fault analysis for optical cables · 2010-04-10 · fault analysis for optical cables fo6 part 1...

$: Fault analysis for optical cables · 2010-04-10 · Fault analysis for optical cables FO6 Part 1 ... in a microfocus CT scan. fibre optics CT Consulting & Testing GmbH FibreOptics\Beratung\FO6\Part1$
fibre opticsCT Consulting & Testing GmbH

FibreOptics\Beratung\FO6\Part1 FO 6 Part 1 LWLK1 Slide1

Fault analysis for optical cables

FO6 Part 1 LWLK 1

The inner structures of an optical cable which has beenused in a particularly harsh environment are revealed in a microfocus CT scan



The first investigations were carried out on cut-out cable length, using the back scatter methodin the 1625 nm wavelength range

First the results were evaluated with specialsoftware, then the cable was divided into15 sections, based on sudden attenuationlosses or inhomogeneities.

Fault analysis carried out on optical cables employedas cable car and aerial cables



The second stage in the investigation was to determine actual cable excess length in relation to design type, with the aid of the MTS Kimmich measuring technology service.

The results of this measurement for 2 cable samples showed that there was excessivescatter distribution in both. This could cause inadmissible attenuation and PMDchanges in individual fibres in the case of temperature fluctuation.

1480 m

rel. fibre excess length Delta L in rel to MW (°/°°)Cable partially armoured, Lmess=39,20 m

-1,50

-1,00

-0,50

0,00

0,50

1,00

1,50

2,00

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Fibre No.

Del

ta L

/MW

L (°

/°°)

Überl.

rel. fibre excess length Delta L bez. auf MW (°/°°)Cable 1, length 1663,5-1535,3=128,20 m

-1,00

-0,50

0,00

0,50

1,00

1,50

2,00

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Fibre No.

Del

ta L

/MW

L (°

/°°)

Überl.




LWL 1 1625nm

-0,500

-0,300

-0,100

0,100

0,300

0,500

0,700

A B C D E F G H I J[Zyklus]

[dB

]

2pt Loss [dB]Ins. Loss [dB]Sollwert +0,05 [dB]Sollwert -0,05 [dB]

JIHGFEDCBACycle

/105,2[m]Length under stress

175017501750200200020014501000200[N]Pull. strength(2)

4 cyclesshutopen

13,313,3[m]Length under stress

20210022502000202500202000150020[N]Pull. strength(1)

Torsion under tensionFO-Test No. 1471

Cable tensile strengthFO-Test No. 1461Test

For the next stage, the testing samplewith the highest attenuation jump was chosen for the verification test forattenuation change and fibre elongation, "Cable tensile strength" in acc. with. EN 60794-1-2 Verf. E1 and "Torsion resistance under tension" sim. to Bellcore GR20 (R6-61). Theunarmoured cable was then tested withreference to the guideline value for„Pulling and stretching of the armouredcable„.

Diagram:Attenuation change (overview)after "Long-term tensile stress" and"Torsion under tensile stress" carriedout on Fibre 1 (average excess length)

Specified value +/- 0,1 dB under tensile stress

(1) load cell 20 KN E-End (2) load cell 5 KN A-End




8 L2

(F2) 5 KN (F1) 20 KN 8 L1

A

A

1539

1658 Twisted section 3 m Twisted length 13 m E

Test set-upCable tensile strength in acc. with IEC EN 60794-1-2 Method E1Torsion under tension, Bellcore GR 20

L1 Load end (20 KN load cellCable elongation 1)Inner metre measuring tape 1658,0 m; Counting direction = continual strandingtwist to the left.Length under tensile stress & torsion: 13 m

L2 Holding end (5 KN load cellCable elongation 2)Inner metre measuring tape 1539,5 m;Length under load 105 m

A Length under torsion / twisted length8 Fixed deflecting device 320 mm




After testing the tensile strength of the cable, a redlight source was used and a CT scan carried out onthe sample length (inner sheath removed).This made it possible to make the attenuationjump in the cable length visible as fibre compression. The picture shows testing section A (L1).

Picture:Fault detected "Fibre compression due to inhomogeneities of the core filling material" Specimen1 with metre number 1651,30

Fibre compression can be seen at thefault points marked

1 Fault identification marking(visible under red light)

2 Counting tube, marked as No. 63 Fibre compression in the "red"

counting tube (source of fault)4 Central GFK pulling & supporting

element




Picture:Fibre compression D1 red (3)in comparison with adjacentfibres and tubes D2 and D6 (2)




Picture:1 Optical fibre compression in the

red counting tube2 Optical fibre in tubes 2 or 6

Picture :Density variation in thetube filling material (side view) Picture :

Density variation in thetube filling material (seen from below)




Picture:Air trapped in tube D2

Picture:D2 Density variation

Cause: trapped airD6 Counting direction

marker (direction tube)




dead zone fibre

Determination of the fibre radius of curvature at 1625 nm at the point of compression (attenuation jump)a mandrel (4) of varying dimensions is positioned between two identical cable samples (2) taken fromthe test cable (2) and the optical fibre (2) looped around it through 360° (5) in the measuring directionof the OTDR-Meßrichtung (6), which positions it in front of the fusion splicer (3.2).

1 Radius 20,0 mm2 Radius 12,5 mm = 1,115 dB3 Radius 15,0 mm = 0,347 dB4 Radius 0,0 mm


dead zone fibre



Result of testing:

Fibre compression is pinpointed

The faulty section is removedfrom the tube sheath :TGA analysis "6,9% residue"resulting concentration of SiO2This led to malfunctioning underoperating conditions, due to theinfluence of segregationprocesses, heat, vibration etc. on the compressed fibre overlength.




A comparison of the FT-IR spectra of tube filling materials (plastic tube and metal tube)

Plastic tubeproduced in1998,filled with 3 optical fibres(aged under extreme conditions)

Metal tubeproduced in 2007/2008,filled with 30 optical fibres (not aged)

The FT-IR spektra images of the filling materials for plastic and metal tubes have been superimposed.Both exhibit the typical absorption bands of saturated hydrocarbons. The plastic tube filling material has two additional bands at 1106 und 812cm -1, which indicate thepresence of silicium dioxide (SiO2): these are not present in the spectrum of the metal tube filling material. The metal tube filling material has an additional band at 699 cm-1, which is not present in the spectrumof the plastic tube filling material.


Metal tube

Plastic tube

fault analysis for optical cables · 2010-04-10 · fault analysis for optical cables fo6 part 1...

Documents