Patent ID: 9146214
Filing Date: 2015-09-29
Classification: G01N

Abstract:
1. A magnetic flux leakage inspection method comprising: applying an alternating magnetic field in a predetermined magnetic field application direction with a magnetic field application unit so that a magnetic flux parallel to a surface of an inspected object is generated; detecting an intensity of a magnetic field parallel to the predetermined magnetic field application direction at a plurality of positions on the surface of the inspected object by at least one sensor configured to detect a leakage magnetic flux that leaks from the inspected object; detecting an output from the at least one sensor as two signals having frequencies the same as a frequency of the alternating magnetic field and phases orthogonal to each other; inputting the two signals to an analyzer configured to analyze changes of the two signals and the phases output from the at least one sensor; and identifying a defect in the inspected object by calculating data on the intensity of the magnetic field and data on the phase at each of the plurality of positions from the two signals input to the analyzer, obtaining a sine value or a cosine value of the calculated phase data by adding a correction phase for calibration to the phase, obtaining a product of the calculated data on the intensity of the magnetic field and the sine value or the cosine value, and using values of the product at the plurality of positions, wherein the correction phase for calibration comprises a common adjustment phase commonly added to the phases at the plurality of positions to adjust the phases, and wherein the values of the product at the plurality of positions comprises the values of the product at the plurality of positions obtained with the common adjustment phase allowing only a change of the magnetic field due to the defect to be extracted among the values of the product at the plurality of positions obtained by changing the common adjustment phase as desired.