Patent GB-719609-A (GB)
Title: Improvements in electric lamp signalling systems
IPC: B66B19/06
Filed: 1952-12-12
Abstract: 719,609. Electric indicating systems; mine signalling systems. FORGES ET ATELIERS DE CONSTRUCTIONS ELECTRIQUES DE JEUMONT. Dec. 12, 1952 [Jan. 5, 1952; April 16, 1952], No. 31509/52. Class 40 (1). An electric lamp signalling system comprises an energizing centre-tapped transformer, a plurality of luminous signal panels each with a number of signalling lamps, two groups of selective energizing wires connected respectively to corresponding lamps of the panels, control contacts interposed between the transformer and the selective wires for controlling the operation of the system, each of the groups having an additional direct wire unconnected to the panel signalling lamps, at least one return wire, and a plurality of electromagnetic current responsive elements for controlling, security, and signalling purposes, wherein the two groups of wires form a three-wire distribution circuit in which the signalling lamps are energized at a reduced voltage between different selective wires and the return wire, so as to form two approximately balanced loads, while the electromagnetic elements are supplied under full transformer voltage between the wires of the group. Fig. 2 shows a selective lamp signalling system for use in a mine wherein a panel M containing six indicator lamps 1 to 6 and individual disabling switches i is placed in the engine room, and similar panels J, R1, R2 &c. are situated at bank and at the several pit levels. Lamps 1, 3, 5 of each panel are respectively connected to control conductors d1, d3, d5 of a multicore cable C1 traversing the pit and lamps 2, 4, 6 are respectively connected to control conductors d2, d4, d6 of a similar cable C2; the condnctors being connected through respective control contacts r1, r3, r5 and r2, r4, r6 to the opposite secondary terminals of a transformer T whose centre point is earthed and connected to the neutral return N of the lamp signalling panels. The cables also contian lines l1, l2 which are directly connected to the respective secondary terminals, and control or signalling relays in series with interlocking contacts (e.g. A, A3 A4; a, a3, a4) which may be branched between the direct line of one cable and the appropriate control line of the other cable or between the two direct lines whereby such relays are operable by closure of the necessary lamp control circuit contact or by energization of the entire apparatus over transformer T. The relays are thus selectively operated by the entire secondary voltage while the lamps are operated by half the secondary voltage and are arranged in balanced groups so that the return current in the neutral N is reduced to a low value. False operation of relays and lamps due to their being effectively in series across one half of the transformer secondary when the control contacts are open is prevented (Fig. 4) by providing two neutral conductors equally spaced along the transformer secondary, of which N1 is the return for grouped signal lamps 2, 4, 6 while N2 is the return for grouped lamps 1, 3, 5. The secondary centre point is earthed as before, and when the operating contacts are open the relays and lamps are in series only across 1/3 of the secondary, so that the current therein is reduced below the operation or display level.