This work presents the results of evaluating and measuring the dc leakage effects associated with programmable Josephson voltage standards (PJVSs) caused by unintended currents flowing in the circuit. Two types of leakage error can occur in PJVS systems: (1) involves leakage currents to Earth ground, which typically result from the finite resistance of cable insulation and the bias electronics, and (2) leakage paths on the precision output leads giving rise to a voltage divider effect between the leads and the load impedance. Both effects impact the PJVS's measurement accuracy and must be monitored regularly. We have developed assessment methods, including both manual and automated measurements, that should be applied to any disseminated PJVS systems currently in use. If these recommended techniques are followed and the leakage current to Earth ground remains below 150 pA when the PJVS array is biased at 10 V, the resulting voltage error at the room-temperature terminals will be less than 0.2 nV.

Primary voltage standards rely upon the ac Josephson effect, in which the voltage across a junction made of two superconducting electrodes separated by a thin layer of normal metal is proportional to the rate of change of the phase difference between the junction’s two electrodes. When the junction is biased with a periodic current of appropriate amplitude and frequency through irradiation with continuous microwaves or periodic pulses, the junction produces synchronized voltage pulses with quantized area over a range of dc bias current. The generated voltage pulses are governed by the ac Josephson equation, which depends only on two fundamental constants of nature: the Planck constant h and the elementary charge e. In the revised SI, Josephson Voltage Standards (JVSs) have become a direct realization of the unit volt. Since 1991, the BIPM has been piloting an on-site comparison program with National Metrology Institutes (NMIs) of direct (dc) voltages from JVSs. Between 2004 and 2016, 25 NMIs participated in this comparison at the 10 V level. Building on the success of this program and recognizing the importance of alternating (ac) voltages, it has been decided to extend the scope of the comparison protocol from dc to ac voltages. Two complementary types of Josephson voltage standards used today in ac voltage metrology are the Programmable Josephson Voltage Standard (PJVS) and the Josephson Arbitrary Waveform Synthesizer (JAWS). Since 2015, BIPM has conducted a series of pilot studies with NMIs that are the most advanced in the research work dedicated to these applications to investigate the evolution of its program of JVS on-site comparisons using its transportable PJVS based on NIST technology. Two of the different technical options that have been tested have been selected for inclusion in the technical protocol. The extended comparison protocol was drafted by the BIPM and reviewed and agreed upon by a dedicated Task Group of the Consultative Committee for Electricity and Magnetism. The BIPM transportable setup for comparisons of dc and ac voltage was improved and allows many measurement configurations using the ac differential sampling technique developed in collaboration with KRISS. The measurement consists of synchronizing in phase the approximated sinewave signal generated by the PJVS and the sinusoidal signal from the generator to be measured and to sample the difference between the two during the quantized Josephson voltage steps of the PJVS signal. The source's ac amplitude voltage is then calculated based on the known quantized voltages provided by the PJVS. Voltage differences of a few parts in 108 with similar Type A uncertainty can be achieved for ac voltages up to 7 V and frequencies below 1 kHz. The major Type-B uncertainty components to be considered for measuring the RMS value of an ac voltage sinewave are: leakage current induced errors and electromagnetic interferences. The poster will present the latest results obtained during the most recent pilot studies.

We investigated the impact of measurement circuit configuration, sampler gain error, sampling trigger delay setting, and the built-in filter of the sampler on the accuracy of quantum-based differential sampling. In addition, we evaluated through numerical simulations how the filter function for NI PXI-5922, which changes with sampling rate, is reflected in differential sampling. We found that the filter introduces ripples throughout the differential signal, resulting in a measurement error proportional to frequency. At 3.125 kHz, the maximum difference among the rms amplitude values obtained with different sampling rates was approximately 2 mu V/V. Finally, we performed differential sampling on 1-V ac waveforms using NI PXI-5922 and Fluke 8588A, with bandwidths set to 3 MHz or higher. We found that the rms amplitude values obtained by the two different samplers agreed within +/- 52 nV in the frequency range below 1.25 kHz.

This paper describes differential sampling measurements of an ac source and a Josephson arbitrary waveform synthesizer (JAWS). A new iterative approach for aligning the phases of the JAWS and the source waveforms was implemented to minimize the differential voltage at the digitizer. A type-A uncertainty of 45 nV/V after 10 min was measured for a commercial ac source at 1 V rms amplitude and 1 kHz.

Main text 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 National Standards Authority of Ireland, National Metrology Laboratory (NSAI-NML), Dublin, Ireland, was carried out from May to June 2024. Two BIPM Zener diode-based travelling standards (Fluke 732B), BIPM_B (ZB) and BIPM_C (ZC), were transported by freight to NSAI-NML and back to BIPM. At the NSAI-NML, the reference standard for DC voltage is a Programmable Josephson Voltage Standard (PJVS). 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 the NSAI-NML against the PJVS developed at the BIPM around a PTB programmable SNS Josephson junctions (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 NSAI-NML, at the level of 1.018 V and 10 V, at NSAI-NML, UNSAI-NML, and those assigned by the BIPM, at the BIPM, UBIPM, at the reference date of the 28th of May 2024. UNSAI-NML - UBIPM = -0.20 V; uc = 0.08 V, at 1.018 V UNSAI-NML - UBIPM = -0.02 V; uc = 0.13 V, at 10 V where uc is the combined standard uncertainty associated with the measured difference, including the uncertainty of the realization of the volt at the BIPM and at NSAI-NML, based on KJ, and the uncertainty related to the comparison. 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 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).

BIPM performed two pilot studies in 2023 to support the uncertainty budget for the programmable Josephson voltage standard (PJVS). The studies involved differential sampling with an ac source, as proposed in the new BIPM on-site comparison protocol. Sinewave signals of 1 V rms at different frequencies (62.5 Hz, 125 Hz, 250 Hz, 625 Hz, 1250 Hz) were investigated with PTB and KRISS. The results exhibited excellent repeatability and reproducibility when comparing measurements with two identical PJVS systems based on the KRISS voltage standard. Conversely, the comparison of two different PJVS systems (BIPM and PTB PJVS systems) led to divergent results. The suspected cause of the discrepancy is likely the presence of larger leakage-current-induced errors on the BIPM PJVS setup. Further pilot studies will be performed in 2024 to resolve this problem.

We conducted an in-depth investigation into the impact of measurement circuit configuration, sampler gain error, sampling-trigger delay settings, and the built-in filter function of the sampler on the accuracy of quantum-based differential sampling of AC waveforms. Our main focus was on Fluke 8588A and NI PXI-5922 samplers with wide bandwidths exceeding 3 MHz and identifying the conditions under which these two samplers gave equivalent measurement results at the 1 kHz frequency level.

Main text 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 INRIM (Italy), from November to December 2023. Two BIPM Zener diode-based travelling standards (Fluke 732B), BIPM_7 (Z7) and BIPM_9 (Z9), were transported by freight to the INRIM and back to the BIPM. In order to keep the Zeners powered during their transportation phase, two additional external batteries were connected in parallel to the internal battery. At the INRIM and the BIPM, the reference standard for DC voltage is a Programmable Josephson Voltage Standard (PJVS). The output electromotive force (EMF) of each travelling standard was measured by direct comparison with the primary standard. The final result of the comparison is presented as the difference between the values assigned to DC voltage standards by the INRIM, at the level of 1.018 V and 10 V, at the INRIM, UINRIM, and those assigned by the BIPM, at the BIPM, UBIPM, at the reference date of the 1st of December 2023. U INRIM - U BIPM = -0.04 µV; u c = 0.03 µV, at 1.018 V U INRIM - U BIPM = -0.18 µV; u c = 0.19 µV, at 10 V where uc is the combined standard uncertainty associated with the measured difference, including the uncertainty of the realisation of the volt at the BIPM and at the INRIM, and the uncertainty related to the comparison. 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 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).

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 SASO-NMCC (Saudi Arabia), from September to November 2023. Two BIPM Zener diode-based travelling standards (Fluke 732B), BIPM_E (ZE) and BIPM_F (ZF), were transported by freight to the SASO-NMCC and back to the BIPM. In order to keep the Zeners powered during their transportation phase, a voltage stabiliser developed by the BIPM was connected in parallel to the internal battery. At the SASO-NMCC and the BIPM, the reference standard for DC voltage is a Programmable Josephson Voltage Standard (PJVS). The output electromotive force (EMF) of each travelling standard was measured by direct comparison with the primary standard. The final result of the comparison is presented as the difference between the values assigned to DC voltage standards by the SASO-NMCC, at the level of 1.018 V and 10 V, at the SASO-NMCC, USASO-NMCC, and those assigned by the BIPM, at the BIPM, UBIPM, at the reference date of the 30th of September 2023. USASO-NMCC - UBIPM = 0.06 V; uc = 0.05 V, at 1.018 V USASO-NMCC - UBIPM = 0.22 V; uc = 0.12 V, at 10 V where uc is the combined standard uncertainty associated with the measured difference, including the uncertainty of the realisation of the volt at the BIPM and at the SASO-NMCC, and the uncertainty related to the comparison. 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 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).

Main text 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 Laboratoire de Métrologie Électrique, DEFNAT (Tunisia), was carried out from April to June 2022. Two BIPM Zener diode-based travelling standards (Fluke 732B), BIPM_E (ZE) and BIPM_F (ZF), were transported by freight to DEFNAT to be measured and back to the BIPM for checking the stability of the traveling standards. At DEFNAT, the reference standard for DC voltage is a Josephson Voltage Standard (JVS). The output EMF (Electromotive Force) of each travelling standard was measured by direct comparison with the primary standard. The final result of the comparison is presented as the difference between the values assigned to DC voltage standards by DEFNAT, at the level of 1.018 V and 10 V, at DEFNAT, U DEFNAT, and those assigned by the BIPM, at the BIPM, U BIPM, at the reference date of the 15th of May 2022. U DEFNAT - U BIPM = 0.03 μV; u c = 0.03 μV, at 1.018 V U DEFNAT - U BIPM = 0.44 μV; u c = 0.12 μV, at 10 V where u c is the combined standard uncertainty associated with the measured difference, including the uncertainty of the representation of the volt at the BIPM and at DEFNAT, based on K J, and the uncertainty related to the comparison. 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 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).

As part of the ongoing BIPM key comparison BIPM.EM-K11, a comparison of the 1.018 V and 10 V voltage reference standards of the BIPM and the Service Métrologie - Metrologische Dienst (SMD), Brussels, Belgium, was carried out from October to December 2021. Two BIPM Zener diode-based travelling standards (Fluke 732B), BIPM_B (ZB) and BIPM_6 (Z6), were transported to SMD and back to BIPM by road. At SMD, the reference standard for DC voltage is a Josephson Voltage Standard (JVS). The output EMF (Electromotive Force) of each travelling standard was measured by direct comparison with the primary standard. The final result of the comparison is presented as the difference between the values assigned to DC voltage standards by SMD, at the level of 1.018 V and 10 V, at SMD, USMD, and those assigned by the BIPM, at the BIPM, UBIPM, at the reference date of the 17th of November 2021. U SMD - U BIPM = -0.03 μV; u c = 0.13 μV, at 1.018 V U SMD - U BIPM = 0.02 μV; u c = 0.28 μV, at 10 V where u c is the combined standard uncertainty associated with the measured difference, including the uncertainty of the representation of the volt at the BIPM and at SMD, based on KJ, and the uncertainty related to the comparison. 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 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).

A high-precision sampler, Fluke 8588A multimeter in the sampling mode, was utilised to perform differential sampling of AC waveforms with a programmable Josephson voltage standard. The systematic error on the differential sampling, induced by the inherent voltage-response characteristics and built-in low-pass filter of the sampler, was estimated. Experimental results and numerical simulations revealed that the sampler could be used for reliable differential sampling of AC waveforms at frequencies up to several kilohertz, with an appropriate number of the voltage steps per the waveform period, when the input bandwidth was set to 3 MHz. In addition, the sampler was compared to an integrating sampler, Keysight 3458A, now widely used for differential sampling. At 62.5 Hz, a key frequency in the future on-site key comparison of the differential sampling on AC voltage, the difference in root mean square (RMS) amplitudes obtained by the differential sampling using the two different samplers is approximately 150 nV V −1 due to the systematic error caused by the limited bandwidth of 150 kHz for the integrating sampler.

Main text As part of the ongoing BIPM key comparison BIPM.EM-K10.b, a direct comparison of the Josephson array voltage standards of the Bureau International des Poids et Mesures (BIPM) and the National Metrology Institute of Finland (VTT MIKES), Espoo, Finland, was carried out in October 2019 at the level of 10 V. For this exercise, the option A of the BIPM.EM-K10.b comparison protocol was partially applied. Option A required the MIKES to provide a reference voltage with its Josephson voltage standard for measurement by the BIPM using an analogue nanovoltmeter and associated measurement cables. Since no sufficiently stable voltage could be achieved in this configuration, a digital detector was used instead. In all cases the BIPM array was kept floating from ground. The final results were in good agreement within the combined relative standard uncertainty of 2.5 parts in 1010 for the nominal voltage of 10 V. 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 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).

Main text As part of the ongoing BIPM key comparison BIPM.EM-K11, 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 November and December 2020. The objective for NSAI-NML in participating in this comparison was to demonstrate the international equivalence of its DC voltage measurement results and to support their calibration and measurement capabilities (CMCs) published in the Key Comparison Database of the BIPM (KCDB). Two BIPM Zener diode-based travelling standards (Fluke 732B), BIPM_8 (Z8) and BIPM_9 (Z9), 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 EMF (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, developed at the BIPM. The output EMF of each travelling standard was measured against the Josephson Voltage Standard (JVS). 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 comparison result is presented as the difference between the value assigned to a 10 V standard by NSAI-NML, at NSAI-NML, U NSAI-NML, and that assigned by the BIPM, at the BIPM, U BIPM, on the reference date of 2020/11/14, as U NSAI-NML - U BIPM = -2.99 µV; u c = 1.71 µV where u c is the combined standard uncertainty associated with the measured difference, including the uncertainty of the realization of the volt at NSAI-NML, and the uncertainty related to the comparison. 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 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).

Main text 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 Bulgarian Institute of Metrology, BIM, was carried out in April 2019. The objective for BIM in participating in this comparison was to demonstrate the international equivalence of its DC voltage measurement results and to support the calibration and measurement capabilities (CMCs) published in the Key Comparison Database of the BIPM (KCDB). Two BIPM Zener diode-based travelling standards (Fluke 732B) were shipped to Sofia in March 2019. At the BIPM, the reference standard for DC voltage is a primary voltage standard based on the Josephson effect, developed by the BIPM. The output electromotive force (EMF) of each travelling standard was measured against the Josephson Voltage Standard (JVS) before and after the measurements at BIM. At the BIM, the reference standard is a commercial JVS. The final result of the comparison is presented as the difference between the values assigned to DC voltage standards by BIM, at the level of 1.018 V and 10 V, at BIM, U BIM, and those assigned by the BIPM, at the BIPM, U BIM, at the reference dates of the 26 th of March 2019. U BIM - U BIM = - 0.01 µV; uc = 0.02 µV, at 1.018 V U BIM - U BIM = + 0.30 µV; uc = 0.09 µV, at 10 V where uc is the combined standard uncertainty associated with the measured difference. 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 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).

The BIPM (Bureau International des Poids et Mesures) has been carefully maintaining Zener diode secondary voltage standards (ZVS) for about 30 years, which are used in an ongoing international bilateral comparison program with national metrology institutes. The output voltages of the standards are corrected for their sensitivity to parameters such as their internal temperature (relative to the thermistor resistance of the Zener's oven) and atmospheric pressure. In 2016 and 2017, these sensitivity coefficients were redetermined. The corresponding corrections vary between -7 parts in 10(7) k omega(-1) to +6 parts in 10(7) k omega(-1), and from +8 parts in 10(10) hPa(-1) to +2 parts in 10(9) hPa(-1), respectively. In the worst case, the combination of the effect of temperature and pressure are comparable to the 1 f (-1) noise floor of these standards (considered to be 1 part in 10(8) at the BIPM). Most of the sensitivity coefficients have not changed since their previous determination in 1998-2002 which seems to indicate that they are intrinsic characteristics of the ZVS, which are dependent upon the properties of the physical support of the Zener element itself (pressure sensitivity) and the intrinsic behaviour of the internal thermistor (temperature sensitivity). As a follow-up to the determination of the new sensitivity coefficients, the reproducibility of the ZVS calibration was also investigated, using three different and independent measurement setups, each built around a different and independent Josephson voltage standard. The metrological performance of the three primary setups were demonstrated to have an agreement of between 2 x 10(-10) and 1 x 10(-11) when compared directly. The comparison results of the calibration of the BIPM ZVS showed that most artefacts reach an agreement of a few parts in 10(9) while a very few can exhibit a considerable systematic error comparable to the 1 f (-1) noise, which we suspect is due to a nonzero current from the measuring system flowing through the input impedance of the standard.

We have investigated the response characteristics of two different samplers, Keysight 3458A and NI 5922 implemented in setup for differential sampling based on a programmable Josephson voltage standard, to input signals in a frequency range below 1 kHz. The RMS amplitudes measured with the samplers coincides within a few parts in 10 6 at frequencies below 100 Hz. However, the difference between the RMS values increases with the frequency, mainly due to the dramatic change of the value obtained with the Keysight 3458A. The difference reaches up to 25 μV/V at 1 kHz. The feature is inferred to originate from the difference in the input bandwidths for the two samplers.

BIPM has continued its program of pilot studies by investigating the possibilities to derive a protocol for Josephson Voltage Standard comparisons of ac voltages up to 7 V rms at low frequencies (< 1 kHz) based on the differential sampling technique. We have confirmed that an agreement within a few parts in 10(7) can typically be achieved using a commercial calibrator as a transfer standard. We have also investigated other ac generators as possible candidates for a stable transfer standard. The sensitivity of the rms voltage measurement result to key parameters (filtering at the output of the ac source, grounding of the measurement setup, acquisition software, etc.) has been evaluated. The possibility of a measurement system ( meter and software) that performs a full sampling of the ac source signal in addition to the differential sampling has also been investigated. It offers the possibility to follow the drift of the source.

We have implemented a multimeter Fluke 8588A as a sampler for the differential sampling of AC waveforms based on a programmable Josephson voltage standard. The bandwidth of the input low-pass filter for the multimeter in the digitizing mode can be set to two different values, 100 kHz and 3 MHz. To investigate the effect of the bandwidth on the differential sampling, we measured outputs of an AC source in the frequency range of 31.25 Hz ≤ f ≤ 1 kHz. We found that RMS amplitudes obtained with the multimeter in the 3 MHz bandwidth for the 1 V output of the AC source are scattered within 3 μV/V in the frequency range. However, the RMS amplitudes obtained in 100 kHz bandwidth, deviates more and more from that obtained in the 3 MHz bandwidth as the frequency increases, which can be roughly described as a quadratic function of f. In the conference, we will present the measurement results obtained to explore the possibility of using the multimeter for reliable differential sampling over a frequency range well above 100 Hz.

This report presents the GULFMET key comparison (GULFMET.EM.BIPM-K11) results of DC voltages at the 1.018 V and 10 V with two travelling electronic DC reference standards. This comparison was supported by the BIPM and GULFMET associate members, KRISS and SCL, which are from the APMP. The linking difference from the BIPM.EM-K11 KCRV was calculated. The agreement between participating laboratories is good, which could support GULFMET participating laboratories in submitting new calibration and measurement capability entries. 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 CIPM Mutual Recognition Arrangement (CIPM MRA).