| 摘要 |
PURPOSE:To make stable detection possible, by arranging detecting sensors in different positions in the advance direction of a plate material and detecting the same part of the plate material at different points of time and comparing detection signals with one another to detect a welding point. CONSTITUTION:Eddy current sensors 40a-40c are prepared, and sensors 40b and 40c are arranged a length L downstream from the sensor 40a in the carrying direction of an arrow (v) of a plate material 1. The detection signal of the sensor 40a is delayed by such time that it coincides with the timing of generation of detection signals of sensors 40b and 40c in downstream positions, and these detection signals are multiplied, and multiplied outputs are compared with each other; and when the comparison result exceeds a predeterminate level, a welding point detection signal is outputted. Thus, the lowering of the S/N ratio due to vertical vibration and flaws of materials is held down to detect always stably the welding point. |
