Discussion on the practical application of twisted pair wires in the Video Monitoring System

Source: http://tm.eefocus.com/bbs/article_1170_368066.html

I. Overview

Security systems play an important role in the Weak Current System of Modern smart buildings. In traditional design and construction, network cabling and security monitoring cabling are often considered separately. Due to the difference in the use of media, it is impossible for people to unify them well. However, with the increasing number of security monitoring sites in the building, the increasing number of coarse and hard coaxial cable cabling will occupy a large amount of pipeline resources, and the cabling is very difficult, moreover, the image quality may also decrease when the wiring length is too large.

Compared with ordinary highways, as a special type of expressway, it features good linetype, high design standard, large traffic flow, and fast driving speed. However, if advanced management measures are not adopted, traffic accidents and congestion may easily occur in the case of heavy traffic and bad weather. Therefore, it is essential to deploy a full-Process Monitoring System on some highways with extremely heavy traffic. These monitoring systems can implement traffic flow and traffic operation monitoring, conduct meteorological detection on key points, implement timely traffic control on key road sections, detect various abnormal conditions in a timely manner, and take emergency measures, ensure Expressway Operation and Management at high speed, safety, and cost.

With the increasing highway management requirements, toll management, data communication, and image monitoring are already an essential part of modern highway construction. The image monitoring system is mainly composed of a network video server as the core, as well as a camera, cloud platform, decoder, and other devices. The camera is set on toll channels, toll booths, and important road sections. It can monitor vehicle models, reduce vehicle detection equipment, and monitor the working conditions of toll collectors. The monitoring software can overlay Billing Data and date and time on vehicle-permitted images and archive video files to enable real-time monitoring or selectively review suspicious operators, it can supervise and manage the image informatization of paid jobs and provide creden。 for fraudulent behaviors. The monitoring software also displays images of multiple toll channels, toll booths, and important road sections at the same time, and records multiple images at the same time.

However, based on my years of experience in cabling, I realized that with the extension of distance, the main character of traditional cabling-coaxial cable is increasingly unable to meet the needs of construction and application. The starting point of the new cabling technology is to unify network cabling and Security cabling to a single platform as much as possible to reduce the difficulty and cost of cabling. In this Cabling Technology, image signals are transmitted using unshielded cables, such as Category 5 cables, which are widely used in network cabling and powered by spare wires in unshielded cables. To achieve this technology, two key devices are required: twisted pair wire Video Transmission Equipment and remote power supply equipment.

Ii. Basic principles of twisted pair wires for Video Signal Transmission

Video signals must be transmitted in twisted pair wires to solve two problems:Impedance MatchingAndAttenuation Compensation.

The standard video signal interface is generally75 Ω, non-equilibrium ModeWhile the twisted pair wires are100 Ω, balancing ModeIn this way, to transmit video signals with twisted pair wires, we need to try to solve the conversion problem of 75 Ω faster → 100 Ω and non-balanced → balanced. There are two ways to complete this conversion: one is to useTransmission TransformerIt does not require power supply, but it may cause some loss to the signal, and the drive capability is limited. The other is to use the active mode, throughBroadband amplifier and dedicated chipIt not only converts the impedance and the balancing mode, but also provides strong drive and compensation for image signal amplification. The disadvantage is that the power supply is required.

In addition, the video signal isHigh-frequency broadband signal with a bandwidth of 6 MHzIf it is transmitted directly in the twisted pair wire, the signal amplitude will be greatly reduced, and the monitor will show that the image color fades and the brightness fades. Therefore, video signals must be amplified and compensated for long-distance transmission over twisted pair wires to ensure image quality.

3. Advantages of twisted pair wires and twisted pair wires for Image Transmission

1. Twisted Pair wires

Twisted Pair wires (twisted pair wire) are the most commonly used transmission medium in integrated cabling. Twisted Pair wires are composed of two copper wires with an insulating protective layer. The two insulated copper wires are twisted together at a certain density to reduce signal interference, the electric waves emitted by each wire during transmission are offset by the electric waves sent from the other wire. Twisted Pair wires generally consist of 22 ~ The No. 26 insulated copper wires are wound together. If one or more pairs of twisted pair wires are placed in an Insulating Sleeve tube, the twisted pair cables are formed. In a twisted pair Cable (also known as a twisted pair cable), different lines have different twist lengths. Generally, the twist length ranges from 1cm to 14cm, and is twisted in a counterclockwise direction, the twist length of the adjacent line is above 7cm. Compared with other transmission media, twisted pair wires are limited in terms of transmission distance, channel width, and data transmission speed, but the price is relatively low.

Twisted Pair wires can be dividedShielded twisted pair wires (STP) and unshielded twisted pair wires (UTP)Two categories.

In addition, the twisted pair has three categories, four categories,Category 5, Category 5Or even 6 categories. The speed of the three types of twisted pair wires is 10 Mb/s, the speed of the five types of twisted pair wires can reach 100 Mb/s, and the rate of the five categories can reach more than 155 Mb/s. Only five or more category 5 wires can be mounted.100base-tx. Shield twisted pair wires because the outer layer of the cable has an aluminum mooring package to reduce radiation, making it more troublesome, and the price line is more expensive than the unshielded twisted pair wires, therefore, among the 10base-t or 100base-tx networks, we often use unshielded cat5e and cat5e twisted pair wires.

2. Advantages of twisted pair wires for Image Transmission

Twisted Pair wires are used in many industrial control areas that require large interference and long-distance transmission. Lan is also widely used with twisted pair wires, it has the advantages of strong anti-interference ability, long transmission distance, easy wiring, space saving, and low price. Currently, advanced technologies and dedicated chips are used to transmit high-quality image signals on twisted pair wires.

Easy wiring and high cable Utilization

One pair of unshielded twisted pair wires widely laid in smart buildings can transmit a channel of video signal. Because a category 5 cable contains four twisted pair pairs, four video images can be transmitted, this will undoubtedly greatly reduce the difficulty of wiring construction for buildings with many monitoring sites and intensive cabling. In addition, one pair of four pairs of twisted pair wires can transmit video signals, while others can also transmit audio signals, control signals, and power supplies, providing cable utilization, it avoids the trouble of separately wiring various signals, reduces the engineering cost, overcomes the difficulties of coaxial cable wiring and occupies many pipeline resources, and makes the types of Integrated Wiring more unified.

Strong anti-interference ability

Twisted Pair wires can effectively suppress common-mode interference. Even in a strong interference environment, twisted pair wires can transmit excellent image signals. For example, elevators, equipment rooms, and other places in buildings are subject to great interference. Buildings in downtown areas are also subject to various interference from the surrounding environment, the strong anti-interference capability of twisted pair cables is more advantageous than that of coaxial cables.

High reliability and ease of use

When using twisted pair wires to transmit video signals, a dedicated Transmitter must be connected to the front end and a dedicated receiver must be connected to the control center. This twisted pair transmission device is cheap, easy to use, and stable to work.

Overall Cost Reduction

Category 5 unshielded cables are widely used in smart building integrated wiring. Their prices are lower than those of coaxial cables. With the application of Category 5 cables in communication, the price will be further reduced, so the cost and convenience of using twisted pair wires are more prominent.

Real-time transmission and real-time monitoring

The image signal transmitted by twisted pair wires uses analog signal technology, which ensures the real-time performance of the monitoring system and allows real-time monitoring of on-site images in the control room.

Iv. Remote Power Supply

In the smart building security project, the power supply of cameras must be considered. The increase in the number of cameras complicate the power supply line. If camera power supply and image signal transmission can be considered in combination with network wiring, wiring resources will be greatly reduced and efficiency will be improved. In addition, if a new monitoring site is added to the connected building, it is more difficult to provide power to the camera.

The remote power supply device can use the spare twisted pair wires in Category 5 cables through the RJ45 interface to provide DC power to the camera within 1 or two hundred meters, the power supply and image signal of the camera can be transmitted in the same category 5 cable, solving the problem of centralized remote power supply of the camera.

According to the current requirements of the monitoring system and the development trend of the Integrated Wiring System, many manufacturers of Integrated Wiring products, based on its powerful technical advantages, such as commsbench, Simon Edison on, And rihai silk Integrated Wiring products of the company, the company has developed a series of products suitable for monitoring systems to welcome the arrival of the monitoring system twisted pair era, it is believed that in the near future, the Integrated Wiring System will no longer only serve the traditional voice and data network systems, and will increasingly occupy the important position of the transmission media in the weak current system.