Normalized functions of eddy current measuring transducers with spatially periodic field structure for multiparameter control of metal products

The article deals with the problem of multiparameter control of metal products in the scope of their structurescopy. It is shown that an eddy current measuring transducer with a spatially periodic structure of the electromagnetic field favorably differs from other methods by a wide range of application, simplicity and provided reliability of control. The solution of the inverse problem of eddy current control is of a great interest from the practical and theoretical point of view, namely, the determination of the parameters of the object by the reaction to its appear in the electromagnetic field. The electromagnetic field model of such a transducer with a metal object with controlled parameters of conductivity, magnetic permeability and diameter is considered. It is theoretically grounded that with a certain approach to the mutual arrangement of the excitation and measuring windings, and by connecting the voltmeter and phase meter according to the proposed scheme, a signal proportional to the amplitude and phase of the first and third field harmonics can be obtained in the output signal of the transducer. The analytical relations are given that allow to obtain dependences of the conversion factors for the amplitudes and phases of the harmonics, as well as their sensitivities on the generalized function, the arguments of which are the field frequency and the parameters of the sample. The conclusion is made that it is possible to single out a rational operating mode of the eddy current transducer used in the testing of metal products with various electromagnetic and geometrical parameters, the selection of a rational mode being carried out by selecting the frequency of the excitation field and that the solution of such a problem will make it possible to more accurately select the necessary measuring equipment for the realization of the multi- parametric eddy current testing method with the use of primary transducers with a spatially periodic structure of the excitation field.