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EuroWire – January 2012
84
Technical article
In the FFT plot in
Figure 9
, the signatures are seen from both
pairs in the one plot. The FFT components previously mentioned
can be seen for primary lays, twinner bow speeds, and pretwist
ratios in both pairs. However, at lower frequencies there are
other signatures of interest. The measurement equipment is
also sensitive to mechanical variations in the manufacturing
equipment.
Figure 10
shows a strong component that is related to the bow of
the cabler. Also visible is a sloping signature that is believed to be
related to the rotation of the take up reel in the cabler. The slope
is due to the increase in the take up reel barrel diameter during
the run, decreasing the spool rotation rate.
The cabler bow speed is an extremely strong and steady signal
that is a measure of the effect on the cabler bow on the short
term cabling speed. For a perspective on the amount of cabler
induced variation, the pairs entering the cabler had an 8% peak
to peak variation in instantaneous speed. It is likely that much of
that speed change is accommodated by short term stretching
and relaxing of the pair.
2.2.2 NEXT Response for Various
Process Set Points
As mentioned in Section 2.1.4, without replication actual
statistical significance of performance cannot be determined.
However, repeated samples were taken from the trial to validate
qualitative findings noted below.
Distinct differences can be seen in some of the set points mainly
in the form of spikes in the NEXT graphs. At one combination of
pretwist ratio and bow speed an obvious spike appears in the
NEXT graph at 80 MHz. By changing only the pretwist ratio for
both pairs, this spike is reduced or eliminated.
At the opposite setting of bow speed, the change in pretwist ratio
has a similar effect on a spike that is seen at about 125 MHz.
3 Conclusion
As a result of this study there were a number of important
findings.
It has been shown that the high speed measurement technology
used in this study provides an accurate and repeatable method
for measurement of lay length value of twisted pairs.
The use of this technique over long lengths along with real
time data collection of the speed of the pair provides insight,
through FFT analysis, into the stability of, and patterns within, the
twinning process.
two pairs were run under constant process settings as control
points. The crosstalk interaction of the two pairs under study
was the primary point of interest although the interactions with
control pairs were also measured. Near End Crosstalk (NEXT)
measurements were swept to a frequency of 1.2 GHz.
2.2.1 FFT of the individual pair lays
at cabling
The basic form of the FFT graphs was consistent with what was
found at the rewind station also described in Section 2.1.3. In this
case, the FFT is performed on the ratio of two pairs measured
at cabling.
▲
▲
Figure 10
:
FFT signature of cabling bow and takeup spool
▲
▲
Figure 7
:
Main effects plot of set points and lay length
▲
▲
Figure 8
:
Interaction plot of set points and lay length
▲
▲
Figure 9
:
FFT of pair ratio showing signatures of both pairs
as well as other effects such as the cabler equipment
Pair 1 Lay
Pair 2 Lay
Pair 1 Bow
Pair 2 Bow Pair 1 Pretwist
Pair 2 Pretwist
Cabler bow signature
Takeup Spool signature
Main effects Plot for Pair 2 % Dev
Data Means
Ineraction Plot for Pair 2 % Dev
Data Means
Mean of % Deviation fromTarget
Mean
Bow