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Uncertainty evaluation and validation of a comparison methodology to perform in-house calibration of platinum resistance thermometers using a Monte Carlo method.

Silva Ribeiro, A*; Alves e Sousa, J*; Olivera Costa, C*; Pimenta Castro, M*; Cox, M G (2008) Uncertainty evaluation and validation of a comparison methodology to perform in-house calibration of platinum resistance thermometers using a Monte Carlo method. Int. J. Thermophysics, 29 (3). pp. 902-914.

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Abstract

The uncertainty required in laboratories and industry that is associated with temperature measurement based on the practical use of platinum resistance thermometers (PRTs) can commonly be achieved by calibration using temperature reference conditions and comparison methodologies (TCM) instead of the more accurate primary fixed points comparison (ITS90) method. The TCM procedure is suitable for establishing internal traceability chains, connecting reference standards to transfer and working standards.
The data resulting from the TCM calibration method can be treated in a similar way to that prescribed for the ITS90 (International Temperature Scale) interpolation procedure, in order to determine the calibration curve coefficients. When applying this curve, two major tasks are performed: (i) the evaluation of the uncertainty associated with an estimate of a required temperature (a requirement shared by the ITS90 method), based on knowledge of the uncertainties associated with the temperature fixed points used and measured electrical resistances, and (ii) the validation of this practical comparison considering that the reference data is obtained using the ITS90 method.
A conventional approach, using the GUM uncertainty framework, might not provide an adequate uncertainty evaluation for the methods mentioned, because the conditions for its valid use, such as the near-linearity of the mathematical model relating temperature to electrical resistance, and the near-normality of the measurand (temperature), might not apply. Moreover, there can be some difficulty in applying the GUM uncertainty framework relating to the formation of sensitivity coefficients through partial derivatives for a model that, as here, is somewhat complicated and especially not readily expressible in explicit form. Alternatively, uncertainty evaluation can be carried out by a Monte Carlo method (MCM), a numerical implementation of the propagation of distributions that is free from such conditions, and straightforward to apply.
In this paper, (a) the use of MCM to evaluate uncertainties relating to the ITS90 interpolation procedure, and (b) a validation procedure to perform in-house calibration of PRTs by comparison are discussed. An example illustrating (a) and (b) is presented.

Item Type: Article
Keywords: Monte Carlo method, platinum resistance thermometer calibration, uncertainty evaluation
Subjects: Mathematics and Scientific Computing
Mathematics and Scientific Computing > Measurement Uncertainties
Last Modified: 02 Feb 2018 13:15
URI: http://eprintspublications.npl.co.uk/id/eprint/4197

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