Abstract: The invention relates to a method for finding holes, and other related defects and measuring characteristics of sheets of industrial material. Optical detections systems are constantly plagued by intense ambient light and challenged in accuracy. The invention exhibits a defect detection method and means that is resistant to intense ambient light and is capable of inspecting sheets of material (410, 510, 610, 710) continuously, without integration of long periods. In the invention, synchronous detection between the optical transmitters and receivers is utilised. The invention is applicable for inspecting and measuring materials like paper, metal, rubber, plastic, aluminium foil, copper foil, film, coated metal sheet or any other sheet-like material that could run on a production line. The invention is also applicable for finding special defects like holes, pinholes, scratches, spots, cracks, edge faults, streaks, surface faults or any other conceivable defects.

Abstract: A method for finding holes, and other related defects and measuring characteristics of sheets of industrial material. Optical detections systems are constantly plagued by intense ambient light and challenged in accuracy. The invention exhibits a defect detection method and apparatus that is resistant to intense ambient light and is capable of inspecting sheets of material (410, 510, 610, 710) continuously, without integration of long periods. In the invention, synchronous detection between the optical transmitters and receivers is utilized. The invention is applicable for inspecting and measuring materials like paper, metal, rubber, plastic, aluminum foil, copper foil, film, coated metal sheet or any other sheet-like material that could run on a production line. The invention is also applicable for finding special defects like holes, pinholes, scratches, spots, cracks, edge faults, streaks, surface faults or any other conceivable defects.