How to rectify non-compliant radiation emissions from human-machine interface (HMI) deliveries?

To rectify HMI radiated emission failures, a systematic diagnostic and remedial approach is required. First, analyze the test report to identify the out-of-range frequencies, amplitudes, and potential internal noise sources. For example, tens of kHz to hundreds of kHz might originate from the switching power supply, tens of MHz from clock harmonics, and hundreds of MHz from the high-speed data bus. Use a near-field probe to scan the device surface and internally to pinpoint the areas and components with the strongest radiation. Common remedial measures include: strengthening shielding by checking the shielding of chassis gaps, openings, and cable entry points; adding conductive pads or replacing with materials offering higher shielding effectiveness.

Strengthening filtering by adding ferrite beads (e.g., PBZ series) to the power lines of noise sources; connecting ferrite beads or resistors in series on clock or high-speed signal lines; and adding common-mode chokes (e.g., CMZ series) to I/O ports. Optimizing the PCB by adding local shielding to chips or areas with strong radiation; checking and optimizing the return paths of critical signal lines to reduce loop area. Adjusting operating parameters, such as appropriately reducing the clock frequency or switching frequency of the switching power supply without affecting functionality. For switching power supply modules, consider replacing them with models offering better EMI characteristics. Through gradual testing and targeted enhancement using the shielding and filtering products from Yinte Electronics, the problem of excessive radiated emissions can usually be effectively solved.