GB1140294A - Fire alarm system with monitoring device for fire alarms connected in groups to a central station - Google Patents

Abstract

1,140,294. Fire alarm systems. CERBERUS A.G. 9 May, 1967 [9 May, 1966], No. 21516/67. Heading G4H. A fire alarm system comprises a central signal station to which individual fire alarm devices are connected in groups, the number of conductors being independent of the number of devices in a group, and testing means are provided by which alarm conditions are simulated in the fire alarm devices to produce a binary signal from each, the binary signals being received by an evaluation device in such a way that monitoring of the responses from individual devices is independent of the number in a group. Each fire-alarm device consists of a pair of ionization chambers 1, 2 Fig. 2 of which one, 1, detects the presence of combustion gases and the other provides a reference. The junction between them is connected to a switching device e.g. a field-effect transistor 3 connected between conductors 10, 20 which pass to the central station 18 having a voltage source Ub. When combustion gases enter chamber 1 the resistance changes and transistor 3 conducts causing a voltage drop on resistor 5 sufficient to ignite SCR 6. Current passes through Zener diode 15 and indicating lamp 12, or resistor 13 if the lamp is defective. The change in current in conductors 10, 20 operates a relay A at the central station. The voltage drop necessary to operate transistor 3 can be produced for test purposes by reducing the potential on line 10. This may be done by introducing a Zener diode 8 into the circuit by opening switch 7. The lower voltage prevents Zener diode 15 igniting so that current flows only through the resistor 14. The current is much smaller than the normal alarm current and relay A does not respond but the secondary winding of transformer 11 passes a pulse to the counter 19. The alarm devices in a group are arranged by capacitor 9 to have different response times so that the pulses arrive sequentially and are counted. The count indicates whether all the alarm devices in the group have responded. The system is reset by switch 16. In a modification (Fig. 1, not shown), a sequential response of the alarm devices is achieved by a serial connection of the several devices so that only if the first responds to the test signal can the second respond and so on. A relay shows that the last device has responded or a counter indicates as before that all devices have responded or shows the number of the defective device. In another modification each alarm device has an oscillator which oscillates until the device responds, when the oscillations are suppressed. The several devices are connected by way of an Or gate the output of which indicates whether or not all the devices have responded.