The metallic sensor of the existing innovation is recognized from the before art by the fact that the method for cancelling the main industry on the side of the entry aperture along with the method for cancelling the key industry along the side of the get out of aperture are no more symmetric and equal to each other relative to a core plane in the aluminum detector. To put it differently the metal sensor in the present invention includes a first cancelling means organized at the front door aperture plus a distinct, secondly cancelling means organized on the get out of aperture. The first and second cancelling means differ from each other not only in their configuration, but also in their ability to cancel the primary electromagnetic field. For that reason, the principal discipline is cancelled above the first range through the entry aperture and beyond some other, secondly range in the get out of aperture. Accordingly, the metal detector according to the invention has a first metal-free zone which, relative to a travel path of said objects under inspection, extends upstream to a first distance from the entrance aperture, and a different second metal-free zone which extends downstream to a second distance from the exit aperture.