Estimate of the Ratio of the Data and Background Signals in Detecting the Magnetic Fields of Surface Defects by Magnetic
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ESTIMATE OF THE RATIO OF THE DATA AND BACKGROUND SIGNALS IN DETECTING THE MAGNETIC FIELDS OF SURFACE DEFECTS BY MAGNETIC MEASUREMENT TRANSDUCERS
Yu. L. Nikolaev, E. F. Akhmetshina, A. A. Samorukov, and A. V. Chernova
UDC 621.317.4: 620.179.14
The problems of identifying defective segments of the surface of monitored objects and estimating the parameters of the defects are examined. The use of magnetic measurement transducers is described as a means of detecting and measuring the parameters of the locally distributed magnetic fields which appear above defective segments of the surface of a monitored object in an applied constant magnetic field. Algorithms are proposed for quantitative evaluation of the ratio of the data and background components of the output signal from magnetic measurement transducers. A method is derived for separating the data and background components. It is based on the summation property and the determined character of the distributions of the magnetic field intensity of a defect and the background magnetic field along the coordinate axis parallel to the monitored surface and on an analysis of the topography of the distribution of the magnetic field intensity. The approach to the choice and experimental definition of the estimated parameters characterizing the level of the data and background signals is validated. Formulas are given for calculating the signal-to-background ratio from the measured estimates for ordinary magnetostatic, differential magnetostatic and differentiating magnetic measurement measurement transducers taking into account the direction of orientation (normal, tangential) of their sensitivity axis. The signal-to-background ratio of a transducer is calculated for the example of the output signal from a magnetic measurement transducer during detection of the distribution of the magnetic field intensity over the surface of a monitored sample with artificial defects of specified sizes. A comparative analysis is made of these kinds of magnetic measurement transducers in terms of their signal-to-background ratio and general recommendations are made for increasing that ratio. Keywords: magnetic measurement transducers, magnetic field of defect, signal-to-background ratio.
Introduction. Magnetic measurement transducers (MMT) [1–4] are widely used as means of detecting and measuring the parameters of nonuniform magnetic fields locally distributed over crack-type defects in the surface layer of a magnetized test object. This makes it possible to identify defective segments of the surface and, under certain conditions, to evaluate the parameters of a defect. During scanning of the surface of a monitored object, the sensitivity axis of the MMT is oriented for detection of the tangential or normal (parallel or perpendicular to the surface of the monitored object) components of the magnetic field intensity Recording of the intensity distribution along the coordinate axes reveals segments with sharp changes in the intensity owing to the presence of defects. The measured values of th
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