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Low-Cost Multi-Frequency Eddy Current Coating Thickness Measurement System

A low-cost coating thickness gauge based on Eddy Current Testing (ECT) is reported in this paper. This measurement system employs a Direct Digital Synthesizer (DDS) to generate pure sinusoidal stimulus applied to a measurement coil whose impedance varies with the measured coating thickness. The coil current and voltage are digitally acquired using an ARM Cortex M4F microcontroller where sine-fitting digital signal processing algorithms are applied to estimate the coil inductance and resistivity at different operation frequencies. Post-processing implements a simple multi-frequency estimate algorithm providing accuracy improvements around 10% when compared with the use of a single frequency.