How to design a PLC with multiple modules sharing a common ground?

The common ground design for multi-module PLCs using power line carrier communication requires ensuring consistent ground potential and noise isolation. A star-shaped common ground structure is adopted, with all module ground wires converging at a central grounding point, connected using copper busbars with a cross-sectional area ≥4mm². A PBZ1608A-102Z0T ferrite bead or a 0Ω resistor is deployed at the entrance of each module to provide DC connectivity while isolating high-frequency noise. For digital and analog modules, the ground planes are separated and connected via a single point. Differential transmission, such as RS-485, is used for communication interfaces, in conjunction with an ADM2483 isolation device to break ground loops. The impedance characteristics of the common ground system are analyzed through simulation to optimize the grounding point location. In actual testing, the voltage difference between the ground wires of each module is measured using a millivoltmeter and should be less than 50mV. After the common ground design, the system immunity test should pass IEC61000-4-4 EFT ±4kV, conducted emissions should meet EN55032 Class B limits, and the bit error rate for communication between multiple modules should be less than 10^-5.