Joint Committee For Guides In Metrology Research Articles

An experimental study on capacitive and ultrasonic measurement principles and uncertainty assessment in laboratory wave measurements

Many studies in ocean engineering and related fields need physical wave modelling in controlled environments. Monitoring the free surface elevation over time is essential to forming accurate waves. Various wave height measurement instruments can be used to determine the free surface elevation. However, measurements based on only one principle might lead to uncertain results. This study aims to compare measurements taken with capacitance-type and ultrasonic-type wave height gauges for the same wave models and analyze uncertainty in wave modelling. Nine different wave cases were tested using three-wave heights and three-wave frequencies. In a two-dimensional wave flume, the amplitude and frequency of the waves were controlled with a mechanical wave generator. The Guide on the Expression of Uncertainty in Measurement (GUM) presented by the Joint Committee for Guides in Metrology (JCGM) was used following ITTC procedures and guidelines. The processes for acquiring data, selecting data intervals, estimating amplitude and frequency, and analyzing uncertainty are presented and discussed. The measurements by the ultrasonic-type wave height gauge required a different input stroke for the wave generator and had more uncertainties associated with the amplitude of the measured waves. The findings highlight that identifying differences in measurement principles is significant for wave modelling.

On quantity, value, unit, and other terms in the JCGM International Vocabulary of Metrology

The Joint Committee for Guides in Metrology (JCGM) is in the process of revising the third edition of the International Vocabulary of Metrology (VIM3). Open discussion of the concepts, terms, and definitions used in metrology by the international community in peer reviewed journals could be constructive inputs to the JCGM deliberations on revising the VIM3. The VIM3 definitions of quantity, quantity value, unit of measurement, measurement standard, measurement, uncertainty in measurement, true quantity value, coverage interval, coverage probability, and metrology are reviewed. Some defects are observed. Proposals are offered to stimulate discussions which may lead to better concepts, terms, and definitions for metrology.

Measurements of Natural Radionuclides by Gamma Spectrometry: Analytical and Numerical Approach with Uncertainty Evaluation

Guide to the Expression of Uncertainty in Measurement (GUM) based on Law of Propagation of Uncertainty is widely used in estimation of uncertainty associated with measurements. However, Joint Committee for Guides in Metrology (JCGM) (JCGM 101:2008, 2008) suggests the use of Monte Carlo method (MCM) which is based on propagation of distributions as an alternate tool for evaluation of uncertainty of measurement. The present study deals with procedure for application of MCM to estimate the uncertainty of measurement of radioactivity in soil, carried out by Gamma spectrometry. In order to enhance the sampling efficiency and to obtain a desired level of accuracy of the outcomes, Latin hypercube sampling strategies are applied in uncertainty assessment in MCM approach in addition to conventional random sampling. A comparison of the findings of two methodologies is discussed, and conclusion is drawn.

Monte Carlo Simulation in Uncertainty Evaluation: Strategy, Implications and Future Prospects

Monte Carlo simulation (MCS) is an approach based on the propagation of the full probability distributions. It was introduced by the Joint Committee for Guides in Metrology (JCGM) in the supplement I-JCGM 101:2008. It is used to resolve the problem of calculating measurement uncertainties of complex measurands through simulation of random variables. Further, supplement II on “Extension to any number of output quantities” was published in 2011 and supplement III on “Modelling” is under publication. These supplements cover broader range of measurement issues which are not handled using law of propagation of uncertainty (LPU) alone and provide an alternative method to the conventional LPU approach. The MCS method plays a vital role in cases, where the linearization of the model does not provide enough depiction, or the probability density function of the output quantity deviates considerably from the Gaussian distribution. The SWOT analysis describes the strengths, weaknesses, opportunities and threats associated with the use of MCS in the measurement uncertainty evaluation and is addressed in this paper. The paper also summarizes the implications and prospects associated with the use of MCS in uncertainty evaluation for wide usage in solving problems in physical, biological and engineering sciences.

True value and uncertainty in the GUM

The signal contribution of the Guide to the Expression of Uncertainty in Measurement (GUM) is the operational view of the uncertainty in measurement as a parameter, associated with a result of a measurement (measured value), that characterizes the dispersion of the values that could reasonably be attributed (assigned) to the measurand. Subsequent documents from the Joint Committee for Guides in Metrology (JCGM) have restored an essentially pre-GUM view of uncertainty and called it a coverage interval. The idea of a coverage interval requires the measurand to have a unique true value; therefore, it does not apply to an ordinary measurand that has a range of true values. Most measurands of interest in metrology are ordinary measurands. Therefore, the JCGM idea of a coverage interval is of little use in metrology. We think that the divergence of the JCGM documents from the GUM is a consequence of misunderstanding (i) the true value and related concepts in the GUM, and (ii) the operational view of uncertainty. This paper is an attempt to correct these misunderstandings.

Measurement uncertainty and its connection with true value in the GUM versus JCGM documents

This paper discusses the concept of uncertainty in measurement and its connection with true value as defined in the Guide to the Expression of Uncertainty in Measurement (GUM), and three subsequent documents from the Joint Committee for Guides in Metrology (JCGM): JCGM 101 (GUM-S1), JCGM 104, and JCGM 200 (VIM3). An ordinary measurand is specified by its description. The GUM and the JCGM 200 explain that every ordinary measurand has a range of true values. The GUM requires that the measurand should be described in sufficient detail with the consequence that the range of its true values is small enough for it to be adequately characterized by a single scalar measured value with standard uncertainty. The concept of uncertainty in measurement as established by the GUM does not refer to the theoretical concepts of true value and error. So, it applies whether the measurand has a unique true value or a range of true values. The JCGM 101 has introduced a concept of uncertainty in measurement called a coverage interval with a stated coverage probability. The concept of a coverage interval requires the measurand to have a unique true value, so it does not apply to an ordinary measurand that has a range of true values. Most measurands of interest in metrology are ordinary measurands; therefore, the JCGM idea of a coverage interval is of little use.

Redressing grievances with the treatment of dimensionless quantities in SI

The International System of Units (SI) and its associated methods adhere to a design principle in which all kinds of quantities are described in terms of a standard set of dimensions. It is a corollary of that principle that quantities having no extent in any of those dimensions (“dimensionless quantities”) will not be distinguishable as different kinds through dimensional analysis alone, and the formality of quantity calculus will be of no help in preventing mistakes where different kinds of dimensionless quantities are confused.This corollary has led to controversies involving abuse of the unit hertz and elimination of radians and steradians as being equivalent to the number 1. In addition, official rejection of the use of so-called counting units in conjunction with accepted units has been repeatedly criticized and is often ignored.The proposed resolution is to extend quantity calculus to discern different kinds of dimensionless quantities as well as it currently discerns different kinds of dimensional quantities. The extended system provides a formal interpretation of commonly-used workarounds in terms that are compatible with SI. Should the extended quantity calculus become accepted by consensus in the future, a guide to its use would expand the set of references provided by the Joint Committee for Guides in Metrology (JCGM), which currently lacks a definitive reference on quantity calculus.

Comparing methods for evaluating measurement uncertainty given in the JCGM ‘Evaluation of Measurement Data’ documents

The Joint Committee for Guides in Metrology (JCGM) publishes and maintains reference documents relating to general aspects in metrology. Working Group 1 of the JCGM is responsible for the Evaluation of Measurement Data series of documents that gives information for evaluating and expressing uncertainty in measurement. This paper compares several methods for evaluating measurement uncertainty that are described in these documents. Emphasis is given to situations where more than one input quantity is measured simultaneously. This leads to an investigation into how these methods perform when these quantities are high-frequency electromagnetic scattering parameters. It is shown that for measurements involving a large number of input quantities, such as those involving microwave scattering parameters, the required number of observations for the approach given in the supplements to the Guide to the Expression of Uncertainty in Measurement (GUM) to work can be prohibitively large.

Towards a new GUM—an update

The contents of the current edition, JCGM 100:2008, of the Guide to the Expression of Uncertainty in Measurement (GUM) and its Supplements are reviewed and remarks made concerning a proposed revision of the GUM. A committee draft of the revision was circulated to member organizations of the Joint Committee for Guides in Metrology (JCGM) and all national metrology institutes in December 2014. The motivation for the proposed changes is given and reactions to the committee draft are summarized. Some of the contents of this paper are solely an expression by the authors and do not constitute an official statement by the JCGM.

Removing divergence of JCGM documents from the GUM (1993) and repairing other defects

The mission of the Joint Committee for Guides in Metrology (JCGM) is to maintain and promote the use of the Guide to the Expression of Uncertainty in Measurement (GUM) and the International Vocabulary of Metrology (VIM, second edition). The JCGM has produced the third edition of the VIM (referred to as VIM3) and a number of documents; some of which are referred to as supplements to the GUM. We are concerned with the Supplement 1 (GUM-S1) and the document JCGM 104. The signal contribution of the GUM is its operational view of the uncertainty in measurement (as a parameter that characterizes the dispersion of the values that could be attributed to an unknown quantity). The operational view promulgated by the GUM had disconnected the uncertainty in measurement from the unknowable quantities true value and error. The GUM-S1 has diverged from the operational view of the uncertainty in measurement. Either the disparities should be removed or the GUM-S1 should not be referred to as a supplement to the GUM. Also, the GUM-S1 has misinterpreted the Bayesian concept of a statistical parameter and the VIM3 definitions of coverage interval and coverage probability are mathematically defective. We offer practical suggestions for revising the GUM-S1 and the VIM3 to remove their divergence from the GUM and to repair their defects.

Revision of the ‘Guide to the Expression of Uncertainty in Measurement’. Why and how

The ‘Guide to the Expression of Uncertainty in Measurement’ has now served for more than twenty years. In this communication, after attempting a balance over this period, the logical reasons are given that, on the one hand, led to the decision to update such a successful document, and, on the other hand, dictated the modifications that are being carried out with respect to the current 2008 edition.The author is convener of the Joint Committee for Guides in Metrology (JCGM) Working Group 1 (Guide to the expression of uncertainty in measurement, or GUM). The opinion expressed in this paper does not necessarily represent the view of this Working Group.

Expanding needs for metrological traceability and measurement uncertainty

In our daily life, numerical evaluation of a quantity is normally required not only for scientific decision but also for judgment of products. Under the Metre Convention, ideal system of the International System of units (SI) is globally recognized and utilized in many fields of science and technology [1]. Some documented standards such as International Vocabulary of Metrology (VIM) [2], and Guide to the expression of Uncertainty in Measurement (GUM) [3] are edited and published by the Joint Committee for Guides in Metrology (JCGM) and commonly introduced in the fields of metrology, science and conformity assessment in connection with ISO/IEC 17025. This paper describes the recent situation in measurement science, and how to obtain a reliable measurement result using the expression of metrological traceability together with measurement uncertainty. In the paper, a response to Prof. Ludwik Finkelstein’s message for ‘challenges and problems to future advancement in measurement science’ is also reported.

Glossary of Analytical and Metrological Terms from the International Vocabulary of Metrology (2008)

The Joint Committee for Guides in Metrology (JCGM) has introduced a revised third edition of the International Vocabulary of Metrology – basic and general concepts and associated terms (VIM: 2008) that replaces the second edition which was published in 1993. This article includes a table containing the terms and definitions that are most relevant to geoanalysis, designed to extend awareness and to promote best practice in the use of this terminology. Comparison is made, where appropriate, with definitions from the earlier 1993 definitions, to demonstrate the way in which thinking in metrological concepts has evolved over this time period.

Two Evaluation Budgets for the Measurement Uncertainty of Glucose in Clinical Chemistry

BackgroundMeasurement uncertainty characterizes the dispersion of the quantity values attributed to a measurand. Although this concept was introduced to medical laboratories some years ago, not all medical researchers are familiar with it. Therefore, the evaluation and expression of measurement uncertainty must be highlighted using a practical example.MethodsIn accordance with the procedure for evaluating and expressing uncertainty, provided by the Joint Committee for Guides in Metrology (JCGM), we used plasma glucose (Glu) as an example and defined it as the measurand. We then analyzed the main sources of uncertainty, evaluated each component of uncertainty, and calculated the combined uncertainty and expanded uncertainty with 2 budgets for single measurements and continuous monitoring, respectively.ResultsDuring the measurement of Glu, the main sources of uncertainty included imprecision, within-subject biological variance (BVw), calibrator uncertainty, and systematic bias. We evaluated the uncertainty of each component to be 1.26%, 1.91%, 5.70%, 0.42%, and -2.87% for within-run imprecision, between-day imprecision, BVw, calibrator uncertainty, and systematic bias, respectively. For a single specimen, the expanded uncertainty was 7.38% or 6.1±0.45 mmol/L (κ=2); in continuous monitoring of Glu, the expanded uncertainty was 13.58% or 6.1±0.83 mmol/L (κ=2).ConclusionsWe have demonstrated the overall procedure for evaluating and reporting uncertainty with 2 different budgets. The uncertainty is not only related to the medical laboratory in which the measurement is undertaken, but is also associated with the calibrator uncertainty and the biological variation of the subject. Therefore, it is helpful in explaining the accuracy of test results.

‘Verification’ versus ‘validation’: a terminological comparison

The present diversity in the definitions and relations of ‘verification’ and ‘validation’ is impractical for such transdisciplinary concepts. General dictionaries, international special language vocabularies and minor lists show that the respective recent formulations by the International Organization for Standardization (ISO) and the Joint Committee for Guides in Metrology (JCGM) are the most quoted. The characteristics of these concepts are elucidated terminologically, and separate concept systems are made for ISO and JCGM to arrive at a preference for a generic rather than an associative relation.

Comparison of ISO-GUM and Monte Carlo methods for the evaluation of measurement uncertainty: Application to direct cadmium measurement in water by GFAAS

The propagation stage of uncertainty evaluation, known as the propagation of distributions, is in most cases approached by the GUM (Guide to the Expression of Uncertainty in Measurement) uncertainty framework which is based on the law of propagation of uncertainty assigned to various input quantities and the characterization of the measurand (output quantity) by a Gaussian or a t-distribution. Recently, a Supplement to the ISO-GUM was prepared by the JCGM (Joint Committee for Guides in Metrology). This Guide gives guidance on propagating probability distributions assigned to various input quantities through a numerical simulation (Monte Carlo Method) and determining a probability distribution for the measurand.In the present work the two approaches were used to estimate the uncertainty of the direct determination of cadmium in water by graphite furnace atomic absorption spectrometry (GFAAS). The expanded uncertainty results (at 95% confidence levels) obtained with the GUM Uncertainty Framework and the Monte Carlo Method at the concentration level of 3.01μg/L were ±0.20μg/L and ±0.18μg/L, respectively. Thus, the GUM Uncertainty Framework slightly overestimates the overall uncertainty by 10%. Even after taking into account additional sources of uncertainty that the GUM Uncertainty Framework considers as negligible, the Monte Carlo gives again the same uncertainty result (±0.18μg/L). The main source of this difference is the approximation used by the GUM Uncertainty Framework in estimating the standard uncertainty of the calibration curve produced by least squares regression. Although the GUM Uncertainty Framework proves to be adequate in this particular case, generally the Monte Carlo Method has features that avoid the assumptions and the limitations of the GUM Uncertainty Framework.

Some remarks on definitions and, in particular, on the definition of the term calibration

Confucius (Analects xiii:3) ‘It is not possible to have any valid argument until rigorously defined terms are agreed’. In radiation protection dosimetry, we perhaps need to take as the fundamental sources of our definitions for personal dosimetry and area monitoring, mainly those three committees—the Joint Committee for Guides in Metrology (JCGM), which gives definitions for metrology generally; the International Commission on Radiation Units and Measurements (ICRU), which gives basic physical quantities and units for ionising radiation; and the International Commission on Radiological Protection (ICRP) for quantities considering the health effect of ionising radiation, for example effective dose, equivalent dose and the quality factor/linear energy transfer function. The JCGM, chaired by the Director of the BIPM, is formed by the seven international organisations that had prepared the original versions of the Guide to the Expression of Uncertainty in Measurement (GUM) and the International Vocabulary of Basic and General Terms in Metrology (VIM), namely the International Bureau of Weights and Measures (BIPM), the International Electrotechnical Commission (IEC), the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC), the International Organization for Standardization (ISO), the International Union of Pure and Applied Chemistry (IUPAC), the International Union of Pure and Applied Physics (IUPAP) and the International Organization of Legal Metrology (OIML). In 2005, the International Laboratory Accreditation Cooperation (ILAC) joined the seven founder international organisations. The Joint Committee took on the work of the ISO Technical Advisory Group 4 (TAG 4), which had developed the GUM and the VIM. Two of the organisations involved in the JCGM, ISO and IEC are also jointly revising the ISO 31 series of standards as the new 80 000 series on quantities and units.

Evolution of the ‘Guide to the Expression of Uncertainty in Measurement’

A number of Joint Committees of the Bureau International des Poids et Mesures and other international organizations carry out particular tasks of common interest. The Joint Committee for Guides in Metrology (JCGM) has amongst its tasks the promotion of the ‘Guide to the Expression of Uncertainty in Measurement’ (GUM), the preparation of further documents for its broad application, and revision and promotion of the use of the ‘International Vocabulary of Basic and General Terms in Metrology’. This paper summarizes the documents relating to the GUM planned by JCGM.

Meeting of JCGM (Joint Committee for Guides in Metrology), Working Group 2 (Successor of ISO/TAG 4/WG 1) April 30, 1998, Geneva, Switzerland

Meeting of JCGM (Joint Committee for Guides in Metrology), Working Group 2 (Successor of ISO/TAG 4/WG 1) April 30, 1998, Geneva, Switzerland