| 摘要 |
Smoke detection apparatus including a pair of photoelectric cell which receive illumination selectively from a very low level light source. One of the cells is termed the "direct" cell because it is in the direct path or on the axis of a narrow conical beam of light emanating from the source, the other cell being termed the "reflected" cell because it receives a significant part of its light input upon reflection of light from smoke particles or the like as such particles are drawn into the path of the light beam. Under predetermined smoke conditions, i.e., when there is smoke obscuration of the light of 2% per foot (.01 optical density), an alarm signal is triggered. The very low level light source is a light-emitting diode which sensitively monitors the smoke obscuration; only a slight change in the illumination to the pair of photocells, connected in a sensing circuit, is required to produce the triggering signal. Accordingly, the smoke detection apparatus is highly sensitive to the presence of either so called "white" smoke of "black", i.e. non-reflective smoke, and either or both will trigger the alarm signal. |
