Directly-digitized pulsed eddy current based quantification of aluminum sheet thickness

Direct interfacing technique (DIT) eradicates additional circuit requirements for sensor-embedded system interface and digitization of analog signals. This technique provides advantages in designing an efficient, portable, and low-cost sensor system. Pulsed eddy current testing (PECT) systems are used for thickness and defect measurements of conductive materials. Circuitous sensor-interfacing methods and tedious data interpretation processes make PECT systems inapt for miniaturization and portable applications. In this work, DIT is used in conjunction with PECT for thickness estimation of conductive material. Change in the de-energizing time of a single coil probe with sample thickness, with respect to air, is used as a signal. The curve fitting method yields a maximum relative error of & AP;2% in the thickness estimation. Effects of temperature and liftoff on system accuracy are also investigated. A liftoff compensation method using a 3-signal data group is proposed. It is shown that for thicknesses in the range of 0.508 mm-3.175 mm and liftoffs up to 3.000 mm (step size: 0.500 mm), the proposed scheme produces a maximum relative error of 5.2%. The DIT and PECT combination can be applied for different structural eddy current testing in the future.