17-11-2012, 04:54 PM
Construction of Cable and Connectors
L-2 Construction of Cable.doc (Size: 1.31 MB / Downloads: 33)
CABLE CONSTRUCTION
Cabling is an outer protective structure surrounding one or more fibres. Cabling protects fibres environmentally and mechanically from being damaged or degraded in performance. Important consideration in any cable are tensile strength, ruggedness, durability, flexibility, environmental resistance, temperature extremes and even appearance. Evaluation of these considerations depends on the application.
Fibre Optic Cables have the following parts in common ;
(I) Optical Fibre
(II) Buffer
(III) Strength member
(IV) Jacket
Tight Buffer
The loose buffer uses a hard plastic tube having an inside diameter several times that of the fibre. One or more fibres lie within the buffer tube. As the cable expands and shrinks with temperature changes, it does not affect the fibre as much. The fibre in the tube is slightly longer than the tube itself. Thus the cable can expand and contract without stressing the fibre. The buffer becomes the load-bearing member.
The tight buffer has a plastic directly applied over the coating. This construction provides crush and impact resistance. It is more flexible and allows tighter turn radius. It is useful for indoor applications where temperature variations are minimum and the ability to make tight turns inside walls is desired.
Strength member :
Strength members add mechanical strength to the fibre. During and after installation, the strength members handle the tensile stresses applied to the cable so that the fibre is not damaged. The most common strength members are Kevlar, Armid Yarn, Steel and Fibre glass epoxy rods.
Kevlar is most commonly used when individual fibres are placed within their own jackets. Steel and fibre glass members find use in multifibre cable. Steel offers better strength than fibreglass but in some cases it is undesirable when one wishes to maintain an all-dielectrical cables. Steel attracts lightening whereas fibreglass does not.
Jacket
It provides protection from the effects of abrasion, oil, ozone, acids, alkali, solvents and so forth. The choice of jacket material depends on degree of resistance required for different influences and on cost.
The outer layers are often called the sheath. The jacket becomes the layer directly protecting fibres and the sheath refers to additional layer.
MULTIFIBRE CABLE :
It often contain several loose buffer tubes, each containing one or more fibres. The use of several tubes allows identification of fibre by tube, since both tubes and fibres can be colour coded. These tubes are stranded around a central strength member of steel or fibre glass rod. The stranding provides strain relief for the fibres when the cable is bent.