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A suppression method of lift-off effect in pulsed eddy current detection

A technology of pulsed eddy current and lift-off effect, applied in the direction of material magnetic variables, etc., can solve problems such as poor lift-off effect, insufficient real-time performance, and increased error in lift-off distance judgment

Inactive Publication Date: 2015-09-16
NANCHANG HANGKONG UNIVERSITY
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

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Problems solved by technology

It is found that when the feature quantity has a large defect, the judgment error of the lift-off distance increases, the effect of suppressing lift-off becomes worse, and the real-time performance is not strong enough

Method used

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  • A suppression method of lift-off effect in pulsed eddy current detection
  • A suppression method of lift-off effect in pulsed eddy current detection
  • A suppression method of lift-off effect in pulsed eddy current detection

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Embodiment

[0047] Embodiment: an embodiment of the flow process of the present invention can be described as follows:

[0048] (1) First, place the probe on the test block without defects and no lift-off, collect the signal at this time as the reference signal ref, and gradually increase the lift-off height according to a certain ratio, and collect N lift-off calibration signals {lift_off(n );n=0,1,…,N-1}, build the lift-off calibration signal database.

[0049] For example, lift-off height: 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6mm, 7 lift-off calibration signals are generated. n=0, 1, 2, 3, 4, 5, 6.

[0050] (2) After collecting the lift-off calibration signal, make a difference with the reference signal to obtain the differential signal {LoDiff(n); n=0,1,...,N-1}, filter it, and filter the filtered The signal is subjected to the second-order differential operation to find the value at zero time, and the second-order differential zero-time value database {diff2zero_LoDiff(n); n=0,1,…,N-1} is...

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Abstract

The invention discloses a method for restraining a lift-off effect of impulse eddy current testing, which comprises the following steps: establishing a lift-off calibration signal database, establishing a second-order differential zero moment value database of calibration signal and reference signal differential values, determining an approximate height of lift-off and a lift-off calibration signal by matching second-order differential zero moment values, and correcting signals by using the approximate height of lift-off and the lift-off calibration signal. The method disclosed by the invention has the typical characteristics that the distance of lift-off is judged by using new characteristics, and second-order differential zero moment values of difference signals constitute a good instruction for the distance of lift-off, so that the judgment on the distance of lift-off is relatively accurate, and because only values near a zero moment are required to be processed, calculation is performed quickly, thereby facilitating the application of the method in real-time detection.

Description

technical field [0001] The invention relates to a detection method for detecting defects such as corrosion and cracks existing in conductive material structures, in particular to a method for suppressing the lift-off effect of pulsed eddy current detection. Background technique [0002] Eddy current testing has considerable advantages in inspecting conductive structures and has very common applications. It is non-destructive and can detect cracks that are invisible to the naked eye. Non-destructive detection is usually achieved with a single frequency, and sometimes two or more frequencies can be used to improve detection capability and detection reliability. Eddy currents can penetrate multiple layers of materials to find hidden damage that threatens a material or structure. However, the traditional eddy current technology is limited by a single frequency, which affects its detection efficiency and sensitivity to a certain extent. Pulsed eddy current testing uses square ...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): G01N27/90
Inventor 付跃文吴少文方霆
Owner NANCHANG HANGKONG UNIVERSITY