Optical smoke detector using pulsed light beam detector - has triggered monostable system and filter circuit to suppress noise

摘要

A smoke detector circuit uses a pulsed light beam generator and detector and an amplifier, monostable multivibrator and filter circuit which are insensitive to the disturbance effects normally occurring in such equipment. A pulsed light beam generator using an optical diode generates a beam of light which falls on a receiver circuit via a test area to which the smoke to be detected has access. The receiver circuit comprises a preamplifier threshold detector, monostable multivibrator, resistance capacitance low pass filter circuit a discharge circuit and an output alarm stage. The preamplifier stage is arranged to produce small pulses when no smoke and higher amplitude pulses where smoke is present in the test area. These different levels are differentiated between by transistorised circuits.