Distributed fire alarm network - has maintenance checking facility for all local transducers and circuits when suitably primed from central control

摘要

In the distributed fire alarm network a number of local units (A) are connected in parallel across a cable pair (L1, L2) to a central alarm station (B). Each local station contains a transducer (1), an alarm signal generator (2) and a current limiter (3), and in addition, a timing network (4) a test signal circuit (6) and a faulty operation signal circuit (5) connected in parallel with the fire alarm signal generator (2) and current limiter (3). The central control contains two separate circuits, selected by a switch (11), one of which supplies and monitors normal operation (7, 9) while the other (8, 10) provides a different, possibly reversed voltage for test purposes and a corresponding detector circuit (8). When a test is conducted, the test signal circuit (6) at each local monitor point, accepts the test signal from the central station on the cable pair and primes the timing network and the fire transducer.