Patent ID: 6593737
Filing Date: 2003-07-15
Classification: G01B

Abstract:
A method of measuring the wall thickness of an electrically conductive object using a probe, which probe comprises a transmitter coil for inducing eddy currents in the object, and a receiver system for providing a signal indicative of the strength of the electromagnetic field generated by the eddy currents or of changes in the strength of this electromagnetic field, wherein the receiver system comprises a first receiver and a second receiver that is spaced apart from the first receiver, which method comprises the steps of:(a) arranging the probe near the object at a distance from the surface of the object that is nearest to the probe; (b) inducing transient eddy currents in the object by activating the transmitter and recording the signal of the receivers with time, wherein Vl(t) is the signal of the first receiver with time (t) and Vu(t) is signal of the second receiver with time (t); (c) measuring the wall thickness from a characteristic of one of the signals; (d) calculating a characteristic value, &PHgr;, from a combination of Vl(t) and Vu(t); and (e) correcting the measured wall thickness for the distance between the probe and the surface of the object that is nearest to the probe using a pre-determined relationship between the wall thickness and the characteristic value for different values of the distance between the probe and the surface of the object that is nearest to the probe.