1,721,032 research outputs found
Joint Random-Fuzzy Variables: A Tool for Propagating Uncertainty Through Nonlinear Measurement Functions
No full textA still open issue, in uncertainty evaluation, is asymmetrical distributions of the values that can be attributed to the measurand. This problem generally becomes not negligible when the measurement function is highly nonlinear. In this case, the law of uncertainty propagation suggested by the Guide to the Expression of Uncertainty in Measurement is not correct any longer, and only Monte Carlo simulations can be used to obtain such distributions. This paper shows how this problem can be solved in a quite immediate way when measurement results are expressed in terms of random-fuzzy variables. Under this approach, nonrandom contributions to uncertainty can also be considered. An experimental example is reported and the results compared with those obtained by means of Monte Carlo simulations, showing the effectiveness of the proposed approach
LA COMBINAZIONE DELLE DISTRIBUZIONI DI POSSIBILITA’ NELL’OTTICA DELL’INCERTEZZA DI MISURA
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Processing Dependent Systematic Contributions to Measurement Uncertainty
No full textIn the measurement field, the correlation of two
uncertainty contributions is a form of probabilistic association
that can significantly affect the final uncertainty associated to the
measurement result. The Guide to the expression of uncertainty in
measurement recommends a mathematical approach to deal with
correlated random contributions to measurement uncertainty. A
similar kind of association, or dependence, can characterize also
different systematic contributions to uncertainty and should be
taken into account when evaluating their effect on the final measurement uncertainty. This paper discusses a new approach to
handle such systematic contributions when they are represented
by symmetric possibility distributions (PDs) of the same shape.
This method allows one to build the joint PD of two systematic
contributions, both dependent and independent, and propagate
them through a generic measurement function
The Construction of Joint Possibility Distributions of Random Contributions to Uncertainty
Full text linkAn application to combine and compare measurement results expressed in terms of Random-Fuzzy Variables
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Simplified Modeling and Identification of Nonlinear Systems Under Quasi-Sinusoidal Conditions
Full text linkThis paper proposes a simplified Volterra model able to represent the steady-state behavior of nonlinear systems in quasi-sinusoidal conditions. A wide class of nonlinear systems can be modeled using the conventional Volterra approach, but as the order of nonlinearity or the memory length increases, the number of coefficients grows exponentially, thus making the identification of the Volterra model troublesome. By considering a system whose input is a periodic signal containing a main frequency component which is much higher than the others, it is possible to drastically reduce the number of coefficients of its frequency-domain Volterra model without affecting the model accuracy. The proposed technique is particularly suitable to represent the behavior of the electrical devices connected to the ac mains, since they typically operate in quasi-sinusoidal conditions. In particular, its application to voltage and current transducers takes on great importance in the field of instrumentation and measurement, since it allows overcoming their usual characterization. Thanks to the proposed model, dynamics and nonlinearities can be considered simultaneously, while avoiding the complexity usually associated with the conventional Volterra approach. For example, the proposed technique is applied to model a Hammerstein system, which is often employed to represent the behavior of electrical devices, and the results are deeply discussed
Modello semplificato per la valutazione dell'effetto di ripple di corrente su una fuel cell commerciale
No full textLa crescente diffusione delle fuel cell ha fatto emergere negli ultimi anni problematiche di misura di particolare importanza in fase di caratterizzazione delle prestazioni della cella e identificazione di parametri di circuiti equivalenti. Questo articolo riaffronta il problema della valutazione degli effetti che il ripple di corrente introdotto dai convertitori di potenza può avere su una fuel cell, mettendo in evidenza i problemi di misura che si presentano nella caratterizzazione di questi effetti e le criticità associate all’utilizzo di circuiti equivalenti per l’interpretazione dei dati sperimentali
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