Patent ID: 6265871
Filing Date: 2001-07-24
Classification: G01N,G01V

Abstract:
A toroidal plane sensing face eddy current probe for detecting a flaw in a conducting workpiece by means of detecting an asymmetry in a rotating hemispherical driving field, said probe comprising:a) a toroidal core formed of a high permeability material for conducting a diameter-wise rotating field;i) poly-phase excitation winding distributions wound through the toroid window to symmetrically cover the core surface;ii) ramping poly-phase excitation currents being applied to the said excitation winding distributions for inducing a rotating driving dipole, fringing from the toroidal plane and forming complementary hemispheres of effective flux for inducing a hemispherical eddy current pattern in said workpiece;iii) a first pick-up coil wound coaxially around the circumference of the toroid core disposing the pick-up turns coplanar to the said driving dipole for generating a signal null in proximity to a flawless workpiece, net flux linkage to the first pick-up coil being dependent on an asymmetry in the said eddy current pattern for generating a first flaw signal;iv) said first pick-up coil shunted by a variable capacitor to form an oscillatory tank circuit for building up a resultant accumulative signal being a sub-harmonic of the said ramping poly-phase excitation currents;v) a second pick-up coil of many turns wound toroidally around the said toroid core, the spacing between adjacent turns being uniform for a signal null, said second pick-up coil for detecting an asymmetry in the said eddy current pattern.