X-ray image processing for high voltage cable inspection

High voltage polymeric cables can be insulated using an automated extrusion process to a predefined standard up to a maximum continuous length. For longer cables, lengths are joined together manually. Consequently, the manufacturing quality of the cable joint is likely to be lower than that of the cable; therefore joints must be assessed prior to energisation. One method of manually inspecting joints uses conventional X-ray techniques. This could be automated using digital technology and image processing techniques. One possible sensor that could be used to replace the film would be a CCD camera coupled to a scintillating screen. Two post-processing algorithms for inspection of the digital images produced have been implemented; these are a statistical approach using mean, variance, skewness and kurtosis, and a method that equates pixels to Newtonian bodies. In order to verify that digital X-raying of cable joints is a feasible inspection procedure, CCD camera and film images have been taken of three test pieces. The film-based images were converted into a digital format using a high resolution scanner. Both sets of images were processed using the algorithms. The results of this test show that images generated by the camera are more distinct than film.