Due to the short transmission distance of the monitoring cable, we recommend that the network cable for network monitoring should not exceed 90 meters. Even if it is 75-5 commonly used for analog monitoring, we also recommend that it should not exceed 500 meters. Therefore, for remote monitoring Monitoring requires optical fiber transmission. Next, we will briefly introduce the application of optical fiber in video surveillance projects from the following points.
Optical cables are divided into indoor optical cables, outdoor optical cables, branch optical cables, and distribution optical cables according to different use occasions.
Optical fibers can be divided into single-mode and multi-mode according to the transmission mode, so single-mode optical fibers are generally used for monitoring.
Single-mode optical fiber: An optical fiber that only transmits one mode of optical signals. Generally, there are transmission levels such as G.652, G.653, G.654, and G.655. Single-mode optical fiber transmits 100M signals. The distance can reach tens of kilometers.
Multi-mode optical fiber: An optical fiber that can transmit multiple modes of optical signals. It is G.651 grade. It is divided into OM1, OM2 and OM3 according to the optical mode. The longest transmission distance of multi-mode optical fiber can transmit 100M signals 2 kilometer.
Optical cable structure: 1. The most common optical cable structure is a layered optical cable. Optical cables with more than 12 cores generally have this structure. The optical cable cavity can accommodate multiple loose tubes to loosen the tubes. As the basic unit, each loose tube can accommodate 6-12 cores; the stranded optical cable is the central strengthening component, and the loose tube surrounds the central strengthening core.
For practical application, the fiber core needs to be covered with different colors, a total of 12 colors, and the number of loose tubes of the stranded optical cable is generally within 12, so the number of cores of the stranded optical cable Generally from 12 cores to 144 cores.
Little knowledge about optical fiber: 1. The tensile strength of optical fiber is very high, close to the tensile strength of metal; 2. The ductility of optical fiber (1%) is worse than that of metal (20%); 3. When optical fiber There are cracks, bubbles or debris in the memory, which are easy to break under a certain tension; 4. The optical fiber is easy to break due to rain, and the shear loss increases greatly; 5. At low temperatures, the loss increases as the temperature decreases; 6. The optical fiber needs to enhance its mechanical properties Protection requires waterproof protection to ensure transmission performance; wavelength: communication window for optical fiber communication optical signals, of which 850 and 1310nm are multi-mode optical fiber communication windows and short wavelength windows; 1310, 1550, 1640nm, etc. are single-mode optical fiber communication windows. is the long wavelength window.
Simplex: In communication, signals are only received but not sent, or only sent but not received. One-way communication is understood to mean that a single-core optical fiber only receives optical signals or only sends optical signals.
Duplex: Both receiving and sending signals, divided into half-duplex and full-duplex. Half-duplex can be understood as one optical core. After receiving the signal, the signal can be sent and fed back through the same core optical fiber, but at this time only It can send but not receive signals; while full-duplex still uses a single-core optical fiber, which can continuously send signals while receiving signals. The two communications of receiving and sending do not interfere with each other, usually through frequency division multiplexing, time division multiplexing, wave Implemented by multiplexing.
Characteristics of optical fiber transmission: the transmission distance is relatively long. Single-mode optical fiber can transmit 100M signals up to dozens of kilometers, and Gigabit signals can reach 5 kilometers.
And the use of optical fiber for long-distance transmission signal fidelity and picture clarity are not affected.
Optical fiber is not subject to electromagnetic, strong current and other interference during the transmission process, and has strong anti-interference ability.
Theoretically there is no limit to the bandwidth of optical fiber, so a single optical fiber with hundreds of cameras can completely guarantee the bandwidth. Therefore, the appropriate optical fiber transceiver must be selected according to the number of signal channels transmitted by the optical fiber. If there are less than 10 monitoring points, you can choose a 100M optical fiber transceiver. If there are more than 10 monitoring points, you need to choose a Gigabit optical fiber transceiver.
Optical fiber can be laid underground or overhead. When installing overhead, try to keep the height at 6-7 meters. When buried underground, it is recommended to dig a deeper trench, no less than 50cm.
