How to design an industrial servo hybrid grounding system?

Servo systems often require hybrid grounding to balance low-frequency safety and high-frequency EMC performance. Audiotech's hybrid grounding design divides grounding into three categories: Protective Earth (PE), Shielded Ground (SHG), and Signal Reference Ground (SGND). PE is directly connected to the cabinet and equipment enclosure to ensure safety. SHG is used for cable shielding and filter housings, and is connected to PE at high frequencies via a capacitor (e.g., 1nF/Y1) near the noise source for low-frequency isolation.

SGND is the internal circuit ground, connected to SHG at a single point via a resistor (e.g., 10Ω) or a ferrite bead (PBZ1608A-102Z0T). The key is to clearly distinguish the areas of these three ground types within the PCB and cabinet to avoid unintentional connections. High-frequency noise is discharged from SHG to PE through the capacitor, while power frequency leakage current is blocked. A well-designed hybrid grounding system meets IEC 61140 protection against electric shock requirements, provides >20dB common-mode attenuation in the 30-200MHz range, and has a noise voltage of <10mV for the signal ground.