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Types of Fire Alarm Systems
All Fire Alarm Systems essentially operate on the same principle.  If a detector detects smoke or heat, or someone operates a break glass unit, then alarm sounders operate to warn others in the building that there may be a fire and to evacuate.  For the system protecting property, it is additionally likely that the Fire Alarm will incorporate remote signalling equipment which would alert the fire brigade via a central station.
Wired Fire Alarm Systems can be broken down into three categories, Conventional, Addressable and Analogue Addressable.
Conventional Fire Alarm System
In a Conventional Fire Alarm System, a number of call points or a number of call points and detectors are wired to the Fire Alarm Control Panel in Zones.  A Zone is a circuit and typically one would wire a circuit per floor or fire compartment.  The Fire Alarm Control Panel would have a number of Zone Lamps. The reason for having Zones is to give a rough idea as to where a fire has occurred.  The accuracy of knowing where a fire has started is controlled by the number of Zones a Control Panel has, and consequently, the number of circuits that have been wired within the building.  The Control Panel would then be wired to a minimum of two sounder circuits which could contain bells, electronic sounders or other audible devices.  Sounder Circuits and Detection Zones are wired in a star configuration.  Each circuit would have an end of line device which is used for monitoring purposes. 
Photain Controls currently use 20K resistors for use on the end of all sounder circuits and HRMODULES for use on the end of the Detection Circuits for all of their Conventional Control Panels except the PCS800HR Panel and PCS1200HR range which uses a 4K7 resistor.

Removal of Detectors while maintaining the Break Glass Operation

BS5939 part 1 1988 (6.6.2) - amendment 6317 January 1991, requires that :
A where Detectors are designed to be removed from the circuit, removal of any detector from the circuit should not affect the operation of any manual call point. @
On Conventional Fire Alarm Systems one of the following three methods of wiring could be used to meet the Head Removal requirements:
Type 1 All Manual Call Points could be wired to one Zone or Zones and all Smoke or Heat Detectors could be wired to a separate Zone or Zones
Type 2 All Manual Call Points and Smoke Detectors could be wired to the same Zone providing all manual Call Points are wired in front of all the automatic detectors. [2]
Type 3 An active end of line module (HRMODULE) could be wired to the end of the Zone/s in place of the normal end of line unit.  This would allow for the wiring of Call Points and Automatic Detectors in any combination on a circuit zone.  If any Detector head is removed from its base then all call points will continue to be operative
It should be noted that with Addressable and Analogue Addressable Fire Alarm Systems the method of wiring to a detector base is different to the method of wiring to a Conventional Base.  In addition the method of operation of Addressable and Analogue Addressable Systems means that the requirements of the amendment 6317 (as detailed on the previous page) are always complied with, irrespective of the sequence in which the devices are connected.

Addressable Systems
The detection principle of an Addressable System is similar to a Conventional System except that the Control Panel can determine exactly which detector or call point has initiated the alarm.
The detection circuit is wired as a loop and up to 99 devices may be connected to each loop.  The detectors are essentially Conventional Detectors, with an address built in.  The address in each detector, is set by dil switches and the Control Panel is programmed to display the information required when that particular detector is operated.  Additional Field Devices are available which may be wired to the loop for detection only ie: it is possible to detect a normally open contact closing such as sprinkler flow switch, or a normally closed contact opening.
Sounders are wired in a minimum of two sounder circuits exactly as a Conventional System.  Loop Isolation Modules are available for fitting on to the detection loop/loops such that the loop is A sectioned @ in order to ensure that a short circuit, or one fault will only cause the loss of a  minimal part of the system. [3]

Analogue Fire Alarm Systems

Analogue Fire Alarm Systems are often known as Intelligent Fire Alarm Systems.

There are several different types of Analogue Systems available which are determined by the type of protocol which they use.  The bulk of Analogue Detectors available are A fairly stupid @ as the Detectors can only give output signals representing the value of sensed phenomena.  It is left up to the Control Unit to decide whether there is a fire, fault, pre alarm or whatever.  With the Photain True Intelligent Analogue System each detector effectively incorporates it= s own computer which evaluates the environment around it, and communicates to the Control Panel whether there is a fire, fault or the detector head needs cleaning.

Essentially however, Analogue Systems are far more complex and incorporate far more facilities than Conventional or Addressable Systems.  Their primary purpose is to help prevent the occurrence of false alarms.

With the Photain Analogue Addressable System up to 127 input devices ie: Smoke Detectors, Call Points, Heat Detectors, Contact Monitors and other interface devices may be wired to each detection loop.  In addition to the 127 Input Devices, up to 32 Output Devices such as Loop Sounders, Relay Modules and Sounder Modules may also be connected.

Photain Analogue Systems are available in 2,4 and 8 loop versions which means large premises can be monitored from one single panel.  Isolator units should be connected between Asections@ of detectors as described for Addressable Systems.


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