GB1265893A - - Google Patents

Abstract

1,265,893. Smoke detectors; fire alarms. VIGIFEU. May 5, 1969 [May 7, 1968], No. 22725/69. Heading G1N. [Also in Division G4] General In a smoke detector with series connected reference and analyzing chambers, increase in output signal due to smoke operates a fire alarm, but decrease in signal due e.g. to moisture operates a fault indicator relay. A plurality of detectors may be connected to a central station with their alarm circuits in parallel and fault indicator relay contacts in series. Smoke Detector Fig. 1 The sensor output signal U is amplified by transistors T1, T2 and an increase, due to smoke, above a threshold level determined by R3 and Zener diode Z1 fires thyristor Th1 to operate audible or visible signalling appartus 8 and local lamp L1. (T 1 is an F.E.T. for impedance matching). Reduction of signal U, due to e.g. moisture, releases relay 5 to indicate fault at 8 and light L1. (diode D1 isolates alarm line 9). In a modification Fig. 2 (not shown) the thyristor is replaced by a second set of contacts on relay 5 operative at a predetermined value (greater than the normal current which operates contacts 6). Central Station arrangements Fig. 3 Parallel connected alarm circuits energized from sources 12, 13 are connected to relay S 2 and loaded by an end-of-line resistor 27 so that its contacts float (both open). Alarm signal closes "fire circuit" contact 16 and a decrease or open circuit closes fault signal contact 17. The detector fault relays are series connected to relay S3 having a contact 15 in parallel with contact 17 in the fault signal circuit.