Pulsed light barrier transmitting light modulated by noise generator - has sync. demodulation correlating received signal with noise generator signal

摘要

The light barrier has a transmitter radiating intensity-modulated light and a photo-electric receiver followed by a signal evaluator. The intensity of light from a LED (2) is modulated by a noise generator (6) via a drive amplifier (1). The generator produces statically independent noise. A sync. demodulator (5) follows the receiver (3) to correlate the received signal with the signal from the noise generator. A low-pass filter (7) follows the demodulator to supply a comparator (8). The generator contains a Zener diode or uses the base-emitter path of a bipolar transistor as the noise source. ADVANTAGE - Prevents interference from periodic foreign light pulses.