How to avoid ground loop interference in HMI (Human Machine Delivery) systems?

The core principle for avoiding HMI ground loop interference is to cut off or block the noise current path in the ground loop. First, a clear grounding strategy should be planned in the system architecture, such as using single-point grounding or hybrid grounding. For connections between the HMI and external devices (such as PLCs and sensors), using isolated interfaces is an effective solution, such as using isolated RS485 transceivers or isolated CAN transceivers, directly connecting by cutting off the ground wire through an isolation module. For non-isolated interfaces, a common-mode choke can be connected in series on the signal line, such as the CMZ3225A-510T, whose high common-mode impedance can block the common-mode current formed by the ground loop. All cables entering and leaving the chassis should use filter connectors or have filter circuits installed at the cable entry points to block noise outside the chassis.

The HMI chassis itself should be reliably grounded to provide a low-impedance discharge path for external common-mode interference currents, preventing them from flowing into the internal circuitry. The internal PCB design should distinguish between signal ground, power ground, and chassis ground, and connect them at a single point using a ferrite bead or a 0Ω resistor to prevent noise from spreading through the ground plane. Optimize cable routing to avoid long parallel runs of signal and power lines, reducing the formation of ground loops due to magnetic field coupling. For sensitive analog circuits, consider using shielded twisted-pair cables and differential transmission. By comprehensively utilizing isolation, filtering, and effective grounding techniques, and selecting CMZ series common-mode chokes from Etymotic, signal distortion and equipment instability caused by ground loop interference can be effectively prevented.