Aerospace series - Fibre optic systems - Handbook - Part 001: Termination methods and tools

1.1   General
Part 001 of EN 4533 examines the termination of optical fibre cables used in aerospace applications. Termination is the act of installing an optical terminus onto the end of a buffered fibre or fibre optic cable. It encompasses several sequential procedures or practices. Although termini will have specific termination procedures, many share common elements and these are discussed in this document. Termination is required to form an optical link between any two network or system components or to join fibre optic links together.
The fibre optic terminus features a precision ferrule with a tight tolerance central bore hole to accommodate the optical fibre (suitably bonded in place and highly polished). Accurate alignment with another (mating) terminus will be provided within the interconnect (or connector) alignment mechanism. As well as single fibre ferrules, it is noted that multi-fibre ferrules exist (e.g. the MT ferrule) and these will also be discussed in this part of the handbook.
Another technology used to connect 2 fibres is the expanded beam. 2 ball lenses are used to expand, collimate and then refocus the light from and to fibres. Contacts are not mated together. It helps reducing the wear between 2 contacts and allows more mating cycles. This technology is less sensitive to misalignments and dust. Losses are remaining more stable than butt joint contact even if the nominal loss is higher.
A Note on Terminology
Current terminology in the aerospace fibre optics community refers to an optical terminus or termini. The term optical contact may be seen in some documents and has a similar meaning. However, the term contact is now generally reserved for electrical interconnection pins. The optical terminus (or termini) is housed within an interconnect (connector is an equivalent term). Interconnects can be single-way or multi-way. The interconnect or connector will generally house the alignment mechanism for the optical termini (usually a precision split-C sleeve made of ceramic or metal). The reader should be aware of these different terms.
An optical link can be classified as a length of fibre optic cable terminated at both ends with fibre optic termini. The optical link provides the transmission line between any two components via the optical termini which are typically housed within an interconnecting device (typically a connector) with tight tolerancing within the alignment mechanisms to ensure a low loss light transmission.
Part 001 will explain the need for high integrity terminations, provide an insight into component selection issues and suggests best practice when terminating fibres into termini for high integrity applications. A detailed review of the termination process can be found in section 4 of this part and is organised 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 very difficult. Therefore, this handbook concentrates on the common features of most termination practices and 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.
It is noted that the adhesive based pot-and-polish process is applicable to the majority of single-way fibre optic interconnects connectors and termini for multi-way interconnects and connectors. They share this commonality.
1.2   Need to high integrity terminations
(...)

Luft- und Raumfahrt - Faseroptische Systemtechnik - Handbuch - Teil 001: Anschlussverfahren und Werkzeuge

Teil 001 der EN 4533 untersucht die Anschlussaspekte von Lichtwellenleiterkabeln für Anwendungen in der Luft  und Raumfahrt. Anschließen bezieht sich hierbei auf die Installation einer optischen Endstelle am Ende einer gepolsterten Faser oder eines Lichtwellenleiterkabels. Der Prozess umfasst mehrere Verfahren oder Praktiken, die nacheinander ausgeführt werden. Obgleich verschiedene Anschlüsse spezifische Anschluss¬verfahren aufweisen, teilen viele gemeinsame Elemente und diese werden in diesem Dokument besprochen. Ein Anschluss ist notwendig, um eine optische Verbindung zwischen zwei Netzwerk- oder Systemkompo¬nenten herzustellen oder Lichtwellenleiter zusammenzuführen.

Série aérospatiale - Systèmes des fibres optiques - Manuel d'utilisation - Partie 001 : Méthodes des terminaisons et des outils

La Partie 001 de l’EN 4533 examine la terminaison des câbles de fibres optiques utilisés dans les applications aérospatiales. La terminaison est l'action qui consiste à installer un contact optique à l'extrémité d'une fibre gainée ou d’un câble de fibre optique. Cette action comporte plusieurs modes opératoires ou méthodes séquentielles. Les contacts sont régis par des procédures de terminaison spécifiques ; cependant, nombre d'entre eux partagent des éléments communs qui sont exposés dans ce document. Une terminaison a pour obligation de former une liaison optique entre deux composants d'un réseau ou d'un système, ou d'accoupler des liaisons optiques.
Un contact de fibre optique comporte une ferrule de précision avec un trou central alésé à une tolérance rigoureuse pour recevoir la fibre optique (adéquatement collée en position et hautement polie). Un mécanisme d'alignement dans l’interconnexion (ou le connecteur) permet un alignement précis avec un autre contact (d'accouplement). De même que les ferrules monofibre, il est à noter l'existence de ferrules multifibres (par exemple : ferrules MT à transfert mécanique) qui sont également exposées dans cette partie du manuel d’installation.
La technologie à faisceau élargi est une autre technique d'accouplement de 2 fibres. Elle met en œuvre deux lentilles sphériques pour élargir, collimater et enfin, rétablir le centre optique du rayon lumineux en entrée et en sortie des fibres. Les contacts ne sont pas contraints ensemble, ce qui contribue à diminuer l'usure entre deux contacts tout en permettant d'augmenter les cycles de montage/démontage. Cette technologie est moins sensible aux défauts d'alignement et à la poussière. Les pertes optiques demeurent plus stables que les contacts à accouplement direct même si la perte nominale est plus élevée.
[...]

Aeronavtika - Sistemi iz optičnih vlaken - Priročnik - 001. del: Metode določanja in orodja

General Information

Status
Published
Publication Date
25-Feb-2020
Technical Committee
Drafting Committee
Current Stage
6060 - Definitive text made available (DAV) - Publishing
Due Date
26-Feb-2020
Completion Date
26-Feb-2020

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SLOVENSKI STANDARD
SIST EN 4533-001:2020
01-maj-2020
Nadomešča:
SIST EN 4533-001:2009

Aeronavtika - Sistemi iz optičnih vlaken - Priročnik - 001. del: Metode določanja in

orodja

Aerospace series - Fibre optic systems - Handbook - Part 001: Termination methods and

tools
Luft- und Raumfahrt - Faseroptische Systemtechnik - Handbuch - Teil 001:
Verarbeitungsmethoden und Werkzeuge

Série aérospatiale - Systèmes des fibres optiques - Manuel d'utilisation - Partie 001 :

Méthodes des terminaisons et des outils
Ta slovenski standard je istoveten z: EN 4533-001:2020
ICS:
33.180.10 (Optična) vlakna in kabli Fibres and cables
49.060 Letalska in vesoljska Aerospace electric
električna oprema in sistemi equipment and systems
SIST EN 4533-001:2020 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN 4533-001:2020
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SIST EN 4533-001:2020
EN 4533-001
EUROPEAN STANDARD
NORME EUROPÉENNE
February 2020
EUROPÄISCHE NORM
ICS 49.090 Supersedes EN 4533-001:2006
English Version
Aerospace series - Fibre optic systems - Handbook - Part
001: Termination methods and tools

Série aérospatiale - Systèmes des fibres optiques - Luft- und Raumfahrt - Faseroptische Systemtechnik -

Manuel d'utilisation - Partie 001 : Méthodes des Handbuch - Teil 001: Verarbeitungsmethoden und

terminaisons et des outils Werkzeuge
This European Standard was approved by CEN on 2 March 2018.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this

European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references

concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN

member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by

translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management

Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,

Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,

Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and

United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels

© 2020 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 4533-001:2020 E

worldwide for CEN national Members.
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SIST EN 4533-001:2020
EN 4533-001:2020 (E)
Contents Page

European foreword ....................................................................................................................................................... 5

Introduction .................................................................................................................................................................... 6

a) The Handbook .................................................................................................................................................. 6

b) Background ....................................................................................................................................................... 6

1 Scope .................................................................................................................................................................... 7

1.1 General ................................................................................................................................................................ 7

1.2 Need to high integrity terminations ......................................................................................................... 8

2 Normative references .................................................................................................................................... 8

3 Component Selection ..................................................................................................................................... 8

3.1 Elements ............................................................................................................................................................. 8

3.2 Fibre optic cables ............................................................................................................................................ 9

3.2.1 General ................................................................................................................................................................ 9

3.2.2 Cable construction .......................................................................................................................................... 9

3.2.3 Fibre choice .................................................................................................................................................... 10

3.2.4 Cladding materials ....................................................................................................................................... 12

3.3 Primary buffer materials........................................................................................................................... 13

3.3.1 Function ........................................................................................................................................................... 13

3.3.2 Acrylate ............................................................................................................................................................ 13

3.3.3 Polyimide ........................................................................................................................................................ 13

3.3.4 Silicone ............................................................................................................................................................. 14

3.3.5 Strength Members ........................................................................................................................................ 14

3.4 Outer jacket .................................................................................................................................................... 14

3.5 Fibre optic interconnects (connectors) ............................................................................................... 15

3.5.1 Introduction ................................................................................................................................................... 15

3.5.2 The Optical interface ................................................................................................................................... 15

3.5.3 Single-way Interconnects/Connectors ................................................................................................. 23

3.5.4 Multi-way Interconnects/Connectors ................................................................................................... 23

3.5.5 Choice of tooling ........................................................................................................................................... 24

4 Health and safety aspects .......................................................................................................................... 25

4.1 General ............................................................................................................................................................. 25

4.2 Chemicals ........................................................................................................................................................ 25

4.3 Sharps ............................................................................................................................................................... 26

5 Termination process ................................................................................................................................... 26

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SIST EN 4533-001:2020
EN 4533-001:2020 (E)

5.1 Objective .......................................................................................................................................................... 26

5.2 Cable preparation ......................................................................................................................................... 26

5.2.1 General .............................................................................................................................................................. 26

5.2.2 Cutting to length ............................................................................................................................................ 26

5.2.3 Removal of outer jacket .............................................................................................................................. 28

5.2.4 Cable Handling tools (gripping the cable) ........................................................................................... 33

5.2.5 Strength member trimming/ removal .................................................................................................. 34

5.3 Removal of secondary coating(s) ............................................................................................................ 35

5.4 Removal of primary coatings .................................................................................................................... 36

5.4.1 General .............................................................................................................................................................. 36

5.4.2 Mechanical techniques for primary coating removal ...................................................................... 36

5.4.3 Alternative techniques ................................................................................................................................ 42

5.4.4 Troublesome coatings – Polyimide and Silicone ............................................................................... 43

5.4.5 Evidence of strength reduction when stripping primary buffer coatings ................................ 45

5.4.6 To clean or not to clean ............................................................................................................................... 46

5.5 Adhesives ......................................................................................................................................................... 47

5.5.1 General .............................................................................................................................................................. 47

5.5.2 Adhesive types ............................................................................................................................................... 47

5.5.3 The importance of glass transition temperature (T ) ..................................................................... 49

5.5.4 Epoxy cure schedule .................................................................................................................................... 51

5.5.5 Usability............................................................................................................................................................ 53

5.5.6 Qualification ................................................................................................................................................... 57

5.6 Connector preparation ............................................................................................................................... 57

5.6.1 Dry fitting ......................................................................................................................................................... 57

5.7 Attachment of fibre to the terminus ...................................................................................................... 59

5.7.1 Application of adhesive .............................................................................................................................. 59

5.7.2 Inserting Fibre ‘Best-Practice’ .................................................................................................................. 62

5.8 Adhesive cure ................................................................................................................................................. 66

5.8.1 General .............................................................................................................................................................. 66

5.8.2 Orientation ...................................................................................................................................................... 66

5.8.3 Curing equipment ......................................................................................................................................... 67

5.9 Excess Fibre removal ................................................................................................................................... 71

5.9.1 General .............................................................................................................................................................. 71

5.9.2 Post-cure rough cleaving ............................................................................................................................ 71

5.9.3 Pre-cleave ........................................................................................................................................................ 73

5.9.4 Safety ................................................................................................................................................................. 73

5.9.5 Cleaving tools ................................................................................................................................................. 73

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SIST EN 4533-001:2020
EN 4533-001:2020 (E)

5.9.6 Sprung blade hand tools ............................................................................................................................ 74

5.9.7 Cleaving fibres in Multi-fibre Ferrules ................................................................................................. 75

5.10 Polishing .......................................................................................................................................................... 75

5.10.1 Rationale ......................................................................................................................................................... 75

5.10.2 Performance metrics .................................................................................................................................. 75

5.10.3 End face geometries .................................................................................................................................... 75

5.10.4 End-face geometry parameters ............................................................................................................... 76

5.10.5 Polishing stages ............................................................................................................................................ 86

5.10.6 Methods for controlling end-face geometry ..................................................................................... 100

6 Beginning of life Inspection .................................................................................................................... 106

6.1 Optical or Visual Inspection ................................................................................................................... 106

6.2 Interferometric Inspection ..................................................................................................................... 109

6.2.1 Inspection and Pass/Fail Criteria ......................................................................................................... 110

Bibliography ............................................................................................................................................................... 113

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SIST EN 4533-001:2020
EN 4533-001:2020 (E)
European foreword

This document (EN 4533-001:2020) has been prepared by the Aerospace and Defence Industries

Association of Europe — Standardization (ASD-STAN).

After enquiries and votes carried out in accordance with the rules of this Association, this document has

received the approval of the National Associations and the Official Services of the member countries of

ASD, prior to its presentation to CEN.

This document shall be given the status of a national standard, either by publication of an identical text

or by endorsement, at the latest by August 2020, and conflicting national standards shall be withdrawn

at the latest by August 2020.

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. CEN shall not be held responsible for identifying any or all such patent rights.

This document supersedes EN 4533-001:2006.

According to the CEN-CENELEC Internal Regulations, the national standards organisations of the

following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia,

Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland,

Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of North

Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United

Kingdom.
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SIST EN 4533-001:2020
EN 4533-001:2020 (E)
Introduction
a) The Handbook

The purpose of EN 4533 is to provide information on the use of fibre optic components on aerospace

platforms. The documents also include best practice methods for the through-life support of the

installations. Where appropriate more detailed sources of information are referenced throughout

the text.

The handbook is arranged into 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, cleaning and inspection.
b) Background

It is widely accepted in the aerospace industry that photonic technology offers 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). Significant weight savings can also be realized in comparison to electrical harnesses

which may require heavy screening. To date, the EMI issue has been the critical driver for airborne fibre-

optic communications systems because of the growing use of non-metallic aero structures. However,

future avionics 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 sensor for monitoring aerostructure.

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 leads 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. This situation is changing with the adoption of more

standardized (telecoms type) fibre types in aerospace cables and the availability of more ruggedized

COTS components. These improved developments have been possible due to significant research

collaboration between component and equipment manufacturers as well as the end users air framers.

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SIST EN 4533-001:2020
EN 4533-001:2020 (E)
1 Scope
1.1 General

Part 001 of EN 4533 examines the termination of optical fibre cables used in aerospace applications.

Termination is the act of installing an optical terminus onto the end of a buffered fibre or fibre optic

cable. It encompasses several sequential procedures or practices. Although termini will have specific

termination procedures, many share common elements and these are discussed in this document.

Termination is required to form an optical link between any two network or system components or to

join fibre optic links together.

The fibre optic terminus features a precision ferrule with a tight tolerance central bore hole to

accommodate the optical fibre (suitably bonded in place and highly polished). Accurate alignment with

another (mating) terminus will be provided within the interconnect (or connector) alignment

mechanism. As well as single fibre ferrules, it is noted that multi-fibre ferrules exist (e.g. the MT ferrule)

and these will also be discussed in this part of the handbook.

Another technology used to connect 2 fibres is the expanded beam. 2 ball lenses are used to expand,

collimate and then refocus the light from and to fibres. Contacts are not mated together. It helps reducing

the wear between 2 contacts and allows more mating cycles. This technology is less sensitive to

misalignments and dust. Losses are remaining more stable than butt joint contact even if the nominal

loss is higher.

NOTE Current terminology in the aerospace fibre optics community refers to an optical terminus or termini.

The term optical contact may be seen in some documents and has a similar meaning. However, the term contact is

now generally reserved for electrical interconnection pins. The optical terminus (or termini) is housed within an

interconnect (connector is an equivalent term). Interconnects can be single-way or multi-way. The interconnect or

connector will generally house the alignment mechanism for the optical termini (usually a precision split-C sleeve

made of ceramic or metal). The reader should be aware of these different terms.

An optical link can be classified as a length of fibre optic cable terminated at both ends with fibre optic

termini. The optical link provides the transmission line between any two components via the optical

termini which are typically housed within an interconnecting device (typically a connector) with tight

tolerancing within the alignment mechanisms to ensure a low loss light transmission.

Part 001 will explain the need for high integrity terminations, provide an insight into component

selection issues and suggests best practice when terminating fibres into termini for high integrity

applications. A detailed review of the termination process can be found in section 4 of this part and is

organised 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 very difficult. Therefore, this handbook concentrates on

the common features of most termination practices and 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.

It is noted that the adhesive based pot-and-polish process is applicable to the majority of single-way fibre

optic interconnects connectors and termini for multi-way interconnects and connectors. They share this

commonality.
---------------------- Page: 9 ----------------------
SIST EN 4533-001:2020
EN 4533-001:2020 (E)
1.2 Need to high integrity terminations

In order to implement a fibre optic based system on an aircraft it is vital to ensure that all 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. Interconnects are a key

component in any fibre optic system or network. Digital communications links, sensor systems,

entertainment systems etc. all require interconnects both at equipment interfaces and for linking cables

and harness sections together over the airframe.

Interconnects need to be robust to mating and demating operations, environmental changes and also the

effects of contamination. They need to be amenable to inspection and cleaning for through life support.

The choice of technology used in optical links and connections is mainly dependant of the environment.

In service performance is a pillar in the component selection. Cable to connector interface needs to be

assessed to prove the effectiveness of the solution.

High integrity terminations are required to ensure reliable, low loss light transmission through the

interconnection. High integrity terminations are produced by observing best practice and using the

correct materials, tools and procedures with appropriate controls.
2 Normative references

The following documents, in whole or in part, are normatively referenced in this document and are

indispensable for its application. For dated references, only the edition cited applies. For undated

references, the latest edition of the referenced document (including any amendments) applies.

All interconnection technologies are taken in account in the context of the EN 4533-001.

EN 4533-002, Aerospace series — Fibre optic systems — Handbook — Test and measurement

EN 4533-003, Aerospace series — Fibre optic systems — Handbook — Looming and installation practices

EN 4533-004, Aerospace series — Fibre optic systems — Handbook — Repair, maintenance, cleaning and

inspection
3 Component Selection
3.1 Elements

It is important to recognise that a fibre optic termination, while appearing straightforward, is in fact a

complex interaction of the constituent elements such as: fibre, ferrule, 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.
The following sections discuss the key elements to the termination.
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SIST EN 4533-001:2020
EN 4533-001:2020 (E)
3.2 Fibre optic cables
3.2.1 General

There are many types of fibre optic cable on the market today. Cables are essentially assemblies that

contain and protect the optical light guide (used to carry the system light signal). The central light guide

is usually made from silica glass although other materials can be used. Glass is inherently strong

although it must be protected from external damage and other factors that could cause weakening

(generally moisture and fluid contamination in the presence of any defects and stress). The cable

provides the protective layers to the glass and generally also incorporates a strength member (this

element is important in the termination for providing strain relief) and a protective outer jacket.

For aerospace applications, most encountered cables will carry a single, central optical fibre (suitably

protected as discussed in the following sections). There can be variation in single fibre cable designs.

Some may be of tight jacket construction, some of loose jacket construction. Cables are also being

developed with many fibres contained within a protective tube construction. It is noted that many of the

cable designs used in terrestrial telecommunications and data communications will not be suitable for

aerospace use. This is generally due to environmental capability limitations often due to environmental

characteristics.
3.2.2 Cable construction
As mentioned in the introduction, the cable construction pr
...

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