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The earliest form of addressable systems stretched conventional detection methods using the emerging technology of the time to allow a greater degree of control over the system components and to provide improved system information for the operator. Whilst the communications basis is similar to the later Analogue Addressable and Intelligent Addressable systems, the simple lower level of Addressable Fire Alarm is worth consideration independently as a large number of existing systems fall into this category.
· Uniquely addressed detection devices
· Individual communications capability to each detection device
· Display of Individual device location
· Detection device compatibility is important
· Separate conventional sounder circuits using commonly available sounders
Addressable fire alarms systems utilise uniquely addressed detection devices which the control panel is able to identify and communicate with individually. This allows a greater degree of control over the system and accuracy in pin-pointing which device may have triggered an alarm. Potential fire events and their investigation may be carried out very quickly. Whilst some early systems simply used a device number for display purposes, many offer text description programming further simplifying device location.
The device address ID may be configured by an engineer during system set-up to suit the site. Addressing technology includes Binary coded DIL switches, Decimal rotary switches, Pre-programmed cards, Hand-Programmed devices, Control Panel operated Soft-Addressing, etc. This is dependent on the manufacturer of the addressable system and may require manufacturer supplied hardware or software.
The total number of device addresses allowable per circuit is dependent on the manufacturers addressable communications protocol, commonly 99, 125, 126, 127 or 200. Whilst a higher number of addresses may sound useful, it is usually more satisfactory to install additional loop circuits and spread the devices rather than risk 100% loading. Industry practice generally limits loop loading to approx 75% of capacity to allow for future expansion.
Addressing types which are dependent on an engineer to select the device or location are generally known as Hard-Addressed or Manually-Addressed. Addressable systems which depend on the Control Panel allocating addresses according to serial number, location or individual menu prompt are generally known as Soft-Addressed or Auto-Addressed. The pros and cons of each type vary dramatically and consideration should be given to both initial set-up procedures and ongoing alteration requirements.
These systems will generally use a loop or ring based circuit, although not exclusively as some have radial (spur) type capability. Loop based topology has the advantage of allowing two independent points of communication with each circuit in order to give greater integrity in the event of circuit failure. This means that the Control panel may attempt to power and monitor devices from both ends of the circuit if communication is lost due to an open-circuit type of cable failure.
Furthermore, to ensure that ‘no more than one area of protection may be lost in the event of a circuit failure’, current-limiting Short Circuit Isolators may be installed at strategic locations. Without this, a short circuit cable fault would cause the entire addressable fire alarm circuit to fail.
In order to protect the loop communications from interference and the corrupting effect of induced EMC, the use of a screened fire cable becomes important. Commonly mistaken as a safety ‘earth’ connection, this data protecting screen is to be connected to ground at the control panel only: not at any other point in the field. Many early systems were robust enough to handle incorrect multiple-earth connections of the screen and were installed using unsheathed (bare copper) mineral insulated cable. However, beware if attempting to upgrade the system with new devices as this cable type is rarely suitable for more modern addressable system communication protocols.
All devices on the addressable loop circuit must be suitably compatible with the loop protocol to allow correct communication. Hence addressable smoke detectors, heat detectors and manual call points must be utilized and more traditional resistance monitored conventional devices are not directly compatible without some form of interface module.
Apart from the obvious advances in addressing and communications technology, this generation of system made use of quite basic fire detection principles similar to the operation found within an individual conventional smoke detector. Detection is generally based on smoke or heat levels passing simple set-thresholds within the detector processor, and does not go as far as the algorithm based Control Panel analysis found in later Analogue-Addressable technology.
The majority of these basic addressable systems provide traditionally monitored Conventional type sounder circuits which would be installed independently of the detection loop. At this stage in the history of fire systems development it is unusual to find addressable loop powered sounders.
These systems are ideal where system programming and set-up flexibility is essential and where complicated detection conditions are not present. Beyond very small systems, savings in cable installation will often justify the increased purchase cost of the equipment.
The experience of the Installation Contractor’ and the ‘Commissioning Engineer’ must also be taken into account. A high level of experience is beneficial when setting up and commissioning an ‘Addressable System’ and the system manufacture may limit access to programming software and technical support depending on training and/or business affiliation. However, with suitable guidance and support many electrical installers are capable of installing these systems ready for a more experienced commissioning engineer to take over towards the end of the installation.
In assessing the suitability of any type of system for your application, often the practical knowledge of an experienced engineer will give more useful insight into their daily practicalities than will the manufacturers ‘Marketing’ information.
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