FIRERAY PRODUCT GUIDE
Page 30
9 Definitions
Addressable Optical Beam Smoke Detector – Optical Beam Smoke Detector, which in addition to
providing alarm and fault indications to a control unit, are capable of communicating a unique
identification (address) in order to show the exact location of a fire.
Analogue Optical Beam Smoke Detector - Optical Beam Smoke Detector that communicates a
unique identification (address) along with analogue (data) signal that indicates the level of smoke at
its location
Automatic Fire Alarm System – A system of controls, initiating devices and alarm signals in which
some or all of the initiating circuits are activated by automatic devices such as Optical Beam Smoke
Detectors
Automatic Gain Control (AGC) – The ability of an Optical Beam Smoke Detector to compensate for
light signal degradation due to dust or dirt and/or building movement. The rate of compensation is
limited to ensure that the detector is still sensitive to slow smouldering fires.
False Alarms – An unwanted alarm generated by a cause(s) other than fire
Fire – A chemical reaction between oxygen and a combustible material where rapid oxidation results
in the release of heat, light, flame and/or smoke.
Listed / Approved – The inclusion of a device in a list published by a recognised testing
organisation, indicating that the device has been successfully tested to meet applicable standards
Obscuration (Cumulative Obscuration) – The reduction of the ability of light to travel from one
point to another due to presence of solids, liquids, gases or aerosols. Cumulative Obscuration is a
combination of the density of these light blocking particles per metre and the linear distance, which
these particles occupy, i.e. smoke density times the linear distance of the smoke field; it is usually
expressed in % / m
Optical Beam Smoke Detector – A device that monitors the amount of infrared light transmitted
between a light source and a photosensitive receiver. When smoke particles enter the infrared light
beam path, some light is scattered and some absorbed, thereby reducing the light reaching the
Receiver. If this obscuration exceeds a set value, the Optical Beam Smoke Detector responds and
communicates its status to a Fire Panel.
Optical Beam Smoke Detector Coverage – The area in which an Optical Beam Smoke Detector is
considered to effectively sense smoke. This area is limited by applicable standards and codes.
Optical Beam Smoke Detector Range – The distance between the Transmitter and the Receiver /
Reflector (prism)
Reflector (Prism) – The device that returns the infrared light back to the Transceiver unit. A
Reflector may utilise prism(s) so that reflected beam path is along the transmitted path even if the
reflector (prism) is misaligned.
Sensitivity – The ability of an Optical Beam Smoke Detector to respond to a given level / threshold
of smoke obscuration.
Smoke – The gaseous and solid airborne results of combustion.
Smoke Colour – The relative lightness or darkness of smoke, ranging from invisible to white to grey
to black.
Point Type Smoke Detector – A device that senses smoke at a particular location only. Point type
detectors have a defined range of coverage.
Stratification – An effect that occurs when air containing smoke particles is heated by smouldering
or burning material and, becoming less dense than the surrounding cooler air, rises until it reaches a
level at which there is no longer a difference in temperature between it and the surrounding air.
Stratification can be also be caused by forced ventilation...
Transmitter / Receiver / Control Unit – The Transmitter projects a modulated infrared light beam
over an area to a Receiver (directly or via Reflector). The Receiver forwards the signal to a Control
Unit for analysis (this can be separated or integrated unit depending on the detector type). The
Control Unit informs the Fire Panel on the status of the equipment.
Transceiver – A unit combining the Transmitter and the Receiver is called a Transceiver.
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