The paper deals with the measurement of R, L, C parameters of passive component in non-sinusoidal conditions. An innovative virtual instrument, implementing a measurement method based on system identification techniques, was realized to be used for the characterization of passive components in arbitrary conditions. After a detailed description of the measurement method the solutions adopted in the realization of the instrument are resumed. Then the quality of the instrument is assessed in comparison with a reference impedance meter in both sinusoidal and non sinusoidal conditions. Finally, the results of tests, carried out in various non sinusoidal conditions on capacitors with different dielectric materials, are shown and discussed.