GB840768A - Methods of and apparatus for the measurement or indication of smoke density - Google Patents

Abstract

840,768. Photo-electric smoke detectors. KELVIN & HUGHES Ltd. July 30, 1957 [May 15, 1956], No. 15103/56. Class 40 (3). [Also in Group XX] A testing tube has a smoke density testing device, which may be photo-electric, at one end and a light source at the other and conduits communicating with a flue for circulating a sample of gases from the flue through the testing tube, the circulation being induced by air drawn into one of the conduits from the atmosphere by the reduced pressure in the flue or fed to the conduit from a supply of air under pressure. In the form shown, conduits 19, 20 communicating with the flue are attached tangentially to the tube 10 with apertures 21, 22 for the flow of the sample gases. Housings secured by flanges to the ends of the tube and enclosed by cover glasses or lenses 16, 17 contain respectively a lamp 12 with reflector 15 and a photo-cell 11. The housings have ventilating holes 36, 37. The conduit 19 is open to the atmosphere but contains a tapered tube 27 which, because of the flow of atmospheric air due to the reduced pressure in the flue, induces a flow of gases from the flue and through the tube 10. A thermally-sensitive device 35 indicates any fall of temperature caused by a cessation of this flow resulting from e.g. a blockage. In a modification, the interior of the conduit 19 is of Venturi form and communicates with the tube 10 in the region of the construction. In a further form, an open-ended tube containing a construction projects from the flue and the lower end of the conduit 19, closed at the top, projects into it. In a still further form, the conduits are concentric and communicate directly with the tube 10, an air blast being directed by a blower across the tube 10 and into the inner conduit to induce the flow from the flue.