Évaluations - 3, GPA: 3.7
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Your Local Authority Having Jurisdiction (AHJ) should always be consulted before beginning the installation of any fire alarm system. 2.0 Glossary of Terms Beam Smoke Detector (Projected Beam Smoke Detector) A device which senses smoke or smoke and heat by projecting a light beam from a transmitter across the protected area to a receiver that monitors the light signal. Smoke and/or heat entering the beam path will decrease the light signal causing an alarm. Detector Coverage The area in which a smoke detector or heat detector is considered to effectively sense smoke and/or heat. This area is limited by applicable listings and codes. Listed The inclusion of a device in a list published by a recognized testing organization, indicating that the device has been successfully tested to meet the accepted standards. Obscuration The reduction of the ability of light to travel from one point to another due to the presence of solids, liquids, gases, or aerosols. Receiver The device, in a projected beam smoke detector system, which monitors the signal level of the light which is sent by the transmitter. Sensitivity The ability of a smoke detector to respond to a given level of smoke. Smoke The solid and gaseous airborne products of combustion. Spot-Type Detector A device which senses smoke and/or heat at its location only. Spot-type detectors have a defined area of coverage. Stratification The effect which occurs when smoke, which is hotter than the surrounding air, rises until equal to the temperature of the surrounding air, causing the smoke to stop rising. Transmitter The device in a projected beam smoke detector which projects the light across the protected area to its associated receiver. Trouble Condition The status of a device or system which impairs its proper operation, i.e., open circuit on an initiation loop. The notification of a trouble condition indicated on a control panel or annunciator is a “TROUBLE” SIGNAL. NFPA 72®, National Fire Alarm Code® are registered trademarks of the National Fire Protection Association. D296/D297 Series Application Guide 3 3.0 Introduction Why should I use Beam Smoke Detectors and where should I use them? • Where there are high ceilings such as in atriums and aircraft hangers. Because the detectors mount on the walls easier access is achieved. • Where there is a dusty environment such as in warehouses, factories and barns. The detectors have built-in compensation to prevent alarms due to dust. • Where there are expansive ceilings. One set of beam smoke detectors can replace up to 24 spot type smoke detectors. This saves on service and installation costs especially is such areas as large offices or department stores. • On ornamental ceilings where spot detectors would be a distraction. • Where there is limited access to the ceiling such as in factories and warehouses. The D296 Series are Long Range Projected Beam smoke detectors which consist of separate transmitters and receivers. The projected beam smoke detectors consist of a transmitter that projects an infrared beam across the protected area to a receiver containing a photosensitive cell, which monitors the signal strength of the light beam. The detector works on the principle of light obscuration. The photosensitive element of the beam smoke detector sees light produced by the receiver in a normal condition. The receiver is calibrated to a preset sensitivity level based on a percentage of total obscuration. This sensitivity level is determined by the length of the beam (the distance between the transmitter and receiver) and the desired response time. Eight sensitivity settings are available for selection by the installer based on the length of the beam used in a given application. The transmitter may be powered independently from the receiver, which can greatly reduce wiring runs and, therefore, installation cost. Since battery back up is required for fire alarm systems, battery back up would be required for the transmitter whether it is powered from the panel or independently. Unlike spot type photoelectronic smoke detectors, beam smoke detectors are generally less response sensitive to the color of smoke. Therefore, a beam smoke detector may be well suited to applications unsuitable for spot-type photoelectronic detectors, such as applications where the anticipated fire would produce black smoke. Beam smoke detectors do require visible smoke and therefore may not be as sensitive as ion detectors in some applications. Beam smoke detectors are sensitive to the cumulative obscuration presented by a smoke field. This cumulative obscuration is created by a combination of smoke density and the linear distance of the smoke field across the projected light beam. Cumulative obscuration, then, is a measure of the percentage of light blockage. Since the sudden and total obscuration of the light beam is not a typical smoke signature, the detector will see this as a trouble condition, not an alarm. This threshold is at a sensitivit...