Measurement uncertainty and traceability

Abstract

Obtaining confidence in a measured value requires a quantitative statement of its quality, which in turn necessitates the evaluation of the uncertainty associated with the value. The basis for the value and the associated uncertainty is traceability of measurement, involving the relationship of relevant quantities to national or international standards through an unbroken chain of measurement comparisons. Each comparison involves calibration of a standard at one level in the chain using a standard at a higher level. Global economy considerations mean that this basis also requires the national measurement institutes to carry out comparative assessment of the degree of equivalence of national standards through their participation in key comparisons. The evaluation of uncertainty of measurement is founded on the use of models of measurement for each stage of the chain and at the highest level to interrelate national standards. Basic aspects of uncertainty evaluation are covered in this paper, and forms for the above types of model considered, with attention given to least squares as a basis for calibration curves (and certain other types of calibration) and also for key comparison data evaluation.

Statistical modeling of thermal radiation transfer in buoyant turbulent diffusion flames

“…A number of works considered this problem, e.g., [8,32]. In this work we have applied a simplified approach, extending that used in [34], to account for the effect of temperature fluctuations on the radiation emission. Decomposition of the temperature and absorption coefficient into average and fluctuating components, T = T + T , κ = κ + κ , followed by time averaging yields:…”

Turbulence radiation interaction in Reynolds-averaged Navier–Stokes simulations of nonpremixed piloted turbulent laboratory-scale flames

“…As a consequence, in turbulent reacting flows, there is interaction between turbulence and radiation (TRI), which is to be considered. The effect of TRI on the radiative heat flux due to temperature fluctuations has been recognized theoretically [1], experimentally [2,3], and by means of computational studies [4][5][6]. Fluctuations of species concentrations are in general assumed to have a minor role, but recent studies illustrated that their impact is not negligible, in particular when advanced spectral methods are applied in the determination of the radiative heat flux [7][8][9].…”

Measurement instability and temporal bias in chemical soil monitoring: sources and control measures

“…Historically, QA progress is the reverse of the direction of the measurement chain. The concept of traceability (e.g., Thompson 1996;Quevauviller 2004;Cox and Harris 2006) which is successful in chemical analysis is less so in soil sampling or site selection, due to lack of appropriate standard calibration samples or sites, and the same holds true for the concept of uncertainty (e.g., Ellison et al 2000, Ramsey andEllison 2007), especially with respect to reference sites. The already mentioned promising approach for coping with measurement instability in chemical soil monitoring covering the measurement chain from the sampling site to the expression of results is to analyze simultaneously site-specific, multiple reference samples with corresponding target samples (Desaules et al 2010), provided all samples are under full control of the sampling theory (Gy 1982;Pitard 1993).…”