Optical flame detector

Claim 1

A flame detector operatively arranged to supervise a remote reference area by sounding a fire alarm in response to the presence of flame occurring at a prescribed fire-detection point within said reference area, said flame detector comprising a first photocell focused upon said reference area without any light-blocking object interposed between it and said reference area so as to optically sense light-level changes occurring in said reference area inclusive of said flame-detection point and to generate an alarm-cancelling voltage corresponding thereto, a cooperating arrangement of a lens and a second photocell similarly focused upon said reference area, said lens being optically effective to further restrict the focus of said second photocell only to said flame-detection point within said reference area so as to restrict said second photocell to the sensing of light-level changes occurring only at said flamedetection point and to generate an alarm-operating voltage corresponding thereto, and separate circuits electrically arranged in opposing relation to each other connected between each of said first and second photocells and said fire alarm, whereby a light-level change occurring in said reference area of necessity also occurs at said flame-detection point to thereby produce opposing alarm-operating and alarm-cancelling voltages of the same extent and which cancel each other while a light-level change occurring only at said flame-detection point only produces an alarm-operating voltage which is effective to operate said fire alarm.