Patent GB-348571-A (GB)
Title: Improvements in electric burglar alarms
IPC: G08B13/22
Filed: 1930-02-11
Abstract: 348,571. Burglar alarms. TIBBLES, H. J., Brodsworth, Blenheim Crescent, Leighon-Sea, and RELY-A-BELL BURGLAR & FIRE ALARM CO., Ltd., 49A, Wilson Street, Finsbury Square, London. Feb. 11, 1930, No. 4584. [Class 118 (i).] In a closed-circuit electric burglar-alarm system of the kind adapted to be operated by the movement of a bolt, an audible signalling device A is operated for a predetermined time when the normallv closed circuit is broken inadvertently. A visible signal 37 and a second audible signal B are also provided, which remain operative until the alarm system is reset. Setting of the alarm circuits is accomplished by first depressing a pushbutton switch 20 to close the circuit of a relay coil 21 which thereby attracts a torque 23. The bolt 4 of an interiorly operated lock 5 is then moved to break this circuit and close the normally closed circuit, thereby energizing a relay coil 7 which alone retains the tongue 23 in the attracted position. The switch 20 is then released. Upon closing the outer door 16, studs 57, 58 on the door engage studs 59, 60, whereby a shunt circuit comprising easily broken wires 61 on the door is included in the normally closed circuit in parallel with the part comprising the lead 9, leaf springs 10, 11, the bolt 12 of an exteriorly operated lock, and lead 14. Moreover, studs 52, 53 are brought into contact, thus closing the circuit of the audible signalling device C, which operates until the bolt 12 is moved to its locked position. In this position the bolt 12 engages a leaf spring 62 in a switch control circuit comprising lead 17, bolt 12, spring 62, leads 63, 64, relay tongue 23, contact pillar 65, lead 66, and coil 67, from which the circuit is completed to a source of supply either by lead 36, lamps 37 and lead 38, or by leads 35, 39, windings 40, armature 41 and leads 42, 25. The alarms are thus finally set by moving the bolt of the exterior look 13 to its locked position, and if the normally closed circuit is subsequently broken by the unauthorized opening of the door, or by severance of the wires 61, the coil 7 is de-energized, releasing relay tongue 23, which then contacts with pillar 65 and energizes the coil 67. The latter attracts a bell-crank lever 68, 69, which presses together contact strips 33, 34 to close the circuits of the visible signal 37 and the audible signal B. The armature 68 is locked in its attracted position by a catch 70. The bridge member 31 of the tongue 23 connects leaf springs 28, 29 so as to energize a solenoid 26 which attracts upwards a core 71, thereby moving a switch 24 to open the solenoid circuit. At the same time an arm 74 on a lever 73 connected to the core 71 releases a pivoted lever 75, which then engages contacts 47, 48, closing the circuit of the audible signal A. De-energization of the solenoid permits the core 71 to return to its normal position by the action of a gravity and/or a spring 76, the rate of return being controlled by a timing mechanism 72 comprising a train of gearing controlled by an escapement 72<1> which, after a predetermined time, breaks the circuit of the audible signal A. The signal A may be arranged outside, and the signals B, C inside the building. The lamps 37 may be directly observed from outside the premises, or they may project light upon a mirror.