EN 4533-004:2006

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.3RSUDYLODLuft- und Raumfahrt - Faseroptische Systemtechnik - Handbuch - Teil 004: Reparatur, Instandhaltung und InspektionSérie aérospatiale - Systèmes des fibres optiques - Manuel d'utilisation - Partie 004 : Réparation, maintenance et contrôleAerospace series - Fibre optic systems - Handbook - Part 004: Repair, maintenance and inspection49.060Aerospace electric equipment and systemsICS:Ta slovenski standard je istoveten z:EN 4533-004:2006SIST EN 4533-004:2009en,de01-junij-2009SIST EN 4533-004:2009SLOVENSKI
STANDARD
EUROPEAN STANDARDNORME EUROPÉENNEEUROPÄISCHE NORMEN 4533-004July 2006ICS 49.060 English VersionAerospace series - Fibre optic systems - Handbook - Part 004:Repair, maintenance and inspectionSérie aérospatiale - Systèmes des fibres optiques - Manueld'utilisation - Partie 004 : Réparation, maintenance etcontrôleLuft- und Raumfahrt - Faseroptische Systemtechnik -Handbuch - Teil 004: Reparatur und InspektionThis 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 4533-004:2006: ESIST EN 4533-004:2009

 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 4533-004:2009

3.4.3 Visible fault locator This technique is based on the injection of visible light into the fibre-optic system under test. Defects such as fibre breaks or cracks scatter this light. If the cable or connector housing allows, this results in flare being visible at, or close to, the location of the fault. Figure 1 and Figure 2 show a visible fault locator.
Figure 1 — Broken fibre under cable SIST EN 4533-004:2009

Figure 2 — Visible fault locator locates break This is an appealing technique being easy to perform and requiring only the visible fault locator. A typical locator would be based on a red (635 nm) laser diode, housed in a torch type package with battery power. A white light or visible LED based device could just as easily be used. The only restriction on the source is that it is eye safe. By pulsing the source (~Hz) its ‘detectability’ to the eye can be enhanced. Also, by connectorising the source, efficient coupling into the harness can be achieved.
Visible fault locators are appropriate to use on fibre breaks combined with translucent cable constructions. They are also a quick and easy way to locate complete optical power loss faults by checking the continuity of point-to-point links. Visible fault locators are limited to these types of fault and have the major drawback that most current avionic harness components are packaged in opaque materials and/or installed in conduit or visually inaccessible areas of the airframe. 3.4.4 OTDR Optical Time-Domain Reflectometer (OTDR) technology has developed to satisfy the demand for fault finding and loss measurement in telecommunications, and latterly commercial data communication networks. They are specialist tools and certain ‘high performance’ OTDRs require training and a good knowledge of fibre-optic technology for effective use. Due to the fact that they were developed for relatively long distance links there are doubts over whether they have the necessary spatial resolution for use on avionics harnesses. On top of the basic functionality discussed in the Test and Measurement chapter, OTDRs can be designed to automatically interpret information from multiple events and present them in user friendly form. Signal processing software can potentially: identify an event and locate it relative to a preceding event or the instrument bulkhead; identify the cause of the event; measure insertion loss increase from preceding event; measure total link loss; analyse only those events over a certain dB threshold; zoom in on sections of the network; etc. Many fault finding algorithms rely on comparison of the current OTDR record with a previously stored ‘footprint’. Automatic fault finding software is usually installed in the latest OTDRs largely de-skilling fault diagnostic operations. The key performance parameters of OTDRs pertinent to avionic optical harness measurements are:  Event Dead Zone – the ability to discriminate between closely spaced events, including the instrument’s bulkhead connector, defined as the distance in metres between the leading edge of a reflective event and the point on the trailing edge where the signal drops to 3 dB below its peak value;  Attenuation Dead Zone (or Loss Measurement Resolution) – the ability to measure insertion loss of two closely spaced events, defined as the distance from the onset of a reflective pulse to the point where the event tail has recovered to within 0,5 dB (or more recently 0,1 dB) of the background noise floor; SIST EN 4533-004:2009

Figure 3 — Dead zone definitions for OTDRs
EDZ is the critical parameter for fault finding as in most cases accurate insertion loss measurement is unnecessary. However, current OTDRs struggle to meet the specific requirements of airborne optical harnesses in this respect. EDZs of less than one metre are of potential interest for basic fault finding in point-to-point avionic harnesses. EDZs and ADZs of ten centimetres for typical harness features would make OTDRs of more general use for both fault finding and insertion loss measurements. Figure 4 shows actual OTDR results from a two metre EDZ commercial instrument interrogating a test installation. Note that the ‘extra’ peaks are due to multiple reflections. This demonstrates the importance of minimising any Fresnel reflections (e.g. from an airgap connector) which otherwise dominate the OTDR trace. This can be achieved through PC terminations. OTDRs may also struggle to interpret more complex avionic optical Local Area Networks (LANs) such as multi-way, star-coupled networks.
Figure 4 — Commercial OTDR trace from a point-to-point avionic link
3 dB 0.1 dB EDZADZ distance dB SIST EN 4533-004:2009
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