When the transmission distance of the signal line is relatively long, the potential of the two ground points may be different due to the different grounding resistances at both ends or the current in the PEN line. cause interference.
Therefore, in this case, one point is generally grounded, and the other end is suspended to avoid such interference.
Ground shielding at both ends is better, but signal distortion will increase.
Please note: The two layers of shielding should be mutually insulated and isolated shields! If not insulated from each other, it should still be regarded as a single shield!
The grounding of both ends of the outermost shield is to induce current due to the introduced potential difference, thus generating a magnetic flux that reduces the strength of the source magnetic field, thereby substantially canceling out the voltage induced without the outer shield.
And one end of the innermost shield is grounded, because there is no potential difference, it is only used for general anti-static induction. The following specifications are the best evidence!