Patent ID: 6344739
Filing Date: 2002-02-05
Classification: G01N

Abstract:
A method of detecting faults in a conductive material to be tested using eddy currents, wherein the differential mode is a pseudo-differential mode, the method comprising the steps of:a) providing a probe head having an arrangement of coils arranged on a surface of the probe to induce eddy currents in the conductive material to be tested, wherein the arrangement allows the probe to cover an area transverse to a direction of displacement of the probe head during inspection; b) selectively exciting one of the coils with an AC source to induce an eddy current in the material; c) measuring and recording over time eddy current flow in the conductive material to be tested using at least one of said coils; d) repeating steps b) and c) to cover the area transverse to the direction of displacement in different measurement configurations in which at least one of alternatives i, ii, iii, iv, and v is used: i. one of the coils used as a receiver coil is reused as a driven coil; ii. the excited one of the coils is reused as a receiver coil; iii. one of two or more coils used as receiver coils in a differential mode is used as a receiver coil with a different other receiver coil; iv. a same transmit conductor is used for connecting the AC source to the probe head, wherein said step b) further comprises switching the excited coil to the transmit conductor; and v. a same receiver conductor is used for connecting a receiver to the probe head, wherein said step c) further comprises switching one of the at least one of the coils to the receiver conductor; and e) subtracting the measurement of eddy current flow of two of said receiver coils to obtain a pseudo-differential measurement from the two receiver coils.