Patent GB-1353615-A (GB)
Title: Fire detection systems
IPC: G08B17/12
Filed: 1970-08-11
Abstract: 1353615 Fire detection systems P M PUCILL 5 Aug 1971 [11 Aug 1970] 38731/70 Heading G4N A fire detection system comprises at least one radiation detector and at least one fire simulator (e.g. lamp), energized during spaced time intervals referred to as " smoke detection epochs ", the intervening intervals being referred to as " radiation epochs " and a control system connected to the detector to give a flame output signal, indicative of a possible flame if the detector responds during radiation epochs and smoke output signal, indicative of possible smoke, if the detector fails to respond to the fire simulator during smoke detection epochs. As described, eight radiation detectors are mounted at a high level in a building and are connected by a multicore cable 2 to a respective zone unit Zb ... Zy. Each detector normally passes a small current but when triggered by infra-red radiation having a flicker frequency between 5 and 35 Hz, passes a much larger current which continues until the detector is reset by removal of its supply. A scanner 9, controlled by a central processor 6 monitors the output of each radiation detector during each radiation epoch and feeds a signal to a flame alarm store 10 if any detector has been triggered. The radiation detectors are distributed about the building (e.g. warehouse) such that any flame is likely to affect at least two detectors. False alarms are minimized by ensuring that store 10 only operates flame alarm relay 11 after two flame output signals. Relay 11 operates a bell, siren, visual alarm or fire extinguisher. Any number of flame output signals in a particular epoch gives rise to a single output pulse from a generator 14. If this number exceeds eight, an output pulse is applied to false operation gate 15 which then operates a non- urgent fault warning 16 provided the flame alarm relay 11 has not been operated. Smoke detection.-A pair of flame simulator lamps is mounted in the warehouse below the level of the radiation detectors and is energized by 12 Hz pulses from a multivibrator along line 3 under control of a simulator controller 7 for twenty seconds at the end of alternate two minute radiation epochs. A further pair of flame simulator lamps is similarly energized by line 4 at the end of the other radiation epochs. A scanner 18 provides an output pulse only if any of the eight radiation detectors has not been triggered, such pulses indicating the possibility of smoke obscuring at least one detector. A primary smoke alarm store 20 pulses a secondary store 21 only if two or more smoke output signals are received in a particular smoke detection epoch. Store 21 operates a smoke alarm relay 22 if it receives more than one smoke input signal during a consecutive pair of smoke detection epochs. The primary store 20 is reset at the end of each smoke detection epoch so that failure of a single detector will not provide a false alarm. A pulse generator 25 issues a single pulse if, in one epoch, one or more detectors gives rise to a smoke output signal. Such pulses are counted in a detector failure store 26 and, if the count exceeds twenty four, a pulse is fed to a gate 27 which is blocked by operation of the smoke alarm relay 22, but otherwise operates a relay 28 and fault indicator 29. A selector 30 feeds fault pulses during the epochs energized by the first pair of simulators to a store 31 and those during the epochs energized by the second pair of simulators to store 32. If store 31 or 32 register a count of greater than fifteen, fault alarm relays 35 or 36 are energized provided gates 33 and 34 are not closed by operation of the smoke alarm relay 22.