How can poor grounding in a Human-Machine Interface (HMI) cause EMC problems?

Poor HMI grounding can cause serious EMC problems in several ways. High-impedance grounding paths can render filters and shielding ineffective. For example, common-mode inductors require low-impedance grounding to conduct noise to ground; if grounding is poor, noise cannot be effectively bypassed, leading to excessive conducted emissions. Uneven ground loop impedance can generate common-mode voltage on the cable shielding or circuit ground, driving cable radiation and becoming a source of radiated emissions. Fluctuating ground potential can cause instability in the reference level of interface chips, leading to data errors or communication interruptions, especially noticeable in differential buses such as RS485 and CAN.

Regarding immunity, poor grounding means that interference currents (such as ESD and surges) cannot be quickly discharged, potentially entering internal circuits through capacitive coupling, causing resets or damage. Poor grounding of the shielding housing significantly reduces its shielding effectiveness, allowing external interference to easily penetrate and internal radiation to escape. Cold solder joints, oxidation, and long, thin wires can all lead to poor grounding. The solution is to adopt the low-impedance grounding design described above, and use Eintratronics' low ESL capacitors and reliable connection devices to ensure that the entire grounding system from the PCB to the system cabinet is robust and reliable, fundamentally eliminating EMC problems caused by grounding.