Data detector for selective control of lift - uses system of standard and non-standard length screens and twin beam detector

摘要

The detector system includes screens fixed in space and set along the path of at least a detector fixed with respect to the lift so as to drive a sreen counter and subractor. The system uses a single file of screens and a single detector. The detector has at least two detection beams arranged so that one follows the other in the displacement sense of the lift. Inserted between the aforementioned standard screens are screens of different length which form a reference system for the standard screens. The detection beams are separated from each other by a gap which is less than the distance between transversal edges of each of the standard screens.