GB340383A - Improvements in automatic electric alarm systems - Google Patents

Abstract

340,383. Electric fire-alarm systems. McNEIL, A. H., St. Keverne, Handsworth Avenue, and ASSOCIATED FIRE ALARMS, Ltd., Jewin House, Redcross Street, both in London. Nov. 21, 1929, No. 35653. [Class 47 (i).] In an automatic alarm system of the kind comprising a series of temperature-sensitive or other circuit-closing devices controlling visual and audible alarms, the opposed contacts of the circuit-closing devices are arranged as links in separate circuits which normally carry a small watching current and include fault-alarm devices which come into operation should the watching current in any circuit fail. In the fire-alarm system shown, all the contacts a<2> of the circuit-closing devices a are in a common circuit c which includes the winding d of a high-resistance watching relay and derives a watching current from a battery b. The other contacts a<1> of the devices are arranged in groups in circuits g each of which includes a fire-alarm lamp i and the winding h of a high-resistance fault relay. The circuits g derive, from the battery b through a resistance e, a watching current which is insufficient to light the lamps i, but sufficient to hold the armatures h<1> of the relays h away from the fixed contacts h<2>. The contacts a<2>, a<1> are maintained at different potentials, so that the operation, by fire, of any circuit-closer a causes a rush of current in the corresponding circuit g. This lights up a lamp i, and actuates a relay f to close a circuit including a battery j and fire-alarm bell k. In case of a fault in a circuit c or g causing the watching current in that circuit to fail, a fault-alarm bell m is rung, and a fault-alarm lamp p or q is lighted, since the relays d or h will release their armatures d<1> or h<1>. The lamps p and q are lighted directly by the battery j, and the bell m is operated through a fault relay o and battery n.