A method for determining the quality of a protective coating or layer on a structure inside of a reactor chamber. The method includes generating a basis, such as a standard scatter band of impedance, as an acceptable standard for the quality of a protective layer on the inside of a reactor chamber. At least one substrate is processed within a reactor chamber containing a protective coating for protecting the inside of the reactor chamber during processing of the substrate. The method further includes determining the quality of the protective coating, such as by measuring protective characteristics of the protective coating. A method for on-line monitoring of a quality of a coating on the inside of a reactor chamber.