The amplitude analysis of a non-linear model of an electric system has been carried out. The possibility of linear and non-linear electric element differentiation has been stated on the basis of impedance measurements. The simultaneous frequency and amplitude analysis of impedance spectra allowed the determination by extrapolation of electric element values corresponding to the zero value of the perturbation signal. The amplitude analysis of impedance spectra allows the determination of the effective amplitude value in an accurate way. The determination of the polarization resistance dependence on the function of the effective amplitude of the perturbation signal is the static characteristic of a tested system.