1. The integrated wiring shielded or not shielded
The purpose of (1) block
Shielding system is to ensure that the transmission performance of electromagnetic interference environment system, the anti-jamming should include two aspects, namely, the ability to resist the electromagnetic interference and the system itself to the outside radiation ability of electromagnetic interference. For the latter, Europe through the electromagnetic compatibility test standard E M C code, but for the former, there is no quantitative standard stipulated in the external electromagnetic field and how strong the V/M should be used under the condition of shielding. Although in theory, a layer of metal on the cable and fittings appearance package material shielding layer, can effectively filter out unwanted electromagnetic wave (which is at present, most of the shielding system adopts the method), however, how far this method is effective?
(2) the gap between ideal and reality
For shielding system, only with a layer of metal shielding layer is not enough, more important is shield must be completely good grounding, in this way can the interference current effectively into the earth. Shielding system, however, the actual construction, there are some difficulties can not be ignored: due to the strict requirements shielding system docking, extremely easy to cause bad earth, such as grounding resistance is too large, and the imbalance of the grounding potential, so the transmission system of a certain will generate an electrical potential difference between two points, thus producing metal shielding layer on the current, caused by the discontinuity, the shield breaking its integrity. At this time, the shield itself has become one of the biggest interference sources, and its performance have far less than shielding system. Shielding wire in high frequency transmission, grounded on both ends of the need, this is more likely to generate an electrical potential difference on the shield. Thus, shielding the requirement of the system itself, but the biggest obstacle to ensure its performance.
A complete block systems require shielding everywhere, once any shield can't meet the requirements, is bound to affect the system's overall transmission performance. Also on the market at present, however, there are few hubs or the computer itself has shield support, so it is difficult to realize the whole transmission link of shielding.
(3) shielding and the shielding, which is more advanced
Current international (Europe, the United States between the two camps) shielding system and the shielding system exist advantages and disadvantages of the debate. Shielding system or the shielding system, largely depends on the consumption idea of integrated wiring market. Dominant in Europe is shielding system. In integrated wiring usage is the largest in North America, however, firmly implement the shielding system. Because of the shielding system or the block system, as long as it is a standard of perfect design and installation, can achieve satisfactory effect, but considering the factors such as price, easy when installation requirements, north American believe that under the condition of high capacity backbone and severe interference using optical fiber is more practical.
(4) advice to the user
In view of the domestic actual situation, we suggest that a user in the overall balance of various factors, it is necessary to carefully consider the following questions:
, the shield type 8 core plug is not standard, between different manufacturers of the plug/socket compatibility, block the effective degree and plug interface can remain stable for a long time and so on are not settled yet.
If improperly installed, shielding system, reach the overall integrity of shield, its performance will be less than the shielding.
, there are currently no effective shielding of the scene test.
UTP (not shielded twisted-pair cable), we think, is a mature, reliable, integrated wiring technology yu incarnation G pavilions squid mountain jain tip on Hun sweat fan ou fat cheng importance neon existing narrow Cheng out H curl fan retting wash Xi brake take medium osprey hydroxyl accidentally men convex Nai ray Qiong shade tail ash seeks the cangue le pepper m: coated tip on wei yan shade capsule out H curl existing no fat Fried Bi Xu cause female fan cattle ㄒ OARS benzene mail existing mold the faint gathering month Chang gorge cape 腅 MC requirements.
2. The shielding and the shielding of myth
When the UTP is applied on the structured cabling system and widely accepted world, some misconceptions about use shielded cable appeared, make the user feel confusion and upset.
Myth: when the frequency is higher than 30 MHZ, UTP cable fails to meet EMC requirements; Or when the frequency is higher than 30 MHZ, STP cable must be used.
Fact 1: Differential transmission Signal Spectrum (Differential Transmitted Signal Spectrum) and radioactive (Radiated Emission Performance) relationship depends on the following factors:
The design of the printed circuit board;
• output filters and magnetic properties;
• indicate the signal intensity;
• use of communication protocols;
Signal the balance (LCL);
Transfer, copper wire and the common mode impedance signal end indicate;
Effective shielding of the fittings.
Above error has nothing to do with the signal spectrum using shielding. SYSTIMAX SCS 384 a broadband video converter have been tested and ensure high high frequency to 550 MHZ, conform to the EMC standards.
Erroneous zone 2: FTP have all balance characteristic of UTP cable, cable and add additional shielding protection.
Fact 2: when a UTP cable with shield, the following things:
, shielding changed the whole cable capacitance coupling, thus attenuation increases;
Balance (L L C) degradation.
Balance the drop will cause strong stranded wire in the cable on coupled normal mode signal, thus caused strong coupling on the shield. Therefore, must have a good grounding. And completely shielded connectors must have the right terminal, otherwise the common mode signal can make the system emit radiation. When the frequency is increased, the situation is more serious.
Myth 3: shielded cable determines the EMC performance of the system.
Three facts: a shielding system just as its weakest EMC components. In the block system, the weakest link for hopping panel, connector information socket and equipment interface itself.
Myth 4: shielded cable can prevent at any frequency interference.
Fact 4: in the low frequency, the noise produced by shielded cable, at least with a shielded cable of the same high. 0.1 cm thick aluminum or copper shield, for example, in the 50 MHZ (power cable) can only provide about 1 db loss (this comparative with the effect of noise reduction 10%).
Myth 5: only shielded cable at one end grounding can be.
Five facts: only when the frequency is lower than 1 MHZ, this is the fact that when the frequency is higher than 1 MHZ, EMC judged it better grounding in multiple locations, generally at least should be grounded at both ends.
Myth: for security reasons, it is necessary to use shielded cable.
Fact 6: by the British government and a famous computer makers a cooperative study, computer security problem is mainly due to accidentally or caused by malicious staff (such as computer data thieves, computer viruses, unauthorized intrusion, etc.). Radiation caused by the VDUs and computer screen is bigger than radiation caused by the cable.
Myth: completely shielded cabling system installation, can use cheaper electronic hardware.
Fact seven: electronic hardware as chip price mainly depends on its production quantity. According to the world about the wiring system market statistical data analysis showed that UTP in twisted-pair cable market accounted for 82%, STP, FTP each accounted for 8%, thus UTP electronic hardware will be more economic.
In conclusion, based on the above facts, the awareness of a shielded cable is superior is untenable. User is impossible to know whether shielding performance of the system as its general, because at present there is no standard to test degree of shielding effective shielding system after installation. This is a big problem, it is difficult because of the shielding system installation, and metal foil shield cable on the installation or use in the future, it is easy to broken.