DEVICE FOR DETECTING FLAW BY EDDY CURRENT

PURPOSE:To make it possible to measure the depth of a minute defect, by dif- ferentiating a vector signal generated when a pair of detecting coils pass the center of the defect and inputting output thereof to a specified computing circuit. CONSTITUTION:The detecting coils 3a and 3b are arranged on the adjacent symmetrical positions with respect to a sweeping axis, and constitute a bridge to- gether with resistors 4a and 4b. The unbalanced output from the bridge circuit is sent to phase detectors 6 and 6b through an amplifier 6 and phase-detected, with the output signals from a phase shifter and a 90 deg. phase shifter circuit 8 as references. Output signals X and Y from the phase detectors 6 and 6b are differentiated by differentiating devices 11a and 11b, and signal x1 and y1 are obtained. Said signal y1 is sent to a halfwave rectifier 16 through an analog gate 13 which is closed when the output of x1 is generated. The positive part y2 of y1 is taken out and the product of y2 and coefficient K is computed by a multiplication coefficient setting device 18. Thereafter, the computation of the expression of relation (I) is processed in an analog subtractor 19 and an analog divider 20, and an output Vo is obtained through the halfwave rectifier.