Browsing by Author "Lira, I"

Now showing 1 - 8 of 8
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    A Bayesian approach to the consumer's and producer's risks in measurement
    (BUREAU INT POIDS MESURES, 1999) Lira, I
    In industrial practice, the decision to accept or reject an inspected item is usually made on the basis of measurement information. Since this information is rarely complete, it is not possible in general to be absolutely certain about the value of the measurand. As a consequence, incorrect decisions may be made. In this paper, formulae for the probabilities of improperly accepting or rejecting an item are derived. Bayesian statistics provides the theoretical framework, and use is made of the Principle of Maximum Entropy. Applications to the inspection of workpieces and to the verification of measuring instruments are considered and examples are given. The conventional, frequency-based approach is also discussed.
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    A proposal for assessing the uncertainty in the measurement of mean nanoparticle diameter with electron microscopy
    (2021) Lira, I
    Of paramount importance in the field of nanotechnology is the ability to measure reliably the properties of nanomaterials, especially their size. In general, just an estimate of size is not sufficient: a quantitative indication of the estimate's quality in the form of an assessment of its uncertainty is necessary as well. For example, standard ISO/IEC 17025:2017 (general requirements for the competence of testing and calibration laboratories) stipulates that appropriate methods and procedures shall be used for laboratory activities and for the analysis of data, including the identification and quantification of all contributions to the measurement uncertainties. In order to facilitate compliance with requirements such as these, a procedure is proposed for assessing the uncertainty in the evaluation of the mean area-equivalent diameter of a nanoparticle population by scanning electron microscopy. We take as reference the general approach proposed in the guide to the expression of uncertainty in measurement, which is globally seen as the de facto standard for the evaluation of measurement uncertainty, and as such, it is normally required for accreditation. Thus, the proposed approach, primarily intended for guidance, will hopefully be found practical, understandable and useful. Ideally, it should be validated, and perhaps improved, through international intercomparison exercises.
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    Bayesian inference from measurement information
    (1999) Lira, I; Kyriazis, G
    Bayesian inference about a quantity is made through the probability density function that describes the state of incomplete knowledge acquired from measurement. This approach can be applied advantageously to evaluate the data obtained from repeated measurements of a quantity, with or without added information on the variances or error bounds of the indicated values. Results are compared with those obtained using conventional statistical theory. It is concluded that Bayesian inference allows a flexible and natural characterization of the measurement uncertainty.
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    Evaluation of cycles of comparison measurements by a least-squares method
    (2001) Lira, I
    This paper discusses the least-squares procedure for evaluating comparison measurements. The input information consists of a series of indicated values of at least two quantities. The measurands are the differences between the quantities involved. Two algorithms are presented in matrix notation. They can handle the general case in which measurements are correlated. Attention is also paid to independent equal-variance measurements, to the case in which temporal drift occurs and to the consistency of the least-squares adjustment. An example illustrates the application of both algorithms.
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    Expression of the uncertainty of measurement in the calibration of thermometers Part II: Thermocouples
    (1999) Lira, I; Santos, PR
    A model is proposed to evaluate the uncertainty of measurement in the calibration of thermocouples. The model applies to thermocouple types standardized in accordance with electromotive force-temperature reference functions. The difference between the calibration uncertainty and the user's uncertainty is established. Equations are illustrated through an example involving a type S thermocouple calibrated at four fixed points of the International Temperature Scale of 1990 (ITS-90). The example demonstrates the strong dependence of the calibration uncertainty on the selected form of the deviation function.
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    Uncertainty analysis of displacements measured by phase-shifting Moire interferometry
    (ELSEVIER SCIENCE BV, 2004) Cordero, RR; Lira, I
    Phase-shifting Moire interferometry is a whole-field optical technique used to measure displacements. Because of its high sensitivity, its results are affected by even small environmental perturbations. In this paper, the influences of these perturbations are characterized and compared with other systematic effects. The experiment was a uniaxial tensile test. In-plane displacement measurements were performed several times under repeatability conditions at different load stages. The dispersions of these results were evaluated by their standard deviations, which showed fluctuations at twice the fringe frequency. An uncertainty analysis was carried out to include other systematic effects. We found that the local displacement uncertainties depended on the sample elongation and on the reference location. An equation was found for these uncertainties as a function of the total number of fringes occurring. (C) 2004 Elsevier B.V. All rights reserved.
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    Uncertainty analysis of positional deviations of CNC machine tools
    (ELSEVIER SCIENCE INC, 2004) Lira, I; Cargill, G
    The assessment of the measurement uncertainty is an indispensable task in all calibration procedures. By international accord, the evaluation is to be done in accordance with the ISO Guide to the Expression of Uncertainty in Measurement (GUM). To calibrate the positional deviations of computer numerically controlled (CNC) machine tools, calibration laboratories will usually follow the guidelines in ISO 230-2 International Standard. However, that standard does not address uncertainty. In this paper, we present an uncertainty evaluation scheme that is firmly grounded in the GUM, and can therefore be of use as a guide to develop appropriate uncertainty calculations in this and similar types of calibrations. (C) 2003 Elsevier Inc. All rights reserved.
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    Whole-field analysis of uniaxial tensile tests by Moire interferometry
    (ELSEVIER SCI LTD, 2005) Cordero, RR; Francois, M; Lira, I; Vial Edwards, C
    Moire interferometry-a high sensitivity whole-field optical technique-was used to follow the evolution of the deformation process of an aluminium sample subjected to a uniaxial tensile test. This technique allowed us to measure the two in-plane displacement components undergone by the sample, to evaluate the strain, stress and rotation fields, and to appreciate the trends in the deformation pattern that characterized the different stages of the test. Through a subtraction process between fields obtained at two different load levels, we were able to identify the area where strains began to localize and to observe the appearance of the diffuse neck. (c) 2004 Published by Elsevier Ltd.