| 摘要 |
PURPOSE:To achieve a higher S/N in the flaw detection with variable distances of detection coil couples in first and second bridge circuits, by arranging the first and second bridge circuits each having a detection coil in a conductor to detect an eddy current thereof with the bridge circuits. CONSTITUTION:A copper wire 1 is made to pierce detection coil couples L1 and L2 and detection coil couples L3 and L4 and AC bridge circuits 5 and 6 are arranged for respective coil couples. The distance l1 between the coils L1 and L2 and the dis tance l2 between the coils L3 and L4 are set as specified while the distance l0 between the coils L2 and L3 is made adjustable as desired. Output signals of the circuits 5 and 6 are outputted in opposite directions to be added up with an arithmetic circuit 7. When any defect exists in the conductor 1, a change in the eddy current causes a variation in the impedance, but not simultaneous in that of the coils. So, there is not the same voltages to be fed in the opposite polarity to the arithmetic circuit 7, which is given a certain voltage without reducing to 0, enabling a flaw detection. The distance l0 is also adjusted to increase the S/N ratio. Thus, detection signals of the two AC bridge circuits are outputted in opposite directions to make the distance l0 variable, thereby achieving a higher S/N ratio in the detection with limited effect of a drag.
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