelling standard, a resistive voltage divider, started in July 1998 and ended in January 2002. The technical protocol requested the measurement of voltage ratios 1000?V/10?V and 100?V/10?V, the measurement of other ratios being optional. Nineteen laboratories reported measurements of the mandatory ratios. For these ratios, the measurement methods used are described and the process to evaluate the comparison reference value and the degrees of equivalence is reported in detail. The relative uncertainty of the comparison, given by the combination of the uncertainty of the reference value and the instability of the transfer standard, was about 0.26?10-6 for ratio 1000?V/10?V and about 0.16?10-6 for ratio 100?V/10?V, at 95% level of confidence. The results for the optional ratios are reported in an appendix. With some exceptions, the agreement between the results is satisfactory. Main text. 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 kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCEM, according to the provisions of the Mutual Recognition Arrangement (MRA).

The purpose of CIPM comparison CCEM-K8 was to compare the scaling capabilities up to 1000 V dc of national metrology institutes. Fifteen institutes participated, with the Istituto Elettrotecnico Nazionale Galileo Ferraris (Turin, Italy) acting as pilot laboratory. Circulation of the travelling standard, a resistive voltage divider, started in October 1998 and ended in June 2001. The technical protocol requested the measurement of voltage ratios 1000 V/10 V and 100 V/10 V, the measurement of other ratios being optional. For the mandatory ratios, the measurement methods used by the participants are described and the evaluation of the key comparison reference value and the degrees of equivalence is reported in detail. For these ratios, the relative uncertainty of the comparison, given by the combination of the uncertainty of the reference value and the instability of the transfer standard, was about 0.23?10-6 at 95% level of confidence. Results for the supplementary ratios are reported in an appendix. With certain exceptions, agreement between the results is satisfactory; in some cases the measurement uncertainty was underestimated.