How to isolate the interface ground and power ground of an HMI (Human Machine Interface)?

Isolating the HMI interface ground and power ground is to prevent high-noise current from the power circuit from entering sensitive signal interface circuits. Power ground typically carries high-current, high-noise ground currents from switching power supplies and motor drives; interface ground serves as the reference ground for communication port signals such as RS485, Ethernet, and USB. Physical isolation is the most effective method, which involves separating the ground planes of the two circuits using copper-free areas during PCB layout. After isolation, specific devices are needed to connect the two circuits, providing a bypass path for electrostatic discharge or high-frequency noise while blocking low-frequency noise.

Commonly used isolation devices include: 0Ω resistors or ferrite beads for single-point DC connections, although ferrite beads offer some isolation against high frequencies; safety Y capacitors, such as 1nF Y2 capacitors, providing a path for high-frequency noise to the chassis ground; and optocouplers or isolation transformers for electrical isolation of the signal itself, completely disconnecting the ground connection. In interface circuit design, isolated interface chips are preferred. In terms of layout, isolation devices should be placed at the connection bridge positions of the split ground planes, and interface circuits should be kept away from power circuits. Eintech's safety-certified Y capacitors and series of ferrite beads offer a variety of options for safe and effective isolation and connection between interface ground and power ground.