An optical arrangement for a light scattering type smoke detector has a radiation transmitter and receiver which are each preceded by a lens for obtaining a generally parallel field of view for each of the transmitter and receiver. The radiation is directed at a detection zone which is surrounded by...http://www.google.es/patents/US4397557?utm_source=gb-gplus-sharePatente US4397557 - Optical arrangement for a light scattering type smoke detector
Optical arrangement for a light scattering type smoke detector
