The so-called "shielding" in the cable structure is essentially a measure to improve the distribution of electric fields. Wires with conductors wrapped around the outside of the conductor is called shielded wire. Conductor outside the conductor wrapped wire called shielded wire, wrapped conductor called the shield, generally woven copper mesh or copper berth (aluminum), the shield needs to be grounded, foreign interference signals can be imported into the earth by the layer.
Shielded cable is the use of metal mesh braided layer of the signal line wrapped transmission line, the braided layer is generally red copper or tinned copper. The shield layer of the shielded cable needs to be grounded, and foreign interference signals can be directed to earth by this layer.
Shielded wire is a wire with a metal braid shell specifically used to reduce the impact of external electromagnetic fields on power or communication lines. This shield also has the role of preventing the line from radiating electromagnetic energy to the outside.
Role: to avoid interference signals into the inner layer, conductor interference while reducing the loss of transmission signals.
Note: In the selection of shielded wire, the shield layer grounded conductor insulation layer has a conductive function, can be conducted with the shield layer (with a certain resistance).
Shielded cable shield is mainly made of copper, aluminum and other non-magnetic materials, and the thickness is very thin, much smaller than the skin depth of metal materials on the use of frequency, the effect of the shield is not mainly due to the metal body itself on the electric field, magnetic field reflection, absorption and generated, but due to the grounding of the shield generated, the grounding of different forms will directly affect the shielding effect. For electric field, magnetic field shield grounding way is different. Can be used without grounding, single-ended grounding or double-ended grounding.
Structure wrapped conductor called shielding layer, generally conductive cloth, woven copper mesh or copper (aluminum) platinum.
Ordinary cable: insulation layer + shield layer + conductor.
Advanced cable: insulation layer + shield layer + signal conductor + shield layer grounding conductor.
Application: shield layer needs to be grounded, foreign interference signals can be imported into the earth by the layer, to avoid interference signals into the inner conductor interference while reducing the loss of the transmitted signal. The role of the shield is to isolate the electromagnetic field noise source and sensitive equipment, cutting off the propagation path of the noise source. Shielding is divided into active shielding and passive shielding, active shielding purpose is to prevent the noise source outward radiation, is the shielding of the noise source; passive shielding purpose is to prevent sensitive equipment from being interfered with by the noise source, is the shielding of sensitive equipment.
Precautions for use: shield wire shield layer does not allow multiple grounding, because different grounding points are always different, there is a potential difference between the points. Such as multi-point grounding, the formation of current in the shield layer, induction to the wire to form a current, induction to the signal line to form interference, not only can not play a shielding role, but the introduction of interference, especially in the frequency converter with more occasions, interference contains a variety of high harmonic components, resulting in greater impact, special attention should be paid.