Patent ID: 8878717

Claim:
A projection detecting apparatus for detecting a projection on a surface of a running metal strip, comprising: a transmission antenna with a first aperture for radiating electromagnetic waves; a reception antenna with a second aperture for receiving reflected electromagnetic waves; and a transmission and reception signal processing section for processing a transmission signal and a reception signal, wherein the transmission antenna and the reception antenna are installed adjacent to each other at a position which is away from the center of the metal strip in a width direction toward an edge of edges of the metal strip in such a way that a plane of the first aperture of the transmission antenna and a plane of the second aperture of the reception antenna are parallel to a running direction of the metal strip and that electromagnetic waves transmitted by the transmission antenna and travelling perpendicular to the plane of the first aperture of the transmission antenna are incident on the surface of the metal strip at an angle, a value of the angle being from 40 to 60 degrees, and the transmission antenna and the reception antenna have unidirectionality and a detection range includes a space of a certain size around the direction of the unidirectionality.