EoW May 2009

technical article

While highly manoeuvrable, this vehicle is better suited for external vice internal inspections. With today’s technology, this was the most compact unit that could be built and still retain the sophisticated features described above. 5 Review of test results 5.1 CommScope Testing Standard outside plant cable testing was completed at the CommScope facility located in Claremont, NC. This testing was performed, not to qualify this cable for use as an everyday terrestrial cable or long haul oceanic cable, but in order to set a benchmark for future deep-sea fibre optic cable designs. The cable was subject to the most severe requirements set out in the ANSI/ICEA S-87-640-2006, the GR-20-CORE and the EN 187105 standards, and tested to failure under the general guidelines of these specifications. 5.1.1 Compression to failure The Telcordia GR-20 was the most stringent of the three standards, calling for 44N/mm of pressure over a one minute period and 22N/mm of pressure over ten minutes. A similar test was adopted by applying a specified load for a period of ten minutes, and then testing the attenuation of the cable at the end of that time period while the cable was still under load. The GR-20 standard had the most rigorous requirements for any increase in attenuation; therefore the GR-20 was the guideline that was followed. The standard stated that the change in attenuation should remain less than 0.05dB for 90% of the fibres under test and less than 0.15 for 100% of the fibres under test. The cable was crushed using a 25mm steel plate with rounded edges having a 10mm radius. A schematic of the test setup can be seen in Figure 7 .

Pressure (N/mm)

Delta (dB)

Pass/Fail

10 15 20 25 30

0.00 0.08 0.03 0.11 0.70

Pass Pass Pass Pass

Fail

Table 2 ▲ ▲ : Compression Test Results

Δ Attn.

Number of Impacts

Force (N.m)

Pass/Fail

1 1 1 1 1

0.1 0.2 0.3 0.4 0.5

0 0 0 0

Pass Pass Pass Pass

N/A

Fail

Table ▲ ▲ 3 : Impact Test Results

This procedure was repeated until a cable failure was achieved. The results of this testing can be seen in Table 3 . From these results it can seen that 0.4Nm is the maximum impact force that this cable could withstand. At 0.5Nm the cable was completely flattened with the broken fibre protruding from the side of the jacket. As a reference, standard outside plant is required to withstand an impact force of 4.4Nm, much higher than what the Deep-Sea ROV cable was capable of achieving. However, this cable will most likely be impacted under water; any falling object located underwater will move with much less velocity, hence much less force will be exerted on the cable. 5.1.3 Tensile to failure All three standards require a specific tensile load with the ICEA-640 and GR-20 standards calling for the highest short- term tensile load at 2670N. The EN-187105 calls for a short-term tensile load that is a factor of the cable’s weight. The mandrel diameter used on the bench was specified to be the most stringent in the GR-20 and ICEA-640 documents. These standards specify a maximum diameter of 560mm and a minimum of 30x the diameter of the cable. Testers utilised a mandrel diameter of 26mm for this test. According the ICEA-640 and GR-20 documents, a cable failure constitutes an attenuation increase of greater than 0.05dB at the 1,550nm wavelength and/ or a fibre strain greater than or equal to 60% of the fibre’s proof strain. Obviously, this test would not be approaching the specified loads, as the cable has a modulus of elasticity in the range of only 12kgf. Testers used an Instron® tensile bench with built-in extensometer to strain test this cable. The tensile bench was set up to run as slowly as possible, to allow for recording

Each of the pressures was performed twice in order to assure a passing or a failing result. The incompressible fluid within the cable may have attributed to the performance of this cable construction under a compressible load. 5.1.2 Impact to failure The EN-187105 standard required a specified impact force be applied once over three different sections of the cable. The ICEA-640 standard required a specified impact force be applied twice over three different sections of the cable. The GR-20 standard required a specified impact force be applied 20 times in one location on the cable. In a real underwater scenario an impact would most likely occur only one time in one location, therefore the GR-20 test procedure was followed. The GR-20 standard had the most severe requirements for any increase in attenuation; therefore the GR-20 was the guideline that was followed. Again, the standard stated that the change in attenuation should remain less than 0.05 dB for 90% of the fibres under test and less than 0.15 for 100% of the fibres under test. A schematic of the test setup can be seen in Figure 8 .

Figure 7 ▲ ▲

With every passing result, the load was increased. This procedure was followed until a cable failure was achieved. The results of this testing can be seen in Table 2 . As we can see from the results, the cable performed surprisingly well, considering that the requirement for a standard outside plant cable is 44N/mm.

Figure 8 ▲ ▲

The test cable was impacted with a specified force for the duration of one cycle. Once the impact was complete, the cable’s attenuation was tested.

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EuroWire – May 2009