Patent ID: 8008913
Filing Date: 2011-08-30
Classification: G01N

Abstract:
1. A method for compensating for the effect of separation between an eddy current probe and a surface of a conductive specimen being tested, the method comprising obtaining set of reference data by locating the eddy current probe at a substantially defect free area and a known reference separation from a surface of the specimen, the probe being excited to generate eddy currents in the specimen and sensing a time-varying reference signal generated by the eddy currents, the set of reference data containing the amplitude of the reference signal at one or more times determining a largest magnitude gradient value of the reference signal; obtaining a set of test data by locating the eddy current probe at an unknown separation from the surface of the specimen the probe being excited to generate eddy currents in the specimen and sensing a time-varying test signal generated by the eddy currents, the set of test data containing the amplitude of the test signal at one or more times; determining largest magnitude gradient value of the test signal calculating a compensation ratio, the compensation ratio being the largest magnitude gradient value of the test signal divided by the largest magnitude gradient value of the reference signal; and determining an amplitude of a compensated signal for one or more corresponding times in the sets of reference and test data by subtracting the amplitude of the reference signal multiplied by the compensation ratio from the amplitude of the test signal.