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EuroWire – March 2011
120
technical article
The GR-20 specification is as follows:
a) Loose tubes stored in a pedestal or
closure shall be capable of having a
minimum of 14ft of expressed buffer
tube stored in a pedestal or closure.
b) No greater than 0.15 dB average
attenuation increase at 1,550nm on all
fibres, during and after the last cycle.
Table 2
is an outline of these tests.
4 PE-90 as compared
to GR-20 and
FOTP-244 test results
4.1 20-ft PE-90 compared to 14-ft
FOTP-244 tube exposure
The current specifications outlined in
sections 2 and 3 have multiple differences
between them, as noted. This section
compares methods defined in the
PE-90 and GR-20 (referencing FOTP-244)
documents by comparing the resulting
attenuation loss using identical seg-
ments of cables from multiple cable
manufacturers.
Table 3
is a comparison of results generated
from testing identical cable samples to the
20-ft PE-90 method to the 14-ft FOTP-244
method. Four cable samples from two
different cable manufactures were tested
to both the five cycle PE 90 test method
and the two cycle FOTP-244 test method.
As can be seen in
Table 3
, the 20-ft PE-90
test consistently has higher maximum
attenuation changes at –40˚C than the
Telcordia GR-20/FOTP-244 14-ft test. The
magnitude of this attenuation increase is
seen to be in the range of two times higher
for the PE-90 method and specification.
As will be shown in the next section, the
main contributor to this attenuation loss
difference is the expressed tube length.
4.2 PE-90 as compared to FOTP-244
method
In order to better understand the
difference between the test methods of
PE-90 and FOTP-244, a 20-ft mid-span test
was completed on six different cables, to
each test method. The six cables that were
tested came from three different cable
manufacturers.
The 20-ft PE-90 test method and 20-ft
FOTP-244 method generally result in
similar fibre attenuation changes, as can
be seen in
Figures 1
and
2
.
Figure 1
shows the average attenuation
increases and
Figure 2
shows the maximum
attenuation increases. Out of the six cables
tested, four resulted in greater attenuation
loss with the FOTP test method over the
fifth cycle PE-90 method. While there
is variation in the results using the two
methods, when applying the RUS limit
of 0.1 dB maximum and 0.05 dB average,
the cable types generally result in either
passing or failing results regardless of the
method.
5 The effect of the
number of cycles
5.1 Cycles and maximum attenuation
peaks
The PE-90 test requires that the last of
at least five cycles be measured and
evaluated. As can be seen in the multiple
cycle PE-90 test data in
Figures 1
and
2
,
the greatest attenuation increases may
not necessarily occur during the fifth cycle
and may occur anywhere from cycle two to
cycle five.
In
Figures 1
and
2
, three out of the
six cables tested show the greatest
attenuation increases between the second
and fourth cycles, not the fifth cycle. By
only measuring the last cycle, attenuation
increases that may occur in the field during
the first one or two seasonal temperature
extremes may be missed during testing.
5.2 The effect of increasing the number
of cycles
In order to better understand the effect
of mid-span test temperature cycles on
attenuation losses, three cables were
Maximum attenuation increase (dB)
Cable 1 Cable 2 Cable 3 Cable 4 Cable 5 Cable 6
Cycle 1
Cycle 4
Cycle 2
Cycle 5
Cycle 3
20ft draft FOTP-244
Cycle Type 3
Average attenuation increase (dB)
Cable Type 1
Cable Type 2
Cycle Cycle Cycle Cycle Cycle Cycle Cycle Cycle Cycle Cycle
1 2 3 4 5 6 7 8 9 10
Figure 2
▼
▼
:
20-ft PE-90 and 20-ft draft FOTP-244 midspan test comparison – maximum attenuation increase
Figure 3
▼
▼
:
20-ft PE-90 mid-span test with five additional cycles – average attenuation increase
abl T 3