Estimation of informative and background signals ratio in the registration of magnetic fields of surface defects by magnetic measuring transducers

Abstract

Authors propose algorithms for quantitative ratio determining of informative and background components of the output signal of magnetic measuring transducers, used as a means of recording and measuring the parameters of locally distributed magnetic fields that occur over defective surface areas of the tested object in an applied permanent magnetic field. The method of separating the informative and background components based on the summation property and the deterministic nature of the distributions of the magnetic field intensity of the defect and the background magnetic field along the coordinate axis parallel to the controlled surface, and analysis of the topography of the distribution of magnetic field intensity is described. The approach to selection and experimental determination of estimated parameters characterizing the levels of informative and background signals is justified. Authors give the formulas for calculating the signal-to-background ratio based on the measured values of the estimated parameters applied to single magnet-static, differential magnet-static and differentiating magnetic measuring transducers taking into account the orientation direction (normal, tangential) of their sensitivity axis. The signal-to-background ratio calculation results are presented using an example of an analysis of the magnetic measuring transducers output signal when registering the distribution of the magnetic field intensity over the surface of a control sample with artificial defects of a given size. The comparative analysis of considered magnetic measuring transducers according to signal-to-background ratio is carried out. General recommendations to increase the value of the signal-to-background ratio parameter are given.