GB309837A - Improvements in or relating to alarms and other apparatus controlled by ultra-violetor infra-red rays - Google Patents

Abstract

309,837. C.E.M.A., (Constructions Electro-Mecaniques d'Asnieres). April 14, 1928, [Convention date]. Light-sensitive cells.-In apparatus for indicating the passage of objects or human beings through a certain zone, of the type wherein the occultation by the movable body of a beam of ultra-violet or infra-red rays falling on alkaline hydride, caesium, selenium or like cells causes a relay to actuate an alarm signal, means are provided for eliminating the effects of " fatigue " of the photo-electric cell. The emitter comprises a lamp 1, a lens 2, a black screen 3, the invisible rays 15 passing to a receiver hidden in a casing 14 and comprising a screen 7, a lens 8, and a photo-electric cell 9 the current through which varies with the " lighting," these variations being amplified by an amplifier 10 the current from which goes to a relay 11 for closing contacts in series with the alarm devices. Fig. 2 shows the connections for a receiver using independent sources of current, the cell 9 being ,connected in series with a high resistance 25 of about the same value as that of the cell. The grid 27 is connected (a) to the junction of the cell 9 and of the resistance 25 through a condenser 26 having a very high insulation, preferably of a capacity of 0.01 to 0.1 microfads, and (b) to a biasing battery 29 through a resistance 28 of several hundred megohms. An occultation of the beam, by increasing the resistance of the cell 9, renders the grid more positive and increases the plate current, thereby causing the relay 11 to function. Several beams may be arranged to fall upon a number of cells connected in series. By the use of a number of mirrors the beam mav be given a complicated path. Modified connections are described for receivers working with direct current from the lighting mains. The relay may be polarized so as to be actuated when the beam is occulted and also when the intensity of the 'beam is increased. The Specification as open to inspection under Sect. 91 (3) (a), describes also the connections, Fig. 4 (Cancelled), for a receiver working with an alternating current supply. A transformer with three windings is used, one being connected to the mains, another to the filament 21 of a three electrode valve 20, while the third 24 supplies the current for the circuit including the cell 9. This subject-matter does not appear in the Specification as accepted.