What is the impact of power FTU switching operation on sampled EMC?

Transient interference generated by switching action affects sampling accuracy through conduction and radiation. Impact analysis: Common-mode interference causes sampling offset, while differential-mode interference introduces noise. Solution: The sampling circuit uses an ISO7240C isolation amplifier with an isolation voltage of 3kVrms. A second-order active filter is added to the sampling input with a cutoff frequency of 2kHz. Shielded twisted-pair cable is used for the sampling lines, with the shield grounded at a single point. On the PCB, the sampling circuit is kept away from the switching circuit, with a spacing greater than 25mm. An independent LDO power supply is used. With this design, the sampling error during switching action is less than 0.1%, meeting the IEC 61869 0.2 accuracy class and IEC 61000-4-4 EFT 4kV immunity requirements.