Patent ID: 8027796

Claim:
A method for measuring an S/N ratio in an eddy current testing on an internal surface of a pipe or tube comprising the steps of: using a microprocessor for; separating an eddy current signal obtained by executing an eddy current testing on the internal surface of a pipe or tube in an axis direction into an X-axis component and a Y-axis component that are different from each other by 90° in the phases thereof to obtain signal waveform data of the X-axis component and signal waveform data of the Y-axis component; excluding predetermined low-frequency components respectively from the signal waveform data of the X-axis component and the signal waveform data of the Y-axis component thus obtained; calculating a noise voltage value V 1 defined by the following Equation (1) based upon a voltage value X(i) of the signal waveform data of the X-axis component with the low-frequency component excluded therefrom and a voltage value Y(i) of the signal waveform data of the Y-axis component with the low-frequency component excluded therefrom; and calculating an S/N ratio defined by the following Equation (2) based upon a voltage value D of an eddy current signal corresponding to a predetermined artificial flaw, obtained by executing an eddy current testing on an internal surface of a pipe or tube with the artificial flaw formed therein, and the noise voltage value V 1 : V ⁢ ⁢ 1 = π / n · ∑ i = 1 n ⁢ ( X ⁡ ( i ) 2 + Y ⁡ ( i ) 2 ) 1 / 2 ( 1 ) where n represents the number of samplings of the signal waveform data, S/N ratio= D/V 1 (2).