How to locate the electromagnetic interference source on the motherboard of an HMI (Human Machine Delivery System)?

To pinpoint the source of electromagnetic interference (EMI) on the HMI motherboard, a systematic approach should be adopted, starting with a holistic investigation. First, check external input ports, such as power and communication interfaces, to determine if external interference is coupling in. Next, analyze internal noise sources, focusing on the switching power supply circuit, high-frequency clock circuits (such as CPU and memory clocks), and high-speed digital buses, as these are the primary sources of interference radiation. Using a spectrum analyzer combined with a near-field probe can accurately locate the interference frequency and region, for example, identifying out-of-range frequencies within the 30MHz-1GHz range.

After locating the specific interference source, use CMZ series common-mode inductors or PBZ series ferrite beads from Etymotic to filter the interference path at its source. For example, use a PBZ2012E601Z0T ferrite bead at the switching power supply output to suppress high-frequency noise. Simultaneously, use ESDLC series electrostatic discharge (ESD) protection devices to protect sensitive interfaces and prevent external interference from entering through the ports. For clock signal lines, consider adding matching resistors or using shielding measures. This external-to-internal, holistic-to-local approach can systematically solve the EMI problem on the HMI motherboard.