Patent GB-248156-A (GB)
Title: Improvements in or relating to electric signal systems
IPC: G08B25/00
Filed: 1925-02-05
Abstract: 248,156. Beach, C. E. Feb. 5, 1925. Fire and like alarm systems.-In order that signalling systems for fire alarm and similar services shall function despite faults such as grounding, and shall give indications of such faults, an electromotive force is applied to a closed signal loop passing through all the substations F - - J and an electromotive force of substantially the same mean effectiveness is applied alternately between each of the terminals 25, 27 and the terminal 26 of a common return conductor for each substation. This may be accomplished, as shown in Fig. 1, by the connection of a three-phase generator A' as shown. The closed loop passes through normally closed contacts 40, 41 at each substation and through relays B, D. A grounded contact 42 at each substation is normally open and terminal 26 of the central station is connected through relay C to ground. In normal operation the first movement of a code wheel 39 at a substation connects all three contacts 40, 41, 42 and so energizes relay C, the front contact of which is connected to a magnet 36 actuating a pen 33. At the first notch in the wheel 39, all contacts 40, 41, 42 are separated, relays B, D are de-energized and as their back contacts are connected to magnets 35, 37, pens 32, 34 are actuated. Signals are thus recorded by all three pens, but pen 33 is in advance of the others. If the code wheels of two stations are actuated at once, one set of signals will be recorded by pen 32 through relay B and the other by pen 34 through relay D whilst pen 33 will record both sets. If the signal loop is broken at 80 relays B, D will be de-energized and warning given, but the signals from a substation can still be received by the contacts 40, 41, and 42 completing a circuit to ground through relav C and either B or D when the code wheel 39 is actuated. If a leakage to ground develops as at 81 relay C will be energized to give warning thereof, but'signals can still be recorded by pen 32 or 34. If the lines become crossed so as to effect a short circuit as at 82 or 83 no warning is given immediately but signals will be recorded: by pen 33 only. Methods of connecting a threephase generator to the system in closed delta and in star connection are described. A single phasealternator A<4> mav be used as in Fig. 4, the primary and secondary phases of the transformer 421, 431 being 120‹ apart. In Fig. 5 the secondary 531 develops the same potential as either battery a, the alternating current alternately assisting and opposing the batteries flows alternately through relays B, D, Fig. 1. A similarresult may be obtained by connecting terminal 26 to the middle point of the transformer secondary, the ends of which are connected through resistance and inductance respectively to 25, 27. Direct current sources only may be used, Fig. 7. Battery a<2> is connected to terminals 26, 27. The relay C is doubly wound, one end of each winding being connected to batteries a<1>, a<3>, the other ends to ground 68<1> through a pole changer P, whichmay be the front and back contacts respectively of a magnet 92 the winding of which is connected to a battery 99 through a vibrator 100. Condensers 97, 98 are preferably connected between the front and back contacts of the windings of relay C. The pulsating current through relay C due to charging and discharging of these condensers is insufficient to attract the armature, but when a ground connection is established at a substation pulsations will pass through both windings and energize relay C.