Shielded wire grounding method
Shielded wire
Shielded cable shielding layer is mainly composed of copper, aluminum and other non magnetic materials made, and the thickness is very thin, far less than the using frequency of metal skin depth, shielding effect is not due to metal body itself on the electric field, magnetic field of the reflection and absorption of, but by shielding layer grounding generated, then to form different will directly affect the shielding effect. For the electric field and the magnetic field shielding layer, the grounding mode is different. Can be used non-grounding, single end grounding or double end grounding.
Single ended grounding:
1) the single end of the shielded cable is helpful to avoid the interference of the low frequency electric field. Or it can avoid the frequency interference of wavelength is far greater than the length of the cable L. L<λ /20
2) the single end of the cable shield can avoid the low frequency current noise on the shield layer. This current causes the common mode interference voltage in the interior and is likely to interfere with analog devices.
3) the single end of the shield is desirable for those sensitive to low frequency interference (analog circuit).
4) the upper and lower fluctuation of the continuous measuring value and the permanent deviation indicates show low frequency interference.
Double ended grounding:
1) to ensure that the cabinet or the plug (circular contact) connected through high conductive region (low inductance). It is better to choose metal than non metal on metal.
2) due to some analog modules using the pulse technology, it is recommended to shield the analog signals from each other to ensure the correct and other potential connection, only in this case, the two ends of the ground.
3) usually metal foil shielding layer of the transfer impedance is far greater than the braided copper wire shielding layer and the effect difference between 5-10 times and cannot be used for digital signal cable.
4) occasional failure of the function to indicate that there is a high frequency interference. This is the wire and other potential connection can not be eliminated.
5) except for the end of the cable, the shielding layer is advantageous to the ground.
6) will not shield connected to the pin, to avoid the "pig tail" phenomenon.
7) should always pay attention to the parallel impedance of the shielding layer should be less than the self impedance of 1/10. Cable tray, machine frame, other shield or other parallel cables to enable the system to achieve the potential.
8) if and when the shielding layer double end grounding cable shielding layer heating, or shielding layer when confronted by a cabinet shell or shielding bus ignition, which indicates that the potential connection is not reliable.

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