The function and principle of shield grounding
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For the signal cables running from the site to the cabinets, the shielding layer of these cables should be grounded at one end, connected to the instrument’s ground terminal; this is known as shielding grounding. What is the purpose and principle behind doing this?
There have been many discussions on this forum; to offer some insights, instrument grounding can be divided into two types: operational grounding and protective grounding. Working ground includes signal circuit grounding, shielding grounding, and intrinsically safe instrument grounding; protective grounding should be easy to understand. Work grounding is mainly used to prevent instrument signals from being interfered with. For more details, you can look up relevant information; I won’t go into it here.
Could you explain the principle of shield grounding to prevent signal interference?
Depending on the shielding purpose, shields can be divided into three types: electrostatic shields, magnetic shields, and electromagnetic shields. Electrostatic shield: Made of diamagnetic materials (such as copper, aluminum) and connected to ground. The function of an electrostatic shield is to terminate the electric field at the metal surface of the shield and transfer the charge to the ground. Magnetic shield: Made of strong magnetic materials with a very high magnetic permeability (such as steel), it can confine magnetic field lines within the shield. Electromagnetic shield: It is primarily used to suppress the effects of high-frequency electromagnetic fields. By inducing eddy currents within the shield, it causes reflections at the boundary between the shield and the space to be protected, thereby **reducing the intensity of the interference field in that space and achieving a shielding effect. Sometimes, to enhance the shielding effect, multi-layer shielding structures can be used; the outer layer is typically made of a material with high electrical conductivity to increase reflection, while the inner layer is made of a material with high magnetic permeability to enhance the eddy current effect. If holes or gaps appear in the shield, it will directly reduce the shielding effect. The higher the frequency, the more pronounced this phenomenon is.