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Addressable Fire Alarm SystemsUntil now we have been concerned with conventional fire

alarm systems. These systems require specialized wiringpractices using in and out connections to devices in orderto maintain supervision of the devices. T tapping is an-other practice also not permitted in conventional systems.These will be covered in detail in a later installment.

Addressable systems are a different matter. No specializedmethods of wiring are required. These systems are controlledby microprocessors and their operation relies on communi-cation between the microprocessor in the central processing(control) unit, and connect-ed devices which have theirown microprocessors. Ad-dressable systems feature

an LCD or similar visualdisplay that may give loca-tion and specific informa-tion about the connecteddevices, depending on howit is programmed. Somesystems show detailed in-formation via an alpha-nu-meric display while othersmaller, economy type sys-tems might display only acode number assigned tothe device. These systems have been nicknamed smart orintelligent systems.

Addressable systems are obviously much more complex thanconventional systems, but they have an infinitely greaterflexibility. Oddly enough, even though they may be exceed-ingly complex, describing them is a relatively simple matter.The initiating devices and notification appliances are eitherconnected to or incorporate a transponder that has a specificaddress assigned to it. These transponders are connected to acircuit of the central processing unit which interrogates eachtransponder in sequence. When interrogated, a device mayrespond that it is normal, or if an initiating device, that it is inan alarm condition. If a device is inoperative, disconnected,damaged, etc., it will not respond. The central processor thencreates a trouble condition and a device missing message

will be displayed.Present standards require a maximum of five (5) secondsfor a CPU to report an alarm from a device. The speed ofinterrogation has increased dramatically in recent yearswith the development of better and faster microprocessors.Now there exists a signaling protocol for certain models ofsmoke sensors where the CPU interrogates a large clusterof sensors instead of individually. This cluster will instantlyreport an alarm condition when interrogated and then indi-cate the address of the specific device in alarm. This saves asignificant amount of time that would be otherwise requiredto interrogate each device individually.

The ABCs of Fire Alarm Systems Part IIIBy Anthony J. Shalna 2009Principal IMSA Representative to the Automatic Fire Alarm Association

President: Southeastern Signalmen of MassachusettsApprovals Manager: Gamewell-FCI by Honeywell

The addressable system operatesover a circuit known as a Signaling

Line Circuit (SLC). Depending on themanufacturer and design, the circuit can be wired in variousmethods in regard to fail-safe operation. These methods arepresently referred to as Styles, but I understand that the2010 Edition of NFPA 72, National Fire Alarm Code, willrevert to an older Class designation. At any rate, I recom-mend consulting the charts of the current edition of NFPA72 for further information.

The SLC does not resemble conventional initiating circuitssince it is a data gatheringcircuit, while conventionaldevices, having normallyopen alarm contacts, place

a short circuit across theirinitiating device circuit. Ashort on an SLC will causea trouble condition insteadof alarm.

Connected to this SLC areaddressable smoke or heatsensors, monitor modules,output modules and/ordata gathering panels. Dif-ferent manufacturers all

have their own various designations for these modules, butgenerically, they are usually referred to as transponders and

in common conversation as modules.

The sensors and modules all may be intermingled on theSLC regardless of their (input or control) function. (Seeillustration) As stated above, they have their own uniqueaddress that is assigned when the system is programmed.This address is assigned to the transponder at installationvia a DIP or rotary switch.Again, the variety of modules, sensors and data gatheringpanels is limited only by the manufacturers imagination andtechnical expertise. Addressable smoke or heat detectors areusually referred to as sensors to distinguish them fromconventional detectors. These sensors may either contain anintegral address switch, or in older or economical systems,

they may simply be conventional detectors installed in anaddressable base. Conventional detectors installed in an ad-dressable base would constitute an Addressable System.Smoke sensors containing microprocessors now report theirstatus to the CPU. While a conventional detector has onlytwo conditions: Alarm or Normal, the newest sensors cannotify the CPU that they smell smoke, or are approachingan alarm condition, or signal that they are dirty and requirecleaning, etc. Their sensitivity can be varied by the controlpanel and new features are being announced continually.

Systems employing these sensors are known as Analog

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The ABCs of Fire Alarm Systems Part III . . . Continued from page 28Addressable since their condition is dis-played in an analog fashion rather than adigital normal or alarm condition.

Many people erroneously use the termAnalog Addressable to describeall devices connected to an SLC, but

technically this term does not apply todevices such as manual pull stationsor electronic addressable heat detec-tors that have been employed in thesesystems until now. Even though heatsensors may be addressable and signalan alarm via the SLC, they can onlyreport the two states, alarm or normal.Now appearing on the horizon are heatsensors that can indicate their chang-ing condition in the same manner asa smoke sensor, such as reporting anincrease in ambient heat, so nothing isetched in concrete regarding the ability

and features of these sensors.

Monitor modules have their own as-signed addresses and commonly fea-ture a conventional initiating circuitcomplete with an end of line resistor.Conventional dry contact initiatingdevices are connected to this circuit.These may be electromechanical heatdetectors, manual pull stations, water-flow switches, etc. When any of thesedevices go into alarm, the monitor mod-ule provides a collective address for thedevices on its circuit. Newer modules

are now available featuring multipleinitiating circuits and provide differentaddresses for each of these circuits.

Some modules are small enough to fitinside a device housing or backbox.These modules are usually intendedfor connection to a single initiatingdevice. An example of this would be amodule installed inside a pull station,providing an address for the station.Some manufacturers preassemble themonitor modules into pull stations, etc.while others prefer to sell the module

only, and allow the installer to connectthe modules in the field.

Other monitor modules have an initiat-ing 2-wire circuit that may be extendedconsiderably, and can accommodate aspecified number of conventional 2-wire compatible conventional smokedetectors in addition to a number ofdry contact initiating devices. Thismodule provides one address for eachcircuit, and is useful in large areas, suchas auditoriums, atriums or gymnasi-

ums where only a collective address isneeded to guide fire-fighting forces tothe source of the fire.

Data gathering panels have been usedsince the earliest days of addressablesystems. These panels resemble a small

conventional fire alarm control paneland contain a number of conventionalinitiating circuits, battery standby,etc. These panels in effect provide asubsystem with its own address, butI wouldnt be surprised if some of thelatest ones provide multiple addresses,one for each initiating circuit.

Output or control modules may alsobe installed anywhere on the SLC.These modules likewise have theirown unique address and may be pro-grammed to perform a function in the

event of an alarm or trouble on anyindividual or combination of monitormodules or sensors. These controlmodules may contain dry contacts thattransfer on command, but again, newconfigurations are arriving on the mar-ket on a daily basis. Some will acceptan audio input and provide supervisedloudspeaker appliance circuits, whileothers will supervise and operate notifi-cation appliance circuits. Still others canbe used to energize releasing solenoidsor provide smoke damper operation insmoke control systems.

System programming also varies withthe manufacturer. In the earlier dayssome small system manufacturersused burn-in chips, or PROMS forthe programming. Larger systems areprogrammed via software. In these sys-tems, the programming is often done inthe office on a computer and then down-loaded to the control panel in the fieldvia lap-top computer. Some softwareprograms are user friendly while othersare not, and usually require specializedtraining. The easiest ones to use contain

drop-down menus and the programmerneed only to literally fill in the blanksin order to complete the program.

When the system is programmed, adescription of the device can also beincluded (in systems with alphanu-meric display) such as ionizationsensor, main lobby, right wing. Thus,when the device goes into alarm, thismessage will display on the readout,giving firefighters explicit informationas to the location of the fire.

OPERATION SUMMARYThe microprocessor in the main controlinterrogates or polls the transponders insequence, with only nanoseconds beingrequired for each device or cluster ofsensors. When a transponder is polled,it responds that it is either in a normal

state or in alarm. In Analog Address-able Systems, a transponder installedin a smoke sensor will also indicate thecondition of the sensor, such as dirty,approaching alarm condition, etc. If thetransponder is disconnected for anyreason (malfunction or break in the wir-ing) the panel will show a system troubleand show a device missing message(or code) on the display, which will givea specific location of the device. Otherfault messages can be for an SLC break,circuit shorted, etc. Some systems mayindicate a circuit break by displaying a

list of missing addresses located beyondthe break or short.

One disadvantage of the addressablesystem is that polling or interrogationconsumes a fraction of a second perdevice polled. If a substantial numberof devices are installed in an individualsignaling line circuit, a considerableamount of time could elapse until analarm is processed. Present controlpanel standards require a maximumof 5 seconds for a panel to process analarm after it is received from an initiat-ing device. The development of sensorsthat will operate in a cluster mode hasmade this an easier matter. However,it is common to use a larger number ofSLCs with fewer devices installed onthem rather than have one huge SLCwith numerous devices.

The addressable system is also pro-grammed to make specific responsesdepending on the device activated.Thus the system can process an alarmfrom a sensor with complete alarm re-sponse including notification of the firedepartment and operation of elevator

capture devices, operation of smokedampers, etc. It may also process a su-pervisory signal from a tamper switchwith sounding of dedicated appliancesonly, or indicate that a control modulehas been activated and has performedits required function.

Now that we have described the basicoperation of both conventional and ad-dressable fire alarm controls, our nextinstallment will concern itself withsmoke detection.