Shielding layer is a kind of wire with metal braid shell specially used to reduce the influence of external electromagnetic field on power supply or communication line. The shielding wire also has the function of preventing the line from radiating electromagnetic energy to a certain extent. In order to prevent the interference signal from entering the inner conductor and reduce the loss of transmission signal, the shielding layer of the cable needs to be grounded. Next, Zhujiang cable will talk about the function and principle of shielding layer grounding in detail!
Why grounding?
It is difficult to ensure that there is no potential difference between the grounding points at both ends. If there is a potential difference, there will be a weak current, so that the shielding layer actually becomes a grounding wire; When the shielded wire grounded at both ends works in the work site with serious high-frequency interference, the line capacitance formed between the shielding layer and the internal signal wire will be coupled to the signal circuit, which will seriously affect the misjudgment of the signal. It is clearly stated in various governors and instructions that the signal wire and shielded wire must be grounded at one end, and the grounding end should be on one side of the controller.

Shielding layer grounding usually means that one end of the cable shielding layer is connected with the equipotential grounding bar, and the other end is not connected; If both ends are grounded, a potential difference will be formed between the two grounding points, which will interfere with the signal transmission. How should they be grounded? There are two main types of grounding:
1. For earth grounding, first ensure the reliability of the main grounding body, the grounding resistance should be small, and keep away from the building lightning protection grounding and high distribution grounding system as far as possible. Ensure the equipotential of each grounding point. It is used for equipment shell grounding and double-layer shielding outer layer grounding. If it is determined that each grounding point is reliable and absolutely equipotential, multi-point grounding must be good.
2. Technical grounding (signal grounding) is mainly used for the second layer shielding grounding to reduce the signal distortion, because the signal ground is actually the zero potential ground of the working power supply of the electronic printing board and the zero point of the system signal power supply. The two layers of shielding shall be mutually insulated and isolated! If they are not insulated from each other, they shall still be regarded as single-layer shielding!

The grounding at both ends of the outermost shield induces current due to the introduced potential difference, so it produces magnetic flux that reduces the strength of the source magnetic field, so as to basically offset the voltage induced when there is no outer shield layer; One end of the innermost shield is grounded. Because there is no potential difference, it is only used for general anti-static induction.
When shielded cables are used, the shielding layer shall be equipotential connected at least at both ends. When the system requires equipotential connection only at one end, two layers of shielding shall be used, and the outer shielding shall be treated according to the above requirements. To prevent electrostatic interference, single point grounding must be adopted, whether it is one or two layers of shielding, because the electrostatic discharge speed of single point grounding is the fastest.

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