Smoke detector using photocell responsive to reflected light - includes light source monitor and RC network connected to level detector (BR 19.7.77)

摘要

The smoke detector comprises a housing defining a tortuous path between a light source (L) and a photocell (C1) so that the latter responds to light reflected or defracted by smoke particles. The electrical characteristics of the photocell (C1) are monitored by a device which supplies a corresponding signal to a voltage level detector (N), connected to a trigger circuit for an alarm (A) to operate the latter when the photocell indicates a given smoke concentration. An RC network (F1, R3) is connected to the level detector (N) followed by a pulse former, connected to the trigger device (SCR). A second photocell (C2) responds to the failure of the light source (L) to activate the pulse former.