EuroWire January 2017

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Technical article
January 2017 49
3 Raise the temperature to -2°C and
hold this temperature for one hour.
4 Raise the temperature to 65°C.
Maintain the temperature until the
water reaches 15°C. Then, return the
temperature to 23°C and hold the
temperature until the water reaches
23°C ±5°C.
At every stage of temperature cycling test,
record the attenuation of each fibre.
3.3 Results
After the test, attenuation changes of
all fibres are really small. The largest
attenuation values at -2°C are shown
in Figure 2 , at 1,310nm and 1,550nm
wavelengths respectively.
3.4 Additional test
Considering extremely cold weather
conditions, the temperature cycling
programme is changed and the above test
is repeated.
3.4.1 Temperature cycling programme (for
extremely cold weather)
1 Lower the temperature from 23°C
to -40°C within 30 minutes and
hold this temperature for 12 hours.
Perform attenuation measurement
2 Raise the temperature to 65°C within
30 minutes and hold it for 12 hours.
Perform attenuation measurement
3 Return the temperature to 23°C
within 30 minutes and hold this
temperature for 12 hours. Perform
attenuation measurement
3.4.2 Results (for extremely cold weather):
During the test, attenuation changes of all
fibres are also small and the OTDR curves
are very smooth. The test results at -40°C
should be the worst. Therefore, the largest
attenuation values at -40°C in Figure 3
are displayed, at 1,310nm and 1,550nm
wavelengths respectively.
3.5 Analysis
After data process, it can be demonstrated
the largest fibre attenuation values in each
loose tube at different temperature points
during the above two tests, at 1,310nm
and 1,550nm wavelengths respectively, as
illustrated in Figure 4.
Considering the micro-duct is rarely full
of water and the actual temperature
change rate is much slower than that
in the experiments, the impact of ice in
micro-ducts on air-blown cables can be
regarded as insignificant.
Until all the above tests have been
finished, the cable is blown out of the
duct by compressed air. It shows that the
blowing performance of the cable is still
good and no visual damage to the cable
sheath has been found.
4 Test for water frozen
around end caps
This experiment is designed to study the
impact of freezing conditions on fibre
attenuation while water is frozen around
end caps. A 1.8km-long micro-duct
air-blown cable and 6m-long micro-duct
are used in this experiment. Move the
micro-duct to the middle of the cable and
record the distance from the test end of
the cable to the micro-duct.
4.1 Test procedures
First, seal one end of the micro-duct with
an end cap and fill water into the duct
until it is full of water. Then seal the other
end of the duct with another end cap and
keep two end caps at the same height.
Before the experiment, record the
attenuation of each fibre at room
temperature (23°C). After that, put the
cable into the temperature cycling
chamber to perform the temperature
cycling test.
4.2 Temperature cycling programme
1 Lower the temperature from 23°C
to -40°C within 30 minutes and
hold this temperature for 12 hours.
Perform attenuation measurement
2 Raise the temperature to 70°C within
30 minutes and hold it for 12 hours.
Perform attenuation measurement
3 Return the temperature to 23°C
within 30 minutes and hold this
temperature for 12 hours. Perform
attenuation measurement
4.3 Results and analysis
Check the end caps at -40°C. Some ice
can be found around them. Therefore, the
experiment has successfully simulated the
situation where water freezes around end
caps, as shown in Figure 5.
Pay much attenuation to the positions
where the end caps are located on the
attenuation curves during measurement.
All the OTDR curves are very smooth.
Figure 6 shows the largest attenuation
▲ ▲ Figure 2: OTDR graphs of the fibre with largest
attenuation values at -2ºC
▲ ▲ Figure 3: OTDR graphs of the fibre with the largest
attenuation values at -40ºC
▼
▼ Figure 4: Largest attenuation values in each loose
tube at different temperature points