Abstract: An electronic circuit to be used in conjunction with eddy current non-destructive flaw detection instrumentation for distinguishing from noise or other undesirable signals a flaw signal having a characteristic frequency and a negative excursion followed by a positive excursion. The circuit includes two channels, each of which comprises a threshold detector, a differentiator, a filter, and a variable pulse width one-shot multivibrator, each of which receives the characteristic signal. One channel processes the negative excursion, and the other channel processes the positive excursion. Each channel produces a pulse of predetermined time duration if the excursion being processed exceeds a predetermined threshold. The leading edge of the pulse produced in association with the negative excursion corresponds in time to the time at which the trailing positive going edge of the negative excursion crosses a predetermined negative threshold.

Abstract: The invention concerns a measuring instrument for measuring phase shifts in four terminal electrical networks, where the network whose phase shift is to be measured is connected into the feedback circuit of an R-C phase shifter oscillator, and where the generated frequency depends on the phase shift of the four terminal network and of the RC-phase shifter, and where the circuit is so dimensioned that the following oscillation conditions are satisfied:.phi.(.omega.) + .phi. = 0 (or integral multiples of 2 .pi.)(1).vertline.F (.omega.).vertline..multidot..vertline.H.vertline..multidot.A = 1 (2)where .phi. = phase shift of the network whose phase shift is to be measured.phi.(.omega.) = phase shift of the R-C phase shifterF (.omega.

Abstract: The proposed eddy current converter for non-destructive testing of electrically conductive coating in holes of printed circuit boards comprises a cylindrical frame enveloped by an exciting winding and a measuring winding and inserted into a hole of a printed circuit board being tested. The coils of the exciting and measuring windings extend along the generatrices of the cylindrical frame.With the use of the proposed converter, the testing accuracy is independent of the parameters of respective contact areas of a hole being tested. The converter of the present invention is sensitive to the most undesired flaws like transversely extending cracks.