Patent ID: 6798197
Filing Date: 2004-09-28
Classification: G01N

Abstract:
The method of measuring anomalies, or defects, in a test material proximate one or more coils of an eddy current probe, comprising the following steps:a. In an electrical circuit, synthesizing a digital carrier signal and two digital sinusoidal functions that all have a same frequency; b. Converting the digital carrier signal to an analog carrier signal; c. Driving a probe test coil in an eddy current probe with the analog carrier signal therein generating a probe electromagnetic field from the probe test coil into the proximate test material which excites eddy currents in the test material that cause a return electromagnetic wave generally out of phase with the probe electromagnetic wave; d. Passing the probe test coil over a material anomaly, or material defect, the anomaly causing amplitude and phase differences in said return electromagnetic wave, which wave causes an electric current in the probe test coil to vary as a modulation of the return electromagnetic wave, amplitude and phase changes constituting an eddy current signature of the anomaly; e. Receiving said return electromagnetic wave in a probe detection coil causing an electrical modulated return analog carrier signal within the coil; f. Amplifying the return analog carrier signal; g. Selectively amplifying segments of the return analog carrier signal; h. Digitizing said analog carrier signal into a modulated digital carrier signal; i. Mixing said modulated digital carrier signal with said digital sinusoidal functions into quadrature components; j. Adjusting amplification achieved in selectively amplifying segments of the modulated digital carrier signal in a gain scaling stage such that resulting amplification of said signal segments is a power of two; k. Isolating the eddy current signature of the anomaly by filtering said mixed modulated digital carrier signal with a low-pass filter; l. Reversing said selective amplification of said signal segments by shifting bits in the modulated digital carrier signal.