How to suppress low-voltage current sampling interference in intelligent low-voltage monitoring units?

Low-voltage current sampling interference suppression begins on the secondary side of the current transformer (CT). A 100Ω/1W load resistor and a 10nF/100V capacitor are connected in parallel on the CT secondary side. Shielded twisted-pair cable is used for the sampling lines. The PCB input stage uses a CMZ3225A-201T common-mode inductor (200μH) for filtering, coupled with ESDLC5V0D3B protection. The operational amplifier circuit uses an AD8629 with a second-order active filter and a cutoff frequency of 2kHz. PCB layout: Minimize the sampling loop area. Through this suppression, the current sampling accuracy reaches 0.5 class, and the common-mode rejection ratio is greater than 80dB, meeting the IEC 61869 standard.