Patent GB-901504-A (GB)
Title: Improvements in or relating to alarm systems
IPC: G08B25/01
Filed: 1960-03-17
Abstract: 901,504. Electric burglar alarm systems. WESTINGHOUSE ELECTRIC CORPORATION. March 17, 1960 [March 18, 1959], No. 9384/60. Class 118. In an alarm system in which the existence of an alarm condition at a substation causes a signal to be sent over a transmission link to a central station to produce an alarm thereat, the central station operator may operate a lighting circuit at the substation over the same transmission link. Producing alarm at central station.-In the burglar alarm system described separate arrangements are made for day and night operation. During the day the switch 34 is in the position shown and the relay 24 is energized by momentary operation of the re-set switch 28 whereafter it holds over its own front contact 30 in series with resistor 32. Closure of one of the manual switches 19 located at teller or cashier windows releases relay 24 by shortcircuit to initiate the alarm signal. For nighttime operation the switch 34 is opened and relay 24 holds in series with a window tape 20 and door and window switches 21 and 22. Test switch 36 and lamp 38 serve to check that the doors and windows are properly secured. On the release of relay 24 its contact 46 applies battery to the amplifier 42 associated with microphone 40, so that audio signals may be transmitted over the line 18 to the central station 17, and to the junction point of the two windings of differential relay 50, one winding of which is grounded via resistor 52 and the other of which is connected over the simplex of the line 18 to a similar relay 54 at the central station 17. Equal currents flow in the two windings of relay 50 which remains unoperated, but the current flows additively in the windings of relay 54 which pulls up and lights the lamp 60 individual to the substation concerned. Relay 54 also operates relay 80 to bring up 86 which locks up over its second winding and completes a positive feed-back loop for the amplifier 66, causing that amplifier to oscillate and generate an audible alarm from loud-speaker 68. Relay 86 may be released by actuation of the audio squelch button 98, thus restoring the connections of amplifier 66 to normal. Switching on lights at substation from central station.-When the alarm is given the operator sets the manually operated selector 62 to the substation indicated by the lighted lamp 60. The bank 62A connects the line transformer 52 concerned to the volume control potentiometer 64 of the amplifier 66 so that sounds picked up by the microphone 40 at the substation are reproduced by the loud-speaker 68, while bank 62B connects the junction of the windings of the relay 54 concerned to the normally open switch 70. Closure of switch 70 by the operator connects battery 72 in series opposition with the battery 26 at the substation so that no current flows in the right-hand winding of relay 50. The resulting operation of relay 50 closes contact 73 so that with relay 24 released the lights 76 are switched on. At the same time contact 77 shunts resistor 51 to lock in relay 50 until the reset switch 28 is operated. Fault testing.-The cutting or grounding of either of the leads of the line 18 (or the shortcircuiting of the two leads) does not produce an alarm at the central station, but periodic tests are carried out to check if the line is opencircuited or grounded. A timing motor 102 operates a cam 104 which periodically closes the switch 106 to connect the battery 82 to the winding junctions of the relays such as 54 of all the substation lines via rectifiers 108. For any substation functioning normally, equal and opposite currents flow in the two windings of the relay such as 54, which is not operated, but if the line 18 is open-circuited or grounded the relay 54 will operate, light the lamp 60, and sound the alarm. To differentiate between a fault indication and a genuine alarm, and to stop automatic testing during the latter, a relay 110 is operated by relay 80 and opens contact 114 to disconnect the testing battery 82 during an alarm condition. During testing, the disconnection of battery 82 causes the relay 54 to fall back, followed by 80 and 110, whereupon the test battery 82 is re-connected and the sequence is repeated. Consequently the test indication is given by a flashing of lamp 60 and an intermittent audible signal from the loudspeaker 68 as distinct from the continuous signal given by the alarm condition. Operation at substation during fault conditions.-If relay 24 is released while the line 18 is open-circuit or grounded, relay 50 will operate and light the lamps 76.