Analysis of shielding technology in Integrated Wiring System

Overview of shielded twisted pair wires

Electromagnetic Waves with frequencies greater than 5 MHz can only pass through 38 μm thick aluminum foil. If the thickness of the shielding layer exceeds 38 μm, for exampleFTPThe cable is shielded with aluminum foil with a thickness of 25 μm, so that the frequency of electromagnetic interference that can enter the cable through the screen is below 5 MHz, the dual-twisting principle can effectively offset low-frequency interference below 5 MHz.

US Parkson bas victor system cat6 shielded cable

Transmission Media

WiringThe transmission media used by the system mainly include twisted pair wires and optical cables. Twisted Pair wires are composed of copper wires with two insulating protective layers. They are divided into unshielded twisted pair wires (UTP) and shielded twisted pair wires (STP). shielded twisted pair wires are divided into aluminum foil shielded twisted pair wires (FTP) and independently shielded twisted pair wires (STP ).

In system cabling, the use of shielded twisted pair wires or unshielded twisted pair wires remains controversial in the industry. Those who insist on the non-blocking view believe that the shielding system refers to the whole process of the system. It is a good idea in itself and can increase the signal transmission rate, but the installation standards are high and the investment is high; although shielding can resist noise interference and improve the transmission rate, the shielding effect of the entire system will be affected if you are careless during the wiring process, but the system performance will be reduced; the transmission bandwidth of Fully shielded cabling is lower than that of Multi-edge optical fiber at the same cost.

From the perspective of performance-to-price ratio, the horizontal cabling subsystem will remain unshielded in the world of twisted pair wires and optical fibers. Those who hold a blocking view believe that the blocking system can improve stability and high-quality transmission signals, provide high transmission bandwidth, and support high-speed network systems in the future, and increase the transmission distance. High construction requirements are a matter of professional installation companies. As long as they operate in strict accordance with the requirements of wiring specifications, they will provide users with a shielded wiring system.

The cabling system adopts unshielded twisted pair wires or shielded twisted pair wires. There are significant differences in the construction quality, construction period, and investment. The unshielded twisted pair wires are used in the unshielded system. The construction is simple, the quality standards are low, the construction period is short, and the investment is low. The shielding system uses shielded twisted pair wires, which have high requirements on the processing of the shielded layer. In addition to requiring that the shielded layer of the link cannot have breakpoints, the shielding channel must be completely shielded throughout the process.

From the current construction conditions, it is difficult to shield the whole process of the system. Therefore, objectively, designers are required to have an understanding of the technical indicators of unshielded twisted pair wires, shielded twisted pair wires, and optical fiber cables when selecting voice communication, data communication, and image communication transmission media. Voice communication: 3 categories or higher 100 Ω unshielded twisted pair wires; General Data Communication: 5 categories of 100 Ω unshielded twisted pair wires, 150 Ω shielded twisted pair wires; high-speed data communication: 2-core 62.5/125 μm optical fiber; Visual Communication: 5 categories of 100 Ω unshielded twisted pair wires, 2-core 62.5/125 μm optical fiber.

Balanced Transmission

The UTP cable achieves EMC performance through a twisted pair of core wires, which means that EMI is first received by the UTP cable before it is offset. However, as the frequency increases, the EMC performance of UTP will decrease. After measurement, it is found that the cable twisted pair can only meet the EMC performance of up to 30 MHz, and it will be powerless for higher electromagnetic interference. At present, most actual network applications work at a frequency lower than 30 MHz, and the ideal balanced transmission system does not exist. The UTP cable balance is not only determined by the quality of the components, such as twisted pairs), but also affected by the surrounding environment. This is because the metal around UTP, concealed "Ground", traction, bending, and other conditions will undermine its balanced characteristics, thus reducing EMC performance.

In fact, our installation cable usually inserts it into a metal catheter, plastic catheter, or other protection with different Grounding Impedance. Therefore, there is only one solution to achieve permanent ground-to-ground performance, and grounding is performed on all core wires with multiple layers of aluminum foil. Aluminum Foil protects the fragile twisted pair core wires and creates a balance environment for UTP cables. This means that the FTP cable-based shielding solution is independent of the environment, that is, it has nothing to do with the environment. FTP integrates UTP's Balance Characteristics and Construction Flexibility and STP's shielding effect, that is, the perfect combination of balance and shielding principles.

FTP and UTP Attenuation

FTP cable attenuation indicators fully comply with ISO/IEC11801, EIA/TIA568B and other related standards. If the UTP cable is put into a metal catheter, Its Impedance will decrease, resulting in increased attenuation. The effects of surrounding aluminum foil have been taken into account in the manufacturing process of FTP cables, and compensation has been made in the manufacturing process.

Transmission Distance of FTP and UTP

The transmission distance of the cable is determined by the attenuation and transmission delay of the cable, and is irrelevant to whether the cable is shielded. The most critical factor affecting the transmission distance is the transmission latency, which is determined by the NVP value of the cable: About 0.66 NVP of the common UTP cable, the NVP of UTP, FTP, and STP cables in US Parkson is about 0.68.

Radiation and grounding

The shielding performance of the system is determined by the performance of the worst part. the weakest part of the shielding system is the information outlet and the modular patch board in the Cabinet. The EMC performance can be improved through the following methods: away from interference sources, such as elevators, air conditioners, power equipment, fluorescent lamps, and mobile communication base stations. Information sockets and jumpers with EMC shielding are used. The cables are compared with information sockets and jumpers, cables are widely distributed throughout the building, and the surrounding electromagnetic environment is more complex and cannot be predicted and controlled. Therefore, the cable part is the most electromagnetic protection part in the entire wiring system.

The shielding principle of the FTP cable shows that the shielding layer is not grounded, and the shielding effect of the aluminum foil shielding layer is irrelevant to the grounding. However, if the grounding is poor, the FTP shield layer will become the interference source. As a passive product, the Integrated Wiring System does not produce electromagnetic radiation. However, if the grounding is poor, the shielding layer of the cable will absorb external electromagnetic interference and radiate outward after transmission. Of course, outward radiation also requires certain conditions, that is, the energy required by the radiation and the size of the antenna must be at the same order of magnitude as the wavelength of the electric wave. Only when the above conditions are met can the screen of the cable become a "potential antenna ". During the development and development of the Integrated Wiring System, the high-frequency Grounding problem has been fully taken into account to realize the large area surrounding grounding of the cable shield layer, avoiding the so-called "antenna effect ".

Measurement shielding

The advantage of the FTP cable shielding system is to provide better EMC performance than UTP cables, which is based on isolating the system from the external electromagnetic environment, because the external electromagnetic environment will affect the data transmission of the entire wiring system. So far, no performance indicators or test methods have been provided to express or compare EMC performance. However, the European standardization Commission CENELEC has begun this work. Coupling Attenuation is defined as an indicator for measuring EMC performance, which is also written into international Cabling Standards.

For more information about shielding technology in the cabling system, see the analysis of shielding technology in the integrated cabling system.

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