How to handle multiple I/O modules sharing a common ground?

Handling a multi-I/O module common-ground system requires establishing a clear ground hierarchy and connection rules. First, a main grounding copper busbar or ground plane should be set up as the system's zero-potential reference. Each module is connected to the main grounding point via a low-impedance grounding busbar or backplane ground plane. Differential interfaces, such as RS-485, should be preferred for signal connections between modules. If single-ended signals must be used, ensure a good common ground between the transmitting and receiving ends, or connect a common-mode choke, such as the CML series, in series on the signal lines to suppress interference caused by ground potential differences.

For high-speed digital buses, a complete ground plane should be provided on the backplane as a signal return path. In power distribution, the power ground of each module should be connected to the backplane ground via a ferrite bead or small inductor to isolate the module's own switching noise. During system installation, the resistance between each module chassis and the main grounding busbar should be measured to ensure consistency and sufficiently low resistance. In software, checksums and retransmission mechanisms can be added to communication protocols susceptible to ground noise. Finally, the system must pass radiated emissions and conducted immunity tests to verify the effectiveness of the common-ground design.