Metrological Traceability Chain Research Articles

Wideband Current Transducer Traceable Calibration up to 10 A and 1 MHz.

Energy efficiency is an important issue in industry, especially with the ever-increasing consumption of electrical energy. The power quality and the traceability of metering devices are essential when integrating energy metering systems for energy efficiency. This management requires an understanding of electrical current events such as pulse and transient currents. Current transducers are widely used to measure these electrical current events up to a few megahertz. Their use makes it possible to measure not only the main current flowing through the transducer, but also the bypass current that affects electrical equipment. Calibration of these sensors up to a few megahertz then becomes an essential step. Currently, most calibration methods are limited to 100 kHz frequency for a current of 10 A. This paper presents an improvement of a traceable calibration methodology for current transducers up to 10 A and 1 MHz, thus increasing, by 10 times, the current level for such high frequency applications. This calibration methodology is based on a metrological traceability chain (uninterrupted link to the International System of Units) with respect to a calculable current shunt and is currently the only traceable method for calibrating current transducers at 10 A and up to 1 MHz. The uncertainty obtained for the transimpedance ratio is less than 0.2%, which is considerably reduced with respect to the existing capabilities.

Comparative analysis and classification of measurement procedures and procedures for transferring of unit of quantity as elements of metrological traceability chain of measurement results

The article analyzes types of measurement procedures and procedures for transferring a unit of quantity, such as: primary reference measurement procedures, reference measurement procedures, calibration procedures, validation procedures, end-user measurement procedures and measurement procedures. The article discusses requirements for developing the presented procedures, their research and approval. The article presents a classification of procedures depending on their place in metrological traceability chain, type of determined metrological characteristics and their application in the field of regulation. Based on the results of the analysis of regulatory documents, a table that describes basic requirements for development and approval of measurement procedures and procedures for transferring a unit of quantity is presented. The article also discusses requirements established for conformity assessment procedures for measurement procedures and procedures for transferring а unit of quantity, such as certification, validation and verification of procedures. The article presents definitions and scope of application for conformity assessment of measurement procedures and procedures for transferring a unit of quantity. Based on the analysis of requirements for conformity assessment of procedures, a flowchart for selecting appropriate conformity assessment procedure is presented. Due to this scheme, laboratories will be able to unambiguously choose one or another conformity assessment procedure to approve the required measurement method or method of transferring a unit of value. In particular, in preparation for accreditation for compliance with the requirements of ISO/IEC 17025-2017 “General requirements for the competence of testing and calibration laboratories.” The proposed scheme of choosing a procedure for conformity assessment of a specific measurement procedure eliminates ambiguity of the requirements of regulatory documents.

Calibration Techniques for Water Content Measurements in Solid Biofuels

This paper presents methodologies and equipment for SI-traceable inline measurements of water content (a critical quality parameter) in solid biofuels. Inline measurement systems for water content are commonly used at CHP plants, providing continuous real-time data. However, the accuracy of these systems is in most cases unsatisfactory, mainly because the systems are not calibrated representatively for the relevant material, and until now, calibrations traceable to the SI system have not been available. To provide reliable and accurate inline water content data, new procedures and equipment for calibrating measurement systems were developed. Two reference methods for the determination of water content were developed; one measures the airflow and dewpoint of desorbed water in the air passing a test sample, while the other uses a P2O₅-sensor. Additionally, a transfer standard based on a cavity resonance sensor was developed for fast onsite calibration of the inline sensor at the power plant. This new instrument allows for quick and accurate measurements. The transfer standard is made metrologically traceable to the primary measurement standards. The entire system was demonstrated by calibrating an inline microwave-based (MW) sensor at the CHP plant of VERDO in Randers, Denmark. Thus, a complete metrological traceability chain was established from an industrial to a primary standard.

Ensuring metrological traceability of the gas flow measurements at high pressure in Ukraine

Described is the PVTt primary measurement standard used to calibrate primary standard critical flow nozzles with throat diameters from 2 mm to 8 mm over a flow rate range of 100 m3/h up to 1800 m3/h. Means and methods of the working standard critical flow nozzles calibration are considered. The metrological traceability chain for the gas flow measurements is presented. In the metrological traceability chain, the primary standards are the primary standard critical flow nozzles, the metrological characteristics of which are established through calibration using the primary measuring system and the primary measurement procedure. The secondary standards are working standard critical flow nozzles, the metrological characteristics of which are established by comparing them with primary standard nozzles. The metrological traceability chain has a branched structure, as the measurement model includes various physical quantities: pressure, temperature, volume, time, and gas properties.

Characterisation of the Performance of a Structured Light Digitising Sensor by Using Different Materials and Surface Finishes

The advantages of non-contact digitising systems over contact systems are undeniable. They allow capturing more information per unit of time with less accessibility problems and without alter the digitised surface. Although many of these systems have been developed with the aim of replacing contact systems in metrological verification tasks, generalist techniques such as photogrammetry, structured light, etc., have been developed over the years for digitising archaeological remains, works of art or living biological systems, among others. As is the case for non-contact measurement-oriented systems, for these generalist systems there are still difficulties in positioning them along a metrological traceability chain if they are required for any kind of measurement. This is due to the lack of specific standards, as well as the strong influence of the optical properties of the digitised surface on the quality of the results obtained. It is therefore necessary to develop calibration procedures and characterisation work to analyse this influence. The aim of this work is to characterise the metrological performance of one of these generalists structured light devices, Einscan-SP by Shining 3D, in the digitising of different calibration spheres made of different materials (WC, Al2O3, ZrO2, etc.) with different surface finishes (shot-blasted, polished, coated). As quality indicators, the number of points captured, the quality of the point cloud as well as the dimensional and geometrical deviation from the results obtained with a high-performance contact measurement system shall be used. Apart from the raw data, the influence of applying filtering to the captured clouds is analysed. The results of this work allow recommendations to be made regarding the material and finish of the spheres to be used, as well as the filtering to be applied, if necessary, in order to assess the metrological performance of this type of equipment.

Mathematical modelling of metrological traceability chains

Metrological traceability is a property of the measurement result and requires an established multi-level calibration hierarchy. The metrological traceability chain is established through the calibration hierarchy and is used to establish the metrological traceability of the measurement result. Approaches to the establishment of metrological traceability chains are based mainly on graphic images.
 Special international guidelines and European recommendations on the measurement uncertainty are used to evaluate the measurement uncertainty during the calibration of measuring instruments. The measurement uncertainty necessarily increases along the calibration sequence and is different for different levels of the metrological traceability chain. The measurement uncertainty depends on measurement standards or measuring instruments used during calibration.
 A mathematical model of the metrological traceability chain for different levels of the calibration hierarchy is proposed. This model includes, as components, such basic metrological characteristics for a certain level of the chain as the measurement range, measurement uncertainty, measuring instrument or measurement standard. As additional parameters for the metrological traceability chain, it is proposed to use data from the calibration certificate of the corresponding measuring instrument or measurement standard used at a certain level of the chain.
 Recommendations regarding practical application of the developed mathematical model of the metrological traceability chain, which can be used for chains of any measurements, are proposed. They can be used to establish the required metrological characteristics for a certain level of the metrological traceability chain. Such a model and recommendations for its practical application can be used in national metrology institutes and calibration laboratories.

Metrological traceability of the breath alcohol measurements

Breath alcohol measurements are widely used worldwide to detect the presence of alcohol in the human body. For those measurements, different metrological traceability chains are used, both in the international normative documents and at the national level. Different measurement standards used to calibrate breath analysers reproduce different quantities: on the one hand, an «actual» ethanol mass concentration, and, on the other hand, the operationally defined «ethanol mass concentration by Dubowski (or Harger)». This makes the comparability of the breath alcohol measurements questionable. According to various studies, the discrepancy between the operationally defined quantity and the concentration not related to the empirical interphase distribution coefficients, lays within (1-2) %, although there is also an evidence of a larger deviation. It is possible to construct a common metrological traceability chain by using reference gas mixtures in cylinders and dynamic gas mixture generators based on the principles not related to empirical equations, as well as determining more accurately the interphase distribution coefficient and evaluating its uncertainty. SE «Ukrmetrteststandart» possesses internationally recognised calibration and measurement capabilities for measuring ethanol concentration and producing reference materials: calibration gas mixtures of ethanol with nitrogen or air in cylinders and reference aqueous solutions of ethanol that provide metrological traceability for the breath alcohol measurements.

Metrological traceability chains for high DC voltage and voltages ratio

The current stage of scientific and technical development is characterized by the widespread use of high-voltage technology. Metrological traceability has such important elements as calibration of measurement standards and measuring instruments and evaluation of measurement uncertainty. The range of values of specific measurands, the range of necessary measurement uncertainties and the measurement standards used are presented as metrological traceability chains. Building such chains for different types of measurements is important for national metrology institutes and calibration laboratories.
 An urgent task is to build metrological traceability chains for high direct current voltage measuring instruments. The proposed metrological traceability hierarchy chains are used in the State Enterprise “Ukrmetrteststandard” for calibration of working standards and working measuring instruments for high DC voltage and voltages ratio. These chains can be used also by accredited calibration laboratories, which carry out calibration of working measuring instruments for high direct current voltage and voltages ratio according to their own scope of accreditation.

Application of systems thinking to the establishment of metrological traceability chains

International agreements in the field of metrology and accreditation of calibration laboratories are the basis for establishing global metrological traceability. Important elements of metrological traceability are calibration of measurement standards and measuring instruments, assessment of measurement uncertainty. The International Laboratory Accreditation Cooperation has a specific policy regarding on traceability of measurement results and estimation of measurement uncertainty in calibration.
 The partial concept diagram around metrological traceability in accordance with the International Vocabulary of Metrology is proposed. This diagram contains a total of nine metrological concepts, which have most of the associative relations. There are associative relations between the concept of metrological traceability chain and concepts of metrological traceability, measurement standard, calibration and calibration hierarchy, and through the concept of measurement standard with the concept of measurement uncertainty.
 Systems thinking to the analysis of state of proposed terminological system around metrological traceability was applied. For construction of generalized metrological traceability chain, all the established properties of the system elements around the terminology system of metrological traceability were taken into account.
 Generalized metrological traceability chain for different levels of the calibration hierarchy was proposed. The proposed chain can be used to develop appropriate chains for specific areas of measurement. To achieve this, it is necessary to determine the specific measured value, the required measurement uncertainty for different levels of the calibration hierarchy and select the necessary measurement standards. Such schemes should be used in national metrology institutes and calibration laboratories.

Measurement Standards of Ukraine for Gas Volume Flow Rate at Pressures of 1 MPa to 5 MPa

The characteristics of the primary measurement standards of the volume gas flow rate at high pressure developed in various countries are considered. A hierarchical scheme for gas flow measuring instruments and a corresponding metrological traceability chain are presented. Described is a PVTt method, on which the primary standards of gas flow rate used in the USA, France, Japan, and Taiwan are based. The need to create in Ukraine primary measurement standards of gas flow rate at high pressure covering different parts of the total flow rate interval from 0,3 m3/h to 1800 m3/h at a pressure of 1 MPa to 5 MPa is substantiated. Metrological traceability of gas flow measurements is realized through a sequence of critical flow Venturi nozzles, which play a role of the reference flow rate material measures. The standards might be used to calibrate the primary reference Venturi nozzles of the most common 0,1 mm to 8 mm diameters. The characteristics and parameters of the standards are determined. By their metrological and technical characteristics, the standards will correspond to the state-of-the-art level. According to the programme of developing the measurement-standard facilities in Ukraine, in 2019 the primary standard PVTt-65 was created and work had started on the development of the primary standard PVTt-1800 and the working standard PE-5400. A detailed study of the metrological characteristics of the measurement standards will be the topic of further work.

The need for reference machines when energy labelling electric household appliances that are tested to international standards

There are over 80 countries in the world that currently use some kind of energy label for electric household appliances. In Europe, as an example, a lot of appliances are obliged to have an energy label when shown for sale, including online. Energy labels give relevant information to the consumers to help them make an environmentally beneficial choice when buying a new appliance. However, the desire for an energy efficient appliance does not outweigh the wish for good performance. Therefore, some energy labels provide information about the performance of the appliance based on international performance measurement standards (hereafter: “international standards”). Indeed, within the one appliance, increased performance can often mean increased energy consumption, so a balance between these parameters needs to be made by product designers and users. Unlike measurements that are traceable to Systeme Internationale units through metrological traceability chains, there is no natural reference data for performance measurements. Therefore, some international standards use a reference machine to relate their testing results to. The comparison of test and reference machine eliminates variances, for example, due to the auxiliary materials used and the influence of manual preparation or assessment methods. Three international standards that are currently using reference machines are examined closely in this paper. It is assessed how the reference machines and their testing results are treated, whether the reference machines are comparable with their corresponding test machines and if the use of a reference machine can be considered beneficial for the testing procedure. Additionally, three key questions are developed that will indicate whether 13 other international standards for electric household appliances could also benefit from using a reference machine. The paper concludes with six recommendations for standardisation groups and energy policymakers that will help with deciding whether a reference machine should be implemented.

Development and strategy of reference materials for the DNA-based detection of genetically modified organisms.

The enforcement of GMO labeling regulations requires validated analytical methods and certified reference materials (CRMs). The early labeling regulations stipulated that the GMO content should be expressed as percentage, but did not specify what unit this percentage referred to. Two reference systems, using mass fraction and copy number ratio as measurement units, individually, are established for GMO analysis using different metrological traceability chains. Three types of CRMs, powder CRMs certified for mass fractions, genomic DNA CRMs, and plasmid DNA CRMs certified for copy number ratios, were developed for calibration and quality control. The type, certification, and measurement unit commutability of current GMO CRMs are presented and discussed in this paper. Both existing reference systems are facing a metrological challenge, although later EU regulations specified that the measurement unit of GMO content must be expressed in mass fraction and recommended to convert one unit into another by introducing a conversion factor, further efforts are required to explore which reference system is more metrologically sound. The determination of conversion factor per CRM batch is recommended to be based on the pure CRMs produced from pure GM materials, which is expected to be the best choice for calibration of PCR measurement results.

Traceability of on-machine tool measurement: Uncertainty budget assessment on shop floor conditions

Almost every new machine tool is equipped with a probing system nowadays, which means that machining and measuring processes could take place on the same machine tool. Thus, the integration of a traceable measurement process into the machine tool is currently one of the main research objectives of production engineering. It provides the traceability of the quality inspection on the machine tool, during or after machining process, which allows the reduction of manufacturing costs and offers high productivity and zero-defect manufacturing processes. Nevertheless, the traceability of a measurement process on a machine tool is not ensured yet and therefore, measurement results are not reliable enough yet for a self-adapting manufacturing process. On-machine tool measurement is affected by multiple uncertainty contributors related to shop floor conditions, such as, machine tool geometric error, temperature variation, probing system, vibrations, dirt, etc that are not fully understood yet, which leads to a lack of a metrological traceability chain, which in turn means a lack of reliability of the manufacturing process. The aim of this paper is to review a medium size on-machine tool measurement uncertainty assessment and give an overview about the significance of each uncertainty contributor on shop floor conditions. For that purpose, an experimental test according to ISO 15530-3:2011 standard is executed for a medium size prismatic component.

Metrological traceability and harmonization of medical tests: a quantum leap forward is needed to keep pace with globalization and stringent IVD-regulations in the 21st century!

Abstract In our efforts to advance the profession and practice of clinical laboratory medicine, strong coordination and collaboration are needed more than ever before. At the dawn of the 21st century, medical laboratories are facing many unmet clinical needs, a technological revolution promising a plethora of better biomarkers, financial constraints, a growing scarcity of well-trained laboratory technicians and a sharply increasing number of International Organization for Standardization guidelines and new regulations to which medical laboratories should comply in order to guarantee safety and effectiveness of medical test results. Although this is a global trend, medical laboratories across continents and countries are in distinct phases and experience various situations. A universal underlying requirement for safe and global use of medical test results is the standardization and harmonization of test results. Since two decades and after a number of endeavors on standardization/harmonization of medical tests, it is time to reflect on the effectiveness of the approaches used. To keep laboratory medicine sustainable, viable and affordable, clarification of the promises of metrological traceability of test results for improving sick and health care, realization of formal commitment among all stakeholders of the metrological traceability chain and preparation of a joint and global plan for action are essential prerequisites. Policy makers and regulators should not only overwhelm the diagnostic sector with oversight and regulations but should also create the conditions by establishing a global professional forum for anchoring the metrological traceability concept in the medical test domain. Even so, professional societies should have a strong voice in their (inter-) national governments to negotiate long-lasting public policy commitment and funds for global standardization of medical tests.

Defining permissible limits for the combined uncertainty budget in the implementation of metrological traceability

In addition to the correct implementation of calibration traceability, the definition and the achievement of an appropriate analytical performance specification for the total uncertainty budget (GU) is essential to ensure that laboratory measurements are clinically usable. To understand if it is possible to fulfil these specifications, limits for combined uncertainty across the entire metrological traceability chain should be defined. We recommended that no more than one third of GU should be consumed by the uncertainty of higher order references and ≤50% of GU by the combined measurement uncertainty at the manufacturer's calibration level. The remaining allowable uncertainty should be available for random sources, i.e. for the imprecision of the commercial measuring system (including the reagent batch-to-batch variation) and the individual laboratory performance, as a safety margin to fulfil GU. Based on this approach, it is of interest to assess for each analyte measured in the clinical laboratory the status of the uncertainty budget of its measurement associated with the selected metrological traceability chain. Accordingly, we report three didactic cases that could occur in the clinical practice. This approach is very helpful to identify those analytes for which further technological improvements are probably needed to reduce uncertainty associated with their measurement.

Traceability in laboratory medicine: a global driver for accurate results for patient care

Laboratory medicine results influence a high percentage of all clinical decisions. Globalization requires that laboratory medicine results should be transferable between methods in the interests of patient safety. International collaboration is necessary to deliver this requirement. That collaboration should be based on traceability in laboratory medicine and the adoption of higher order international commutable reference materials and measurement procedures. Application of the metrological traceability chain facilitates a universal approach. The measurement of serum cholesterol and blood HbA1c serve as examples of the process of method standardization where an impact on clinical outcomes is demonstrable. The measurement of plasma parathyroid hormone and blood HbA2 serve as examples where the current between-method variability is compromising patient management and method standardization and/or harmonization is required. Challenges to the widespread adoption of traceability in laboratory medicine include the availability of reference materials and methods, geographical differences, the use of variable units, complex analytes and limited global coordination. The global collaboration requires the involvement of several different stakeholder groups ranging from international experts to laboratory medicine specialists in routine clinical laboratories. A coordinated action plan is presented with actions attributable to each of these stakeholder groups.

The application of a cavity ring-down spectrometer to measurements of ambient ammonia using traceable primary standard gas mixtures

A correction for the undesirable effects of direct and indirect cross-interference from water vapour on ammonia (NH3) measurements was developed using an optical laser sensor based on cavity ring-down spectroscopy. This correction relied on new measurements of the collisional broadening due to water vapour of two NH3 spectral lines in the near infra-red (6548.6 and 6548.8 cm−1), and on the development of novel stable primary standard gas mixtures (PSMs) of ammonia prepared by gravimetry in passivated gas cylinders at 100 μmol mol−1. The PSMs were diluted dynamically to provide calibration mixtures of dry and humidified ammonia atmospheres of known composition in the nmol mol−1 range and were employed as part of establishing a metrological traceability chain to improve the reliability and accuracy of ambient ammonia measurements. The successful implementation of this correction will allow the extension of this rapid on-line spectroscopic technique to exposure chamber validation tests under controlled conditions and ambient monitoring in the field.

Measurement of 177Lu activity and its metrological traceability

The paper presents the work deployed to improve the measurement uncertainty, for the establishment of the international equivalence and national metrological traceability chain in the activity measurement of 177Lu. The work is in direct connection with two international projects, involving this radionuclide. Some aspects are analyzed: (i) Absolute standardization of the solution by the method of 4π(PC)β-γ coincidence method; (ii) Measurements by the gamma-ray spectrometry; (iii) Establishment of the equivalence degree through the key comparisons; (iv) Calibration of the secondary standard, ionization chamber.

A new approach to test torque transducers under dynamic reference regimes

A system is proposed to test torque transducers under reference dynamic regimes, where the reference torque is provided by the application of angular acceleration to a coupled mass moment of inertia. The dynamic regimes include different angular velocity intervals, angular velocity steps and high torque rates. A basic general assembly is proposed and theoretical and practical analyses are performed to determine the primary parameters and depict components. The results show that the angular velocity and torque curves are repeatable and also that the simultaneous responses of torque and acceleration are linear. The mass moments of inertia involved in the measurement process are evaluated. The results provide a positive direction for future tests with transducers and the objective to fill the gap in the metrological traceability chain for torque measurement with dynamic tests and sensor verification.

Does understanding metrological traceability in analytical measurement require going “back to basics”?

Traceability of a measurement result to a common reference is termed ‘metrological traceability’ in the International vocabulary of metrology, VIM [1], entry 2.41. It is a concept of basic importance because metrological traceability is a precondition to ‘metrological comparability of measurement results’ (entry 2.46 in [1]), and comparing measurement results is a major goal of measurement. Comparing measurement results, which are not traceable to a common reference, is a meaningless operation. Sadly enough, the term traceability was not really well understood in the analytical measurement community until about 20 years ago (the first Workshop on ‘‘comparability’’ and ‘‘traceability’’ was held at IRMM in Geel, Belgium in November 1992). Pictures of ‘metrological traceability’ of analytical measurement results have been shown in the form of a ‘metrological traceability chain’ (entry 2.42 in [1]), for instance in an IUPAC study released in 2011 [2]. Yet, the concept and associated term metrological traceability are still giving rise to complicated reasonings, confusing descriptions, and erroneous conclusions. Is it indeed so difficult? Let us try to improve understanding of ‘‘metrological traceability.’’ Usually, a measurement involves the measurement of a ‘certified reference material, CRM’ (entry 5.14 in [1]), i.e., a ‘reference material, RM’ (entry 5.13 in [1]) in which a known quantity or property value with associated uncertainty is embodied. To calibrate the measurement, we like to choose a CRM whose certified value is as close as possible to the expected measured value (entry 2.10 in [1]) of the test sample. We even like the CRM to have a chemical structure (‘‘matrix’’) as similar as possible to the test material structure in which the analyte is embodied. Note: an RM, hence also a CRM (a special case of an RM) can only serve one purpose in one and the same measurement: either being used as a calibrator, or as a trueness control material (entry 5.13 Note 2 in [1]). In our discussion here, we only consider the first of these two functions: using it as a calibrator. What then is a ‘‘reference’’ needed for the definition of metrological traceability? The answer is given in Note 1 of entry 2.41 in VIM [1]: