Approaches to evaluate the virtual instrumentation measurement uncertainties

The paper deals with the metrological characterization of virtual instruments. After a brief description of the features, the constitution and the working principle of the virtual instruments, the various uncertainty sources are analyzed. Then two methods to evaluate the uncertainty of the measurement results 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". With both methods, the combined standard uncertainty of the measurement result is obtained starting from the standard uncertainty generated by each single source. The results obtained by means of the theoretical analysis are compared with the ones obtained from numerical simulation and with the ones obtained by means of experimental tests.