EuroWire July 2015

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July 2015 35
The production of optical fibres is a single process that some
manufacturers have specialised in.
After the drawn fibre has been proof-tested and wound onto
reels, the fibre is coloured in a separate step and subsequently
processed to an optical cable in a loose tubing or tight buffering
line. During the production of optical fibre cables, one important
aspect is the protection of the fibre inside the cable.
Typically, optical fibre cables receive an outer insulation layer
made from PE as an outer protective coating. For this cable
type, the measurement of the wall thickness of the outer
insulation layer is usually necessary, especially with regards to
the eccentricity of the insulation layer. The measurement of the
diameter is naturally also of importance. However, a diameter
measurement alone is generally not sufficient.
The applied measuring technique for the measuring of the
diameter, wall thickness and eccentricity of optical fibre cables
also has to be applicable for ‘loose tube’, ‘fibre ribbon’, ‘loosely
bundled’ and ‘tight buffered’ cables. Furthermore, the measuring
technique should be independent of the shielding material
under the outer coating.
Inductive and optical measuring principles, as applied by the
Centerview 8010 and 8025, have proven their effectiveness for
the measuring of the eccentricity of cables with an electrical
conductor made from copper or aluminium. For larger
dimensions, measuring by means of X-ray is a process offering
continuous quality control during production. The applied
X-ray technology is convincing as no calibration is required for
different insulation materials or ambient conditions.
The devices of the X-Ray 6000 series are suited to the measurement
of optical fibre cables. The diameter, minimum wall thickness,
eccentricity and ovality are directly defined from the X-ray image.
The recording of the measuring values is carried out by an X-ray
sensitive image sensor within fractions of a second.
When the eccentricity of the wall thickness of the insulation
layer is non-critical and the focus lies on the compliance with
the specified average wall thickness, the diameter of the optical
fibre cables is measured online before and after the extruder
crosshead, and the average wall thickness is defined by the
difference of the measured values.
Generally the line speed is controlled for a singular insulation
layer and the extruder rpm for multi-layer extrusion. For an
optimum use of resources, an automatic allowance of material
shrinkage, resulting from the cooling of the insulation layer, is
recommended.
The applied measuring and control technology can only be
successful when it receives a high acceptance of the operator.
This implies that the workload of the operator is lightened and
that he can concentrate on other tasks.
Sikora AG – Germany Website:
Quality assurance for production of optical
fibres