International Bureau of Weights and Measures

This paper presents the results of a collaborative pilot study conducted at the National Institute of Standards and Technology (NIST) to evaluate the differential sampling technique. This method utilizes a Programmable Josephson Voltage Standard (PJVS) to generate a stepwise-approximated waveform that is compared to a sinusoidal waveform of an ac source – in this study, the Josephson Arbitrary Waveform Synthesizer (JAWS). The differential sampling measurement technique used in this study was developed by the Korea Research Institute of Standards and Science (KRISS) and the Bureau International des Poids et Measures (BIPM). Utilizing the NIST 2 V JAWS as a fundamentally stable ac source, the study leverages the system’s intrinsic linearity and spectral purity to determine the metrological limits of the sampling method. Measurements of the root mean square (rms) of an ac signal were performed at 0.75 V across a frequency range from 10 Hz to 1 kHz. The study investigated Type B uncertainties, repeatability, and reproducibility. Notably, the relative difference between the two standards follows a linear evolution from a few parts in 1×108 at 50 Hz to 1.5 ×10-7 at 1 kHz. The contribution of capacitive leakage current to Earth ground is suspected to explain this drift. The study also characterized systematic errors introduced by the digitizer as a function of sampling parameters, including sampling rate, delay time, and sampling window. These results will contribute to the uncertainty budget of future BIPM on-site comparisons.

Following the new protocol of BIPM.EM-K10, extended to AC voltages, BIPM performed the two first on-site Josephson comparisons of AC voltage signals in 2025 with its transportable Programmable Josephson Voltage Standard, based on an array of NIST Superconductor/Normal Metal/Superconductor (SNS) Josephson junctions and associated differential sampling system. Sinewave signals of 0.75 V RMS amplitude at 62.5 Hz, 125 Hz, 312.5 Hz, 625 Hz, 1250 Hz, and 7 V RMS at 62.5 Hz were investigated for both participants: PTB (Germany) and CENAM (Mexico). A relative agreement of a few parts in 108 was achieved, validating the large program of pilot studies performed to develop this comparison scheme.

This paper reports on the development and validation of a new 4πβ(TDCR)-γ digital coincidence counting system at the International Bureau of Weights and Measures (BIPM) for absolute, high-precision disintegration rate determinations. The system integrates a triple-photomultiplier liquid scintillation system operating on the Triple-to-Double Coincidence Ratio (TDCR) principle. It constitutes the beta channel of the system in which a NaI(Tl) detector acts as the gamma channel, and with four input signals are processed by a CAEN digitizer. We introduce the DigiCoinc-2025 software, which implements a revised version of the classical Müller correction model for accidental coincidences. This new approach replaces theoretical parametric approximations with transmission factors derived directly from measured digital live times, resulting in superior stability and accuracy. The system was validated through measurements of 60Co sources, demonstrating agreement within 0.4

Abstract A common understanding of measurement data is fundamental to our society and the Système International (SI) is a central foundation in that regard. To prepare the SI for upcoming decades, its underpinning knowledge model needs to be accessible by software agents for interoperable use of measurement data. In this work, the knowledge model is extracted from the SI Brochure and implemented using Semantic Web standards. In addition, web services are developed around the knowledge model to showcase and simplify the use of the developed ontology. The quality of the implementation is tested based on key questions which the knowledge model will be expected to answer.