| 摘要 |
An optical scatter smoke sensor comprising an optical smoke sensing chamber having an inlet to allow smoke into the chamber, an optical emitter 12 and an optical detector 13 disposed inside the chamber at spatially separated positions. The emitter 12 has a major optical output path B1 which is directed through an aperture 15 in the top wall 10 of the chamber so that little or none of the emitted light falls upon the walls of the chamber where dirt or dust may have collected. In this manner, the standing scatter level inside the chamber does not vary, even if there is a build up of dust and grease on the walls of the chamber. Accordingly, the trigger level of the sensing circuit can be set at a relatively low value without the need to allow for changes in the standing scatter level. |
