I. Overview In the weak current system of modern intelligent buildings, the security system has a very important position. In traditional design and construction, network cabling and security monitoring cabling are often considered separately. Due to differences in the media used, people cannot unify them together. However, in the case of increasing security monitoring points in the building, the increase in the number of thicker coaxial cable wiring will take up a lot of pipeline resources, and the wiring is very difficult, and the length of the wiring will also cause image quality. decline. Compared with ordinary highways, as a special building expressway, it has the characteristics of good line shape, high design standards, large traffic flow, and fast driving speed. However, if advanced management measures are not adopted, traffic accidents and traffic jams are extremely likely to occur under heavy traffic and severe weather conditions. For this reason, it is necessary to deploy a full-range monitoring system on some highways with very large traffic. These monitoring systems can implement traffic flow and traffic operation monitoring, carry out meteorological detection on key points, implement timely traffic control on key road sections, find various abnormal situations in time and take emergency measures to ensure high-speed, safe and economical operation and management of expressways. With the continuous improvement of highway management requirements, toll management, data communication, and image monitoring have become an indispensable part of modern highway construction. The image monitoring system is mainly composed of a network video server as the core, as well as cameras, PTZ, decoders, and other equipment. The cameras are installed at toll passages, toll booths, and important road junctions. They can monitor vehicle types, reduce vehicle detection equipment, and monitor the work of toll collectors. The monitoring software can superimpose and display the charging data and the date and time on the image of the releasing vehicle, and record the video file, so that it can be used for real-time monitoring or selective review of suspicious operators, to realize the information management of the charging operation image, and to Provide evidence for cheating violations. The monitoring software can also display pictures of multiple toll channels, toll booths, and important road junctions at the same time, and record multiple related images at the same time. But based on the author's many years of wiring experience, I realize that with the extension of distance, the protagonist in traditional wiring, coaxial cable, is increasingly unable to meet the needs of construction and application. The starting point of the new wiring technology is to unify the network wiring and security wiring on one platform as much as possible, reducing the difficulty and cost of wiring. In this wiring technology, unshielded cables (such as category 5 cables) widely used in network wiring are used to transmit image signals, and the spare pairs in the unshielded cables are used to power the cameras. In order to realize this technology, two key equipments are used: twisted pair video transmission equipment and remote power supply. Second, the basic principle of twisted pair transmission video signal Two problems must be solved when the video signal is transmitted in the twisted pair: impedance matching and attenuation compensation. The standard video signal interface is generally 75Ω, unbalanced mode, and the twisted pair transmission is 100Ω, balanced mode, so the use of twisted pair transmission video signal must try to solve the conversion problem of 75Ω ↠→ 100Ω and unbalanced →→ balanced. There are two ways to accomplish this conversion: one is the passive method using a transmission transformer, which does not require power supply, but it will have a certain loss of signal, and the driving capacity is limited; the other is the active method, which uses a broadband amplifier and The special chip can not only complete the conversion of impedance and balance mode, but also provide strong driving and amplification compensation for the image signal. The disadvantage is that it needs power supply to work. In addition, the video signal is a high-frequency broadband signal with a bandwidth of 6MHz. If it is transmitted directly in the twisted pair, the amplitude of the signal will be greatly attenuated, and the color of the image will become lighter and the brightness will become darker on the monitor. . Therefore, if the video signal is to be transmitted over a long distance on a twisted pair, it must be amplified and compensated to ensure the image quality. Third, the advantages of twisted pair and twisted pair transmission image 1. Brief introduction of twisted pair Twisted pair wire, Twisted Pair wire, is the most commonly used transmission medium in integrated wiring projects. The twisted pair consists of two copper wires with an insulating protective layer. Twisting two insulated copper wires with each other at a certain density can reduce the degree of signal interference. The electric wave radiated by each wire during transmission will be cancelled by the electric wave emitted by the other wire. Twisted pair is generally made of two 22 to 26 insulated copper wires intertwined with each other. If you put one or more pairs of twisted pairs in an insulating sleeve, it becomes a twisted pair cable. In twisted pair cable (also called twisted pair cable), different pairs have different twist lengths. Generally speaking, the twist length is within 38.1cm to 14cm, twisted counterclockwise, adjacent pairs The twist length is more than 12.7cm. Compared with other transmission media, twisted pairs are subject to certain restrictions in terms of transmission distance, channel width, and data transmission speed, but the price is relatively low. Twisted pair can be divided into shielded twisted pair (STP) and unshielded twisted pair (UTP) two categories. In addition, twisted pairs are classified into categories 3, 4, 5, 5 and 6, etc. The rate of category 3 twisted pair is 10Mb / S, the rate of category 5 twisted pair can reach 100Mb / S, and the category 5 can reach 155Mb / s or more. Only Category 5 or category 5 can be used for 100Base-TX . Shielded twisted pair because the outer layer of the cable has a layer of aluminum wrap to reduce radiation, making it more troublesome, and the price line is more expensive than unshielded twisted pair, so we are commonly used in 10Base-T or 100Base-TX network It is unshielded category 5 and super category 5 twisted pair. Logic Comparators,Comparator Circuit Logic,Comparator Gate Logic,Comparator Circuit Digital Logic Shenzhen Kaixuanye Technology Co., Ltd. , https://www.icoilne.com