The sensors mounted onto the cylinders detect the position of the piston by communicating an electric signal when approaching the magnetic field produced by the magnet incorporated in the piston itself. They are manufactured using two different technologies: electromechanical with Reed bulb; electronic with magnetic-resistive effect (normally open with PNP output); upon request with NPN output. The first one, with Reed bulb function both in D.C. and A.C.; the second ones, electronic type function only in D.C. 30V max. In both versions the active status is indicated by the lighting of a luminous diode.