SIST EN 4533-001:2009
(Main)Aerospace series - Fibre optic systems - Handbook - Part 001: Termination methods and tools
Aerospace series - Fibre optic systems - Handbook - Part 001: Termination methods and tools
1.1 General
This Part of EN 4533 examines the termination aspects of fibre optic design for avionic installations. By termination is meant the mechanism used to interface from one component (usually a fibre) to another. This is normally performed by a connector, which aligns the fibre with another component (usually another connector) to a sufficient accuracy to allow continued transmission of an optical signal throughout the operational envelope.
This Part will explain the need for high integrity terminations, provide an insight into component selection issues and suggests best practice when terminating fibres into connectors for high integrity applications. A detailed review of the termination process can be found in Clause 4 of this part and is organised broadly in line with the sequence of a typical termination procedure.
The vast number of cable constructions and connectors available make defining a single termination instruction that is applicable to all combinations almost impossible. Because of the problems of defining a generic termination instruction, this handbook has concentrated on defining best practice for current to near future applications of fibre optics on aircraft.
This has limited the studies within this part to currently available ‘avionic’ silica fibre cables and adhesive filled butt-coupled type connectors. Many of the principles described however would still be applicable for other termination techniques. Other types of termination are considered further in the repair part of this handbook.
1.2 Need for high integrity terminations
In order to implement a fibre optic based system on an aircraft it is vital to ensure that the constituent elements of the system will continue to operate, to specification, over the life of the system. An important aspect of this requirement is the need for reliable interconnection components. (continued)
Luft- und Raumfahrt - Faseroptische Systemtechnik - Handbuch - Teil 001: Verarbeitungsmethoden und Werkzeuge
1.1 Allgemeines
Dieser Teil von EN 4533 untersucht die Anschlussaspekte bei der Gestaltung von Lichtwellenleitertechnik für die Installation in Luftfahrzeugen. Der Begriff Anschluss bezieht sich auf den Mechanismus, mit dem die Schnittstelle zwischen einem Bauteil (gewöhnlich einer Faser) zu einem anderen hergestellt wird. Dies erfolgt üblicherweise durch einen Steckverbinder, der die Faser mit einem anderen Bauteil (gewöhnlich einem anderen Steckverbinder) mit einer Genauigkeit ausrichtet, die ausreichend ist, um durchgehende Übertragung eines optischen Signals durch die gesamte Betriebshülle zu ermöglichen.
Dieser Teil erläutert die Notwendigkeit von hochintegrierten Anschlüssen, bietet Einblick in die Problematik der Bauteilauswahl, und enthält Vorschläge für die beste Verfahrensweise für das Anschließen von Fasern in Steckverbindern bei hochintegrierten Anwendungen. Ein detaillierter Überblick über die Anschlussprozesse ist in Abschnitt 4 dieses Teils enthalten und wird weitestgehend in Übereinstimmung mit der Abfolge eines typischen Anschlussverfahrens vorgenommen.
Die große Vielfalt an erhältlichen Kabelkonstruktionen und Steckverbindern macht es beinahe unmöglich, eine einzelne, auf alle Kombinationen zutreffende Anschlussvorschrift festzulegen. Aufgrund der Probleme bei der Festlegung einer allgemeinen Anschlussvorschrift liegt das Hauptaugenmerk dieses Handbuchs auf der Festlegung der besten Verfahrensweise für derzeitige und in naher Zukunft vorhandene Lichtwellen¬leiteranwendungen in Luftfahrzeugen.
Dadurch waren die Studien im Rahmen dieses Teils auf derzeit erhältliche Kabel mit Quarzglasfasern für die Luft- und Raumfahrt sowie mit Klebstoff gefüllte Steckverbinder mit Stirnflächenkopplung begrenzt. Viele der beschriebenen Grundsätze wären jedoch ebenfalls auf andere Anschlusstechniken anwendbar. Andere Anschlussarten werden ausführlicher im Reparatur-Teil dieses Handbuchs berücksichtigt.
Série aérospatiale - Systèmes des fibres optiques - Manuel d'utilisation - Partie 001 : Méthodes des terminaisons et outils
Aeronavtika - Sistemi iz optičnih vlaken - Priročnik - 001. del: Metode določanja in orodja
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2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.RURGMDLuft- und Raumfahrt - Faseroptische Systemtechnik - Handbuch - Teil 001: Verarbeitungsmethoden und WerkzeugeSérie aérospatiale - Systèmes des fibres optiques - Manuel d'utilisation - Partie 001 : Méthodes des terminaisons et outilsAerospace series - Fibre optic systems - Handbook - Part 001: Termination methods and tools49.060Aerospace electric equipment and systemsICS:Ta slovenski standard je istoveten z:EN 4533-001:2006SIST EN 4533-001:2009en,de01-junij-2009SIST EN 4533-001:2009SLOVENSKI
STANDARD
SIST EN 4533-001:2009
EUROPEAN STANDARDNORME EUROPÉENNEEUROPÄISCHE NORMEN 4533-001July 2006ICS 49.060 English VersionAerospace series - Fibre optic systems - Handbook - Part 001:Termination methods and toolsSérie aérospatiale - Systèmes des fibres optiques - Manueld'utilisation - Partie 001 : Méthodes des terminaisons etoutilsLuft- und Raumfahrt - Faseroptische Systemtechnik -Handbuch - Teil 001: Verarbeitungsmethoden undWerkzeugeThis European Standard was approved by CEN on 28 April 2006.CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this EuropeanStandard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such nationalstandards may be obtained on application to the Central Secretariat or to any CEN member.This European Standard exists in three official versions (English, French, German). A version in any other language made by translationunder the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the officialversions.CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania,Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.EUROPEAN COMMITTEE FOR STANDARDIZATIONCOMITÉ EUROPÉEN DE NORMALISATIONEUROPÄISCHES KOMITEE FÜR NORMUNGManagement Centre: rue de Stassart, 36
B-1050 Brussels© 2006 CENAll rights of exploitation in any form and by any means reservedworldwide for CEN national Members.Ref. No. EN 4533-001:2006: ESIST EN 4533-001:2009
EN 4533-001:2006 (E) 2 Contents Page Foreword.4 Introduction.5 1 Scope.6 1.1 General.6 1.2 Need for high integrity terminations.6 2 Normative references.6 3 Component selection.7 3.1 Elements.7 3.2 Fibre optic cables.7 3.2.1 General.7 3.2.2 Cable construction.7 3.2.3 Fibre choice.8 3.2.4 Cladding materials.8 3.3 Primary coating materials.8 3.3.1 Function.8 3.3.2 Acrylate.8 3.3.3 Polyimide.9 3.3.4 Silicone.9 3.4 Aramid yarn versus fibreglass strength member.9 3.5 Fibre optic connectors.9 3.5.1 Purpose.9 3.5.2 Connector types.9 4 Health and safety aspects.13 4.1 General.13 4.2 Chemicals.13 4.3 “Sharps”.13 5 Termination process.14 5.1 Objective.14 5.2 Cable preparation.14 5.2.1 General.14 5.2.2 Cutting to length.14 5.2.3 Removal of outer jacket.15 5.2.4 Strength member trimming/removal.18 5.3 Removal of secondary coating(s).19 5.4 Removal of primary coating.19 5.4.1 General.19 5.4.2 Mechanical techniques for primary coating removal.20 5.4.3 Alternative techniques.24 5.4.4 Removal of troublesome coatings.26 5.4.5 Evidence of strength reduction when stripping primary buffer coatings.26 5.4.6 To clean or not to clean.27 5.5 Adhesives.28 5.5.1 General.28 5.5.2 Adhesive types.28 5.5.3 The importance of glass transition temperature (Tg).30 5.5.4 Epoxy cure schedules.30 5.5.5 Usability.32 5.5.6 Qualification.33 5.6 Connector preparation.33 SIST EN 4533-001:2009
EN 4533-001:2006 (E) 3 5.6.1 Dry fitting (Don’t do it).33 5.6.2 Cleanliness.34 5.7 Sleeves, boots and backshells.34 5.8 Attachment of fibre to connector.35 5.8.1 Application of adhesive.35 5.8.2 Inserting fibre ‘best-practice’.36 5.9 Adhesive cure.37 5.9.1 General.37 5.9.2 Orientation.37 5.9.3 Curing equipment.37 5.10 Excess fibre removal.39 5.10.1 General.39 5.10.2 Post-cure rough cleaving.40 5.10.3 Pre-cleave.41 5.10.4 Cleaving tools.41 5.11 Polishing.42 5.11.1 Rationale.42 5.11.2 Performance metrics.42 5.11.3 End-face geometry parameters.43 5.11.4 Methods for achieving end-face geometry.44 5.11.5 Polishing stages.45 5.11.6 Polishing tools and equipment.49 5.12 Inspection.54 Bibliography.55
SIST EN 4533-001:2009
EN 4533-001:2006 (E) 4 Foreword This European Standard (EN 4533-001:2006) has been prepared by the European Association of Aerospace Manufacturers - Standardization (AECMA-STAN). After enquiries and votes carried out in accordance with the rules of this Association, this Standard has received the approval of the National Associations and the Official Services of the member countries of AECMA, prior to its presentation to CEN. This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by January 2007, and conflicting national standards shall be withdrawn at the latest by January 2007. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights. According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and the United Kingdom. SIST EN 4533-001:2009
EN 4533-001:2006 (E) 5 Introduction a) The handbook This handbook draws on the work of the Fibre Optic Harness Study, part sponsored by the United Kingdom’s Department of Trade and Industry, plus other relevant sources. It aims to provide general guidance for experts and non-experts alike in the area of designing, installing, and supporting multi-mode fibre-optic systems on aircraft. Where appropriate more detailed sources of information are referenced throughout the text.
It is arranged in 4 parts, which reflect key aspects of an optical harness life cycle, namely: Part 001: Termination methods and tools Part 002: Test and measurement
Part 003: Looming and installation practices Part 004: Repair, maintenance and inspection b) Background It is widely accepted in the aerospace industry that photonic technology offers a number of significant advantages over conventional electrical hardware. These include massive signal bandwidth capacity, electrical safety, and immunity of passive fibre-optic components to the problems associated with electromagnetic interference (EMI). To date, the latter has been the critical driver for airborne fibre-optic communications systems because of the growing use of non-metallic aerostructures. However, future avionic requirements are driving bandwidth specifications from 10’s of Mbits/s into the multi-Gbits/s regime in some cases, i.e. beyond the limits of electrical interconnect technology. The properties of photonic technology can potentially be exploited to advantage in many avionic applications, such as video/sensor multiplexing, flight control signalling, electronic warfare, and entertainment systems, as well as in sensing many of the physical phenomena on-board aircraft. The basic optical interconnect fabric or `optical harness’ is the key enabler for the successful introduction of optical technology onto commercial and military aircraft. Compared to the mature telecommunications applications, an aircraft fibre-optic system needs to operate in a hostile environment (e.g. temperature extremes, humidity, vibrations, and contamination) and accommodate additional physical restrictions imposed by the airframe (e.g. harness attachments, tight bend radii requirements, and bulkhead connections). Until recently, optical harnessing technology and associated practices were insufficiently developed to be applied without large safety margins. In addition, the international standards did not adequately cover many aspects of the life cycle. The lack of accepted standards thus lead to airframe specific hardware and support. These factors collectively carried a significant cost penalty (procurement and through-life costs), that often made an optical harness less competitive than an electrical equivalent.
c) The fibre-optic harness study The Fibre-Optic Harness Study concentrated on developing techniques, guidelines, and standards associated with the through-life support of current generation fibre-optic harnesses applied in civil and military airframes (fixed and rotary wing). Some aspects of optical system design were also investigated. This programme has been largely successful. Guidelines and standards based primarily on harness study work are beginning to emerge through a number of standards bodies. Because of the aspects covered in the handbook, European prime contractors are in a much better position to utilise and support available fibre optic technology. SIST EN 4533-001:2009
EN 4533-001:2006 (E) 6 1 Scope 1.1 General This Part of EN 4533 examines the termination aspects of fibre optic design for avionic installations. By termination is meant the mechanism used to interface from one component (usually a fibre) to another. This is normally performed by a connector, which aligns the fibre with another component (usually another connector) to a sufficient accuracy to allow continued transmission of an optical signal throughout the operational envelope. This Part will explain the need for high integrity terminations, provide an insight into component selection issues and suggests best practice when terminating fibres into connectors for high integrity applications. A detailed review of the termination process can be found in Clause 4 of this part and is organised broadly in line with the sequence of a typical termination procedure. The vast number of cable constructions and connectors available make defining a single termination instruction that is applicable to all combinations almost impossible. Because of the problems of defining a generic termination instruction, this handbook has concentrated on defining best practice for current to near future applications of fibre optics on aircraft.
This has limited the studies within this part to currently available ‘avionic’ silica fibre cables and adhesive filled butt-coupled type connectors. Many of the principles described however would still be applicable for other termination techniques. Other types of termination are considered further in the repair part of this handbook. 1.2 Need for high integrity terminations
In order to implement a fibre optic based system on an aircraft it is vital to ensure that the constituent elements of the system will continue to operate, to specification, over the life of the system. An important aspect of this requirement is the need for reliable interconnection components. This is often expressed as the need for reliable connectors, but in reality it is the need for a reliable cable to connector termination process. The essence of this requirement is the need to assure reliable light transmission through each optical connector throughout the operational envelope. This needs to be achieved through a robust process that enables a high level of optical performance over the lifetime of the terminations. Many factors can contribute to an optical connector’s in-service performance, such as basic connector design, choice of optical fibre, cable, operating and maintenance environment etc. However, one of the main factors governing in-service connector performance is the quality of the cable to connector termination. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. EN 4533-002, Aerospace series – Fibre optic systems – Handbook – Part 002: Test and measurement.
SIST EN 4533-001:2009
EN 4533-001:2006 (E) 7 3 Component selection 3.1 Elements It is important to recognize that a fibre optic termination, while appearing straightforward, is in fact a complex interaction of the constituent elements such as: fibre coatings, connector design, cable strength member anchorage method, adhesive type and cure regime (where used), material properties and so on. Each of these elements will have an impact on the termination, in terms of reliability, integrity and process complexity. 3.2 Fibre optic cables 3.2.1 General One of the main aspects to be addressed is the implication of choosing one cable construction over another.
There are various types of fibre optic cable on the market ranging from loose tube to tight jacket construction, containing a single fibre or an array of many fibres; however, at the time of publication of this handbook the range of options available to aerospace users is somewhat limited. Most of the possible cable types are only suitable for telecommunication applications due to environmental capability limitations, with avionic solutions being generally limited to single fibre, tight jacket constructions. 3.2.2 Cable construction Although the design of fibre optic cable for use on aircraft is fairly similar from one manufacturer to another there are important differences between cables. The two main areas of difference are fibre coatings and cable strength member materials. Each has its own positive and negative attributes in the context of termination procedures. Avionic fibre optic cables are typically constructed as follows, see Figures 1 and 2.
Key 1 Outer jacket 2 Buffer 3 Cladding 4 Core 5 Primary coating 6 Strength member Figure 1 — Typical avionic fibre optic cable construction 1 2 6 5 4 3 SIST EN 4533-001:2009
EN 4533-001:2006 (E) 8
Figure 2 — Examples of typical avionic fibre optic cables 3.2.3 Fibre choice From the perspective of termination there is little difference between small and larger core optical fibres. The main fibre issues that impact upon the termination process relate to cladding and primary coating materials. Current generation of avionic fibre sizes tend to be larger than the standard high volume fibres such as those used in the datacomm/telecomm market and so have an associated cost and availability penalty. 3.2.4 Cladding materials Most avionic fibres employ an “all silica” fibre, i.e. both the core and the cladding are made from glass and may be treated as a single glass filament. Some designs use non-glass materials for the cladding e.g. plastic (acrylate) or epoxy. These fibres are referred to as Plastic Clad-Silica (PCS) and Hard Clad-Silica (HCS) respectively. Although these fibres have been used in a number of aircraft applications they are somewhat limited in thermal endurance capabilities and thus tend to be confined to the more benign environmental applications. The termination processes described in this handbook refer to all-silica fibres. 3.3 Primary coating materials 3.3.1 Function The major function of the fibre buffer coating [1] is to protect the fibre from abrasive and environmental damage. Many materials have been used for the primary coating of optical fibres but the most widely known and used of these are, acrylate, polyimide and silicone. The pros and cons of each are briefly described below. It should be noted that most fibres use an acrylate type material for the primary coating. Other materials can be encountered however, such as silicone, proprietary polymers and even metal, such as Gold or Aluminium (although these are somewhat specialised and will not be considered here). 3.3.2 Acrylate This is perhaps the most common of optical fibre primary coating materials and is relatively easy to remove with hand tools. The coating is usually a UV cured acrylate that is translucent and typically is the same thickness as the fibre. Acrylate’s have a limited temperature performance of up to approximately 100 °C therefore, for high temperature applications other additional coatings are also applied.
SIST EN 4533-001:2009
EN 4533-001:2006 (E) 9 3.3.3 Polyimide This coating has a higher temperature range than UV cured acrylates and can be used in temperatures up to approximately 350 °C. Although useful for high temperature applications polyimide coatings are difficult to remove and are not amenable to tool stripping. Widely used on aircraft programmes in the United States. Fibres employing this material are designed to be installed into connector ferrules without the need to remove the primary coating. This is only possible because the core/cladding/primary coating concentricity and outer diameter tolerances are tightly controlled. This would appear to be an ideal design solution because the fibre surface does not need to be touched. However the enlarged polyimide diameter is not compatible with standard connector bore dimensions, thus non-standard ferrule bore sizes need to be used with an associated cost and availability penalty. 3.3.4 Silicone The main benefits of silicone as a primary coating are the reduction of fibre micro-bend effects due to the “cushioning” effect of the soft primary coating layer, it’s high temperature (up to 200 °C) capability, its resilience to water absorption and its low flammability. However, as with acrylate, this material needs to be stripped prior to inserting optical fibres into fibre optic connectors. This is by no means easy (see later section on removing troublesome primary coatings). 3.4 Aramid yarn versus fibreglass strength member Almost all fibre optic cables employ some form of strength member layer. Its function is to isolate cable external loads from the fibre within. The most common material used for this purpose is Kevlar®; a very tough, strong aramid yarn. However, it is by no means the only material used for this purpose – fibreglass being one of the main alternatives. Fibreglass is better matched to the optical fibre’s thermal coefficient of expansion than Kevlar® and has been used where high temperature (> 135 °C) dimensional stability is required of a cable. This aspect should be considered if a cable is to be subjected to prolonged exposure of rapid thermal cycling stresses over a wide temperature range. However, Kevlar® appears to meet most current avionic temperature requirements (− 55 °C to 135 °C). These two materials need to be treated in quite different ways in order to achieve effective optical fibre load isolation during the termination process. Kevlar® and other similar aramid yarns can be crimped directly onto a connector or termini; fibreglass cannot because it is too brittle. Cables employing fibreglass strength members should be bonded with adhesive or crimped via the cable outer jacket. 3.5 Fibre optic connectors 3.5.1 Purpose The purpose of any fibre optic connector is to align two optical fibres and to keep the fibres positioned within tight physical constraints such that a good optical interface is maintained. This can be achieved in a number of ways. 3.5.2 Connector types 3.5.2.1 General There are a large variety of connectors available, ranging from single way “crimp and cleave” to complex multi-way “pot and polish” devices. It is therefore necessary to understand the differences between these connector types and their associated features. When specifying a fibre optic connector it will be necessary to define: the optical interfacing method, the fibre attachment method and the number of fibres to be accommodated. SIST EN 4533-001:2009
EN 4533-001:2006 (E) 10 3.5.2.2 Optical interface Fibre optic system designers have the option of using optical connectors with one of two types of interfaces, these being “butt-coupled” or “expanded beam”. A typical butt-coupled arrangement is shown in Figure 3. The fibres physically ‘butt’ together at the connection.
Key 1 Ferrules 2 Optical fibre 3 Spit alignment sleeve 4 Optical fibre Figure 3 — Butt-coupled fibre optic connector interface This is the simplest of the two in terms of the number of elements in the optical path. However, the performance of this interface is highly dependent upon the quality of the fibre end-face. This implies stringent requirements in terms of cleanliness and polishing (or cleaving).
An alternative to the butt-coupled interface is to place lenses between the two fibre ends (see Figure 4). Connectors employing such lenses are referred to as ‘Expanded Beam’ connectors. The purpose of the le
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