Patent GB-613965-A (GB)
Title: Improvements relating to burglar alarms
IPC: G08B13/22
Filed: 1946-05-27
Abstract: 613,965. Burglar alarms. D'OMBRAIN, G. L. May 27, 1946, No. 16058. [Class 118 (i)] In an electrical alarm system comprising a relay arranged to be energized under alarm conditions by a circuit which passes through a front contact of the relay and to operate the alarm when de-energized on the interruption of its normally closed circuit at a pair of actuating contacts, the relay is not re-energized by the closing of the actuating contacts and the resetting of the relay is effected by connecting the source of current supply independently of the front contact of the relay to a point in the relay winding such that the current then flowing through a part only of the winding provides sufficient ampere turns to pull up the relay armature. In the normal alarm position, shown in Fig. 1, with the arms d1, d2 of a control switch D in the vertical position, the circuit for the relay R extends over high and low resistance windings r1, r2, front contact e1 engaged by the relay armature, contact s1 engaged by arm d1 and actuating contacts Cl, C, C2. The opening of any actuating contact de-energizes relay R which at back contact e2 closes the circuit of the bell A which rings continuously. For the testing position the switch arm d1, d2 is moved through 60 degrees to engage contacts s2, s3 so that a circuit exists for the lowresistance winding r2 which passes sufficient current to energize the relay R. A circuit is also completed over contacts C1, U, U2 to a test lamp G and contact s4 so that the lamp is illuminated if all the contacts C1, C ... are closed. When the switch D is moved through a further 60 degrees to the " safe " position with arms d1, d2 engaging contacts s5, s6 an energizing circuit is completed through windings r1, r2 and the back contact e1, but in addition the windings are energized over a circuit independent of the contacts C1, C, C2, e1 so that windows, doors, &c. can be opened without setting the alarm into operation. The switch D may be operated by a barrel lock 4 connected to gears 2, 3 having a 3: 1 ratio so that the 60 degrees movement of the arm of the switch D is obtained by rotation of the barrel through 180 degrees. Alternatively, a lever lock may be employed with a rack and pinion to provide the desired rotation-or by an arm fixed to the spindle 1 and having a pin engaging a slot in the bolt of the lock and extending at right angles to the direction of movement of the bolt. The contact C2 in the switch unit S is closed by a button 6, Fig. 7, when the front 5 of the casing is screwed down, and the contact C1 is closed by a stud engaged by the cover of the wall casing W. Each contact assembly C is mounted within a fixed casing H and the contact members are closed by a stud 9 engaged by the movable window or door member in its closed position. The circuit arrangement facilitates the interconnection of two complete installations by means of a two-core cable, the interconnection being rendered inoperative by providing a short-circuiting switch at each installation. Some further protection may be provided by means of two or more cores each connected to the negative side of the battery B and having its other end unconnected so that if by transfering, one of the additional cores were connected to one of the main conductors, the cutout F would fuse and the bell A of both installations would be sounded.