Patent GB-371954-A (GB)
Title: Improved system for indicating the presence and location of fire
IPC: G08B25/00
Filed: 1930-11-05
Abstract: 371,954. Fire-alarm systems. KIDDE & CO., Inc., W., 140, Cedar Street, New York, U.S.A.-(Assignses of Grant, H. C.; 470, West 159th Street, Manhattan, New York, U.S.A.) Nov. 5, 1930, No. 33233. Convention date, Nov. 21, 1929. [Class 40 (i).] In a fire-alarm system in which a plurality of heat-responsive means is connected in a single protective circuit, actuation of any one of said means effects the operation of switching means which connect the circuit into a Wheatstone bridge which is adapted to be balanced automatically or manually to provide an indication of the actuated heat-responsive means. Figs. 1, 1a, and 1b show a protection system employing a plurality of circuits A, B in each of which thermostats TT1, TT2, &c. are connected. The protective circuits are connected in parallel across the supply and include series connected " trouble " and " fire " relays T1, M1, through which a normal supervisory current flows. In the arrangement shown, when any one thermostat in a protective circuit is operated, the particular circuit affected is indicated by a group of lamps A1 .. J1 and the particular thermostat is identified by a group of lamps operated by selector switches which act automatically to re-balance a Wheatstone bridge, the balance of which is disturbed upon operation of the thermostat. Supervision of protective circuits. In the event of a breakage in the protective circuit, the normally-energized trouble relay T1 is released, and an individual lamp L1 and a common alarm bell TB are operated over a circuit including a switch S1, which when operated frees the bell TB for use in association with other circuits. When the fault is removed, relay T1 is again energized but the lamp L<1> remains lighted over the switch S1 until the switch is restored to normal. Supervision of battery. If the current from the supply battery BAT fails the series connected relay 2 is released to operate lamp L2 and bell TB. A switch S7 is provided for the purpose of clearing the bell TB to allow for further use. Normally the battery BAT is under charge from mains 212 which supply the system through resistances 215, 216, 217. When the fire-alarm bells are rung resistance 216, 217 is short-circuited to provide greater current. In the event that the battery becomes disconnected resistance 220 is switched into circuit to prevent the voltage across the system rising owing to the decreased current taken from the supply. The power supply is supervised by a relay 224 in a manner similar to that previously described. Switches SM, SC and meter M are provided for ascertaining the values of the supervising and battery charging currents. Supervision of fire-alarm bells. The system is provided with two bells UA, SA the latter of which is connected in series with a supervising relay 43 the resistance of which normally prevents operation of the bell. If the bell becomes inoperative the supervisory current fails and relay 43 is released to operate lamp L3 and alarm TB. A fuse 221 is connected in the bell circuit so that in the event of a shortcircuit across the bell SA upon operation of relay 62 in response to a fire alarm, the fuse is blown and a short-circuit across the supply is prevented. Fire alarms. Each protective circuit has a terminal resistance 49 which normally limits the current to such a value that fire-alarm relay remains inoperative. Upon operation of a thermostat such as T, T2 resistance 49 is shortcircuited and relay Ml is operated to connect, at 17, the protective circuit into a Wheatstone bridge circuit, and establish a locking circuit for itself over switches 194, 208. Relay 62 also is energized by relay M1 over a circuit including a cabinet door switch CDS to operate the bells UA, SA. Indicating affected protective circuit. A plurality of lamps A1, B1, C1, D1 .. are provided corresponding to the protective circuits A, B, C, &c. the lamps being normally connected in series together with a supervisory relay 75 which, if any one of the lamps becomes defective, is de-energized to operate a lamp and trouble alarm TB. When a fire-alarm relay M<1> operates relay 118 is energized to operate contacts 114 &c. which connect the lamps in parallel and cause the lamp corresponding to the affected circuit to be illuminated. Indicating affected thermostat. Each thermostat such as TT1, TT2, in a protective circuit has an associated resistance U1, U2 and the arrangement is such that upon operation of a thermostat, the resistances preceding the thermostat are connected in one arm of a Wheatstone bridge, the other arms of which comprise fixed resistances 133, 134 and a variable resistance automatically adjustable by a stepping switch. A second stepping switch is provided for operating the indicating lamp. The bridge controls relay contacts 161 which in turn control the operation of the stepping switches. Upon occurrence of a fire, relay contacts 161 energize relay 162 which closes the circuits of stepping magnets MOT1, MOT2. Slow-acting relay 237 also is operated and relay 162 thereby de-energized and these relays interact to impulse the magnets MOT1, MOT2 and drive the associated stepping switches so long as the contacts 161 remain closed. The switch arms 146, 151 associated with magnet MOT1 thus move over contacts interconnected by resistances until balance is restored, the resistances connected between the first nine contacts in the upper row being multipled to similar contacts throughout the row, whilst resistances having values of the sum of the unit resistances are connected at every tenth contact in the second row. The upper rows of contacts of the second switch control the illumination of the appropriate lamps in the banks of lamps TC, UC. In order to preserve substantially uniform sensitivity throughout the entire range of operation of the bridge a resistance 138 is included in the bridge at first and is short-circuited by a relay 182 after, say, the tenth step of the switch. Restoration of equipment to normal. Operation of push button 194 into engagement with the contact 192 energizes relays 252,253 which lock and establish homing circuits for the stepping switches over contacts 191, 198. The operated fire-alarm relay M<1> also is released and the associated apparatus restored to normal. Central station equipment. The central station equipment is arranged in a cabinet the door of which controls a switch 208 connected in series with the resetting switch 194. As soon as a fire alarm is given, the attendant enters the cabinet, the switch 208 being operated to cause resetting of the equipment. When, however, the switches are restored, the indication is repeated and after the attendant has noted the signal the switch 194 is operated to again reset the apparatus, after which the indication is further repeated. Closing the door of the cabinet restores the system to normal provided the protection circuit is restored to its normal condition. In a modification, Fig. 2 (not shown), a single stepping switch is used instead of the two switches shown in Fig. 1. Moreover, the switches for balancing the bridge may be manually operated, suitable means being provided for indicating the point of balance. Specifications 372,248 and 372,249 are referred to.