Abstract: The invention has an X-ray emitting tube and a linear detector on opposite sides of a plane containing a strip to be measured and an electronic acquisition, measuring and control unit. A mask transversely moveable relative to the strip occludes radiation from the X-ray emitting tube which is not intercepted by the strip or which passes through the edge region of the strip. This device offers an improved degree of precision measurement near the edge of the strip.

Abstract: Images of successive portions of a surface of a strip are formed and converted as analog signals. Signals typical of each image are stored in an image storage whereas the analog signals relating to each image are converted in numerical form by splitting up the image into image elements. Each of the image elements is given a numerical value, and then filtered, in order to sense the relative variations of the numerical values of the image elements. To determine whether or not to deliver a defect-sensing signal in terms of the sensed variations, the filtered signal is scanned. The typical image is stored in response to the transmission of the defect signal. Every read-in information is stored and displayed at a check station long enough for a visual check of the image it represents.

Abstract: An electric arc furnace comprising at least one pair of electrodes extending through the roof of the furnace for the creation of electric arcs between each of the electrodes and the charge to be melted, and a source for applying direct current to each of said pairs of electrodes, respectively of different polarities. Preferably the furnace contains also an electric probe extending through the bottom of the furnace to determine the potential of the molten charge and means for adjusting the vertical position of each electrode for maintaining the potential difference between each electrode and the molten charge at a predetermined value.