In ac losses in type II superconductors three contributing factors may be distinguished. These are connected with the three parameters in the Critical State Model: the critical current density Jc, surface screening currents denoted by Ben(Ba) and Bex (Ba), and the flux conductivity σff. In this paper the authors present an inductive technique which makes it possible to determine these three parameters separately. For this purpose, ac magnetic fields of trapzoidal waveform are applied. The theoretical background of the technique will be discussed together with the experimental equipment designed for these experiments. The technique has been verified by means of numerical model calculations. Finally, some experimental results are given to illustrate the possibilities of the technique.