Abstract: The invention concerns apparatus for inspecting the flat surfaces of a metal billet and includes a carriage mounted scanning head having a high frequency eddy-current probe (21) mounted on the periphery of a disc (18) rotatable above the billet surface about an axis perpendicular to said surface. The carriage (1) is located in abroad of the rotating scanning head. The eddy-current probe is connected to transmit electrical signals representative of the condition of the billet surface under inspection to signal processing equipment remote from the apparatus.

Abstract: Inspection equipment for detecting defects in the surface of steel billets or other elongate members includes high-frequency energized eddy-current surface scanning probe which transmits signals representative of the surface condition and the probe surface spacing to a dual-channel receiver.The signals from both channels of the receiver are combined to provide outputs representative of the surface condition compensating for changes in sensitivity resulting from changes in the probe spacing during scanning.Probes may be positioned above the plane surfaces and/or the corners of the billet. The latter being positively located through rollers which bear against the two sides of the billet which flank the edge under inspection.

Abstract: Apparatus for detecting surface defects in steel billets comprises an h.f. energized eddy current probe for scanning over the surface of the billet and a dual channel receiver responsive to signals from this probe dependent on (a) any surface defects, and (b) the probe surface spacing, in a manner such that in one channel a predominant factor in the signal waveform is characteristic of (a) while in the other channel a predominant factor in the signal is characteristic of (b). The signals from the two channels are combined in a summing amplifier and a difference amplifier whereby the outputs therefrom are conditioned to be exclusively characteristic of (a) and (b) respectively.