Patent GB-521621-A (GB)
Title: Improvements in means for detecting and giving warning of the presence of smoke or suspended matter in air or fluid streams
IPC: G01N21/53
Filed: 1938-11-23
Abstract: 521,621. Photo-electric smoke and like detectors; valve relays. CHAMBERS, W. A., and BRITISH ELECTRICON (LONDON), Ltd. Nov. 23, 1938, Nos. 34085/38, 1455/39, and 1581/39. [Classes 40 (iii) and 40 (v)] Solid suspended matter in fluids, such as smoke in air, is detected by means of a pair of similar light-sensitive devices differentially connected in a bridge circuit controlling signalling means and equally illuminated by light beams which are so projected through zones in a locality to be protected or observed or across fluid streams conveyed from such localities that each beam lies in a potential path of travel of solid suspended matter appearing in the fluid under test, whereby both cells are equally employed in detecting changes of light values due to suspended matter and signal means are operated when a disturbance of the balance of the system occurs due to differential changes in light value. As shown in Fig. 2, a header 39 with outlets 38 is connected by conduits 40 to various localities from which fluid is forced or sucked. The outlets 38 are arranged in rows between pairs of photo-electric cells 1, 2 and pairs of lamps 3, 4, two pairs of each being shown, so that. any smoke in the fluid from any of the outlets 38 causing a disturbance of the light balance on a pair of cells produces an output signal by the circuit shown in Fig. 1. The lamps 3, 4 arc across the mains M, M<SP>1</SP> with a resistance 8 and adjustable contact 7 to adjust the relative luminosity of the lamps. A resistance 10 in series with the lamps serves to give the requisite voltages to the cells 1, 2 in series and to the heater 13 of a thermionic valve. The cathode 14 of the valve is biassed by an adjustable contact 18 on the resistance 10 and for stabilizing purposes is connected by a high resistance 14<SP>1</SP> to the point between the cells which is connected to the grid 12 through a resistance 17. A screen grid 16 is connected to the mains through a resistance 24. And the anode 15 is connected to the mains through a coil 20 balanced by a coil 19 connected across the mains in series with an adjustable resistance 22. If the balance of illumination on the cells is upset, one of the coils 19, 20 overpowers the other and an armature 21 is rocked to close a contact 27 or 28 leading respectively to visible and audible signals 37, 35 and 36,34, corresponding respectively to the two rows of outlets 38. A visual inspection at the outlets will reveal which particular outlet in the row is the disturbing one. If desired the signal may be caused to set in operation a fire fighting installation or to make a graphic record. Where vibration might upset the system, the arrangement of Fig. 4 is provided. The light beams 45, 46 from the lamps 3, 4 are reflected by spherical mirrors 47, 48 to produce images 51, 52 on diffusing screens 49, 50 in front of the cells 1, 2, the screens being sufficiently larger than the images so that vibrations do not affect the luminosity on the cells. These parts and the amplifying valve 41 are all in a dust-proof casing 53 with windows 54, 55 for the passage of the beams. Lens systems may be interposed between the screens and the cells to form on the light sensitive areas of the cells images of the diffused screen images. The diffusing screens of the two cells may be made as a single unit and arranged to act also as a differential light admission control for adjusting the balance. This is shown in Fig. 5, where a combination screen 56 has a maximum density in the middle and the density decreases towards each side. The screen is adjusted over apertures 58, 58 in front of the cells 1, 2 by a screw 62 in conjunction with springs 59, 60, the screw being secured in adjusted position by a lock nut 63. Specification 394,853 refers to a different photo-electric apparatus for a similar purpose.