Abstract In this paper, two methods to evaluate the measurement uncertainty of a virtual instrument are presented: a numerical method simulating the physical process of the A/D conversion, and an approximated theoretical method applying the “uncertainty propagation law” of the “guide to the expression of uncertainty in measurement”. After a brief description of the features, the constitution and the working principle of the virtual instruments, the various uncertainty sources, are analyzed. With both methods, the combined standard uncertainty of the measurement result is obtained, starting from the standard uncertainty generated by each single source and without taking into account the parameters, which regard the overall behaviour of an acquisition board, such as the effective number of bits. The results obtained by means of the theoretical analysis are compared with the ones obtained from numerical simulation. Then the results of experimental tests on a virtual instrument, with a complex measurement chain for flicker evaluation, are presented.
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