The Laser - Doppler - Velocimeter LDV250 is an optoelectronic device to determine non intrusively and continuously the velocity of a strand or profile after leaving the exit nozzle of an extruder.The system is also appropriate for the velocity measurement at any moving surface as e.g. from metal, paper, polymers, wood in continuous processes dealing with hoops, pipes, plates, tapes, foils, wires, and cables etc.By integration of the measured velocity the system is able to generate a signal for cutting at a preselected length.