METHOD FOR EDDY CURRENT-MEASUREMENT OF THICKNESS OF METAL COATINGS Russian patent published in 2012 - IPC G01N27/90 

FIELD: physics.

SUBSTANCE: for probing, a harmonic signal at a selected frequency is transmitted to an exciting coil placed in the middle of a ferrite core; signals are picked up from identical measurement and compensation coils placed on opposite ends of the ferrite core; their difference signal is found and its phase φ is measured; when probing the measuring object, the end of the ferrite rod with the measurement coil is pressed to said object; according to the invention, the optimum frequency of the exciting coil is selected based on the relationship: f_opt=(0.3…0.7)/(πµ₀σ_n T² _nax), where µ₀ is the magnetic constant; σ_n is conductivity of the coating; - maximum thickness of the coating, before the beginning of measurement, the measurement and compensation coils are balanced by achieving a zero difference signal in the absence of the measuring object; a spacer made from non-ferromagnetic metal whose electroconductivity is close to that of the coating material is placed between a ferrite core and the measuring object; the thickness of the spacer is such that with tentatively known parameters of the analysed object and the ferrite core with windings, maximum calculated sensitivity of amplitude-phase characteristics of the difference signal from the thickness of the coating of the object is provided; during probing, the amplitude A of the difference signal is further measured; the measuring device is graduated, for which measuring objects are probed, having characteristics close to the analysed object, with several known coating thicknesses T_n and for several known values of gaps h between the ferrite core with the spacer and the surface of the measuring objects; the relationship between the amplitude and phase of difference signals and the thickness of the coating and gaps A, φ(T_n h) is stored; the analysed object is probed; the thickness of the coating T_n and the gap h between the ferrite core with the spacer and the surface of the coating of the object is calculated based on measured values of amplitude A and phase φ of the difference signal using the relationship A, φ (T_n h).

EFFECT: possibility of measuring thickness of thin non-ferromagnetic metal coatings deposited on non-ferromagnetic bases, including in conditions when electroconductivity of the coating is lower than that of the base, with possibility of measuring objects with rough surfaces and curvilinear surfaces, having an additional non-electroconductive coating.

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