Three experimental methods of nonlinear characterization of elastic behaviour are compared, based upon constant voltage, constant current and constant frequency respectively. Equivalence between them is shown, and implementation of the last one is described in detail. The best way to describe nonlinear behaviour is to look at the alteration of the electrical impedance as a function of the current level, around the resonance frequency. By taking this description, we are able to compute the onset of hysteresis phenomena. Between the nonlinear increment of the reactance X and the resistance R appears a fairly linear relationship, while the quantities of X and R depend on the motional current through a fractional power function. In order to avoid the overheating inherent to high signal measurement, an excitation by bursts is proposed, and electrical response and velocity, obtained during the steady state, has been treated afterwards. This method has been applied to hard and soft PZT ceramics. Elastic electrical and piezoelectric behaviours have been compared, leading to some relations that can be explained by the predominance of the extrinsic processes over the intrinsic onaes.