EuroWire January 2016

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Technical article
January 2016 84
(oscillating) conductor prior to the extruder
crosshead. Picture 5 shows an ellipse type
distribution of the scatter plot, which can
happen, for example, when the conductor
is oscillating or vibrating in one direction
directly before entering the crosshead
and which therefore additionally causes
eccentricity variations.
This permanent rotation eccentricity
would also not be visible with a standard
presentation of eccentricity (as shown in
Picture 2).
In order to ensure a high measuring
accuracy of the conductor within the
insulation, the optical measurement axes
should be positioned at the same level as
the inductive sensors. In this positioning,
the optical paths are shaded by the
inductive sensors. For that reason, the
optical measuring planes are divided.
One optical measuring plane is arranged
before and one after the inductive sensor
plane. As a consequence, only an absolute
straight and horizontal conductor can
generate accurate measuring results.
In practice, however, slightly angled
positions or bends in the conductor
typically have to be expected. This means
that the measuring device has to be able
to record precise measuring values even
under these conditions.
Measurement of a
sloping position
of the cable
Picture 6 shows a cable running in
reference to a straight line. The cable,
however, is running in an inclined position
to the actual intended production line.
In the illustration, the inclined position
of the cable is exaggerated for a better
understanding. A straight or inclined
line, in this case a straight conductor,
is defined by two points. By means of
the first and second optical measuring
device, the sloping positions of the cable
will be identified and its influence on the
measuring results will be determined and
fully compensated.
Determination and
compensation of a sag
or bend of the cable
Picture 7 illustrates a cable that shows a
sag or bend. For a better understanding,
the illustration of the bend of the cable is
extremely exaggerated and, in practice,
not likely. The bend of a conductor can be
described by a circle, whose position and
curve radius is defined by three points.
With this information, the processor
system is able to calculate the exact
position of the cable in the inductive
measuring plane and to fully compensate
for the influence of angled position and/or
bends.
As shown in the picture, the measuring
system is built in a way that the position
of the cable is measured at four points,
shown in the illustration as P1, P2, P3 and
P4. Due to this, the measuring system is
able to detect even irregular deformations
of the conductor.
▲
▲ 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