WCA March 2016

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Wire & Cable ASIA – March/April 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
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
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.
❍
❍ Picture 2: Standard presentation of
eccentricity
❍
❍ Picture 3 : Random type distribution of
the single values of the eccentricity
❍
❍ Picture 4: Ring type distribution of the
single values of the eccentricity
❍
❍ Picture 5: Ellipse type distribution of the
single values of the eccentricity