How to rectify EMC issues related to packet loss in the PMS communication of an electrical power measurement switch?

Packet loss in PMS communication, after ruling out protocol and software issues, is most likely caused by EMC interference leading to signal distortion or transceiver transient failure. Rectification requires locating the interference path.

First, observe the communication signal waveform with an oscilloscope to check for overshoot, ringing, or superimposed noise. If overshoot/ringing is present, connect a small resistor (22-100Ω) in series at the transceiver output or increase the accuracy of the terminating resistor. If high-frequency noise is present, check if the port filtering is sufficient; consider adding a common-mode inductor CML3225A-510T or a small capacitor (e.g., 47pF) in parallel.

Second, check the protection circuit: ensure the TVS diode (e.g., SMBJ6.5CA) is appropriate, and check if the clamping voltage is too low, causing normal signals to be limited.

Check the grounding: ensure the communication shielding layer is properly grounded, and check if the communication ground is contaminated by power ground noise; consider adding isolation.

Check the power supply: check if the power supply ripple to the communication transceiver is excessive; consider adding a PBZ1608E600Z0T ferrite bead and a capacitor for filtering.

In terms of spatial arrangement, check whether communication cables run parallel to power cables. Rewiring should be done to maintain distance or allow them to cross perpendicularly. Through targeted rectification, the packet loss rate can be reduced from 10% to below 0.01%.