| 摘要 |
A high sensitivity smoke detector comprises a housing (10) incorporating a sampling chamber (16) through which air to be sampled is forced through the inlet (18) and outlet (20) in the direction of the arrows. A modulated light source (22), such as a laser, directs modulated light through the chamber (16) to a beam dump (26). The light beam (24) is offset from the axis of the housing (10) by an acute angle of between 15 and 50 degrees. If any smoke particles are positioned within a sampling volume (42), the light is scattered along a path (30) defined by baffles (32 to 40) to a light sensor (28) whose electrical output is passed through a phase-sensitive detection circuit which is referenced by the frequency at which the light source (22) is modulated, so as to produce an output dependent on the light scattered by the smoke particles. <IMAGE> |
