Patent GB-776078-A (GB)
Title: Electric alarm system
IPC: H04M11/04
Filed: 1954-09-20
Abstract: 776,078. Electric intruder and fire alarms. DANSKE SECURITAS AKTIESELSKAB. Sept. 20, 1954 [Sept. 19, 1953], No. 27182/54. Class 118 (1). An electric intruder or fire alarm system operating over telephone lines D comprises a known signal starter N, an audio frequency generator G, and a damper H which normally permits only a supervisory signal of low voltage to be sent out to a test amplifier O and a common amplifier P in a main station W, the damper H being cut out by the starter N on alarm so that alarm signals of full generator terminal voltage may be transmitted. The input side of amplifier O is connected by a rotary switch S to multiple contacts T to which the lines D are connected. In normal operation weak signals equal to or greater than the supervisory signal but less than the alarm signal are integrated over a fixed time interval by a checking relay M which operates a control member V to rotate the switch S over the lines D, the movements of S being repeated by a rotary switch Q in a supervisory station I. The relay M is connected to a switch relay U which may be switched from station I from a normal first position to a second over-riding position. In the first position the relay M is connected to V so that when power fed to O from line D is equal to or greater than the supervisory signal power but less than alarm power the control member V switches ST to the next line D. The relay R reacts when O receives from a line D power equal to or greater than alarm power to retain ST on the faulty line D. As a result Q is moved by relay equipment Y to indicate the faulty line D on a subscriber's lamp tableau X. The watchman may then operate a pushbutton or insert a plug into a socket corresponding to the identified line, and thereby act on equipment Y to switch relay U to its second over-riding position in which the relay U switches the control member V so that when the power supplied to O is less than the supervisory signal or greater than alarm the switch ST is caused to move off the identified line D and start a new integration on the next line. If the socket corresponding to said next line holds a plug, the switch relay system U will remain in its second position. If no plug is in the socket, the relay U will change to its first or normal position at the moment connection is made with the next line. When normal conditions are re-established the watchman receives a buzzer signal and removes the cancelling plug, thus permitting relay U to return to its first position. In the ease of an alarm signal the amplifier P is connected to the lines D and the relay L is connected through the relay system U and the control member V in such a manner that the member V speeds up the movement of the arm S to rapidly locate the alarm line. Condition of alarm.-When an alarm signal is given, relay L accelerates arms S and Q and a buzzer sounds in station I. When the arm S reaches the alarm line the relay R of test amplifier O causes S to stop and identify the line. The watchman then inserts a plug into the line and causes arms S and Q to move on. When normal supervision signals resume the arms S and Q stop after testing the erstwhile alarm line and a green lamp is lighted in Z. The lamp in tableau X is also lighted and the buzzer sounded to indicate that normal conditions are restored and that the plug may be removed. Condition of fault.-If the supervisory signal fails, relay equipment Y lights a lamp in the apparatus Z, sounds a buzzer in station I, and lights a lamp in tableau X. The watchman then inserts a plug, thereby producing an impulse for moving on the arms S and Q. When the fault has been cleared and the supervisory signal returned, the arms S and Q will stop because relay U is in its second position, lamps are lighted in X and Z, and the buzzer sounded. The plug is then removed and normal conditions restored.