Operation of light barrier for use with automatic doors

摘要

A light barrier system for use with automatic doors uses a two channel infra red transmission path. The low frequency pulses sent along it are multiplexed and for each channel, the received pulses are evaluated in a suitable comparison window. The frequency lies between thirty and sixty kilohertz, and the value of 32.768 kHz is especially recommended. The pulses are sent out in packets with a time width of half a millisecond, and the reception window has a time width of 0.15 ms. Both transmitting and receiving stages have separate power supplies. A suitable transmitter is a LED and a suitable receiver is a phototransistor.