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General Description
A fibre optic harness comprises a variable number of individual
light transmitting cables or lightguides, which may or may not
be of variable thicknesses and lengths. These individual lightguides
terminate at the light output end in a special metal ferrule
and at lightsource input all the lightguides are brought together
and bonded into a single common end.
Care of the common end
Where all the fibres come together at the common end for fixing
into the lightsource, the surface of the core glass is very highly
polished. This should remain protected at all times, as supplied,
prior to insertion when installation is ready to complete and
commission.
Bend tolerance of fibres
The glass fibre lightguides are clad in fire-retardant halogen-free,
megolon sheathing for general coherence and protection. Although
these lightguides are quite flexible, bending them too sharply
at any point can fracture some or all of the individual light
transmitting glass threads, which will in turn reduce or completely
obstruct the transmission of light from source to output. The
larger the active diameter of the transmitting glass bore, the
greater the bend radius that is required to avoid stress and
damage to the fibres. Fibres used in the Mini Track system will
require a free-bend radius of 25mm (standard) and 20mm (small).
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Weight and Impact Tolerance of Fibres
Due to the inherent fragility of fine glass threads, it is essential
that no heavy weight or pressure is applied to the lightguides,
and that they are not jolted, subjected to any impact or tightly
secured in a fixed location in any way. Care should be taken
to ensure that they are not left exposed where they might be
accidentally damaged,and in handling at all times during installation.
Elasticity of fibres
The glass fibres within the sheathing material have absolutely
no elasticity whatsoever. Undue tension can pull the glass fibres
away from the output ferrules, or break individual fibres themselves,
rendering the performance of the lightguides sub-standard. Additionally;
vibration and/or shift in building structures can: impose undue
tension stress on fibre if too tightly installed. Always ensure
that the lightguides are laid and held in place fairly loosely.
Tortional tolerance of fibres
Fibre optic lightguides have limited tortional tolerance. Where
a threaded ferrule is used at the output end of the lightguide
to locate within a threaded light output fitting, always rotate
the fitting onto the fibre. Do not twist or rotate the lightguide
into the fitting, as this will rapidly stress and break the individual
fibres. When ever possible, the output ferrule should be handled
rather than the fibre lightguide when locating fittings.
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General disposition of lightguides
All fibre optic lightguides are joined at the common end of the
harness, and their precise location within the common bundle
may or may not relate to their output allocation. Undue tangling
of lightguides at the common end can render free lengths too
short, and lead to the temptation to mishandle them. Always carefully
take individual light guides from source to output to avoid such
tangling. |
