There are different opinions on the single-end and double-end grounding of shielded cables on the Internet, which are summarized as follows:
Active shielding and passive shielding:
Active shielding: to prevent noise sources from radiating outward;
Passive shielding: to prevent sensitive equipment from being interfered with by noise sources.
Single-end grounding:
It can avoid frequency interference with wavelength λ much greater than cable length L (L＜λ/20).
The electrostatic discharge speed is the fastest unless there is strong external current interference.
When single-end grounding, the metal shielding layer at the non-grounded end has an induced voltage to the ground, and the induced voltage is proportional to the length of the cable, but there is no potential circulation through the shielding layer. Single-end grounding is to eliminate electromagnetic interference by suppressing the potential difference.
It is suitable for short lines, and the induced voltage corresponding to the cable length cannot exceed the safe voltage. Because the existence of electrostatic induced voltage will affect the stability of the circuit signal, it may sometimes form an antenna effect.
The signal current flows from the core wire into the shielded wire, and after flowing through the load resistor, due to the single-end grounding, the current returns to the signal source through the shielding layer, so the magnetic field interference generated cancels each other out, which can effectively resist the magnetic field coupling interference.
Double-end grounding:
The metal shielding layer will not generate induced voltage, but the shielding layer will generate shielding loop current under the influence of interference magnetic flux. If the potentials at both ends are not equal, a large potential loop current will be formed, which will have a canceling and attenuating effect on the signal.
The current flowing through the shielding layer is superimposed on the ground loop current, so it cannot completely offset the magnetic field interference generated by the signal current, and its ability to suppress magnetic field coupling interference is worse than that of single-end grounding.
Double-layer shielding:
The double-layer shielding separated by the insulation layer, the inner layer is single-end grounded, and the outer layer is double-end or multi-end grounded.
The inner layer single-end grounding does not form a potential difference, which is used to prevent electrostatic induction; the outer layer double-end grounding, due to the potential difference, induces current, generates a magnetic flux that reduces the source magnetic field strength, thereby basically offsetting the voltage induced by the absence of the outer shielding.
Cable trays can actually be used as outer shielding.
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Post time: Nov-18-2024
