MAGNETIC FOREIGN MATERIAL DETECTOR IN NONNMAGNETIC WIRE OR ROD

摘要

PURPOSE:To eliminate noise accompanying with vibrations of a wire and perform normal detection by providing the two differentially connected detecting coils inserting onto a non-magnetic wire or rod in a DC magnetic field and enclosing the circumference of the above-mentioned wire or rod with a sleeve on the inner side of the coils. CONSTITUTION:Coils a, b are wound to a common winding frame 6 and are differentially connected. The circumference of a non-magnetic wire or rod 2 is enclosed by a sleeve 7 composed of copper and is disposed to the inner side of the winding frame 6. When the coils a, b exist in a DC magnetic field H0 and the magnetic field H0 changed by DELTAH in the wire 2, eddy current i flows in the direction of generating such a magnetic field which generates this. This current is induced in the coils a, b. If, however, there is a conductor 7 around the wire 2, the change in the magnetic field owing to the above-mentioned eddy current i causes the eddy current corresponding to the conductive sleeve 7 to flow, as a result of which the magnetic change quantity on the outside circumference of the sleeve 7 becomes lower than that when there is no conductive sleeve 7. In other words, shield effect markedly appears. Namely, the noise owing to the vibrations of the wire is considerably reduced.