| 摘要 |
Two surveying columns (10, 11) placed on opposite sides of an area that must be monitored have a set of reflectors (12), aligned and facing the opposite column, and an equal number of aligned emitter/receiver units (14). The latter comprise a radiation emitter (16) oriented for illuminating an associated reflector (12) of the opposite column, and a radiation receiver (18) oriented for receiving radiation reflected by the reflector that is illuminated by the associated emitter. The barrier is driven by a control unit (30) programmed for causing each emitter (16) to emit a radiation signal, for causing the receiver (18) associated in the same emitter/ receiver unit to receive said radiation signal after reflection on a target, and for computing the distance of the target from the emitter/receiver unit considered. |
