Patent GB-681165-A (GB)
Title: Improvements in or relating to automatic burglar alarms
Inventor: HOLLAND NORMAN
IPC: G08B13/22
Filed: 1949-06-29
Abstract: 681,165. Burglar alarms. MADEWEL PRODUCTS, Ltd. Aug. 16, 1950 [June 29, 1949], No. 17143/49. Class 118 (i). In an automatic burglar alarm system for buildings, of the type giving audible warning that a  door or window has been opened or a protected section of floor trodden upon, the circuit elements which when energized set the warning device in operation, together with a secondary warning device and means for disabling the alarm system are protected by a casing associated with a combination switch, one or both of the warning devices being automatically operated upon opening of the said casing unless the combination has previously been set to a specific position. The arrangement is energized from A.C. mains over a transformer 1, Fig. 1, and rectifier 2, a "change-over" relay 5 with its coil in series with the rectifier output providing alternative energization from a local battery 9 should the mains supply fail. A master "on-off" switch 10, 11 allows of the apparatus being put out of action. The alarm is operated by an "actuating" relay 12 connected in a selfholding circuitcomprising, in series, relay contacts 14, 16, a switch 50 detecting the door of the casing housing the apparatus, a selector switch 29 and the alarm circuits, which are connected between terminals 20 and 30-32. If the relay 12 "falls off" closure of contacts 14, 15 completes the circuit of an external alarm bell connected to terminals 18, 19, via a "master control" switch 26; a parallelconnected bell 17 is housed within the apparatus, a fuse 21 preventing it being silenced if the external bell is short-circuited. A further pair of contacts 23, 24 are closed by the relay "falling off," whereby' a warning lamp 25 is illuminated. The coil of the relay 12 is shunted by a condenser 22 in order to prevent "falling off" during the momentary interval required for the relay 5 to change over between mains and local battery supply. To energize the relay 12 the "master control" switch 26 must be placed in the "test". position shown and the combination switch set, closing contacts 37b, c and opening contact 37a; in this way the alarm bell circuit is broken and relay contacts 14, 16 short-circuited. If the alarm circuit is complete the relay 13 is energized and a lamp 28 illuminated; the switch 26 may then be rotated to the alternative "alarm set" position. Failure to energize the relay causes illumination of a warning lamp 27 over relay contacts 14, 15. The selector switch 29 permits of protection being applied to part or all of the premises concerned, while a further combination switch (not shown) in parallel with the switch protecting the exit door of the building permits of entry by an authorized person. The protective casing housing the apparatus, Fig. 2, is divided into a lower compartment provided with a removable cover 39 and housing the batteries 9. internal alarm bell 17, combination switch 37-provided with external setting knob 49-fuse 21, master "on-off" switch 48 and a terminal board 36. Enclosed upper compartments house the indicator lamps, for which windows 42, 43 are provided, the door detecting switch, the dolly of which projects at 54, and the "master control" and selector switches, which are provided with setting knobs 46, 47.