| 摘要 |
A smoke detector comprising; a light source 26 generating a beam along an optical axis 154, a sensor 30 for receiving light scattered off the optical axis by smoke and a light trap (11, fig 7) comprising walls that define a volume for receiving unscattered light. The volume comprises a closed region with an open first end and at least one wall that is sloped between the first and second end such that the volume narrows from the first end towards the second. The light trap may be embodied as a cone, such as a right circular or oblique cone, and may have an axis of rotational symmetry parallel to the optical axis. The detector may also comprise a generally circular disc-shaped base (2, fig 1) connected to a generally circular dome-shaped cover (7, fig 1). The cover (7, fig 1) may have a peripheral serpentine air inlet to permit the passage of smoke but block external light from entering. |
