The centre gradient threshold method for distinguishing three types of defect in insulated cladding components based on the capacitive imaging technique

Surface defects on the insulation layer, hidden defects in the insulation layer and surface defects on the metal layer of insulated cladding components can significantly affect their normal operation. Distinguishing these three different types of defect helps to adopt corresponding maintenance plans early on, which have practical industrial application value for ensuring the safe operation of insulated cladding components and enhancing economic benefits. This paper uses the capacitive imaging (CI) technique to distinguish the three different types of defect in insulated cladding components. Considering the amplitude, gradient and defect size of CI detection signals, a centre gradient value (CGV) is proposed. Based on the CI technique, a centre gradient threshold method (CGTM) is developed to distinguish the three different types of defect using the CGV and threshold. The influence of the defect width, defect depth and insulation layer thickness on the CGTM discrimination method for the three different types of defect is studied through simulation and experiment. Simulation and experimental results indicate that when there are surface defects on the insulation layer, hidden defects in the insulation layer and surface defects on the metal layer of the insulated cladding component simultaneously, the CGTM discrimination method can effectively distinguish these three different types of defect. In addition, the results also demonstrate that when there are only one or two types of defect in the insulated cladding component, the CGTM discrimination method can effectively distinguish the types of defect and the discrimination results are not affected by the defect width, defect depth and insulation layer thickness.