GB1003075A - Improvements in or relating to fire detection and alarm apparatus - Google Patents

Abstract

1,003,075. Radiation sensitive fire alarms. THRING'S ADVANCED DEVELOPMENTS Ltd. April 9, 1964 [April 11,1963], No.14599/63. Heading GIA A fire alarm includes a detector 17 with a filter 18 capable of giving an electrical output in response to radiation in the 2-7 micron region and a rotary scanner serving to direct on to the detector in sequence radiation from sections of the space to be protected. As shown the scanner consists of a curved mirror strip 12 mounted on a drive shaft 10 for rotation, either directly or through gearing, by a motor 5. Thin ribs 15 position, the detector and also support a thin infra-redtransparent protective globe 19. Opaque material may be stuck on the globe to prevent operation of the alarm by, for example, a fixed electric fire. Provision may also be made to exclude direct sunlight and the globe may be opaque to visible light. It is contemplated that one or more units should be mounted overhead to cover the required space, the rate of scanning being between 1 and 10 revolutions a second. If a fire breaks out the output of any unit viewing the fire will include pulses at the rotation frequency which can be used to initiate operation of an audible and/or visual alarm. Each unit may include means producing low amplitude pulses at each rotation, and pulses being used to indicate correct rotation of the scanner. To prevent a uniform but dangerous rise of temperature in the space protected fairly to give an alarm it is proposed to fit a blanking element covering a small arc and driven at a different speed of revolution to the scanner so that the position of the blind spot varies.