How to avoid ground loops in hybrid grounding of HMI (Human Machine Delivery) systems?

When implementing a hybrid grounding strategy in an HMI system, carefully designing grounding paths for different frequencies is crucial to avoid ground loops. Hybrid grounding combines the advantages of single-point grounding (better for low frequencies) and multi-point grounding (better for high frequencies). The basic principle is: low-frequency circuits, analog circuits, and sensitive signal circuits use single-point grounding to prevent ground current coupling; high-frequency circuits, digital circuits, and shielding layers use multi-point grounding to reduce high-frequency grounding impedance. The key to avoiding ground loops lies in the proper configuration and location of these grounding points. Typically, a main grounding point is designated, to which all single-point grounded circuits ultimately connect.

Parts requiring multi-point grounding are connected to the chassis or a complete ground plane via low-impedance paths. At I/O interfaces, signal ground may be connected to chassis ground via a ferrite bead or small capacitor. This provides low impedance grounding for high-frequency interference and near-open circuit for low-frequency signals, preventing low-frequency ground loops. Using a common-mode choke, such as the CMZ3225A-510T, connected in series on signal lines that might form loops can impede ground loop currents. Verifying the potential distribution and noise current path of the grounding network through simulation and actual measurement is an effective method to optimize the design and avoid potential loops.