Secondary light testing in optical smoke detectors

摘要

One type of smoke detector has a housing forming a dark chamber into which light is directed on a path viewed by a smoke sensing photocell. Smoke in the viewed light path scatters light to the cell exciting the cell to alarm state if the smoke is of density predetermined to be dangerous. The detector is tested for its ability to respond to the predetermined smoke density by means of an external owner-operated button. Depressing the button turns a lever or bell crank which intercepts the light path in the chamber and scatters light to one or more large areas within the dark chamber. These secondary areas in turn rescatter the scattered light to the photocell simulating smoke and exciting the cell to alarm state.