Answers to four questions about the shielded Cabling System

Answers to four questions about the shielded Cabling System

In integrated wiring, two types of wiring are classified from the largest category: unshielded wiring and unshielded wiring. the unshielded wiring was first originated in Europe, it mainly adds a metal shielding layer to the external of a common unshielded wiring system. The principle is to use the emission, absorption, and skin effect of the metal shielding layer to prevent electromagnetic interference and electromagnetic radiation, the shielding system utilizes the balanced principle of twisted pair wires and the shielding effect of the shield layer. Therefore, the shielding system has very good electromagnetic compatibility (EMC) characteristics. In addition, the advantages of shielded wiring in electromagnetic compatibility are also gradually revealed. Currently, many countries in Europe, America, and North America have used this type of wiring.

The advantages of shielded cabling can help the rapid development of the Internet. Many large data centers use shielded cabling systems. Therefore, the use of shielded cabling systems is one of the main trends of network cabling in the future. Next, let's take a look at the problems related to shielding the cabling during network cabling.

First, what are EMC features?

EMC is electromagnetic compatibility. It refers to the ability of electronic devices or network systems to resist electromagnetic interference and prevent excessive electromagnetic radiation. That is to say, it is required that the device or network system work normally in a harsh electromagnetic environment, and that the electromagnetic waves cannot be excessively radiated to interfere with the normal operation of other equipment and networks.

2. How to measure performance differences between shielded and unshielded systems?

The advantage of the FTP cable shielding system is to provide better EMC performance than the UTP cable, 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, there are no performance indicators or test methods to express or compare EMC performance.

Third, the UTP cable is an ideal balanced transmission system. Why do FTP cables need to be used?

The UTP cable achieves EMC performance through a twisted pair of core wires, which means EMI is first received by the UTP cable and then 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. For more electromagnetic interference twisted pair, it will be ** done. So far, most actual network applications work at a frequency lower than 30 MHz.

In addition, the ideal balanced transmission system does not exist. The balanced characteristics of UTP cables are not only dependent on the quality of components (such as twisted pairs), but also on the surrounding environment. This is because the metal around UTP, concealed "Ground", pulling, bending, and other conditions will undermine its balanced characteristics, thus reducing EMC performance.

In fact, our installation cable is usually used to penetrate 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: grounding with multiple layers of aluminum foil on all core wires. 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 ** environment-independent. FTP integrates UTP's Balance Characteristics and Construction Flexibility and STP's shielding effect, that is, the perfect combination of balance and shielding principles.

4. What is the principle of shielding FTP cables?

Different from the balanced offset principle of twisted pair wires, the FTP cable adds one or two layers of aluminum foil to the outer of four pairs of twisted pair wires, the principle of reflection, absorption, and skin effect of metal on electromagnetic waves (the so-called skin effect refers to the distribution of electric currents in the conductor section tends to the conductor surface with the increase of frequency, the higher the frequency, the smaller the skin depth, that is, the higher the frequency, the weaker the electromagnetic wave penetration ability), effectively prevent external electromagnetic interference from entering the cable, and also prevent internal signal radiation at the same time, interfere with the work of other devices.

Experiments show that electromagnetic waves with frequencies greater than 5 MHz can only pass through 38 μm thick aluminum foil. If the thickness of the shield layer exceeds 38 μm, for example, the FTP cable of nexson is shielded by two layers of 25 μm thick aluminum foil, so that the frequency of electromagnetic interference that can pass into the cable through the shielding layer is below 5 MHz. The principle of twisted pair can be used to effectively offset low-frequency interference below 5 MHz.