Abstract: The proposed method of carrying out diagnostics on a process for the thermo-chemical treatment of steels and alloys in a glow discharge involves monitoring the ionization characteristics of the atmosphere as revealed by the intensity of the electromagnetic radiation in various frequency intervals. The proposed device for carrying out the method in question comprises a primary converter (1) in the form of an electromagnetic radiation emitter unit and contains filtering elements (5) mounted in such a way that they can be positioned in the radiation zone in front of the receiver (6) on a rotating disk (4). The disk (4) is provided with a rotation drive (7) for positioning the elements (5).