Metrology Community Research Articles

Ultra-low frequency calibration of broadband seismometers using a tilt table

Abstract The calibration of current broadband seismometers with the aim to provide traceability to the International System of Units (SI) is an active topic in the vibration metrology community. As it turns out, this exercise has its specific challenges at very low frequencies. A major problem faced at that end of the applicable frequency range, is the influence of tilt as a disturbance on the measured motion component of the sensor. In the presented work, the roles of the quantities are swapped. Tilt is used as a means of excitation of a seismometer and the rectilinear motion is considered as a disturbance, which is, however, well defined by the facilitated set-up. As it is demonstrated, this approach can be very beneficial for very low frequency calibration, and if applied correctly, it can provide a reliable link to base units of the SI.

Feasibility of the Josephson voltage and current standards on a single chip

The quantum Josephson voltage standard is well established across the metrology community for many years. It relies on the synchronization of the flux tunneling in the S/I/S Josephson junctions (JJ) with the microwave radiation (MW) of frequency f such that V=Φ0fm, where m = 0, 1, 2, …. The phenomenon is called the Shapiro steps. Together with the quantum Hall resistance standard, the voltage standard forms the foundation of electrostatic metrology. The current is then defined as the ratio of the voltage and resistance. Realization of the quantum current standard would close the electrostatic metrological triangle of voltage–resistance–current. The current quantization I=2efm, the inverse Shapiro steps, was recently shown using the superconducting nanowires and small JJ. The effect is a synchronization of the MW with the Cooper pair tunneling. This paves the way to combine the JJ voltage and current standards on the same chip and demonstrate feasibility of the multi-standard operation. We show the voltage and current quantization on the same chip up to frequency of 10 GHz, corresponding to the amplitudes ∼ 20.67 μV and ∼ 3.2 nA, respectively. The accuracy of the voltage and current quantization, however, is relatively low, 35 and 100 ppk, respectively. We discuss measures to optimize the JJs, circuit, and environment to boost the amplitude and accuracy of the standards.

Enabling the use of digital calibration certificates in industrial calibration management systems

Abstract. Metrology has been a slowly digitalizing field in which a significant part of the handling of data has been dependent on paper-based processes. Due to the need for the improved efficiency and reliability of these processes, digitalization has become a major topic of interest in the metrology community. Data formats such as the digital calibration certificate (DCC) have an essential role as an enabler of further digitalization, acting as the harmonized data format for calibration data. Naturally, introducing these data formats into industrial usage sets new requirements with respect to the calibration management and associated systems. Diversity of metrology also means that the systems need to be flexible and scalable to fulfill the needs of actors in the global calibration infrastructure with very different requirements. This paper presents a conceptual approach for enhancing the communications between the existing systems in a calibration ecosystem and enabling DCC-based data exchange with third-party systems using the Beamex calibration ecosystem as an example. Thus, the presented system architecture concept that introduces data and DCC exchange services would provide a solution to enable the use of DCCs on Beamex systems.

Study of metrological characteristics of the state primary measurement standard of volume flow and mass consumption of liquid in preparation for participation in international comparisons

The paper discusses the results of a study of metrological characteristics of the state primary measurement standard of volume flow and mass consumption of liquid, as well as the volume and mass of liquid flowing through pipelines (DETU 03-04-04). The study was conducted at the National Scientific Centre “Institute of Metrology” in preparation for international comparisons. Metrological characteristics of the components of the state measurement standard were studied, including the stability of the flow by experimentally determining the standard measurement uncertainty of the mass consumption of liquid at the measurement section of the standard. Based on the obtained results, the measurement standard was modernized. In addition, the paper discusses possible directions for further research aimed at improving measurement methods and analysing the measurement uncertainty of Type A. Further work in this direction can contribute to increasing the competitiveness across the national and international metrological community. The paper also examines the procedure for processing measurement results during international comparisons and identifies basic requirements for complying with international standards for further research of the measurement standard to meet these requirements.
 Metrological comparisons are an important part of metrology, as they ensure the equivalence of measurement units, which is essential for ensuring uniformity of measurements in various industrial and scientific areas. Such measures do not only promote scientific progress, but also ensure high standards of quality and safety in modern society. The results of this research will help to prepare for international comparisons, which are important for comparing measurement units. This, in turn, will contribute to more efficient transfer of measurement units to secondary measurement standards and measuring instruments.

Metrology supporting the European regulation for radiation protection.

The European Association of National Metrology Institutes (EURAMET) within its research programme European Metrology Programme for Innovation and Research (EMPIR) funded project EMPIR 19NET03 supportBSS that contributes to the establishment of a European Metrology Network (EMN) for Radiation Protection (RP). The EMN-RP was established in September 2021 with the intent to work as a meeting point for the metrology community and all stakeholders in the field of ionising radiation regulation, thus providing quality assurance for measurements in each of the exposure situations contemplated in the European Legislation. Within project EMPIR 19NET03, work package 3 aims at the preparation of a Strategic Research Agenda (SRA) by identifying the metrology needs to support the European legislation and regulation in Radiation Protection and of two Roadmaps for metrology services, one under the European Council Directive 2013/59/EURATOM and the other under the EURATOM Treaty. Following a Gaps Workshop held in September 2020 and a second internal workshop that took place in April 2022, a questionnaire was prepared for distribution to the stakeholders, e.g. RP platforms and authorities, academia, industry, among other, together with an accompanying paper. In this paper, the authors present the state of the art of European legislation in RP, address the importance of metrology, the practices and activities that need metrology to meet the requirements set in the regulations, emphasise the need for quality assured measurements in all fields, highlight the stakeholders contributions in their specific area and show their vision of the EMN-RP.

Construction of a multi-class discrimination matrix and systematic selection of areal texture parameters for quantitative surface and defect classification

The surface of every manufactured component has a topography resulting from its fabrication route, which influences its final functionality (optical performance, wear resistance, aesthetic quality, etc.). While the quantitative characterization of the surface is essential for detecting process-induced variations or defects and predicting functional performance, the plethora of surface descriptors developed by the image processing and surface metrology communities makes the selection of optimal surface descriptors Edisonian in nature and highly dependent on experiential knowledge. This work proposes a systematic approach for selecting surface parameters that best distinguish between different surfaces as grouped by visual or process-related differences. Using a form of univariate analysis rooted in signal detection theory, the predictive capability of a discriminability value, d′, is demonstrated in the classification of mutually exclusive surface states. A “discrimination matrix” that offers a robust feature selection algorithm for multiclassification challenges is also introduced. The generality of the approach is demonstrated on the Northeastern University dataset consisting of intensity images from six different surface classes commonly found in hot-rolled steel strip operations. Using the outlined approach, it was found that only four surface descriptors used in conjunction with a simple decision tree classifier achieved a 95% classification accuracy. Surface descriptors used in the study were limited to those described within the ISO 25178-2 standard, while machine learning approaches were limited to a decision tree classifier. The reasoning for both is to maintain as much algorithm output interpretability as possible; the advantages of such is discussed from the perspective of the larger goal of linking surface texture to manufacturing processes and surface functionality fundamental mechanisms.

Report of the CCU/CCQM Workshop on “The Metrology of Quantities Which Can Be Counted”

This article provides a report of the recent workshop on “The metrology of quantities which can be counted” organised jointly by the International Committee for Weights and Measures’ Consultative Committees for Amount of Substance (CCQM) and for Units (CCU). The workshop aimed to trigger a discussion on counting and number quantities across the metrological community so that a common understanding of counting and a common nomenclature could be achieved and there was clarity on the differences between these increasingly important concepts. This article details the background to the workshop, provides a summary of the presentations given and the discussions on the topics raised. It also reports the conclusions, agreed actions and next steps resulting from the workshop.

Concerning physical quantity, its true value, error, and measurement uncertainty

The former USSR journal «Ismeritelnaja technika» («Measurement technic») published the article by Vitalii Pronenko, one of the modern scientific metrology school creators, «Concerning physical quantity, its true value, measurement error, and uncertainty» («О физической величине, ее истинном значении, погрешности и неопределенности измерений»). As soon as the discussion concerning the review of the «International vocabulary of metrology — Basic and general concepts and associated terms», VIM-3, with the aim to create its new version VIM-4, runs now among the metrological community, our journal editorial team considers the article by Pronenko as actual taking in account its common philosophy content with consideration for modern concepts and associated terms. Due to war conditions in Ukraine, it is impossible to connect the editorial office of «Measurement technic» journal. So, the editorial team of «Measurements infrastructure» journal accepts its responsibility based on the agreement of Mr. Pronenko sons Serhii and Yurii Pronenko (Vitalii Pronenko passed away in 1990), the translation of the article by V. Pronenko, into Ukrainian and English and its publication on the journal site.

Development of a PJVS system for quantum-based sampled power measurements

The paper deals with recent progresses at INRiM towards the development and characterization of a programmable Josephson voltage standard (PJVS) operating in a small liquid helium dewar as well as with its integration for the realization of a practical quantum sampling electrical power standard. The PJVS is based on a 1V superconductor-normal metal-superconductor (SNS) binary-divided array of 8192 Josephson junctions. To ensure proper operating conditions of the PJVS chip, a custom short cryoprobe was designed, built and successfully tested. The overall system is being developed in the framework of EMPIR project 19RPT01-QuantumPower. The goal is to establish a new quantum power standard (QPS) based on a single Josephson voltage standard for sampled power measurements and to gain confidence in running PJVS for precise calibration of digital sampling multimeters and arbitrary waveform digitizers used in the ac-voltage and power metrology community.

Machine Learning Techniques for Acoustic Data Processing in Additive Manufacturing In Situ Process Monitoring: A Review

There have been numerous efforts in the metrology, manufacturing, and nondestructive evaluation communities to investigate various methods for effective in situ monitoring of additive manufacturing processes. Researchers have investigated the use of a variety of techniques and sensors and found that each has its own unique capabilities as well as limitations. Among all measurement techniques, acoustic-based in situ measurements of additive manufacturing processes provide remarkable data and advantages for process and part quality assessment. Acoustic signals contain crucial information about the manufacturing processes and fabricated components with a sufficient sampling rate. Like any other measurement technique, acoustic-based methods have specific challenges regarding applications and data interpretation. The enormous size and complexity of the data structure are significant challenges when dealing with acoustic data for in situ process monitoring. To address this issue, researchers have explored and investigated various data and signal processing techniques empowered by artificial intelligence and machine learning methods to extract practical information from acoustic signals. This paper aims to survey recent and innovative machine learning techniques and approaches for acoustic data processing in additive manufacturing in situ monitoring.

Substrate-transferred GaAs/AlGaAs crystalline coatings for gravitational-wave detectors

In this Perspective, we summarize the status of technological development for large-area and low-noise substrate-transferred GaAs/AlGaAs (AlGaAs) crystalline coatings for interferometric gravitational-wave (GW) detectors. These topics were originally presented as part of an AlGaAs Workshop held at American University, Washington, DC, from 15 August to 17 August 2022, bringing together members of the GW community from the laser interferometer gravitational-wave observatory (LIGO), Virgo, and KAGRA collaborations, along with scientists from the precision optical metrology community, and industry partners with extensive expertise in the manufacturing of said coatings. AlGaAs-based crystalline coatings present the possibility of GW observatories having significantly greater range than current systems employing ion-beam sputtered mirrors. Given the low thermal noise of AlGaAs at room temperature, GW detectors could realize these significant sensitivity gains while potentially avoiding cryogenic operation. However, the development of large-area AlGaAs coatings presents unique challenges. Herein, we describe recent research and development efforts relevant to crystalline coatings, covering characterization efforts on novel noise processes as well as optical metrology on large-area (∼10 cm diameter) mirrors. We further explore options to expand the maximum coating diameter to 20 cm and beyond, forging a path to produce low-noise mirrors amenable to future GW detector upgrades, while noting the unique requirements and prospective experimental testbeds for these semiconductor-based coatings.

Simple informative prior distributions for Type A uncertainty evaluation in metrology

The result of a measurement, including the expression of uncertainty in the measurement, should represent a carefully considered opinion based on the metrologist’s experience and expertise, as well as on the data and other information sources. This is the position of the Guide to the expression of uncertainty in measurement (GUM), where the requirement for such judgment is clear in the case of Type B (non-statistical) evaluation. However, when making Type A evaluations, involving statistical analysis of data, the GUM and related GUM documents implicitly consider the data to be the only relevant information. This perspective is unfortunate, and arguably unscientific, when, as is frequently the case, the metrologist could bring other relevant information to bear. Bayesian statistical methods allow the use of prior information in addition to the data in Type A evaluation and have been advocated by several authors. However, prior information is in principle subjective and, as in other fields, there is some resistance in the metrology community at large to embrace Bayesian methods using meaningful, subjective prior probability distributions. We address our paper to metrologists in measurement and calibration laboratories whose workload is such that new techniques will only be adopted if they have proven advantages and are straightforward to apply routinely. We present two prior distributions for use in the most basic of all Type A evaluations, where the data comprise a sample of indications assumed to be normally distributed. These distributions represent prior information about the observation error variance in a simple form that is readily justified in practice. We show the gains to be achieved by using these prior distributions, both in the single Type A evaluation and in a more complex measurement model, and present simple guidance for verifying their validity.

Metrology Challenges in Quantum Key Distribution

The metrology of the QKD devices and systems grows increasingly important in recent years not only because of the needs for conformance and performance testing in the standardization, but more importantly, imperfect implementation of the devices and systems or deviations from the theoretical models, which could be exploited by eavesdropper, should be carefully characterised to avoid the so-called side channel attack. In this paper, we review the recent advances in many aspects of the QKD metrology in both fibre based QKD and free space QKD systems, including a cutting edge metrology facility development and application, traceable calibration methods, and practical device characterising technologies, all of which have been contributed by the metrology communities and relative institutions.

Achieving traceability to UTC through GNSS measurements

Coordinated universal time (UTC) is the international reference for time and frequency measurement, and the basis of civil timekeeping world-wide. The reception of signals from global navigation satellite systems (GNSS) as a source of time and frequency (synchronization and syntonization) has found widespread use in virtually all user sectors, including electrical power supply, telecommunications, and financial institutions. This paper summarizes the concept of metrological traceability and the practices employed in the time and frequency metrology community for achieving it. Practical steps are proposed to ensure that traceability to UTC from GNSS signal reception is available to a wide community of users, addressing different levels of required uncertainty in time and frequency offset from UTC. We suggest some practical measures that can be followed by users, and improvements to the services provided by National Metrology Institutes (NMIs).

A digital framework for realising the SI—a proposal for the metre

A current focus of the international metrology community is the digitalisation of documents, certificates and services in response to initiatives underway throughout industry and to the requirement to follow the principles of data being Findable, Accessible, Interoperable, and Reusable. We propose the key elements of a digital framework for the SI metre, at the point of realisation, showing how it may be implemented in practice. We give examples of direct benefits of this approach, which may be extended to other SI units.

Characterization and Value Assignment of a Monoclonal Antibody Reference Material, NMIJ RM 6208a, AIST-MAB.

Monoclonal antibodies have been established as the largest product class of biopharmaceuticals. Since extensive characterization is required for development and quality control of monoclonal antibody, a widely available reference material (RM) is needed. Herein, a humanized IgG1κ monoclonal antibody reference material, RM 6208-a, AIST-MAB, was established by the National Metrology Institute of Japan, National Institute of Advanced Industrial Science and Technology (NMIJ/AIST). The monoclonal antibody solution was produced as a pharmaceutical grade using a Chinese hamster ovary-derived cell line. The assigned indicative value represents the concentration of the antibody with a heterotetrameric structure including oligomeric forms, determined by an amino acid analysis using isotope dilution mass spectrometry, and their homogeneity and stability were assessed. In addition to antibody concentration, various physicochemical properties, including peptide mapping data, charge variants, and aggregates, were examined. This RM is intended for use in validation of analytical procedures and instruments such as a system suitability test for quantification of antibody. It is also intended for comparing and evaluating the results of antibody analyses across analytical methods and analytical laboratories such as inter-laboratory comparison. Both the material and the set of data from our study provide a tool for an accurate and reliable characterization of product quality attributes of monoclonal antibodies in biopharmaceutical and metrology communities.

Digitalization of the reporting of key comparisons for radionuclide metrology

The Bureau International des Poids et Mesures operates an international reference system (the SIR) to compare primary standards of radioactivity realized by National Metrology Institutes. Recently, the way of managing data relating to this system has been redesigned. The new model is fully integrated into the SI digital transformation initiated by the metrology community. The new approach automates the production of reports on the results from key comparison exercises for publication in the key comparison database, aiming to reduce the time needed to prepare reports without impacting quality. In operation for a year, the new system has produced 12 comparison reports within deadlines at a quality that meets the needs of the stakeholders in radionuclide metrology. The database and the software are controlled using the states-of-the-art Git version control system. In addition, thanks to the machine-readable database it produces, it paves the way for more digital data exchanges meeting the FAIR principles and directly accessible through a new application programming interface that is under development.

The Statistical Power and Confidence of Some Key Comparison Analysis Methods to Correctly Identify Participant Bias

The validity of calibration and measurement capability (CMC) claims by national metrology institutes is supported by the results of international measurement comparisons. Many methods of comparison analysis are described in the literature and some have been recommended by CIPM Consultative Committees. However, the power of various methods to correctly identify biased results is not well understood. In this work, the statistical power and confidence of some methods of interest to the CIPM Consultative Committees were assessed using synthetic data sets with known properties. Our results show that the common mean model with largest consistent subset delivers the highest statistical power under conditions likely to prevail in mature technical fields, where most participants are in agreement and CMC claims can reasonably be supported by the results of the comparison. Our approach to testing methods is easily applicable to other comparison scenarios or analysis methods and will help the metrology community to choose appropriate analysis methods for comparisons in mature technical fields.

Potential and scientific requirements of optical clock networks for validating satellite-derived time-variable gravity data

SUMMARY The Gravity Recovery and Climate Experiment (GRACE) and GRACE-FO missions have provided an unprecedented quantification of large-scale changes in the water cycle. However, it is still an open problem of how these missions’ data can be referenced to a ground truth. Meanwhile, stationary optical clocks show fractional instabilities below 10−18 when averaged over an hour, and continue to be improved in terms of stability and accuracy, uptime and transportability. The frequency of a clock is affected by the gravitational redshift, and thus depends on the local geopotential; a relative frequency change of 10−18 corresponds to a geoid height change of about 1 cm. Here we suggest that this effect could be exploited for sensing large-scale temporal geopotential changes via a network of clocks distributed at the Earth’s surface. In fact, several projects have already proposed to create an ensemble of optical clocks connected across Europe via optical fibre links. Our hypothesis is that a clock network with collocated GNSS receivers spread over Europe—for which the physical infrastructure is already partly in place—would enable us to determine temporal variations of the Earth’s gravity field at timescales of days and beyond, and thus provide a new means for validating satellite missions such as GRACE-FO or a future gravity mission. Here, we show through simulations how glacial, hydrological and atmospheric variations over Europe could be observed with clock comparisons in a future network that follows current design concepts in the metrology community. We assume different scenarios for clock and GNSS uncertainties and find that even under conservative assumptions—a clock error of 10−18 and vertical height control error of 1.4 mm for daily measurements—hydrological signals at the annual timescale and atmospheric signals down to the weekly timescale could be observed.

Establishment of air piston gauge as primary pressure standard at CSIR-National Physical Laboratory INDIA

The air piston gauge (APG) was established at CSIR-National Physical Laboratory, India (NPLI) since 2000. Later the same piston- cylinder(p-c) assembly was calibrated in NIST USA; however, it was never published for metrology communities. As per international protocol, the establishment of the APG as a primary standard, the effective area of p-c assembly, and masses must be directly traceable to SI units. The first time we have calculated the effective area and associated uncertainty of p-c assembly using dimension and mass metrology, traceability to the SI units, i.e., meter and kilogram. To realize the APG as primary pressure standards, we have calculated the effective area of p-c assembly of APG directly from dimension metrology, which is further supported by various other methods. The effective area values obtained in the pressure range of 6.5 – 360 kPa lie in the range of 3.356729 – 3.357248 cm² due to uncertainty limitation in the measurement of dimension of internal diameter of cylinder. The expected values of the effective area which are also measured from cross-float technique against ultrasonic interferometer manometer (UIM), primary pressure standards. The accuracy in effective area measurement is possible only when the resolution in the internal radius of the cylinder should at least be up to 5th decimal order and the uncertainty is 80 nm. The expanded uncertainty was measured nearly 11 ppm at <em>k</em> = 2 by considering the uncertainty in internal radii of cylinder and radii of piston around 80 nm.