WCA March 2016

Moreover, measuring values with tight tolerances are of significant importance for the assembly. Each of these values influence the wave impedance (eg twisted LAN-cables) and consequently the value for the Structural Return Loss (SRL) of a data transfer cable, especially when deviations of these values occur periodically. With the help of the Fast Fourier- Transformation (FFT), the high scan rate of 2,500 measurements/ second is suitable for creating a forecast for the SRL in dependence of the transmission frequency even at line speeds of 3,000 metres/minute for both current and future CAT-specifications. If a specification is given concerning the minimum wall thickness for the cable insulation, then any eccentricity leads inevitably to an increased consumption of insulation material. Therefore, eccentricities should be reduced for economic reasons. Recording of oscillating eccentricity values With a scan rate of 2,500 measurements per second, the measuring system records oscillating eccentricity values with high single value precision. These are visualised in form of a scatter plot ( Pictures 3, 4 and 5 ). The scatter plot provides an additional way to visualise the ongoing measurement at processor-based display and control devices, and with its help, the distribution of short-term variations of the eccen- tricity can be shown graphically. Each dot represents a single value of the eccentricity concerning value and direction. The overall distribution of the scatter plot highlights the standard deviation of the eccentricity. It is often sufficient to amend the guiding of the conductor close to the cross head in order to avoid these oscillations, which usually occur within a certain speed range and/or certain filling degrees of the coiler or decoiler, respectively. The standard way of representing

❍ ❍ Picture 2 : Standard presentation of eccentricity

❍ ❍ Picture 3 : Random type distribution of the single values of the eccentricity

❍ ❍ Picture 5 : Ellipse type distribution of the single values of the eccentricity

❍ ❍ Picture 4 : Ring type distribution of the single values of the eccentricity

shadows the outer diameter and the ovality are calculated. The measuring values of the outer diameter, if required in combination with the conductor diameter (the wall thickness), are suitable to amend the output capacity of the extruder or the haul-off speed of the cable in such a way that the measuring values are set to the respective nominal value.

eccentricity using a cross-section of the cable ( Picture 2 ) is additionally helpful for the operator when centring the crosshead. Picture 3 shows a random type distribution of the single values of the eccentricity, while Picture 4 shows a ring type distribution of the eccentricity values, which is often

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Wire & Cable ASIA – March/April 2016