Independent. Reliable. 100% Canadian. Canada s largest domestic fire alarm manufacturer, with 17 service locations!

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1 AUGUST AOÛT

2 Independent. Reliable. 100% Canadian. Canada s largest domestic fire alarm manufacturer, with 17 service locations! Vancouver Victoria Calgary Edmonton Saskatoon Regina Winnipeg Toronto Hamilton London With projects in more than 50 countries and branches in most major cities, Mircom Engineered Systems is uniquely positioned to serve the Canadian market. Systems and Peripherals that span Fire Detection, EVAC and Industrial Fire and Gas Detection. Advanced Products, 24hr Service and Design Support for any commercial, industrial or multi-unit high rise project. Whitby Ottawa Montreal Quebec City Moncton Halifax Contact Mircom regarding your facility or upcoming project today! x4060 cdnsales@mircom.com St. John s

3 Contents 2 From the Editor s Desk 3 Du bureau du rédacteur en chef 4 UPDATES on Three Important Items 5 Fibre Optics for Fire Alarm Part 1 9 Fibre optique pour l alarme incendie Part 1 16 CFAA 1st ALBERTA Technical Seminar 21 Tech Tip Conseil tech er séminaire technique de l ACAI/CFAA au QUÉBEC 24 1st CFAA/ACAI QUEBEC Technical Seminar 25 NRC-IRC completes Phase I of Fire Performance of Houses project 28 La Phase 1 du projet sur le comportement au feu des maisons est terminée 30 Code of Ethics 31 Code d éthique 32 CFAA Membership 33 CFAA Membership Application Form 34 CFAA 2009 Officers and Directors 35 CFAA Chapters 36 Advertising Rates/Index Maximize the Use and Effectiveness of Fire Alarm Systems in the Protection of Life and Property in Canada Volume 8. Number 3 The Journal is published four times per year in the interest of safety from fire, through the use of properly designed, installed and maintained Fire Detection and Alarm Systems. Association President: Gerry Landmesser Publisher: Allen Hodgson Advertising Coordinator: Ruth Kavanagh Publishing & Printing: Business & Office Centro, Inc. (905) Unless otherwise indicated, the opinions expressed herein are those of the authors and do not necessarily reflect the opinions of the Canadian Fire Alarm Association. The Association hereby disclaims any liability resulting from information or advice given in articles or advertisements. Reproduction (for non-commercial purposes) of original articles appearing in this publication is encouraged, as long as the source credit is shown. Permission to reproduce articles from other sources must be obtained from the original source. All rights reserved. Front Cover Design: Our thanks to Earl Muise for creating the front cover art-work. Comments, suggestions, letters and articles are always welcomed. Please send them to: Allen Hodgson, Editor-in-Chief Canadian Fire Alarm Association #5-85 Citizen Court Markham, Ontario, L6G 1A8 Tel: Toll Free: Fax: Advertising inquiries should be directed to: Ruth Kavanagh, Office Supervisor Tel: Toll Free: Fax: admin@cfaa.ca CANADIAN FIRE ALARM ASSOCIATION 1

4 From the Editor s Desk This August Issue suggests that the fall season is almost upon us. And that suggests that things are about to get a lot busier. (You thought the summer was busy, right?) Well, look at the activities about to happen in your neighborhood. Our new and energetic Alberta Chapter has decided to host a Technical Seminar this fall. The City of Calgary will host this event, and it promises to be a blockbuster with dynamic presenters and solid topics. You will want to register early for this event to ensure your seat. The date is Wednesday 21 October Look at the powerful agenda on Page 16. Not to be outdone, our Quebec Chapter will also host a Technical Seminar, in the beautiful City of Montreal, on Tuesday 10 November Read about it on Page 24. For many years, the Quebec Chapter of the CFAA has been working to resolve issues that are of importance to the Fire Alarm industry in Quebec. The Chapter has been, and continues to be, a key voice that educates and lobbies our industry to help raise the standards and better protect people and assets through proper usage of Fire Alarm Systems. CFAA Quebec holds Monthly meetings that are open to anyone who wishes to participate in promoting a safer province. Call Louis Pedicelli at x326 as your first step to become an active member of CFAA Quebec Chapter. Fibre optic cabling has become a major component in many communications systems, because of great bandwidth capabilities, high transmission speeds with low distortion, and many other advantages over copper. Seldom used in Fire Alarm Systems in the past, fibre none-the-less is becoming less expensive and easier to install. Michael Hugh has penned an excellent two-part article on the potential use of fibre in networked Fire Alarm Systems. Part One begins on Page 5. Watch for the second part in our November Issue. The content of Tech Tip #10, in this issue, follows on from the idea put forth in Tech Tip # 9 in our February Issue: you may want to go back and re-read that earlier tip. You will remember reading how to locate shortcircuits in field wiring using a clamp-on meter. Paul Jewett s Tech Tip #10 discusses how to locate a ground fault using similar means. Enrollment in our Codes and Standards Update Course has been continuing quite well with over 100 Technicians having successfully completed the course: and with high average grades. Read about it on Page 4. Underwriters Laboratories of Canada and the CFAA have negotiated an agreement whereby CFAA- Registered Technicians (in good standing) will be able to purchase the three common standards (Installation, Verification and Inspection) as a group, and therefore at a greatly reduced price. Take advantage of the offer by starting on Page 4. So lots happening and much more to come, from your Association. Stay tuned! Yours in Fire Safety, Allen Hodgson, Editor-in-Chief 2 CANADIAN FIRE ALARM ASSOCIATION

5 Du bureau du rédacteur en chef Ce numéro du mois d août suggère que l automne approche. Et avec l automne, les activités vont s intensifier. (Et vous pensiez que l été était bien chargé?) Et bien, regardez ce qui va se passer dans votre région. Pleine d énergie, notre nouvelle section locale de l Alberta a décidé d organiser un séminaire technique cet automne. La ville de Calgary accueillera cet événement qui promet d être un grand succès, avec des conférenciers dynamiques et des sujets fort intéressants. Inscrivez vous sans tarder pour vous assurer d avoir une place à ce séminaire qui aura lieu le 21 octobre Vous trouverez à la page 16 l ordre du jour prévu. Notre section du Québec ne sera pas de reste puisqu il organise aussi un séminaire technique dans la belle ville de Montréal, le 10 novembre Vous trouverez des détails à ce sujet à la page 23. Depuis plusieurs années, la Section du Québec de l ACAI œuvre activement à la résolution de questions qui présentent de l importance pour l industrie de l alarme incendie au Québec. La Section a été, et continue d être, une voix essentielle dans l éducation et la promotion de notre industrie afin de rehausser les normes et de mieux protéger les personnes et les biens grâce à l utilisation judicieuse des systèmes avertisseurs d incendie. L ACAI Québec tient des réunions le lundi. Ces réunions sont ouvertes à toute personne qui souhaite participer à la promotion de la sécurité dans la province. Pour devenir membre actif de la section du Québec de l ACAI, veuillez commencer par appeler Louis Pedicelli au poste 326. La fibre optique occupe désormais une place importante dans de nombreux systèmes de communications, en raison des avantages qu elle présente par rapport aux conducteurs de cuivre, notamment une bande de fréquences étendue, une vitesse de transmission élevée et une faible distorsion. Rarement utilisée dans les systèmes d alarme incendie dans le passé, la fibre optique est néanmoins devenue moins coûteuse et plus facile à installer. Michael Hugh a rédigé un excellent article en deux parties sur les possibilités offertes par la fibre optique dans les systèmes d alarme incendie raccordés en réseau. La première partie commence à la page 9. La deuxième partie sera publiée dans le numéro de novembre. Le Conseil tech. n 10, que vous trouverez dans le présent numéro du Journal, fait suite au concept exposé dans le Conseil tech n 9, publié dans notre numéro de février : vous aurez peut-être intérêt à relire ce conseil qui explique comment repérer un court-circuit sur le câblage externe au moyen d un ampèremètre à pince. Dans le Conseil tech. n 10, Paul Jewett explique comment repérer une fuite à la terre avec le même genre d appareil. La participation à notre Cours de mise à jour sur les codes et les normes se poursuit avec succès. Plus d une centaine de techniciens et techniciennes ont suivi ce cours et l ont réussi avec, en moyenne, d excellentes notes. Vous trouverez de l information à ce sujet à la page 4. Les Laboratoires des Assureurs du Canada (ULC) et l ACAI ont négocié une entente aux termes de laquelle les techniciens inscrits de l ACAI (dont l inscription est à jour) pourront acheter les trois normes les plus courantes (Installation, Vérification et Inspection) en tant que groupe et donc à un prix nettement réduit. Profitez de cette aubaine! (voir page 4). Comme vous le voyez, notre Association est très dynamique et les activités ne manquent pas. Tenezvous au courant! Cordialement, Le rédacteur en chef, Allen Hodgson CANADIAN FIRE ALARM ASSOCIATION 3

6 UPDATES on Three Important Items Codes and Standards Update Course A huge effort (in excess of twelve months) was expended by CFAA personnel and by George Brown College professionals in the preparation of this webbased course presentation. Released in late spring, enrollment by CFAA Technicians in the CSU Course is progressing smoothly according to Mr. William Juranic of George Brown College who has greatly assisted the CFAA during the implementation of this web-based learning opportunity. Several hundred Technicians have enrolled, and over one hundred have successfully completed the Course. A surge in enrollments is anticipated now that summer vacations are a thing of the past, and Technicians decide to take early advantage of this mandatory learning experience. The results, based on the first wave of course completions, tell us that the learning experience appears to be of a high level, with an average mark for the final exam being just slightly below 90%. This is a satisfying end-result for both GBC and CFAA. Acknowledging that finding quiet time each day can be a challenge for Technicians with families, Mr. Juranic recommends that each Technician dedicate a small amount of time, each day, to achieve maximum results from the course. Those who have completed the course report that the experience was very positive, with inter-active information packages being well-paced and clearly understandable. New Course 5 Red Manual A small group of dedicated individuals has been diligently working this past several months to re-write the Course 5 Manual. Much excellent progress has been made. It is anticipated that the writing will be completed by September, with vetting taking a month, leading to on-the-shelf copies early fall. Watch our web-site for further announcements. In the meantime, our current Course 5 materials have been up-dated to reflect the new codes and standards, and will remain in use until the new Course 5 Manual is introduced this fall. ULC Standards We are extremely happy to be able to announce that we have come to an agreement with Underwriters Laboratories of Canada related to the availability of the three standards commonly used by Technicians: CAN/ULC-S524 Installation of Fire Alarm Systems CAN/ULC-S536 Inspection and Testing of Fire Alarm Systems CAN/ULC-S537 Verification of Fire Alarm Systems These three standards, purchased separately, would cost well over $ The CFAA is happy to advise that CFAA-Registered Technicians will be able to purchase a bound set of these three standards at the special price of $ If you are a Registered Technician, in good standing with the CFAA, look to our website and follow the instructions. The standards are available only through Orderline. This is a great opportunity for you to obtain these vital documents at a very affordable cost. 4 CANADIAN FIRE ALARM ASSOCIATION

7 Fibre Optics for Fire Alarm Part 1 By Michael Hugh, SimplexGrinnell Fibre Optic cable seems to be favoured over copper wiring at an escalating pace. Why is this happening? Throughout this document we will examine a number of subjects related to the use of Fibre Optics in Fire Alarm. What is Fibre? What is good about it? What is bad about it? What do the various governing Codes and Standards say in relation to the use of fibre optic in fire alarm? What cautions must be realized in using fibre optics in fire alarm? Hopefully, you will gain a greater understanding of not only what benefits fibre can provide, but also, how to differentiate between a fibre installation that is fire alarm compliant in Canada, and one that is not. Firstly, what is fibre? No, it is not that stuff that all the breakfast advertisements encourage us to add to our diet. Rather, it is an alternate type of cable that contains a light-conducting core instead of an electricity conducting core. A typical fibre optic cable has a protective buffer coating, some type of filler (cladding) and a fibre core, which is the portion of the cable that conducts light. Notice that the core is made of fibre, rather than fiber? This is true in Canada. In the USA, the cables cores are composed of fiber instead. And yes, these are exactly the same thing, except the "fibre" spelling retains our Canadian identity, rather than those US based spellcheckers that most word processing software provides! If you were to connect two data communication devices together over a copper cable and then monitor the voltage levels of the signal being sent with an Oscilloscope, you would probably notice that the data transmitted would look like a square wave. The higher voltage level would represent a 1 being transmitted and the lower voltage would represent a 0 being transmitted. This is basic ones and zeros allowing two computer-based products to exchange information. If I was to connect the same data communication devices together over a fibre cable and then monitor the light level being sent via a light meter, I would probably notice that the data being transmitted would look like someone flicking the lights on and off in very rapid succession. When the cable was bright with light, it would represent a 1 being sent and when the cable was dark (no light) would represent a 0 being sent. Pretty simple stuff- just ones and zeros. Essentially we are taking the high vs. low voltage levels being sent over copper conductors and translating Now that we know what fibre optic cable is made of, let s examine how it can be used instead of copper core cable. CANADIAN FIRE ALARM ASSOCIATION 5

8 those two voltage levels into bright vs. dark light being sent over fibre cables. That light being used could be provided by an LED or Laser or other light source, but the concept is the same. Types of Fibre Optic: There are 3 different types of fibre optic cable that are fairly common. They fall into 2 categories called Multi-Mode and Single-Mode fibre optic cable. If you happen to trip on a piece of fibre cable that was installed way back when, it is likely Multi-Mode fibre cable. When fibre was being introduced to the market, Multi-Mode was much less expensive. Now, the majority of installations are using Single-Mode as it seems to perform better and the cost difference is not as severe as it used to be. The first type, Multi-Mode fibre, has a larger diameter core than Single Mode fibre and is thus, easier to work with. In addition, due to the larger core diameter, it can be driven by less expensive light sources like LEDs, rather than the more expensive lasers. The drawback lies in the bandwidth limitation and the transmission distance, which are both less appealing compared to the capabilities of Single-Mode fibre. Of the two types of Multi-Mode fibre, the first is called Step-Index. Step-Index fibre: As you can see in the diagram above, Step Index uses a type of fibre core that allows multiple light waves to travel through the fibre at the same time. In result, the light signals can suffer modal dispersion, which can lead to distortion of the signal. If you compare the signal entering the fibre core at one of the cable, you can see that the signal leaving the fibre core looks significantly different. This can cause errors in data transmission. Graded-Index: The second type of Multi-Mode fibre is called Graded- Index. Graded Index uses a type of fibre that varies the density of the core to allow the multiple light signals to arrive at the destination at relatively the same time. Graded index uses a larger diameter core than Step-Index. This technique provides a cleaner, more accurate data transfer and reduces the distortion of the waveform. As you can see, the waveform at the entrance to the fibre appears much more similar to the waveform exiting the cable than in the previous cable (Step-Index) instance. Single Mode Fibre: The third type of fibre is called Single Mode. Single-Mode fibre concentrates the light signals down the centre of the fibre with a much more focused transmission. The diameter of Single-Mode fibre core is much smaller than either type of Multi-Mode fibre. In result, the signal transfer is much more accurate, and the wave form created at the output of the fibre is extremely close to the waveform that is being input at the entrance to the fibre medium. What is so GREAT about Fibre with respect to Fire Alarm Systems? The first great thing about fibre optic conductors in fire alarm is that all of the major fire alarm manufacturers can provide fibre optic drivers to utilize fibre cables. (More on what these fibre drivers can use the fibre optic to do in a moment.) First off, none of the major fire alarm manufacturers provide fibre optic connections on their detection devices. Thus it is presently impossible to use fibre optic cabling on DCL circuits used for fire detection. That is not to say that fibre optics cannot be used in fire detection. It is just not used to interconnect a fire detection peripheral to another fire detection peripheral or to the fire alarm control panel. On the other hand, fibre optics is being used as a fire detection device! There are products available that utilize a fibre optic cable to sense changes in temperature (which can ultimately detect fire) in areas that are too severe for normal detection peripherals. One example for the use of fibre optic fire sensing is in underground motorways, underground subways, and underground railway lines. But how is fibre optic used by the major fire alarm manufacturers in North America? Easy. It is used to serve as the communication link between networked 6 CANADIAN FIRE ALARM ASSOCIATION

9 fire alarm panels. In CAN/ULC-S524, this communication is termed DCL, or data communication link. One of the advantages that fibre optic can provide, when used in DCL panel-to-panel communications, is transmission distance. While some manufacturers can accept copper-based communications between panels that are located up to 2 miles apart, the same two panels could communicate over fibre optics at distances up to 20 miles apart. This translates to a 10-times increase in transmission distance! Another advantage inherent to fibre comes into play when network fire alarm panels are connected via underground cable links. It is quite common for those underground cables to be plagued with water-filled conduits which often occurs during rainstorms. The result is a system trouble when the ground fault is sensed by the fire alarm panel. Naturally, this problem is only associated with underground copper conductors. When these same underground conduit systems carry fibre-optic based communications, the problem of grounded communication circuits disappears! So what kind of signals can fibre optic actually carry in the Fire Alarm world? Some manufacturers that use fibre optic to allow their fire panels to communicate over a network require 2 strands of fibre optic cable for each data communication link. One fibre strand is used for one panel to transmit to the other panel. At the same time, the other fibre strand is used for the other panel to transmit and the first panel to receive. Communication can occur simultaneously, but 2 strands are required to accomplish one link. If the panels required a DCLC type of communication path, there would need to be 4 strands available to provide the 2 separate communication paths demanded by DCLC. Recent innovations in the fire alarm industry have provided alternate transmission methods that have effectively reduced the number of fibre strands required. Some fire alarm panels can now communicate over a single strand of fibre optic cable. For DCLC type communication, 2 strands would be required to provide the dual paths demanded by DCLC, but the number of strands required today is just half the number that used to be required. How is this accomplished? To allow 2 fire alarm panels to simultaneously communicate with each other (in both directions), special fibre modems are used. These transceivers utilize different frequencies to determine transmit and receive functions. In one particular instance, the first panel would transmit at 1300 nm (while the other received at this frequency) and the second panel would transmit at 1550 nm (while the first panel received at this frequency). With this scheme in place, both panels can simultaneously communicate with each other while avoiding collisions on the same strand of fibre. Another related advantage with fibre optics lies with another phenomenon associated with rainstorms lightning damage. Most underground copper-based installations require lightning suppressors installed at building entrance and exit points to protect the fire alarm equipment from the ravages of lightning strikes. Often these devices are disposable; once they are struck by lightning they must be replaced. On the other hand, with fibre optic cable, the high voltage spikes generated during a lightning strike is not conducted to the fire alarm equipment as the fibre optic cable does not conduct electricity, only light. In result, no suppressors are required, and there is no danger of equipment damage due to lightning. While those in the fire alarm industry may be overwhelmingly excited with the idea of networking 2 fire panels together with just 1 strand of fibre, those in the IT world may be less than impressed. Considering the large bandwidth that fibre cable can provide, they CANADIAN FIRE ALARM ASSOCIATION 7

10 may say that the one strand of fibre is still being underutilized. And they re probably correct. Thus, further fire alarm innovations have been developed which allow more information to be broadcast over a single strand of fibre. Now some fire alarm panels can transmit audio signals as well as data communication signals on the same strand of fibre. In fact, up to 8 separate audio channels (or signals) of audio data, plus the communications data, can be delivered over the same fibre strand. This type of innovation provides much cost savings on the installation. Consider that prior to fibre optic cable, multiple cable runs would have been required to mimic the functionality that 1 single strand of fibre can provide today. So what is so BAD about Fibre? OK, so we ve listed a number of pretty cool benefits available via fibre optic conductors. So, where s the catch? (There is always a catch, right?). The catch is that fibre is not quite as easy to install as copper. Consider that when two copper conductors need to be connected, the splice can be accomplished with something as simple as a Wire Nut without introducing much line loss on that connection. The process is pretty simple: The electrician strips the insulation from the wires, twists the wires together with a Wire Nut to provide insulation so the copper doesn t ground to the electrical box, and presto, the wires are joined. Not so with fibre optic cable. With fibre splices, extreme care must be taken to ensure that the light traveling down the glass pipe in the centre of the cable does not become spilled outside of the pipe. To prevent this light-based line loss, the fibre must be continuous, as if the two cables were, in fact, one cable. To accomplish these immaculate unions, special equipment is available that actually welds the two fibre cables together to create a splice in the two cables that provide such a seamless joint that the light can continue to travel from one cable to the next without a significant loss of signal. With these specialized devices, the fibre welding process takes just a few moments, so it is relatively easy to accomplish in the field during the fibre installation. In short, the fibre cable splicing device accepts the two fibre segments, orients their alignment, and heats the tips of the fibre cores to bond them together. This type of splicing is called fusion splicing. It provides a very low line-loss connection. The other obstacle with fibre is that special training is required to prepare those responsible to execute the installation. These fibre specialists are trained on the use of fusion splicing machines. They are trained on appropriate techniques to use to pull in fibre cable (care must be taken to avoid extreme bends in the cable to ensure the fibre core is not damaged as it is not as rugged as copper core cables). And these people are also trained on fibre connection/termination installation to ensure the end-connections provide low-loss, efficient paths for the light to travel through. So what do the Fire Alarm related Codes say about the use of fibre optic cables? You ll have to wait for the next issue of the CFAA Journal for the answer For further study, please consult: References: cation_fot-cfi.aspx ber-optic-cable-fi re-rating/ CAN/ULC-S Canadian Electrical Code 8 CANADIAN FIRE ALARM ASSOCIATION

11 Fibre optique pour l alarme incendie Part 1 Par Michael Hugh, SimplexGrinnell Le câble en fibre optique semble de plus en plus privilégié au détriment du fil de cuivre. Pourquoi ce changement rapide? Tout au long de ce document, nous examinerons un certain nombre de sujets en rapport avec l utilisation de la fibre optique pour l alarme-incendie. Qu est-ce qu une fibre? Quels sont ses avantages? Quels sont ses inconvénients? Que disent les divers codes et normes applicables concernant l utilisation de la fibre optique pour l alarme-incendie? Quelles précautions doit-on prendre lorsqu on utilise la fibre optique pour l alarmeincendie? J espère que cet article vous permettra non seulement de comprendre les avantages que la fibre optique peut apporter à notre industrie, mais aussi comment reconnaître une installation à fibre optique qui est conforme au Canada de l une qui ne l est pas? Pour commencer, qu est-ce qu une fibre? Mais non, ce n est pas ce que toutes les publicités vous encouragent à consommer pour votre déjeuner. Il s agit plutôt d un type différent de câble dont le cœur a la propriété de conduire la lumière plutôt que l électricité. Typiquement, un câble en fibre optique comprend un revêtement de protection, un matériau de remplissage (gaine) et un cœur, qui est la partie du câble qui propage les rayons lumineux. En français, le problème ne se pose pas, mais en anglais, vous trouverez dans la littérature le mot «fibre» avec deux orthographes, fibre (orthographe correcte au Canada) ou fiber (orthographe utilisée aux États-Unis). Si vous raccordez deux dispositifs de communication de données au moyen d un câble de cuivre puis surveillez la tension du signal transmis au moyen d un oscilloscope, vous noterez probablement que les données transmises ont l apparence d une onde carrée. La tension la plus élevée correspondrait à la transmission d un «1» et la tension inférieure à la transmission d un «0». Il s agit du principe binaire de base des «1» et «0» de l informatique qui permet à deux appareils d échanger des données. Si je raccordais les mêmes dispositifs de communication avec un câble optique, puis surveillais le niveau de lumière transmise au moyen d un posemètre, je remarquerais probablement que les données transmises ressemblent à ce qui se produirait si quelqu un allumait et éteignait les lumières très rapidement. Lorsqu un rayon lumineux entre dans le câble, cela correspond à l envoi d un «1» et lorsque le câble est sombre (pas de rayons lumineux), cela correspond à l envoi d un «0». En fait, c est très simple, juste des uns et des zéros! Examinons maintenant comment on peut utiliser une fibre optique à la place d un câble en cuivre. CANADIAN FIRE ALARM ASSOCIATION 9

12 En bref, nous prenons les tensions élevées et faibles transmises par des conducteurs en cuivre et convertissons ces deux niveaux de tension en rayons lumineux vifs ou sombres transmis par un câble optique. Ce rayon lumineux utilisé peut être produit par une diode lumineuse, un rayon laser ou une autre source de lumière, mais le concept reste le même dans tous les cas. Différents types de fibre optique Il existe trois types de câble à fibre optique relativement courants. Ils peuvent tous être subdivisés en deux catégories appelées les fibres multimodes et les fibres monomodes. Si vous tombez par hasard sur un câble optique installé il y a longtemps, il s agit probablement d un câble à fibre multimode. À l origine, lorsque la fibre optique a été introduite sur le marché, les multimodes étaient beaucoup moins coûteuses. Aujourd hui, la majorité des installations utilisent le monomode qui semble fonctionner mieux, avec une différence de coût qui n est pas aussi élevée que dans le passé. Le premier type, la fibre multimode, a un cœur de diamètre supérieur à celui de la fibre monomode et est donc plus facile à manipuler. De plus, en raison de ce diamètre supérieur du cœur, il permet d utiliser des sources de lumière moins coûteuses, notamment des diodes électroluminescentes, plutôt que des lasers qui sont plus coûteux. Par contre, l amplitude et la distance de transmission sont plus restreintes, ce qui est un désavantage par rapport aux capacités de la fibre monomode. Des deux types de fibre multimode, la première est appelée «à saut d indice». Fibre à saut d indice : Comme vous pouvez le voir dans le schéma cidessus, le saut d indice utilise un cœur d un type qui permet à plusieurs ondes de lumière de se déplacer simultanément dans la fibre. De ce fait, les signaux lumineux peuvent subir une «dispersion modale», qui peut provoquer la distorsion du signal. Si vous comparez le signal qui entre dans le cœur de la fibre à une extrémité du câble au signal qui en sort à l autre extrémité, vous constaterez qu ils peuvent être nettement différents. Ceci peut causer des erreurs dans la transmission des données. Fibre à gradient d indice : Le deuxième type de fibre multimode est appelé «à gradient d indice». Le gradient d indice utilise un type de fibre dont la densité du cœur varie afin de permettre à plusieurs signaux lumineux d arriver à destination relativement simultanément. Le diamètre du cœur d une fibre à gradient d indice est supérieur à celui du cœur d une fibre à saut d indice. Cette technique permet d obtenir un transfert des données plus «propre» et plus précis et réduit la distorsion de la courbe d onde. Comme vous pouvez le voir, si l on compare à l exemple précédent (saut d onde), la forme de l onde est moins déformée entre l entrée et la sortie de la fibre. Fibre monomode : Le troisième type de fibre est appelé «monomode». Les fibres monomodes concentrent les signaux lumineux au cœur de la fibre, avec une transmission beaucoup plus concentrée. Ces fibres ont un diamètre beaucoup petit que n importe laquelle des fibres multimodes. La transmission du signal est donc beaucoup plus précise et la forme de l onde à la sortie de la fibre est très proche de celle envoyée à l entrée. Pourquoi la fibre optique présente-t-elle un tel intérêt pour les systèmes d alarme-incendie? Tout d abord, la fibre optique est intéressante parce que tous les grands fabricants d alarme-incendie peuvent fournir des appareils «pilotes» qui permettent d utiliser des câbles à fibre optique (nous parlerons bientôt de ces pilotes un peu plus en détail). Il faut souligner qu aucun des principaux fabricants de matériel d alarme incendie ne fournit de connexions pour câble à fibre optique sur leurs appareils de détection. À l heure actuelle, il est donc impossible d utiliser un câble à fibre optique sur les circuits utilisés pour la détection d incendie. Cela ne veut pas pour autant dire qu il est impossible d utiliser la fibre optique dans la détection d incendie. Cela signifie seulement qu il n est pas possible d utiliser la fibre optique pour relier entre eux des périphériques ou un périphérique au panneau de commande. 10 CANADIAN FIRE ALARM ASSOCIATION