How is noise attenuated in the monitoring loop of an intelligent low-voltage monitoring unit?

Noise attenuation in the monitoring loop requires optimization across the entire link from the sensor to the ADC. A 100Ω/2W damping resistor and a 10nF/100V C0G capacitor are connected in parallel on the secondary side of the current sensor. The voltage divider resistors use 0.1% precision metal film resistors and a 100pF/100V NPO capacitor in parallel. Shielded twisted-pair cables are used for the signal lines, with the shield grounded at a single point. The PCB input stage uses a CMZ20212A-900T common-mode inductor (90μH) with ESD protection from an ESDULC5V0D9B ultra-low capacitance capacitor. The operational amplifier circuit uses an AD8629 instrumentation amplifier with a second-order active filter and a cutoff frequency of 2kHz. The ADC power supply uses a PWRA6045R6R8M0T power inductor (6.8μH) and 10μF + 100nF decoupling capacitors. With this design, the monitoring loop noise is reduced by more than 40dB, the signal-to-noise ratio is greater than 70dB, and the accuracy requirement of IEC 61869 0.5 level is met.