| 摘要 |
PURPOSE:To measure elongation at high accuracy without contact by making a small hole on a test piece so as to take for a gage mark, measuring the impedance change of a detection coil having an oppositely disposed rotating ring and detecting the shift of the gate mark. CONSTITUTION:The small hole is made on the magnetic test piece 2 to form the gage mark 18a, and a gate mark detector 15a is installed opposite the gage mark 18a. The gage mark detector 15a is constituted of the detection coil 16a, a conductive bar-like ring 19a rotating in the coil 16a and an impedance 20a available from projecting and forming some part of the ring 19a. When the ring 19a is rotated in such a way, first the change is detected and compared with a reference pattern, because the impedance of the detection coil 16a changes in accordance with the position of the gate mark 18a. The detector 15a is moved so as to follow the gate mark 18a on the basis of the comparison result, and the moving distance of the gate mark, that is, the elongation of the test piece 2, is detected from the moving amount.
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