GB1401146A - Fire alarm system with remote central station - Google Patents

Abstract

1401146 Fire alarm systems CERBERUS AG 17 July 1973 [17 July 1972] 34094/73 Headings G4H and G4N A fire alarm system comprises one or more parallel connected detector units having a voltage saturation characteristic in the alarm condition, and a central station with a current limiter and a voltage sensor. Detector unit.-Any sensor such as optical, temperature, or smoke type may be used. As shown Fig. 3, a conventional ionization smoke detector actuates a bi-stable switch 18, 19, to (i) energize a local indicator lamp 26, and (ii) effectively connect Zener diode 28 across the lines (using Zener controlled transistor 27) thereby providing a voltage-saturation-characteristic for the detector, and maintaining a constant voltage across the lamp independent of line current. Alternatively a transistor regulator 43 may be used Fig. 4 (not shown). Central station.-The supply voltage U V passes through current limiting transistors 46, 47 to the line 62 connecting to the detector units. The line voltage U M is monitored by transistor 53 having a reference Zener diode 57 and arranged so that it is conducting at the saturation voltage of the detector. Thus a line short-circuit causes transistor 53 to block removing the signal to AND-gate 59 and fault indicator 61. A "fire-signal" from a detector unit draws increased line current causing transistor 47 (in the limiter circuit) to conduct and apply the second signal to AND-gate 59 thereby operating the alarm 60. Additional features (i) the alarm operation may apply pulses 76 to transistor 48 to modulate the line current and causes the local detector lamp to flash, (ii) an end-of-line oscillator Fig. 6 (not shown) of the kind described in Specification 1,319,615 may be used, and signals therefrom are amplified by the current limiters 46, 47 and applied through capacitor 78 to operate pulse detector 77, which controls fault indicator 61 to show a line open-circuit, (iii) stations may be located by the voltage U M if the lines are of different lengths.