Resonant frequency tracking mode on eddy current pulsed thermography non-destructive testing

Abstract

Eddy current pulsed thermography (ECPT) has been widely used in the field of non-destructive testing due to its safety, non-contact detection, high spatial resolution and intuitive results. Inductive excitation source is an important component of ECPT and provides high-frequency alternating current to drive the excitation coil. However, a resonant frequency distortion phenomenon exists in the excitation source during the detection process, which seriously affects the output power of the excitation source and the sample detection effect. This paper presents a fast resonant frequency tracking loop for full bridge series resonant inverter which is used to search the resonance frequency in real time through direct digital synthesizer (DDS) and all-digital phase-locked loop. Theoretical analysis and simulation are presented to explain the working principle of the loop. Then, an experimental prototype is manufactured which serves as an excitation source for the ECPT experimental system. Compared with traditional excitation sources, the prototype does not need a water-cooled device and the tracking speed can be adjusted by modifying the parameters of DDS. Finally, experiments have been conducted on both artificial slot of 45# steel and natural cracks of rail and stainless steel to investigate the influence of resonant frequency tracking speed on the crack detection. The results revealed that reducing the resonant frequency tracking time can efficiently improve defect detectability and the manufactured prototype showed more application potential. This article is part of the theme issue ‘Advanced electromagnetic non-destructive evaluation and smart monitoring’.

An automated nondestructive testing system for the surface of pressure pipeline welds

“…Hernandez et al (2018) proposed a combination of pulse‐echo and pitch‐catch ultrasonic testing for automatic inspection of weld areas. Miao et al (2020) proposed a method to improve the defect detection efficiency of eddy current pulsed thermography NDT technology by reducing the resonance frequency tracking time. Hou et al (2020) analyzed computer‐aided automatic detection methods for radiographic weld image defects from the aspects of weld image preprocessing, defect segmentation, and defect classification and provided prospects for weld defect detection technology based on deep learning.…”

Exploring high-frequency eddy-current testing for sub-aperture defect characterisation using parametric-manifold mapping

“…In this paper, 2.0 MHz was selected as the nominal frequency to demonstrate characterisation -corresponding to a typical high-frequency industrial eddy-current probe. However, due to research interest in near-resonant frequency measurements [26,27,28,29,30,31], a broad frequency spectra (1-8 MHz) was simulated and experimentally recorded, and the characterisation accuracy at each single frequency within this range evaluated.…”