How to resist EMI in I/O module AI analog signals?

Improving the EMI immunity of I/O module analog input channels requires multi-level protection. At the signal input, an ultra-low capacitance TVS array such as ESDLC5V0D8B should be used first to provide electrostatic discharge and transient overvoltage protection for each pair of differential signal lines. Its capacitance value of less than 1pF ensures minimal impact on high-frequency analog signals. A common-mode choke, such as CMZ2012A-900T, should then be connected, which can suppress common-mode noise on the line without attenuating the differential-mode signal. At the front end of the signal conditioning circuit, a multi-stage RC or LC filter network should be set up.

PBZ series ferrite beads can attenuate specific noise frequencies. For a 4-20mA current loop, a TVS diode such as SMBJ6.0CA should be connected in parallel at the receiving end to limit high-voltage transients. Simultaneously, a small precision resistor should be connected in series in the loop for sampling, and an MLCC capacitor should be connected in parallel across the resistor to filter out high-frequency noise. When laying out the PCB, the AI channel should be kept away from digital circuits and power modules, and physical isolation should be achieved using shielding covers or grounding isolation strips. Signal traces should be as short as possible and differential pairs should be used to enhance the ability to resist common-mode interference.