Patent ID: 6538435
Filing Date: 2003-03-25
Classification: G01N

Abstract:
A method of detecting the presence of an anomaly of an object of electrically conducting material using a probe, which probe comprises a transmitter which can be activated so as to induce eddy currents in the object in a footprint area that is not rotational symmetric, and in which footprint area the eddy currents have a predetermined principal direction, wherein the transmitter comprises a pair of adjacent transmitter coils, and wherein activating the transmitter comprises energizing the pair of transmitter coils by mutually opposite currents, and which probe further comprises a receiver system for providing a signal indicative of the strength of an electromagnetic field or of changes of the strength of an electromagnetic field, which method comprises the steps of:a) selecting a set of points on the surface of the object nearest to the probe, which points are to be inspected; b) selecting a first inspection point from the set, and selecting a first direction and a second direction that differs from the first direction; c) positioning the probe at the selected inspection point, activating the transmitter to induce eddy currents in the object such that the principal direction of eddy currents in the footprint area is in the first direction, and determining a characteristic value &PHgr;1 of the electromagnetic field generated by the eddy currents; d) activating the transmitter to induce eddy currents in the object such that the principal direction of eddy currents in the footprint area is in the second direction, and determining a characteristic value &PHgr;2 of the electromagnetic field generated by the eddy currents; e) selecting a next inspection point from the set and repeating steps c) and d) until all inspection points have had their turn; and f) inferring that an anomaly is present at an inspection point if a combination of the characteristic values &PHgr;1 and &PHgr;2 pertaining to the first and second direction deviates significantly from a norm.