Patent Number: 055442072
Section: claims

1. An apparatus for measuring the thickness of a nonmagnetic overlay clad of a ferromagnetic pressure vessel of a nuclear reactor comprising: a magnetic yoke;  one or more exciting coils, said coils wrapped around said magnetic yoke for magnetizing said magnetic yoke to form a magnetic path through said magnetic yoke and the ferromagnetic pressure vessel of the nuclear reactor;  means for measuring the spatial distribution of the magnetic field component orthogonally crossing the ferromagnetic pressure vessel of the nuclear reactor. 2. An apparatus is in claim 1, wherein said means for measuring the spatial distribution of the magnetic field component orthogonally crossing the ferromagnetic pressure vessel of the nuclear reactor is a plurality of magnetic field sensors placed in a line along the longitudinal direction of said magnetic yoke above the nonmagnetic overlay clad. 3. An apparatus is in claim 1, wherein said means for measuring the spatial distribution of the magnetic field component orthogonally crossing the ferromagnetic pressure vessel of the nuclear reactor is a single magnetic field sensor moveable along the longitudinal direction of said magnetic yoke above the nonmagnetic overlay clad.