Types of Fire Alarm Systems
 

Standard Conventional Fire Alarm Systems

Is designed for smaller installations and to operate the detection zone using standard call points and detectors. They are used in conventional 4 wire mode, e.g. a pair for detectors and a pair for sounders.

Two Wire Technology Fire Alarm Systems

Is designed for smaller installations and to work with the 2 wire Detectors, Sounders and Call Points 2 wire works by using different voltage bands for quiescent and alarm states, which allows detectors, manual call-points, input or output modules and sounders or beacons to be connected to the same pair of wires, thus making installation quicker and more flexible

Analogue Addressable Fire Alarm Systems

Is designed for larger installations and multi-building networked systems, addressable fire alarm system provides the user with the status of the initiating devices that comprise the system network; that is, smoke detectors, call points, etc. The fire alarm system control unit allows the user to easily view the system status and features information about the emergency device as well as detailed information about the device's "address." The system hardware or software can also assign digital addresses for each device. The location of an operated addressable device is communicated via annunciation, printout, or other communication, and is also visibly indicated according to building, floor fire zone, or other approved subdivision.

Optical Smoke Detector - Responds to Smoke from a Smoldering Fire

Optical smoke detectors incorporate a pulsing LED located in a chamber within the housing of the detector. The chamber is designed to exclude light from any external source. At an angle to the LED is a photo-diode which normally does not register the column of light emitted by the LED.In the event of smoke from a fire entering the chamber, the light pulse from the LED will be scattered and hence registered by the photo-diode. If the photo-diode "sees" smoke on the two following pulses, the detector changes into the alarm state and the indicator LED lights up. The detector housing is identical to that of the ionisation detector but has an indicator LED which is clear in quiescent state but produces red light in alarm.

Ionisation Smoke Detector - Responds to Smoke and gas particles from a Flaming Fire

The sensing part of the detector consists of two chambers - an open, outer chamber and a semi-sealed reference chamber within. Mounted in the reference chamber is a low activity radioactive foil of Americium 241 which enables current to flow between the inner and outer chambers when the detector is powered up. As smoke enters the detector, it causes a reduction of the current flow in the outer chamber and hence an increase in voltage measured at the junction between the two chambers. The voltage increase is monitored by the electronic circuitry which triggers the detector into the alarm state at a preset threshold. An externally visible red LED lights up when the detector changes to alarm state. An integrating ionisation detector, suitable for use in areas where transient levels of smoke may be expected, is also available.

Heat Detector - Activated by Heat

The A1R, BR and CR (rate-of-rise) heat detectors operate by using a matched pair of thermistors to sense heat. One thermistor is exposed to the ambient temperature, the other is sealed. In normal conditions the two thermistors register similar temperatures, but, on the development of a fire, the temperature recorded by the exposed thermistor will increase rapidly, resulting in an imbalance, causing the detector to change into the alarm state.

Rate-of-Rise Detectors

Are designed to detect a fire as the temperature increases, but they also have a fixed upper limit at which the detector will go into alarm if the rate of temperature increase has been too slow to trigger the detector earlier. The CS (static response) heat detector has only one thermistor and changes to the alarm state at a preset temperature. Externally, the heat detectors are distinguishable from the smoke detectors by having wide openings to the surrounding atmosphere to allow good movement of air around the external thermistor.

 
London Areas covered - Bexley, Bromley, Greenwich & Lewisham ~ Kent Areas covered - Dartford, Maidstone & Sevenoaks
 
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