A simple method, based on harmonic wavelet analysis is proposed for the decomposition of a given energy bounded signal into a periodic signal and a pulse.Mike a denoising method, the first part signal it might represent a smooth periodic function while the pulse is a singular unpredicted perturbation (taken as a fault).It will be shown that, under some general conditions, by a simple projection into two disjoint space of functions we can easily separate the periodic component of the signal from the fault(represented by the singular pulse).