What are the reasons for shielding control cables?

I. What are the reasons for shielding control cables?
Control cables have an additional metal shield between the insulation layers, which has the appearance of an additional metal film layer that effectively shields signals and prevents interference. It also reduces the induced overvoltage in the event of a lightning strike. According to the use of the situation can improve the shielding performance requirements, the materials used are different: such as copper wire braided shielding, copper tape winding shielding, copper-clad aluminum wire braided shielding, aluminum-plastic composite tape winding shielding, copper wire sparse winding shielding, aluminum alloy wire braided shielding and so on. In order to ensure the continuity of the shielding layer and to reduce the transmission impedance of the shielding layer, it is usually necessary to place one or more annealed copper wires longitudinally in the shielding layer as evacuation wires for wrapping copper tape and aluminum-plastic composite tape. Shielding characteristics are usually measured by measuring the rejection factor (R) of the shield. Copper wire braided shield R = 0.07> Copper tape wrapped shield R = 0.02> Copper wire sparsely wrapped (plus reverse tie) R = 0.01 The main direction of the shielding current is the same as the helical direction of the copper tape, using the copper wire The shielding current flows through a shorter path and generates less heat, but by using a two-layer shield of copper tape, the cross-sectional area of the shield is increased, the current is reduced, and the amount of heat generated for is also reduced, and this also can shield the signal. Function. However, due to the 500mm2 current-carrying capacity da, so the electromagnetic field generated by itself is also da. When the short-circuit current exceeds a certain value, the effective cross-sectional value of the two-layer 0.12mm copper tape will not be able to reach the relatively da copper wire thinning winding. From the above considerations, copper wire thinning (plus reverse tie) thinning effect is much better than other shielding methods, and the continuity is also more reliable, so the use of copper thinning shielding.

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