Patent GB-882969-A (GB)
Title: Alarm system
Inventor: MUEHTER MANFRED WOLFGANG
IPC: G08B25/00
Filed: 1960-05-23
Abstract: 882,969. Electric burglar alarm systems. AMERICAN DISTRICT TELEGRAPH CO. May 23, 1960, No. 18156/60. Class 118.  In a burglar alarm system two subscribers are connected to the central station by the same single wire with earth return and signalling is by time-division multiplex. The sub-station apparatus of subscribers Nos. 1 and 2 are connected to the line 10 by oppositely poled rectifiers RC3 and RC4, respectively, correspondingly poled rectifiers RC1 and RC2 being provided at the central station between the line 10 and the indicators T1, G1, B1 and T2, G2, BZ, respectively. An alternating voltage is fed to the two sets of indicators in parallel by the generator 12, the positive half-cycles being utilized by subscriber No. 1 and the negative ones by subscriber No. 2. Additional subscribers may be served using one line for every two subscribers. Normal operation-night.-Considering subscriber No. 1 current flows from generator 12 via tapper coil T1, ground drop coil G1 (unoperated), break drop coil B1 (operated), rectifier RC1, line 10, rectifier RC3, resistor DR, day protection circuit 13, front BR1, night protection circuit 14, contact N of day-night switch 15, front BR2, the relay BR, resistor NR, bell contacts BE1, relay TR, day circuit 16 and back TR1 to ground. TR is not energized in this circuit and BR is slow-to-release so as to stay up between alternate half-cycles of the output of generator 12. If a break condition occurs BR is released, B1 falls back and an alarm is given. The occurrence of a ground or short-circuit brings up G1. Subscriber re-enters premises.-Change-over of contacts 14<SP>1</SP> gives a double-drop signal, whereafter the subscriber operates switch 15 to the day position in which contacts N are opened, D1 closed, and D2 changed-over. Relay BR is released and the day circuit extends from line 10 via RC3, DR, 13, back BR1, D1, r6, 16 and back TR 1 to ground; the resistance of DR being such that G1 is held energized, indicative of the day condition. Restoring protection-testing.-The subscriber closes all doors and windows and sets all traps and then actuates switch 15 to its intermediate testing position in which D1 and N are closed and D2 remain changed-over. If the night circuit is normal a circuit is completed via DR, 13, back BR], N, 14<SP>1</SP>, 14, back BR2, D2, relay TR, 16 and back TR1 to ground with D1 and r6 in parallel with port thereof. TR operates and the bell BE is energized but does not operate as a trembler bell since its interrupting contacts BE1  are short-circuited. However, TR follows the low-frequency positive pulses over line 10, thus indicating that the night circuit is in order. If bell BE does not sound, the subscriber checks the circuits, extension bells 17 being provided at points remote from BE for this purpose. With the night circuit in order, he operates switch 15 to the night position thus opening D1, momentarily opening and then closing N, and restoring D2 to normal. The break signal received at the central station by the opening of N advises the operator that he is closing up. The operator operates the test switch TT1 of the subscriber, which has contacts TT1 1  and TT1 2  and is ganged with L1, having contacts L1 1 and L1 2 . In the intermediate position of the switch TT1, contacts L1 1  and L1 2  are changed-over and in the operated position TT1 1  and TT1 2  changeover also. Upon operation of TT1 condenser K4, charged from the battery 19, discharges through relay R which conies up for the discharge period of K4. Contacts R2 transfer the drop indicators from line 10 to grounded resistor r2 which supplies normal night current, but B1 drops out (shunted by L1 1 ), while contacts R1 connect + 125 V. via the primary of test transformer 21 to line 10 to bring up TR and sound the hell BE in the usual manner, the current interruptions effected by contacts BE1 being reflected in the secondary winding of 21 thus operating neon lamp 22 to signal to the operator that the protection circuits are in order. The subscriber, having heard the bell ringing, may leave the premises, the operator then restoring the drop indicators after receiving the double drop signal initiated by the opening of the door contacts 14<SP>1</SP>.