EoW January 2012

Technical article

Main effects Plot for Pair 2 % Dev Data Means

Ineraction Plot for Pair 2 % Dev Data Means

Mean

Mean of % Deviation fromTarget

Bow

▲ ▲ Figure 7 : Main effects plot of set points and lay length

▲ ▲ Figure 8 : Interaction plot of set points and lay length

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.

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.

Pair 1 Lay

Pair 2 Lay

Pair 1 Bow

Pair 2 Bow Pair 1 Pretwist

Pair 2 Pretwist

▲ ▲ Figure 9 : FFT of pair ratio showing signatures of both pairs as well as other effects such as the cabler equipment

Cabler bow signature

Takeup Spool signature

▲ ▲ Figure 10 : FFT signature of cabling bow and takeup spool

84

EuroWire – January 2012