Shielded cable is a transmission line that uses a metal mesh braided layer to wrap the signal line. The braided layer is generally red copper or tinned copper. Shielded cable is a wire with a metal braided shell specially used to reduce the impact of external electromagnetic fields on power or communication lines. This shielded cable also has the function of preventing the line from radiating electromagnetic energy outward. The shielding layer needs to be grounded, and external interference signals can be introduced into the ground by this layer.From some points of view, shielded twisted pair cable It is the core driving force to better promote the rapid development of the surrounding markets. https://www.linkcablecn.com
The shielding layer of the shielded wire is mainly made of non-magnetic materials such as copper and aluminum, and the thickness is very thin, which is much smaller than the skin depth of the metal material at the frequency of use (the so-called skin effect refers to the distribution of current in the conductor cross section tending 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 penetration ability of electromagnetic waves). The effect of the shielding layer is not mainly due to the reflection and absorption of the electric field and magnetic field by the metal body itself, but due to the grounding of the shielding layer. Different grounding forms will directly affect the shielding effect.
Shielding is divided into active shielding and passive shielding. The purpose of active shielding is to prevent the noise source from radiating outward, which is to shield the noise source; the purpose of passive shielding is to prevent sensitive equipment from being interfered by the noise source, which is to shield sensitive equipment. The shielding layer of the shielded cable is not allowed to be grounded at multiple points, because different grounding points are always different, and there is a potential difference between each point. If multiple points are grounded, current will be formed in the shielding layer, which will not only fail to play a shielding role, but also introduce interference. Especially in occasions where frequency converters are used frequently, the interference contains various high-order harmonic components, which have a greater impact and should be paid special attention to.
The shielded wiring system originated in Europe. It adds a metal shielding layer to the outside of the ordinary unshielded wiring system, and uses the reflection, absorption and skin effect of the metal shielding layer to achieve the function of preventing electromagnetic interference and electromagnetic radiation. The shielding system comprehensively utilizes the balance principle of twisted pair cables and the shielding effect of the shielding layer, so it has very good electromagnetic compatibility (EMC) characteristics. Electromagnetic compatibility (EMC) refers to the ability of electronic equipment or network systems to resist electromagnetic interference to a certain extent, and at the same time cannot generate excessive electromagnetic radiation. In other words, the device or network system is required to be able to work normally in a relatively harsh electromagnetic environment, and at the same time, it cannot radiate excessive electromagnetic waves to interfere with the normal operation of other surrounding devices and networks.
The shielding principle of shielded wire is different from the balanced offset principle of twisted pair. Shielded cable is to add one or two layers of aluminum foil on the outside of the four pairs of twisted pair wires, and use the reflection, absorption and skin effect of metal on electromagnetic waves to effectively prevent external electromagnetic interference from entering the cable, and also prevent the internal signal from radiating out and interfering with the work of other devices.