Patent ID: 8432161
Filing Date: 2013-04-30
Classification: G01N

Abstract:
1. A frequency selection method of eddy current measurement, wherein a magnetization coil applies alternating current magnetization signals of a first frequency and a second frequency different from the first frequency on an measurement object so as to generate induced currents including eddy currents respectively corresponding to the first frequency and the second frequency in the measurement object, a detection coil detects detection signals caused by the induced currents respectively corresponding to the first frequency and the second frequency, a phase difference D shown in below formula 1 is calculated based on an amplitude Y the measurement object (the hardening depth thereof) is measured based on the phase difference D, the method comprising: a results of the magnetization and detection process for frequency selection that the magnetization coil applies alternating current magnetization signals of three or more different frequencies on the measurement object so as to generate induced currents respectively corresponding to the three or more different frequencies in the measurement object and the detection coil detects the detection signals caused by the induced currents respectively corresponding to the three or more different frequencies; a phase difference calculation process that phase differences between the alternating current magnetization signals and the detection signals respectively corresponding to the three or more different frequencies are calculated based on the detection signals caused by the induced currents respectively corresponding to the three or more different frequencies detected in the magnetization and detection process for frequency selection; and a frequency sampling process that a combination of two frequencies which make a difference of the phase differences within a predetermined range is extracted from the three or more different frequencies calculated in the phase difference calculation process, and lower one of the two frequencies of the combination is referred to as the first frequency and higher one thereof is referred to as the second frequency