GB678529A - An improved alarm system, more especially a burglar alarm system - Google Patents

Abstract

678,529. Burglar alarms. RELY-A-BELL BURGLAR & FIRE ALARM CO., Ltd. March 9, 1951. [Feb. 1, 1950; June 16, 1950] Nos. 2653/50 and 15169/50. Class 118 (i). In an alarm system, more particularly a burglar alarm, in which the alarm is operated on the interruption of a closed circuit, operation of the setting switch moves the armature of the closed circuit relay into its attracted position, but further operation of the switch to complete the setting operation is prevented if the armature is not then retained in its attracted position. Fig. 1 shows the side view of a setting switch, and Fig. 2 the rear view of the switch and the circuit of a burglar alarm system. The system is set in the alarm condition by means of key K which is used 15 rotate the switch and associated arm H 360 degrees. Rotation of arm H mechanically moves the armature L of relay C into its attracted position, and allows contacts a1 and a2 to make during the rotation. The arm H of the key switch has a detent N, so that if, owing to a fault, the armature L is not held in its attracted position, the armature engages the arm H to prevent further rotation of the switch and thus warn the operator. A bolt E associated with the switch causes contacts a3, a4 and a5, a6 to remain operated after the completion of the rotation. The setting operation establishes a closed circuit including a battery V2 and the coil of relay C which carries a small but sufficient current to hold the armature L in its attracted position. The closed circuit includes a number of door or window contacts W which are opened on the entry of an intruder, so that the closed circuit is broken. The resulting release of relay C causes an alarm T to be operated from a battery V1, the circuit being established through contacts C2, C3 and a3, a4. The arrangement for setting the system in the alarm condition includes 'final door' contacts f1, f2 which are closed when the person setting the alarm leaves the building, and a 'short circuiting' relay S, which having been operated by contacts a1, a2 of the key switch to close contacts 51, 52 and 53, is released by operating push button switch R which is situated outside the final door. The alarm may consist of a message transmitted to a remote point.