How to avoid ground loops in I/O modules

Avoiding ground loops in I/O modules is crucial for preventing low-frequency hum and interference coupling. System design should adhere to the single-point grounding principle, ensuring all module ground wires converge to a single main grounding point. For devices requiring multi-point grounding, isolators such as optocouplers, isolated operational amplifiers, or isolated DC-DC converters can be used to break direct ground loop paths. For signal connections, differential transmission methods such as RS-485 or 4-20mA current loops are preferred, as they naturally suppress ground loop interference.

When using single-ended signals over long distances, shielded twisted-pair cables should be used, with the shield grounded only at the receiving or transmitting end, leaving the other end floating to prevent ground loop current from flowing through the shield. Internally, digital ground, analog ground, and power ground should be laid out separately and connected via ferrite beads or single-point connections. For floating ground modules, a high-value resistor connected in parallel with a high-voltage capacitor should reference the circuit ground to the chassis ground to discharge static electricity while maintaining a low-impedance path for high-frequency noise.