Fire alarm system

Abstract

A novel fire alarm system with a plurality of smoke detectors which are adapted to be installed in different locations are connected through a data transmission line to a receiver where the smoke density signals transmitted from the respective smoke detectors and indicative of the density of smoke in the corresponding locations are processed for determination of fire presence. The receiver is provided with fire judging circuit which identifies the presence of fire only when the smoke density detected by any one of the smoke detectors exceeds a reference density level and when such smoke density lasts over a reference time period. Thus, the information from each smoke detector is analyzed with respect to the smoke density and the time period over which the smoke density of significant level lasts. Accordingly, a reliable detection of fire is effectuated. Also incorporated in the system is a selector by which said reference density level can be selected from a plurality of predetermined density levels of different values and by which the reference time period can be selected from a plurality of predetermined time periods of different values. Consequently, the criterion which is the combination of the smoke density and the related time period for determination of fire presence can be variably set depending upon the differing conditions of the locations under surveillance, enabling the system to be easily and successfully adapted for use in different fire monitoring conditions.