Detection of objects passing through light beam - uses two beams of different wavelengths to eliminate erroneous reflections and has optical filter on reflector support cap

摘要

A photoelectric security system detects products or objects which break a light beam. Reflecting objects can cause erroneous signals and this is overcome by emitting two light beams of different wavelengths in the same direction. Two emitters (1, 2) powered from a common source (9) utilise a separator (5) to emit beams on the same axis. The rays are collected by a lens (8) and a microprism reflector (14) reflects the beams to a receiving lens (7). The received beams are separated (6) for two receivers (3, 4). An optical filter on the reflector support cap (13) permits only certain wavelengths to be reflected. The receiver outputs are applied to amplifier stages (10, 11) and a logic circuit (12) provides a single data output signal.