Security and safety control systems - Intelligent Buildings and Building Automation - page 237

B

bell

more loops

Control
panel

signal lamp

Figure 11.9 A conventional fire alarm panel based on an IDC (Class B).

time, when the fire panel detects that the current in a line has increased, it
relays this information using a bell or a signal lamp to indicate that a fire
has occurred in the corresponding area. There is also a definition of Class
A configuration providing higher reliability but with two more cable lines
which can be relatively more costly.

11.4.4 Addressable fi re panels

Addressable fire panels, or network-based fire panels, use wired or wireless
LANs to connect the sensing devices and actuation devices to the panels. Each
of the automatic and manual fire detectors as well as the actuation devices, as
processor-based smart devices, has a unique address in the network, allowing
the fire control panel to identify which detector has triggered a fire alarm
and which detector has a failure. Typically, two-wire network connection is
used. Four-wire and three-wire networks may be used for the detector loops,
but they are not common. Addressable fire panels are usually used nowadays
for large building systems.
Bus topology and ring topology are usually used for the sensor loops.
Figure 11.10 shows a fire alarm panel using bus topology to connect the
detectors and actuation devices. Figure 11.11 shows a fire alarm panel using
ring topology. The fire alarm panel and its smart detectors and actuation
devices communicate in a master-slave mode. The fire panel, as the master,
supervises the communication and responds to significant state changes
with appropriate actions. As an example, the German standard, DIN EN
54, requests no more than 32 detectors in a detector loop to guarantee that
no more than 32 fire detectors are affected by a single short circuit or cable
break. One single fire alarm panel may involve up to 20 or more detector
loops, but typically less than ten loops. The scanning frequency of the fire
panel on the individual detectors associated is an important factor to ensure
the timely response and reliability of the fire alarm system. The above stand-
ard requests a minimum scanning frequency of once in 10 seconds. The