The influence of the toroidal geometry, and the plasma column displacement, over the usual tokamak poloidal magnetic field configuration was investigated for circular plasmas through a series of simulations. The results obtained clearly showed the existence of a change in phase modulation of the Mirnov signals, which are not usually considered when the magnetic signals are Fourier analyzed in the frame of cylindrical approximation, that is, by neglecting any possible toroidal effect. Furthermore, if the occasional displacements of the plasma column in tokamaks are considered, some differences on the mode composition are also observed. These discrepancies, however, do not seem to affect the analysis of the magnetic signals as strongly as in the former case, when toroidal effects are neglected.