FPGA Based Digital Electromagnetic SensingTechnique for Detection of Pit Corrosion

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Abstract

This thesis describes the development of an eddy current instrument and itsapplication in detecting early-stage pitting corrosion. Eddy current testing haspreviously been used in Non-Destructive Testing (NDT) applications detecting largedefects, like cracks.. However, the challenge of detecting corrosion pits of less than 1mm3 remains unaddressed. This research involved the design of a Field ProgrammableGate Array (FPGA)-based eddy current instrument, and the design and modelling of anovel differential electromagnetic sensor. The FPGA provided accurate synchronisationamong the major electronic components. The firmware developed as part of thisresearch allowed for exact interfacing to A/D and D/A converters, performed a real-timedemodulation and signal generation, the instrument also supported a multi-frequencyeddy current application. The firmware showed promising end-results in terms ofsensitivity and stability in relation to pitting corrosion detection. In summary, thisinstrument offered significant improvement in sensitivity; the size of corrosion detectedis improved more than 10 per cent compared to the previously reported, which enabledthe detection of pits smaller than 1 mm3. For the sensor probe, a novel differentialsensor was proposed to minimise the background signal for plate scanning and improvethe sensitivity. The designed probe has an advantageous feature: the sensor response canbe analysed using a closed form analytical solution.

Keyword(s)

Eddy Current; FPGA

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