Fault analysis for optical cables

Transcription

1 FO6 Part 1 LWLK 1 Fault analysis for optical cables The inner structures of an optical cable which has been used in a particularly harsh environment are revealed in a microfocus CT scan FibreOptics\Beratung\FO6\Part1 FO 6 Part 1 LWLK1 Slide1

2 The first investigations were carried out on cut-out cable length, using the back scatter method in the 1625 nm wavelength range First the results were evaluated with special software, then the cable was divided into15 sections, based on sudden attenuation losses or inhomogeneities. FibreOptics\Beratung\FO6\Part1 FO 6 Part 1 LWLK1 Slide2

3 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 excessive scatter distribution in both. This could cause inadmissible attenuation and PMD changes in individual fibres in the case of temperature fluctuation m rel. fibre excess length Delta L in rel to MW ( / ) Cable partially armoured, Lmess=39,20 m rel. fibre excess length Delta L bez. auf MW ( / ) Cable 1, length 1663,5-1535,3=128,20 m 2,00 2,00 Delta L/MWL ( / ) 1,50 1,00 0,50 0,00-0,50-1, Überl. Delta L/MWL ( / ) 1,50 1,00 0,50 0,00-0, Überl. -1,50 Fibre No. -1,00 Fibre No. FibreOptics\Beratung\FO6\Part1 FO 6 Part 1 LWLK1 Slide3

4 [db] 0,700 0,500 0,300 0,100-0,100-0,300-0,500 LWL nm 2pt Loss [db] Ins. Loss [db] Sollwert +0,05 [db] Sollwert -0,05 [ db] A B C D E F G H I J [Zyklus] Specified value +/- 0,1 db under tensile stress For the next stage, the testing sample with the highest attenuation jump was chosen for the verification test for attenuation change and fibre elongation, "Cable tensile strength" in acc. with. EN Verf. E1 and "Torsion resistance under tension" sim. to Bellcore GR20 (R6-61). The unarmoured cable was then tested with reference to the guideline value for Pulling and stretching of the armoured cable. Test Cycle Pull. strength (1) Length under stress [N] [m] A 20 B 1500 Cable tensile strength FO-Test No C ,3 D 20 E 2500 F 20 G 2000 Torsion under tension FO-Test No H ,3 I 2100 J 20 Diagram: Attenuation change (overview) after "Long-term tensile stress" and "Torsion under tensile stress" carried out on Fibre 1 (average excess length) open shut 4 cycles Pull. strength (2) [N] Length under stress [m] 105,2 (1) load cell 20 KN E-End (2) load cell 5 KN A-End / FibreOptics\Beratung\FO6\Part1 FO 6 Part 1 LWLK1 Slide4

5 Test set-up Cable tensile strength in acc. with IEC EN Method E1 Torsion under tension, Bellcore GR 20 8 L2 (F2) 5 KN 1539 A (F1) 20 KN 8 A L1 L1 Load end (20 KN load cell Cable elongation 1) Inner metre measuring tape 1658,0 m; Counting direction = continual stranding twist to the left. Length under tensile stress & torsion: 13 m L2 Holding end (5 KN load cell Cable elongation 2) Inner metre measuring tape 1539,5 m; Length under load 105 m A Length under torsion / twisted length 8 Fixed deflecting device 320 mm Twisted section 3 m Twisted length 13 m 1658 E FibreOptics\Beratung\FO6\Part1 FO 6 Part 1 LWLK1 Slide5

6 After testing the tensile strength of the cable, a red light source was used and a CT scan carried out on the sample length (inner sheath removed). This made it possible to make the attenuation jump 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 the fault points marked 1 Fault identification marking (visible under red light) 2 Counting tube, marked as No. 6 3 Fibre compression in the "red" counting tube (source of fault) 4 Central GFK pulling & supporting element FibreOptics\Beratung\FO6\Part1 FO 6 Part 1 LWLK1 Slide6

7 Picture: Fibre compression D1 red (3) in comparison with adjacent fibres and tubes D2 and D6 (2) FibreOptics\Beratung\FO6\Part1 FO 6 Part 1 LWLK1 Slide7

8 Picture: 1 Optical fibre compression in the red counting tube 2 Optical fibre in tubes 2 or 6 Picture : Density variation in the tube filling material (seen from below) Picture : Density variation in the tube filling material (side view) FibreOptics\Beratung\FO6\Part1 FO 6 Part 1 LWLK1 Slide8

9 Picture: D2 Density variation Cause: trapped air D6 Counting direction marker (direction tube) Picture: Air trapped in tube D2 FibreOptics\Beratung\FO6\Part1 FO 6 Part 1 LWLK1 Slide9

10 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 from the test cable (2) and the optical fibre (2) looped around it through 360 (5) in the measuring direction of the OTDR-Meßrichtung (6), which positions it in front of the fusion splicer (3.2). dead zone fibre dead zone fibre 1 Radius 20,0 mm 2 Radius 12,5 mm = 1,115 db 3 Radius 15,0 mm = 0,347 db 4 Radius 0,0 mm FibreOptics\Beratung\FO6\Part1 FO 6 Part 1 LWLK1 Slide10

11 Result of testing: Fibre compression is pinpointed The faulty section is removed from the tube sheath : TGA analysis "6,9% residue" resulting concentration of SiO 2 This led to malfunctioning under operating conditions, due to the influence of segregation processes, heat, vibration etc. on the compressed fibre overlength. FibreOptics\Beratung\FO6\Part1 FO 6 Part 1 LWLK1 Slide11

12 A comparison of the FT-IR spectra of tube filling materials (plastic tube and metal tube) Plastic tube produced in1998, filled with 3 optical fibres (aged under extreme conditions) Metal tube produced in 2007/2008, filled with 30 optical fibres (not aged) Plastic tube Metal tube 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 the presence of silicium dioxide (SiO 2 ): 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 spectrum of the plastic tube filling material. FibreOptics\Beratung\FO6\Part1 FO 6 Part 1 LWLK1 Slide12