How to ensure EMC (Enhanced Mechanism Control) of analog I/O in intelligent controllers (PACs)?

Ensuring EMC for analog I/O signals (e.g., 4-20mA, 0-10V) of the intelligent controller PAC requires addressing isolation, filtering, and protection. Isolation amplifiers (e.g., ADuM series) or isolated ADCs are used on the input side for electrical isolation. A common-mode inductor (CMZ3225A-510T) is connected in series on the signal lines to suppress common-mode interference, and a parallel RC filter (e.g., 1kΩ + 100nF) is used to filter out high-frequency noise. For the current loop, a TVS (SMBJ6.5CA) and a Zener diode are connected in parallel at the input for overvoltage protection.

The PCB layout isolates the analog I/O area, using a complete ground plane, and isolates it from the digital area through slots. The power supply provides an independent LDO for the analog circuit, with a ferrite bead (PBZ1608A-102Z0T) for filtering at the input. Tests show that this solution achieves a common-mode rejection ratio (CMRR) greater than 120dB and an accuracy error less than 0.1% for analog I/O, passing IEC61000-4-4 EFT. 4kV and IEC61000-4-6 CS 10V testing;