Patent GB-177567-A (GB)
Title: An improved automatic fire alarm
IPC: G08B17/06
Filed: 1920-11-24
Abstract: 177,567. Gill, H. A., (Vigilant Automatic Fire Alarm Co., Ltd.). Nov. 24, 1920. Fire, police, and like alarms, systems, and apparatus.-Relates to an electrical fire-alarm system in which thermostats are connected to a battery and in which a normally open circuit is employed as the main alarm circuit. As shown in Fig. 1, the thermostat consists of a flexible metal blade 1 normally in contact with a contact 2. When the tube 6 is heated, expansion takes place and the rod 4 moves away from the short arm 5 and permits the blade 1 to make contact with the contact 26, and if heating continues, with the contact 33. In a normally closed circuit, current from the battery 8 flows through the wires 9, 11 to the circuit-breaker 19, flexible connection 13, blade 1, and wire 15. The current then flows through the coil 17 of a drop switch and the wire 18 which is connected to the opposite pole of the battery. When current is flowing, the arm 20 of the circuit-breaker is retained, but immediately the blade 1 leaves the contact 2, the arm will fall and break the circuit at 21 in the wire 18, so that the coil 17 will release the cross bar 49 and drop switch 34 will fall, Figs. 2 and 3. A battery 24 in a normally open circuit sends current through the wires 25, 11, flexible conconnection 13, blade 1, thence through the contact 26, with which the blade will make contact when heating takes place, and along the wire 27 after which it divides between the coils 28, 29. The terminal 30 and contact 61 are bridged by the blade 67 of the knife switch 57 so that the current flows through the wire 31 which leads to the other pole of the battery 24. The coil 28 operates a drop annunciator and when current flows the coil 29 releases the drop switch 57. The drop switch 34 is of the knife pattern and consists of blades pivoted in the contacts 41 to 46 which bridge these contacts with contacts 51 to 56 after the switch has fallen. The drop switch 57 controlled by the open circuit has blades pivoted in contacts 61 to 66 which are bridged with contacts 71 to 76 when the switch has fallen. When the switch is in its normal position the contacts 30, 61 and 66, 69 are bridged. After the drop switch 34 has fallen, a second open circuit is provided from the battery 80, through the wire 83 to the contact 66, from the contact 69 through the wire 84 to contact 42, along the knife blade 36 to contact 52, wires 85, 11 from which it follows the lines of the open circuit before described, the return from terminal 30 being by the wire 86. This circuit will cause the drop switch 57 to fall should the battery 24 be run down or the wires thereof disconnected. The circuit may be completed from the battery 80 through the blade 36, wire 85, wire 88, blade 37, and wire 89 to wire 15 whenever the current cannot pass along wire 11. The metal conduit casings of the wires may. be employed as return paths between the switchboard 7 and the thermostats for the open circuits, thus replacing the wire 27, Fig. 1. Should the line 11 and its conduit be completely severed, current will be cut off from the coil 17 which will cause the drop switch 34 to fall thus indicating that there is a fault on the line. The bell 93 is connected to battery 80 so that it rings when both switches have fallen, and the buzzer 99 connected with the battery 100 is operated by the falling of either of the switches. A transmitter 105 operated by both switches is connected to battery 108 and is used for transmitting a message to the fire brigade station.