GB913666A - Improvements in or relating to fire-detection circuits - Google Patents

Abstract

913,666. Fire-alarm systems. PYRENE CO. Ltd. May 29, 1961 [May 27, 1960; June 21, 1960], Nos. 18826/60 and 21743/60. Class 118. A fire-alarm system comprises one or more normally-open alarm contacts X1, X2, X3, Fig. 3, connected across a current source, and a current-controlling element, e.g. a rectifier MR5 connected across the alarm contacts, monitoring relay M being operated by the positive half-cycles of current from an A.C. source, and alarm relay F being operated by negative half-cycles when an alarm contact X1, X2 or X3 is closed. In another embodiment, Fig. 6 (not shown), both A.C. and D.C. is applied across the alarm contacts, rectifier MR5 is replaced by a capacitor to block the D.C., rectifiers 20, 21 are respectively replaced by a capacitor and a choke, the alarm relay F being operated by the D.C. when an alarm contact is closed. Individual indicator lamps 16, 17, 18 may be provided and are operated by the positive half-cycles of A.C. when the associated alarm contact is closed. A monitoring lamp may also be placed in parallel with each alarm indicator lamp 16, 17, 18, oppositely poled rectifiers being included in the circuit so that the monitoring lamps are normally lit by the negative half-cycles and an alarm lamp is lit by positive half-cycles when the associated alarm contact is closed. In Fig. 5, normally closed alarm contacts X3, X4 are provided in addition to X1, X2, relay M is again normally operated by positive halfcycles, but if X1 closes and X3 opens, the resistance of lamp 16 is sufficient to prevent relay M from operating. Contacts of relays M, F may be used to illuminate alarm- and faultindioating lamps, Fig. 1 (not shown). Specifications 903,342 and 909,517 are referred to.