Abstract: A sensor for detecting the relative position of a workpiece with respect to the tip of a welding or cutting torch, which is movable in optional directions by positioning devices, is provided with a sensing body in annular form which surrounds the tip and is adapted to make contact with the workpiece on any side of the central opening of the sensing body. An arm is attached to the sensing body and is displaced in a direction and to a degree corresponding to the displacement of the sensing body. The displacement of the arm is detected and a signal corresponding to that displacement is generated to reposition the welding head in response to the signal.