| 摘要 |
PROBLEM TO BE SOLVED: To facilitate discrimination between reflected waves due to the difference of materials and reflected waves from a defect part, by discriminating reflected waves reflected from the opposed parts of a ridge line part at the outer periphery of a rotor bar inserted into the inner periphery of a retaining ring from reflected waves due to the difference of materials between the retaining ring and the rotor bar. SOLUTION: In the case that reflected pulses occur at a location of a computed distance to transmitted pulses projected from a probe and in the case that the location obtained from the distance matches with the ridge line part at the outer peripheral part of a rotor bar 7, it is determined that the reflected pulses are from the corners of the rotor bar 7. In the case that the forms of the reflected pulses are not steep, it is determined that the reflected pulses are from a defect part regardless of locations. In the case that steep reflected pulses occur at the inner peripheral surface of a retaining ring 5 and at the side surface of the core side of the retaining ring 5 and in the case that the reflected pulses occur with the same pitch as the pitch lp of the an adjacent rotor bar, it is determined the reflected pulses are due to the difference of materials between the rotor bar 7 and the retaining ring 5 and are not from a defect part. |
