GB876365A - Improvements in or relating to visual indicators - Google Patents

Abstract

876,365. Luminescent and electro-luminescent devices and materials. STANDARD TELEPHONES & CABLES Ltd. Dec. 13, 1957 [Dec. 17, 1956; May 27, 1957], Nos. 38356/56 and 16861/57. Class 39(1). A visual indicator displays a line pattern as a dark trace on a bright background by heat-quenching a photo- or electro-luminescing phosphor along the line of the pattern by means of heating elements arranged in heat conducting relation with the phosphor. In the construction shown in Fig. 1 of the second Provisional Specification a visual indicator panel includes a transparent layer 7 of an electro-luminescent phosphor, such as carbon activated boron nitride, which emits U.V. light under A.C. excitation sandwiched between transparent front and back electrodes 9 and 8, such as glass plates 10 carrying a metallic transparent layer 11, a layer 5 of photoluminescent phosphor, such as copper activated zinc or cadmium sulphide with a killer element such as nickel to enhance the heat-quenching effect, emitting visible light when irradiated by U.V. light disposed adjacent the back electrode 8 for irradiation by the electroluminescent phosphor 7, the luminescence of the photo-luminescent phosphor 5 decreasing with increase of temperature, and a pattern of heating wire elements 14, Fig. 2, on the front face of the heat resistant insulating plate 1 and in contact with the photo-luminescent phosphor layer 5 and arranged for independent electrical heating through extensions of the wires, the terminal block 21 and the stepping switch 22. The insulating plate 1 is spaced from a heat resistant insulating plate 2 by heat resistant insulating pillars 3 and excess lengths of the wires 14, which are all of the same length for equality of heating, are wound on the pillars 3. A.C. voltage is applied between the electrodes 8 and 9 through wires 12 and 13. The wires 14 are individually shaped on the plate 1 and fastened thereto by adhesive. The plate 1 can be provided with shallow grooves 15, Fig. 3, into which the wires are inserted. Where the wires cross over one wire 14A, Fig. 4, is passed behind wire 14B through holes 16, or the wire 14A, Fig. 5, can be looped through a single hole 16 and held by an insulating peg 17. The line patterns can be provided by printed resistance wiring on the plate 1, the printed wiring 14C, Fig. 6, standing proud of the face of the plate or flush therewith as shown at 14D, Fig. 7. Where printed wires cross over as in Fig. 8, one wire 14E is continuous and the other wire 14F discontinuous on the face of the plate 1, the discontinuous wire 14F being led behind the continuous wire 14E by conducting rivets 18 and 19 interconnected at the rear of the plate 1. The printed wires are connected to lengths of wire as before so as to form wires of equal resistance. In a modification the electroluminescent phosphor layer 7 and the electrodes 8 and 9 are omitted, the U.V. light for irradiating the phosphor layer 5 being produced by an external U.V. light-source such as an incandescent or discharge U.V. light bulb, the plate 6 being of a glass transparent to U.V. light, as described in the first Provisional Specification. A multiple indicator can be formed by assembling a number of indicators and flooding the co-planar faces of the indicators from a common U.V. light source as described in the first Provisional Specification. In the construction shown in Fig. 9 of the second Provisional Specification the indicator panel comprises an electroluminescent phosphor layer 23 sandwiched between a transparent front electrode 24 and a back electrode 25, the whole being mounted on an insulating back plate 26. The phosphor layer 23 emits visible light when energized and can comprise zinc or cadmium sulphide incorporating activating and killer elements as above described. Heater wires, each shaped to form a separate character, are embedded in the phosphor layer 23, each wire being preferably provided with heat resistant insulation such as polytetrafluorethylene, this insulation enabling the wires to be crossed over one another in the same plane. Alternatively where uninsulated wires cross over a small strip of heat resistant insulating material such as mica can be inserted between the wires. These crossover arrangements can also be used in the arrangements previously described. According to the first Provisional Specification the arrangement of individual character wires 14 as shown in Fig. 2 of the second Provisional Specification can be replaced by heater wires on the plate 1 in the form of three individual horizontal wires interlaced with three individual vertical wires and an individual diagonal wire, a character being displayed by selective heating of a number of wires in combination.