How to ensure EMC (Electronic Performance Monitoring) for long-distance communication of PMS (Power Measurement System) switches?

Long-distance PMS communication (such as RS485 over 100 meters) cables act like antennas, easily picking up environmental noise and radiating their own interference. EMC assurance requires a comprehensive approach using balanced transmission, shielding, and grounding technologies. First, differential balanced transmission (such as RS485) should be used, as it has strong common-mode interference immunity. Low-capacitance, high common-mode rejection ratio transceivers should be selected. Shielded twisted-pair cables must be used, with the twist pitch smaller than the interference wavelength (for 1MHz, pitch <15cm). Shielding grounding strategy: At the PMS end, the shielding layer is connected to the chassis ground (PE) via a 360° crimp connection; at the remote device end, if the device is well grounded, the shielding layer is also grounded; otherwise, it is left floating to avoid ground loops. If both ends are grounded, a ferrite core PBZ1608E600Z0T can be connected in series in the shielding layer to suppress low-frequency circulating currents. Second, filter and protection circuits should be designed at the PMS communication port as described above. During installation, communication cables should be kept away from high-voltage cables (parallel spacing >30cm), and perpendicular crossings should be avoided if unavoidable. Through the above measures, long-distance communication can operate stably in industrial electromagnetic environments with a bit error rate of less than 10^-7, meeting the requirements of IEC 61000-4-4 EFT and IEC 61000-4-5 surge tests.