Increase of the Informative Value of Magnetic Nondestructive Testing Using Vibration Induction Transducer on the Basis of Spectral Analysis

The ways of increasing the information content of magnetic flaw detection based on spectral analysis when registering magnetic fluxes of leakage from defects by a vibration induction probe (VIP) are considered. It is shown that the VIP signals, caused by the normal and tangential components of the strength of the magnetic scattering fluxes, are linearly independent, and the corresponding harmonic components of the spectra of these signals are weakly dependent on the noise component and carry information about the coordinates and parameters of the defect.

Математическое описание и анализ сигнала виброиндукционного преобразователя при воздействии нормальной составляющей магнитных потоков рассеяния над дефектным участком

Theoretical and experimental researches of vibration-induction transducer (VIT) outlet signal formed during exposure to normal leakage magnetic field intensity component Hn over the defective area were carried out. Theoretical research is based on an assumption that VIT signal is a trigonometric series that is limited by first five harmonics. As initial data for mathematical model creation, well-known conformities for Hn distribution over the defective area were used. Based on acquired mathematical model conformities of VIT signal harmonical composition permutation during its movement over the defective area with varying amplitudes and vibration frequency were found. Theoretical research results were proven experimentally. Moreover, additional possibilities of this way of magnetic testing are shown in comparison with conventional ones.

Modeling of magnetic fields and signals of a ferromagnetic pipe flaw detector induced by a through hole defect

A numerical model has been developed for interaction of the magnetizing field of a short solenoid with a ferromagnetic pipe exhibiting a through hole in the wall, which takes into account nonlinear magnetic properties of the test object. This model was used to calculate spatial distribution of magnetic induction in the pipe wall and spatial distribution of the components of the magnetic induction vector near the pipe surface with a through hole. The validity of the numerical model was confirmed by physical modeling results. The results of theoretical and experimental studies were used to develop a simplified analytical model that describes behavior of the magnetic field of the defect and the electrical signal of the induction transducer of a magnetic flaw detector that implements the method of magnetic flux leakage. It is shown that the dependence of the signal of the induction transducer induced by the through hole on the gap is close to a linear one, and its dependence on the hole diameter is close to a quadratic one. The results obtained in the study can be used for creation, numerical modeling and measurement of magnetic fields.

Displacement Sensor with Controlled Measuring Force and its Characteristics Analysis

A displacement sensor with controlled measuring force and its characteristics analysis are discussed in this paper. The displacement sensor consists of an electric induction transducer with high resolution and a voice coil motor (VCM). The measuring principles, structure of the sensor are discussed. Theory model, dynamic and static characteristics of VCM are analysed. A measuring system for surface topography with large measuring range is constructed based on the displacement sensor and 2D moving platform. Measuring force of the sensor in measurement process of surface topography can be controlled at μN level and hardly changes. It has been used in measurement of bearing ball，bullet mark, etc.