Models of Signals of Eddy-Current Transducers above Defects of the Continuity of Metal

Abstract

The shape of real signals of eddy-current transducers of electromagnetic flaw detectors obtained over continuity defects in the process of monitoring the surface of steel products and metal structures depends both on the type of eddy-current transducer and on the type of continuity defects in the metal (single defects, a group of cracks, pitting corrosion). When solving practical problems of eddy-current flaw detection of steel products and metal structures, there is a need for mathematical modeling of the measured signals of eddy-current transducers of different types (absolute, differential, overhead, throughput) over continuity defects in the metal. Signal models of eddy-current transducers are also important from a methodological point of view, since they allow one to study the transformation of the eddy-current transducer signal shape with an arbitrary change in the parameters of real continuity defects in the metal, which facilitates the analysis and interpretation of flaw detection results. It is shown that the signal waveform of an overhead eddy-current transducer of an electromagnetic flaw detector above a continuity defect is determined by its type, while for an absolute overhead eddy-current transducer it has a unipolar character, the extremum of which is located above the center of the continuity defect; for a differential overhead eddy-current transducer, it has a bipolar character, the extremes of which are located symmetrically on opposite sides of the center of the continuity defect. To describe the signal waveform of the indicated types of overhead eddy-current transducers, mathematical models based on simple algebraic functions have been proposed that have two tuning parameters. It is shown that these tuning parameters are related to the amplitude and half-width of the measured signal for the absolute overhead eddy-current transducer, and with the distance between the extremes for the measured signal of the differential overhead eddy-current transducer over the continuity defects such as a crack in the metal. On the basis of these functions, mathematical models of signals of overhead eddy-current transducers above a group of cracks are proposed. It is shown that a change in the interval between continuity defects and their number in a group of cracks leads to a significant transformation of the signal waveshape of the overhead eddy-current transducers.