Patent GB-326189-A (GB)
Title: Improvements in and relating to electrical automatic fire alarms
IPC: G08B17/02
Filed: 1928-12-06
Abstract: 326,189. Fairbrother, H., (Vigilant Automatic Fire Alarm Co., Ltd.). Dec, 6, 1928. Alarms operated by expansion of solids; electric alarm systems. - In an automatic fire alarm system heat-sensitive actuating devices are adapted to operate a plurality of contacts, the selective actuation of which controls normally open and/or closed main circuits which in turn control local alarm circuits. The heat-sensitive device, Figs. 2 and 3, comprises a tube 7 secured to a web 6 in a casing 1. An insulator 9 on the web carries posts 10, 11 carrying contact springs 12, 13 normally in contact respectively with contacts 15, 18 adjustable in posts 16, 17. The springe 12, 13 are conf['olled by the insulated head 79 of a rod 21 secured to a tubular member 24 secured to the free end of a tube 22 the other end of which is secured to the tube 7. The member 24 has its central portion 25, Fig. 9, cut away so that it is flexible at this point. A rod 26 is adjusted in a plug 27 at the free end of the tube 7 so as to press against a recess 28 in the member 24 and so flex its part 25 that the rod 21 is held in its normal, inactive, position. In case of fire, the tube 7 expands and withdraws the rod 26, so that the member 24 bends and moves the rod 21 to operate the cnntact springs. A slow rise in temperature will heat. the tubes 7 and 22 equally, so that no movement of the rod 21 occurs. An insulator 32 on the web 6 carries terminals 33, Fig. 4, connected to the posts 10, 11. The post 16 is connected to a terminal 35, and the post 17 is connected to earth by a terminal 34. The device so far described is for use with double closed main circuits. For use with a closed and an open main circuit, the device is modified as shown in Fig. 5. The spring 12 is normally in contact with the contact 15, but the spring 13 is held from contact with the contact 18 by an adjustable contact 19. The end of the arm 21 forms a contact which is earthed to the terminal 34 and holds the spring 12 against the contact 15. The posts 16, 18 are bridged by a conducting plate. Fig. 11 shows main switches, of which that indicated at 40 is for control by a normally closed main circuit, and that at 41 by an open circuit. The switch 40 comprises a drum 45, Fig. 13, rotatable. on pivots 46 and carrying a. series of contact pins 61 and a switch arm 47. The upper end of the arm 47 carries a spring- pressed armature for co-operation with the poles 52 of coils 53 in the main circuit, and the arm also carries a pin 54 adapted to close spring contacts 55, 56. When current is flowing in the coils 53, the armature is held to the poles 52, and the contacts 55, 56 are closed. When the armature is released by failure of current in the coils 53, the arm 47 falls away and rotates the drum 45 so that the pins 61 bridge a series of spring contacts 57, 59 arranged in various alarm circuits. The open circuit switch 41 comprises similarly a drum 73, Fig. 14, carrying contact pins 74 for spring contacts 75, 76 in the alarm circuits, and a switch arm 62 which carries a pair of pins 68 for closing two sets of contact springs 69, 70 and 71, 72. In this case, the main circuit coils 67 are normaliy de-energixed, so that a latch on an armature arm 63 holds the arm 62 in closed position. Closure of the normally open main circuit will thus move the arm 63 to release the arm 62 and so close the alarm contacts 75, 76. Fig. 17 shows the system when two closed main circuits, two drop switches, such as 40, and two thermal actuators, as shown in Figs. 2-4, are used. A conductor SO leads to the contact 15 from a battery 81 and returns to it at 82 from the post 10 through the coils 53 and contacts 55, 56. Another conductor 83 leads from a battery 8i4 to the contact 18 through the coils 53 and contacts 55, 56 of the second drop switch 40, and returns to it at 85 from the post 11. When a thermal actuator 1 is heated, the rod 21 moves the blade 12 away from the contact 15. This breaks the circuit of the coils 53, releasing the switch arm 47 to bridge the contacts 57, 59. These contacts are in circuits including, for example, a battery 88 and a transmitter 87, and a battery 90 and bell 89. Continued heating of the actuator 1 then moves the blade 13 away from the contact 18, breaking the circuit of the coils 53 of the second drop switch, so that its alarm contacts 57, 59 are also bridged. A coil 99 for a drop shutter may be included in either or both circuits. The batteries may be replaced by a dry charger with storage battery. In a system comprising combined closed and open main circuits, Fig. 19 (not shown), drop switches 40 and 41, and thermal actuators, such as shown in Fig. 5, the open circuit is tapped across the closed circuit. When the actuator is heated, the rod 21 so controls the open circuit that it is connected successively to two different portions of the closed circuit, thereby providing two different paths for the flow of current.