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In today's high-definition surveillance camera system applications, optical fiber is a way to provide the best bandwidth performance in all connection modes. When using optical fiber transmission systems, the image quality of the system is only limited by the three factors of the camera, the environment and the monitor, and the optical fiber transmission system can transmit the image picture to a very distant place without any distortion of the signal. It will not detract from the sharpness or detail of the picture. It can be said that the optical fiber transmission system is the lifeline of the entire monitoring system.
First, the type of fiber
The optical fibers are classified into indoor optical fibers, outdoor optical fibers, branch optical fibers, and distribution optical fibers according to different occasions. According to laying methods: Self-supporting overhead optical fiber, pipeline optical fiber, armored buried optical fiber and submarine optical fiber.
Divided by optical fiber structure: beam tube type fiber, layered stranded optical fiber, skeleton type optical fiber, clasp type optical fiber, ribbon type optical fiber, non-metal optical fiber and branchable optical fiber. Divided by purpose: optical fiber for long-distance communication, short-distance outdoor optical fiber, mixed optical fiber and in-building optical fiber;
Fibers can be classified into single-mode and multi-mode according to the transmission mode, and monitoring generally uses single-mode fiber.
Single-mode fiber: Optical fiber that transmits only one mode of optical signal. Conventionally, there are G.652, G.653, G.654, G.655, and other transmission class classifications. The transmission distance of single-mode fiber can reach several tens of kilometers. The single-mode fiber transmits only the main mode, which means that light is transmitted only along the inner core of the fiber. This completely avoids the mode dispersion and makes the transmission bandwidth of the single-mode fiber very wide. Therefore, it is suitable for large-capacity, long-distance optical fiber communication. The wavelength of light used by a single-mode fiber is 1310 nm or 1550 nm.
Multi-mode optical fiber: Optical fiber that can transmit multiple modes of optical signals, which is G.651 grade. It is divided into OM1, OM2, OM3 according to the optical mode, and the farthest transmission distance of multi-mode optical fiber transmits the 2 megahertz signal. In a multi-mode optical fiber, multiple modes are transmitted in an optical fiber at a certain operating wavelength. This kind of optical fiber is called a multi-mode optical fiber. Due to dispersion or aberration, the optical fiber has a relatively narrow transmission band and transmission capacity. Smaller, shorter distances.
Second, fiber laying methods and requirements
The conventional outdoor optical fiber is a container with a loose tube as the core, and is the most common fiber core laying method; the indoor optical fiber is usually tightly laid; the core of the large number of optical fibers is also combined in the form of a ribbon to lay fiber fibers. core.
Requirements for laying optical fibers: The bend radius of the optical fiber should be at least 15 times the outer diameter of the optical fiber, and should be at least 20 times during the construction process. When laying out the optical fiber, the rotation of the optical fiber tray should be synchronized with the deployment speed, and the speed of the optical fiber index is general. 15 meters per minute; when laying out the optical fiber, the optical fiber should be kept at a loose arc at the outlet of the optical disk, and the buffering margin should be reserved. It should not be too much to avoid fiber backs; the optical fiber must be reserved at both ends for a length of 5-10 meters. When laying optical fiber, labels should be made and the line should be filled; all optical fibers should not be exposed.
Third, the choice of optical core
The number of fiber cores is the number of glass fibers contained in each fiber. The following small series gives you some methods to determine the number of fiber cores.
First, the number of routing points in the layer is clearly known, the number of switches is calculated, and whether the connections between the switches are stacked or unstacked. If it is stacked and the core switch is dual-system hot standby redundancy, 6 cores are sufficient (2 cores each with 2 cores and 2 cores redundant). If you do not stack a switch to 4 cores, the number of switches is multiplied by 4 plus 4 cores of redundancy. (Note: Redundancy: as long as it is more than the use of, redundant is called redundant master and standby: one used, the other is exactly the same as the backup; hot backup: both at work; cold backup: the backup device is in standby mode.)
Experiences and practices: Each floor wiring closet (horizontal wiring cabinet), set up an optical fiber, generally six-core: two-core use, two-core spare, two-core redundancy; also use eight-core optical fiber. The standard minimum configuration is 2 cores per 48 points. Of course, 48 points can be selected for 4 cores, because 2 cores are the smallest units of fiber, and it is more appropriate to keep 2 cores as a backup.
The above is a description of how to determine the number of fiber cores. Everyone can find out. Backup can be chosen because of people, so the fiber out of the number of differences in the number of more, according to the selection of the election is only to ensure a minimum selection plus a backup core number on it.
Fourth, pay attention to
The selection of optical fiber is based on the number of optical fibers and the type of optical fiber, and the outer sheath of the optical fiber is also selected according to the use of the optical fiber. Attention should be paid to the following points when selecting the optical fiber:
1. When the optical fiber is directly buried outdoors, the armored optical fiber should be selected. When it is overhead, two or more black plastic outer sheathed optical fibers of the reinforcing ribs may be used.
2. The optical fiber used in buildings should pay attention to its flame-retardant characteristics when selected. Generally, in the pipeline and forced ventilation, the type of flame retardant and smoke can be selected. In the exposed environment, flame retardant, smoke-free and Non-toxic type.
In the vertical wiring in the third floor, the layered stranded optical fiber can be used; in the horizontal cabling type, the branching optical fiber can be selected.
4. Optional multi-mode fiber with a transmission distance of less than 2km; relay or single-mode fiber can be used for more than 2km.
The above are just a few of the issues considered from the application side, and they need to be flexibly implemented. In fact, the wiring environment is complex and diverse, and various problems may arise at any time. This requires us to strictly implement the wiring standards in planning and construction. When problems are encountered and the analysis is flexible, it will be resolved satisfactorily.
October 06, 2024