Concept Of Measurement Uncertainty Research Articles

Measurement uncertainty.

Over time, the metrological concept of uncertainty in measurement has been very successfully integrated into laboratory sciences. For proper implementation, an understanding of specific metrology terminology and additional concepts such as metrology traceability and commutability is necessary. Although the original thinking about measurement uncertainty in laboratory medicine suggests the complexity of the concept, it basically refers to the result as the end product of the entire laboratory process. Although the data on measurement uncertainty can be expressed quantitatively, the basis of this concept is the continuous evaluation of all phases of the laboratory process. This means that laboratory experts should keep in mind that the extra-analytical phases (on which the uncertainty of the measurement results may depend the most) must be continuously monitored. The analytical phase can be "held in check" by established internal and external quality control processes. It is the internal/external quality control data that is used to calculate the numerical value of the measurement uncertainty of the measurement results. Although over time the awareness of laboratory experts regarding the concept of measurement uncertainty has increased, there are still many challenges that need to be followed, and the last one is how to achieve a balance between understanding, evaluation process and application of measurement uncertainty data of measurement results for complete and ultimate practical use.

Software for measurement uncertainty assessment and actual metrological characteristics of viscometers

The issue of implementation of software for rapid assessment of uncertainty of metrological control results of measuring instruments used in the field of state metrological control and supervision in calibration and evaluation of actual metrological characteristics of operating viscosimeters was considered. An interpretation of the application of the EXCEL program and other software for the special methodology for automating uncertainty calculations developed by us was carried out, which significantly simplified the work and reduced the time spent by specialists in the metrological laboratory. Basic requirements of comparison of software for calculation, calculation and estimation of uncertainty in the realm of mathematical models of validated techniques are determined. The experimental results of the comparative analysis taking into account the set tasks are presented, the most common and effective universal software for calculating the uncertainty of the results of the experiment. The object of the study is universal software for estimating the uncertainty of measurements and other metrological characteristics of viscometers, structured by types of measurements, in the graphic programming environment. The software can be used both in laboratories and in industrial premises. The workplace can be both a metrological laboratory, the working area of which is a table with instruments, and a production room. As a rule, accredited laboratories do not have a special staff of metrologists or specialists who perfectly understand the basics of mathematical statistics and the concept of measurement uncertainty. The complexity and necessary amounts of calculations that are carried out in assessing the uncertainty of measurements require significant laboratory resources.

Dynamic measurement applied to anemometer verification

This paper strengthens the concept of uncertainty in measurement by testing an anemometer in a wind tunnel and by employing the Least Squares Method (LSM) to fit a curve to the experimental data. Three test procedures were used to verify the anemometer. In the first experiment, the steady state airflow velocity measured by the wind tunnel instrumentation and the velocity readings carried out by the anemometer under test are compared. A second experiment proposes a new method which consists of taking velocity values from a linear fitting performed on a triangular signal, considered as a standard input signal, and the velocity values obtained from the linear fitting performed on the anemometer response. Both sets of fitted data are compared using the same time values. The third experiment considers the anemometer as a linear time-invariant device, so we apply the input triangular signal to an ideal second-order model and the model output values are compared to the anemometer output signal. The first experiment is static as the velocities are constant during measurement. The second and third experiments are considered dynamic as the quantities involved in the measurement change over time. The velocity values and associated uncertainties obtained by employing the static, linearized and second order methods are presented. An uncertainty increase in the order of 10 when going from the static to the linearized method, was observed. The same order of increase is obtained when comparing the uncertainties associated with the linearized and the second order methods.

A practical approach example to measurement uncertainty: Evaluation of 26 immunoassay parameters.

IntroductionMeasurement uncertainty is a non-negative parameter that characterizes the distribution of all values appropriate to the measured size and is associated with the measured result. In this study, we aimed to compare the results with various suggestions and produce more qualified results by calculating the measurement uncertainties of the immunoassays like fertility hormones, drug concentration tests, cardiac markers, thyroid function tests and tumour markers.Materials and methodsUncertainty calculation was made in accordance with the top-down approach according to Nordtest guide. The 12-month study of internal and external quality assessment results were used. The parameters of drug concentration tests were performed on the Abbott Architect c8000, other hormones/markers on the i2000 of the same brand.ResultsFactors that increased the measurement uncertainty of a test were due to external quality control data. The calculations showed that 13 of 26 parameters satisfied quality requirements. The highest uncertainty value, with 28% belonged to cancer antigen 19-9 test. The lowest value was calculated for prolactin with 8.3%. Dehydroepiandrosterone sulfate and phenytoin performed poorly in terms of measurement uncertainty, although internal and external quality control assessment results were considered favourable for both.ConclusionIt is recommended that the concept of measurement uncertainty, which plays an important role in the total quality performance of the laboratory, should be followed up by the clinical laboratory experts at certain time intervals and should be increased the awareness of clinicians about the subject.

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.

A General Mathematical Approach Based on the Possibility Theory for Handling Measurement Results and All Uncertainties

The concept of measurement uncertainty was introduced in the 1990s by the “Guide to the expression of uncertainty in measurement”, known as GUM. The word uncertainty has a lexical meaning and reflects the lack of exact knowledge or lack of complete knowledge about the value of the measurand. Thanks to the suggestions in the GUM and following the mathematical probabilistic approaches therein proposed, an uncertainty value can be found and be associated to the measured value. In the last decades, however, other methods have been proposed in the literature, which try to encompass the definitions of the GUM, thus overcoming its limitations. Some of these methods are based on the possibility theory, such as the one known as the RFV method. The aim of this paper is to briefly recall the RFV method, starting from the very beginning and the initial motivations, and summarize in a unique paper the most relevant obtained results.

Recommendations for the application and follow-up of quality controls in medical laboratories

This is a translation of the paper “Recommendations for the application and follow-up of quality controls in medical biology laboratories” published in French in the journal Annales de Biologie Clinique (Recommandations pour la mise en place et le suivi des contrôles de qualité dans les laboratoires de biologie médicale. Ann Biol Clin (Paris). 2019;77:577-97.). The recommendations proposed in this document are the result of work conducted jointly by the Network of Accredited Medical Laboratories (LABAC), the French Society of Medical Biology (SFBC) and the Federation of Associations for External Quality Assessment (FAEEQ). The different steps of the implementation of quality controls, based on a risk analysis, are described. The changes of reagent or internal quality control (IQC) materials batches, the action to be taken in case of non-conform IQC results, the choice of external quality assessment (EQA) scheme and interpretation of their results as well as the new issue of analyses performed on several automatic systems available in the same laboratory are discussed. Finally, the concept of measurement uncertainty, the robustness of the methods as well as the specificities of near-patient testing and rapid tests are described. These recommendations cannot apply for all cases we can find in medical laboratories. The implementation of an objective alternative strategy, supported with documented evidence, might be equally considered.

51‐1: Invited Paper: The International Commission on Illumination (CIE) and Aspects of Measurement Uncertainty in Photometry

The International Commission on Illumination (CIE) is the umbrella organization of the various national lighting societies. On the one hand it is a standardization authority, on the other hand it is also a scientific organization. This article shows current fields of activity that are relevant for the display industry and provides some information about the concept of measurement uncertainty also applicable to the measurement of displays.

Blood and breath alcohol test results: Uncertainty at the interface of science and law

Alcohol is well known for its ability to impair human faculties, which creates risks when driving a vehicle or when performing safety- and risk-sensitive tasks in workplaces. The article aims to highlight some shortcomings in the legal-scientific approach for alcohol testing in South Africa. In particular, we investigate the measurement uncertainty of blood alcohol test results, which is critical in adjudicating over-the-limit cases. The South African regulatory framework for alcohol testing in the criminal- and private-law environments is examined from an analytical due-process perspective, considering measurement uncertainty and other well-established scientific principles which are essential at the interface of science and law. Special attention is paid to the National Road Traffic Amendment Bill, which aims to decrease the alcohol limit to zero. We found that the measurement uncertainty concept has not yet been received into the South African legal system, even though it is a well-established scientific principle. We suggest changes to the current alcohol legislation to accommodate the measurement uncertainty principle and the related likelihood ratio, which we believe could assist in quantifying the odds of compliance. In particular, we believe that our suggestions regarding quantification and reporting of measurement uncertainty can assist the courts and tribunals to avoid false-positive errors that may have a devastating effect on innocent subjects.

Evaluating uncertainty in sensory analysis. A case study of the panel of tasters of the Dão Regional Wine Commission

Metrological reliability in the sensory evaluation of products is of fundamental importance in ensuring the comparability of results. The issue of uncertainties regarding measured data in such contexts has led to new scientific approaches in the field of sensory analysis, which have become fundamental to studies that seek to compare results of sensory measurement and analysis, including studies regarding wine. The new normative framework, ISO/IEC 17025:2017, which replaces the previous version ISO/IEC 17025, published in 2005, draws attention to the concept of measurement uncertainty, stating that it should be considered by laboratories when assessing conformity and quantifying risks arising in decision-making processes. The present work examines the evaluation of uncertainty and its importance for the interpretation of results from sensory analyses, examining sensory analysis tests related to the certification of the Designation of Origin “Dão”, the Designation of Origin “Lafões” and the Geographical Indication “Terras do Dão”, carried out by a panel composed of 20 tasters of the Dão Regional Wine Commission, trained and accredited by the standard NP ISO/IEC 17025:2018. The results achieved led to a conclusion that the panel presented different values of uncertainty regarding the tests to determine sensory attributes. The results and respective values of uncertainty made it possible to assess the performance of the panel of tasters and to establish a level of risk (false accept, false reject and statistical assumptions) for decision rules used when issuing statements of conformity. In this study, a new methodology was presented to determine an estimate of uncertainty to be applied in the interpretation of results related to sensory analysis tests of wines for the certification of Designation of Controlled Origin “Dão”, Designation of Origin “Lafões” and Geographical Indication “Terras do Dão. This progress led to an evolution in the day-to-day work of the Dão Regional Wine Commission tasting chamber enabling greater solidity in the opinions issued, in line with the requirements of the reference standard NP ISO/IEC 17025: 2018.

RESEARCH AND APPLICATION OF METHODS FOR CALCULATING THE MEASUREMENT UNCERTAINTY OF INDUSTRIAL FLOWMETERS

To create conditions for the recognition of Kazakhstani certificates of conformity and the results of product tests, an assessment of measurement uncertainty is required. In this regard, there has been an increase in the practical application in Kazakhstan of the concept of measurement uncertainty. The authors developed a physical stand for a mobile complex designed to verify electromagnetic flowmeters at the place of operation. To obtain verification results, programs were developed to calculate the uncertainty of an electromagnetic flowmeters using the NI LabView software. In addition, a model for estimating the uncertainty of the relative error of flowmeters was proposed, and the measurement uncertainty was estimated using three methods: standard, Monte Carlo and Kragten. Finally, a comparative analysis was conducted on the results of the estimation of the uncertainty of the relative error of the industrial electromagnetic flowmeter. All methods give standard uncertainty values that do not exceed the acceptable range of relative error (± 1%). However, Monte Carlo method gives better results for sufficiently large number of simulations. No significant differences between the results obtained using standard and Kragten methods were discovered. The Kragten method is preferable in the absence of the need to calculate the sensitivity coefficients when calculating the total standard uncertainty, which is important for complex measurement equations.

ERROR OF CONTROL OF ELECTRICAL INSULATION STRUCTURES BY DIELECTRIC ABSORPTION PARAMETERS ACCORDING TO THE CONCEPT OF UNCERTAINTY OF MEASUREMENTS

Introduction. Measurements on alternating current of dielectric absorption parameters – capacitance and dielectric loss tangent tgδ allow us to evaluate the quality of insulation of cables, electrical machines, transformers, etc., both at the technological stage of manufacture and in operation. An increase in the reliability of the measurement result of the parameters is provided by a decrease in the measurement error due to the improvement of measuring instruments and measurement methods and an increase in the number of measurements Purpose. The estimation of the error of control of electrical insulation structures by dielectric absorption parameters in accordance with the concept of measurement uncertainty. Methodology. The error of measurements of the capacitance and the tangent of the dielectric loss angle is estimated using the example of a twisted unshielded pair of category 5e. A statistical analysis of the results of multiple measurements of the capacitance and the tangent of the dielectric loss angle of an unshielded cable is carried out. The linear regression equations for the measured values of the dielectric absorption parameters of the number of measurements are obtained. Practical value. Ensuring unity in the methods for estimating the error of measurement results, both when using the traditional concept of «measurement result error» and when introducing the concept of «measurement result uncertainty» into practice, it will allow to unambiguously interpret and correctly compare the results of measurements of the capacitance and tangent of the dielectric loss angle of electrical insulation structures.

The Kalman Filter Uncertainty Concept in the Possibility Domain

The Kalman filter (KF) is one of the most important and common optimal recursive data processing algorithms in many applications characterized by linear dynamical behavior and affected by random zero-mean white Gaussian noise. However, when measurement processes are considered, inaccuracy is not only due to noise but also to several contributions to uncertainty that can be due to both random and uncompensated systematic effects. Therefore, when the KF is used on experimental data, all uncertainty contributions should be considered. While several proposals are available in the literature to modify the KF in order to consider different probability distributions and systematic effects, represented both in probability and possibility domains, they are not fully compliant with the uncertainty concept adopted in metrology. The aim of this paper is, hence, to reformulate the KF theory within the possibility domain in compliance with the measurement uncertainty concept, in order to be able to consider both the random and systematic contributions to uncertainty (regardless of their distribution) that may affect the measurement process. An experimental setup is considered and the results obtained under different assumptions are reported.

Use of the Concept of Measurement Uncertainty in Applied Problems of Metrology

Problems related to the use of the concept of measurement uncertainty in different types of metrological problems, such as calibration, type evaluation, and the verification of measuring instruments are considered. A classification of risks in the assessment of the correspondence of measuring instruments to specific requirements is presented. Examples of conformity decision rules used in verification of measuring instruments are presented and the role of measurement uncertainty in these rules is demonstrated.

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.

Development of the Concept of Uncertainty in Measurement and Revision of the Guide to the Expression of Uncertainty in Measurement. Part 2. Comparative Analysis of Basic Provisions of the Guide and Their Planned Changes

A comparative analysis has been done on key provisions of the current edition of the Guide to the Expression of Uncertainty in Measurement and changes thereto caused by the planned revision based on the Bayesian approach. Some possible changes of the calculation of uncertainty in measurement that are the most significant ones for practice are examined in connection with the development and introduction of the new edition of this document.

Development of the Concept of Uncertainty in Measurement and Revision of Guide to the Expression of Uncertainty in Measurement. Part 1. Reasons and Probability-Theoretical Bases of the Revision

Development of the Concept of Uncertainty in Measurement and Revision of Guide to the Expression of Uncertainty in Measurement. Part 1. Reasons and Probability-Theoretical Bases of the Revision

Measurement uncertainty of transmission line resistance calculation using ‘Guide to the Expression of Uncertainty in Measurement’ and adaptive Monte–Carlo method

The study presents the evolution of a measurement uncertainty concept from the traditional error approach up to modern calculation methods. First, a method based on the internationally accepted document Guide to the Expression of Uncertainty in Measurement is presented considering the conditions for its application and fundamental deficiencies. Next, the Monte–Carlo (MC) method, as an alternative, is presented together with an adaptive MC method. After a theoretical comparison between the latter methods, the practical calculation of a transmission line resistance is performed. The results show that the adaptive MC method is reliable, unlike the traditional approach, which shows a significant overestimation of the standard deviation owing to the non-linearity of the mathematical model and associated distributions other than Gaussian.

Assessment on shock pressure acquisition from underwater explosion using uncertainty of measurement

This study aims to verify experimentally the specifications of the data acquisition system required for the precise measurement of signals in an underwater explosion (UNDEX) experiment. The three data acquisition systems with different specifications are applied to compare their precision relatively on maximum shock pressures from UNDEX. In addition, a method of assessing the acquired signals is suggested by introducing the concept of measurement uncertainty. The underwater explosion experiments are repeated five times under same conditions, and assessment is conducted on maximum quantities acquired from underwater pressure sensors. It is confirmed that the concept of measurement uncertainty is very useful method in accrediting the measurement results of UNDEX experiments.

Uncertainty of measurement and clinical value of semen analysis: has standardisation through professional guidelines helped or hindered progress?

This article suggests that diagnostic semen analysis has no more clinical value today than it had 25-30years ago, and both the confusion surrounding its evidence base (in terms of relationship with conception) and the low level of confidence in the clinical setting is attributable to an associated high level of 'uncertainty'. Consideration of the concept of measurement uncertainty is mandatory for medical laboratories applying for the ISO15189 standard. It is evident that the entire semen analysis process is prone to error every step from specimen collection to the reporting of results and serves to compound uncertainty associated with diagnosis or prognosis. Perceived adherence to published guidelines for the assessment of sperm concentration, motility and morphology does not guarantee a reliable and reproducible test result. Moreover, the high level of uncertainty associated with manual sperm motility and morphology can be attributed to subjectivity and lack a traceable standard. This article describes where and why uncertainty exists and suggests that semen analysis will continue to be of limited value until it is more adequately considered and addressed. Although professional guidelines for good practice have provided the foundations for testing procedures for many years, the risk in following rather prescriptive guidance to the letter is that unless they are based on an overwhelmingly firm evidence base, the quality of semen analysis will remain poor and the progress towards the development of more innovative methods for investigating male infertility will be slow.