Patent ID: 6014024
Filing Date: 2000-01-11
Classification: G01N

Abstract:
An apparatus for detecting flaws in conductive material having a material surface, the apparatus is a sensing unit having(a) a magnet having a substantially constant magnetic field with a pole, the magnet placed adjacent to one side of the conductive material, with the pole facing the material surface;(b) a sensor coil that is unilateral and stationary with respect to the magnet wherein the magnet and sensor coil are in relative motion with respect to a conductive material, said sensor coil having a longitudinal axis; and(c) a signal transferrer for data acquisition; wherein the improvement comprises:(i) the sensor coil is positioned within a pattern of a secondary magnetic field and away from the magnet;(ii) said relative motion is oscillatory motion of the magnet and the sensor coil while the conductive material is stationary;(iii) said signal transferrer is selected from the group consisting of slip ring, inductive coupling, and radiofrequency transmitter; and(iv) a liftoff compensator that measures a liftoff distance between the material surface of the conductive material and the magnet.