How to rectify the sampling signal distortion of the intelligent low-voltage monitoring unit?

The causes of sampling signal distortion were analyzed and addressed accordingly. If the interference was high-frequency, a second-order active filter with a cutoff frequency of 2kHz was added. If it was common-mode interference, a CMZ3225A-501T common-mode inductor was added. If it was transmission line reflection, impedance matching was used, with a 120Ω resistor connected in parallel at the termination. PCB modifications included shortening the sampling trace length and using differential routing. The high-precision operational amplifier AD8629 was replaced. Through these modifications, signal distortion was reduced from 3% to 0.2%, and the signal-to-noise ratio was improved to 65dB.