Ultrasonic thickness measurement of the aluminum plate with wavy surface

Abstract

The objective of this work was to investigate the influence of the non-perpendicularity of transducer and curvature of the surface to the errors of thickness measurement of metallic plates. The performed study shows that signal processing methods used to estimate the aluminum plate thickness are quite sensitive to the distortions of the reflected signal waveform. Distortions may be caused by different reasons, among them by diffraction effects of the transducer. The results presented indicate that even small curvature of the front surface (±0.5°) significantly influences measurements of the plate thickness and gives an additional error of ±10μm. Two methods were used to reduce the influence of the surface waviness to accuracy of the thickness measurements: the compensation of the diffraction errors and average of the both zero-crossing and cross-correlation results.