Optical fiber cabling knowledge and precautions
Before carrying out optical fiber wiring, the requirements for laying optical cables must first be considered. Generally, optical cables must meet the following requirements:
The minimum allowable radius of curvature of the optical cable should not be less than 20 times the outer diameter of the optical cable during construction, and should not be less than 15 times the outer diameter of the optical cable after construction. When laying the optical cable, it is required that the traction force of the laid optical cable should not exceed 80% of the allowable tension of the optical cable, and the instantaneous maximum traction force should not be greater than the allowable tension of the optical cable. The main pulling force should be added to the strengthening member of the optical cable, and the optical fiber cannot directly bear the pulling force.
Optical Fiber Cabling
After understanding the basic requirements of optical fiber laying, the next step is to carry out optical fiber wiring. Optical wiring is usually divided into indoor wiring and outdoor wiring, and we will analyze them in detail below.
1. Optical cable classification and wiring knowledge
Indoor optical cables are mainly used in the laying of horizontal subsystems and vertical backbone subsystems. The laying of horizontal subsystem fiber optic cables is very similar to twisted pair cables, except that due to the poorer tensile properties of fiber optic cables, more care should be taken when pulling, and the radius of curvature should be larger. The vertical backbone subsystem optical cable is used to connect the equipment room to the distribution room of each floor, and is generally installed in the cable shaft or the ascending room. In order to prevent sagging or slipping, the optical cables must be firmly fixed at the top, bottom and middle of the channel on each floor. Usually, nylon cable ties or steel clips can be used for effective fixing. Finally, the linseed sealing material should be used to block and seal all the slots and pipe holes where the optical cables pass through in each floor of the building, and fire prevention measures such as adding fireproof materials should be taken to achieve the effect of moisture resistance and fire prevention. When laying the optical cable, an appropriate length should be reserved according to the design requirements. Generally, 5m-10m should be reserved at the equipment end, and it can be extended appropriately if there are special requirements.
The laying of outdoor optical cables can be divided into many types according to different environments. In environments such as long-distance trunk lines, local telephone relays, underwater and submarine communications, local area networks, and private networks, fiber optic wiring is selected in different ways, and the main laying methods are overhead, direct burial, pipeline, underwater, and indoor.
1. Aerial optical cable
Aerial optical cables are mostly used on utility poles. When laying overhead optical cables, the original overhead open wire poles can be used, which can save construction costs and shorten the construction period. However, overhead optical cables are located at high places and are vulnerable to natural disasters such as typhoon, ice, and floods. They are also vulnerable to external forces and weakening of their own mechanical strength. Therefore, the failure rate of overhead optical cables is higher than that of direct-buried and ducted optical fiber cables. There are two main methods of laying:
Suspension wire type: first fasten it to the pole with a suspension wire, then hang the optical cable on the suspension wire with a hook, and the load of the optical cable is carried by the suspension wire. Self-supporting type: A self-supporting optical cable is used. The optical cable is in the shape of "8", and the upper part is a self-supporting wire. The load of the optical cable is carried by the self-supporting wire.
2. Direct buried optical cable
Directly buried optical cable Directly buried optical cable is usually directly buried underground, which requires it to have the performance of resisting external mechanical damage and preventing soil corrosion. Depending on the soil quality and environment, the depth of the optical cable buried underground is generally between 0.8 meters and 1.2 meters. When laying, care must also be taken to keep the fiber strain within the allowable limits.
The laying of direct-buried optical cables requires trenching. The trenching standard is generally 1.2 meters for ordinary soil, 1.0 meters for semi-stone, and 0.8 meters for quicksand, and 1.2 meters for crossing railways and highways. The bottom of the trench should be padded with 10CM fine soil or Sandy soil, the width of the ditch bottom is generally 30CM. If two or more optical cables need to be laid, a distance of 5 cm should be kept between the optical cables. Steel pipes or hard plastic pipes should be pre-embedded in sections where the pavement surface is often under pressure. The laying optical cable should be laid in "S" shape when there is a slope, crossing railways, highways and other special sections.
3. Duct cable
Pipe laying is generally in urban areas, and the environment is not as harsh as overhead optical cables and direct buried optical cables, so there is no special requirement for the sheath of optical cables, and no armor is required. Before the pipeline is laid, the length of the laying section and the location of the connection point must be selected. When laying, mechanical or manual traction can be used. The traction force of a traction should not exceed the allowable tension of the optical cable. The material for making the pipeline can be selected from concrete, asbestos cement, steel pipe, plastic pipe, etc. according to the geography.
The city standard pipe hole size is generally ф90MM, which can accommodate 3 3-4 inch plastic sub-pipes. 1-inch sub-tube is suitable for optical cables with a diameter less than 20MM. It is easy to twist during the laying of the sub-tube. When the twist pitch is within 10 meters, the friction between the optical cable and the inner wall of the sub-tube will increase, which will bring certain difficulties to the laying of the optical cable. Therefore, laying plastic sub-tubes should be avoided. distortion. The laying of the pipeline optical cable must pass through the entrance and exit of the manhole. There are bends on the route, curves and the height difference of the pipeline manhole. The guide device is timely configured to reduce the friction of the optical cable and reduce the traction tension of the optical cable. The special tool "nylon rod" should be used in the optical cable pulling sub-tube, and it can be pulled by appropriate engineers and technicians. After the optical cable pulling is completed, the remaining cables in each manhole should be manually placed on the specified bracket. For future safety, hoses or PE hoses are generally used for protection, and fixed with cable ties. The end of the optical cable should be coiled with an appropriate length and hung on the wall of the manhole, and should not be soaked in water.
4. Underwater optical cable
Among these methods of laying optical cables, the environment for laying underwater optical cables is the most severe, so the techniques and measures for repairing faults are much more difficult. Generally, the underwater optical cable must be armored with steel wire or steel tape, and the structure of the sheath should be considered comprehensively according to the hydrogeological conditions of the river. For example, in stony soils, seasonal riverbeds with strong scouring, optical cables are subject to abrasion and high tension, not only thick steel wires are required for armoring, but even double-layer armoring is required. The construction method should also be selected according to the river width, water depth, flow velocity, river bed, flow velocity, and river bed soil quality.
Second, the skills and precautions of optical fiber wiring
Regarding the problem of fiber optic signal attenuation, it is mainly divided into two aspects: intrinsic attenuation and extrinsic attenuation. The intrinsic attenuation is determined by the material of the optical fiber, while the extrinsic attenuation is closely related to the construction process.
