GB1485117A - Automatic alarm systems - Google Patents

Abstract

1485117 Intruder; fire alarms EMI Ltd 16 Aug 1974 [21 Aug 1973] 39419/73 Headings G4N and G4H An alarm system comprises a plurality of alarm condition detectors 4 each associated with an emitter 5 for producing without interrogation a characteristic alarm signal, an inductive loop 3 for picking up the alarm signals and a monitoring arrangement 2 coupled to the loop 3 and responding to the alarm signals for generating a warning at 8 and to provide an indication of the identity of the emitting element and hence its location. The detectors 4 may be constituted by an intruder sensor, a temperature sensor, a sensor for measuring the rate of increase of temperature, a smoke detector or a sensor for detecting the products of combustion such as carbon dioxide. At each monitored location, the emitter or transmitter 5 and a receiver 6 may be coupled via a separate or common aerial to the loop 3. The signal transmitted by each transmitter 5 include a characteristic code which is decoded by the receiver 7. The monitoring arrangement 2 also includes an interrogate transmitter 9 for applying appropriate test signals to each location and determining if a return signal is received at 7. Alternatively, the transmitters 5 are arranged to periodically transmit signals, the non-appearance of which at the receiver 7 being an indication of a fault.