Perforated tape reader with enhanced security - uses modulated reflected scanning beam and reference comparison

摘要

The perforated tape reader consists of a light source whose beams pass through the perforations and at the same time are partially absorbed and reflected by the material of the tape. The beams emerging on the lower side of the perforations are modulated further and fall onto a reflector. From here they are reflected back through the modulation unit and pass again through the same perforations. The beams strike the photo-cells of transducers. The signals from the photo-electric sensors pass to comparators after having been amplified. The synchronisation inputs of the comparator are fed with a standard signal derived from a reference source.