The increased demand for characterization of plasmas under industrial conditions was mainly driven by the complexity of industrial plasma processes. The interaction of the plasma with the surface determines the quality and performance of the electronic devices on the substrate. Hence a good understanding of the key mechanisms of plasma excitation is required. To address the heating mechanisms of the electrons, knowledge of the electron energy distribution function (EEDF) is imperative - or at least parameters derived from its moments, as the collision rate of electrons for momentum transfer or, taking into account stochastic heating, too, the effective collision rate. Especially the last property, the thermalisation of the electric field's energy, can only be accessed by measuring the self-excited resonance of the electrons in RF plasmas(SEERS, last 's' for spectroscopy). SEERS utilizes nonlinear and resonance effects in the plasma in the sheath and the plasma body leading to a non-sinusoidal RF current. Thus SEERS uses nonlinear and RF effects which usually disturb or even avoid the application of classical methods as Langmuir probes in RF plasmas. The measurement principle is based on a passive RF current sensor and a discharge model involves the effects mentioned above and can be used in reactive plasmas without any restriction. SEERS data based of ten thousands of wafers for different processes show the high efficiency of this approach, in particular under industrial conditions as polymers on chamber wall and sensor itself and undesired effects as arcing at the chamber wall. On the other hand, basic experiments show that plasma physical mechanisms as skin effect in the plasma, ohmic and stochastic heating of electrons can be qualitatively observed in productions tools which are necessary for the understanding and development of process and new chamber types.