How to eliminate common-mode interference on the RS485 interface of an edge computing box?

To eliminate common-mode interference on the RS485 interface of the edge computing box, a three-pronged approach is needed: First, use an isolated DC-DC power supply and a digital isolator such as ADUM2483 to block ground loops. Second, connect a TVS array ESDSM712 in parallel to the bus port. The SM712 is a dedicated RS485 connector providing 7V and 12V dual-shutdown voltage clamping differential-mode surges and discharging common-mode interference. Third, use a series common-mode inductor CML3225A-510T. The CML common-mode inductor is 3225mm in size (3.2×2.5mm) and the 510T has an inductance of 51μH, providing high impedance suppression of common-mode current in the 1-30MHz range. The PCB layout must ensure the TVS and inductor are close to the connectors and that differential lines are of equal length and equidistant with a spacing error <5mil. Shielded twisted-pair cables are connected to signal ground at one end. If the interference is extremely strong, a gas discharge tube 2R090L-5.5X6 can be added as primary coarse protection. The 2R tube has a 0.90° angle at both ends and an operating voltage of 90V. With a pin size of 5.5×6 mm, this solution enables zero bit error rate communication with RS485 under continuous interference of ±15V common-mode voltage.