Raise The Alarm


Paul Dawson of ESP looks at how analogue addressable fire alarm systems are providing a solution for larger premises with more complex system requirements.

Fire alarm systems fall into two main groupings – conventional systems and analogue addressable systems. Analogue addressable fire alarm systems bring a greater degree of flexibility, intelligence, speed of identification and the extent of control. This makes them the preferred option for specificiers and contractors working on bigger and more intricate projects as they overcome the limitations of conventional fire alarm systems.

Conventional Systems
Conventional systems revolve around the division of the building into a number of different areas or zones. Standard conventional systems utilise simple two state detectors, which provide a switch type signal to the conventional control panel. To enable the source of the alarm to be identified, each zone needs to be wired using a separate circuit. In the event of a fire alarm being activated, the panel is only able to identify the zone in which the triggered device is contained. It is then necessary to manually search the affected zone to discover the actual cause of the alarm. In large buildings this could mean that over 50 zones would be needed to correctly protect the property to the prevailing industry standards – proving a costly and time consuming exercise.

There is also a requirement for separate circuits of alarm annunciation devices such as sounders and beacons to signal the existence of a fire alarm condition to the building users. For sounder circuit continuity monitoring to function effectively sounder circuits have to be wired in a single radial circuit, spurs and tees are not permitted. Most conventional control panels will have facilities for more than one sounder circuit and generally the higher the specification of the panel or the higher the number of detection zones provided, the greater number of sounder circuits will be required.

More often than not, there will be fewer sounder circuits than detection zone circuits, so it will be necessary for a sounder circuit to provide cover for more than one zone. This increases the complexity of installation by forcing the sounder wiring to follow different routes to that of the detector wiring.

Intelligent Systems
Intelligent addressable systems overcome these limitations. The system detectors are wired in a loop around the building using a loop circuit which can have multiple zones on each and means that large numbers of devices can be incorporated into each loop. This offers a great cost advantage to the installer as it reduces the amount of cable needed to wire the same quantity of devices and therefore saves on installation time.

Each fire detecting sensor or call point is electronically coded with a unique 'address'. The control panel is then able to conduct two way communication with any of the addressable devices connected to the system by using the unique address number to define with which device it wishes to communicate. Under normal conditions the control panel continuously interrogates each device in a programmed sequence using a low power digitally pulsed signal, and analyses the reply to determine the status of the sensor or call point.

The panel can determine whether each device is functioning correctly and also ascertain the amount of heat or smoke that the device is currently sensing. This technology allows the panel to make 'intelligent' decisions as to the appropriate action to take based on the information it receives from the individual sensors.

This has many advantages, for example, very slow build-up of apparent smoke density seen by a sensor can cause a warning or pre-alarm condition to be triggered by the alarm panel prior to the situation becoming serious enough to warrant a full alarm. This reduction in false alarms is enhanced due to the advanced control panels which constantly monitor the air flowing through the smoke detectors.

Detectors instead of being simple two state devices, now function as sensors continually communicating with the control panel and providing information regarding the temperature or concentration of smoke in their local environment.

This level of sophistication eliminates the need for each zone of the building to be wired as a separate circuit. For this reason intelligent addressable system components are typically connected to the control panel using a small number of large loops, which greatly simplifies the installation of the system and significantly reducing the installation costs.

For further information, contact ESP on 01527 515150, email info@espuk.com or visit www.espuk.com