How to attenuate interference in the concentrator acquisition loop?

The acquisition circuit of the concentrator (used for voltage and current sampling) has a weak signal, which is susceptible to spatial radiation and conducted interference, causing fluctuations in the sampled values. Interference attenuation needs to be addressed through signal conditioning and the transmission path. A 100pF-1nF C0G capacitor is connected in parallel at the output of the sampling sensor (e.g., the secondary side of a CT) for initial filtering. After the signal enters the concentrator, it first passes through an RC low-pass filter consisting of a 100Ω resistor and a 10nF capacitor, with a cutoff frequency of approximately 160kHz. Then, a low-noise, high common-mode rejection ratio instrumentation amplifier (e.g., AD620) is used for amplification. The amplifier power supply uses an LDO regulator and is filtered with a PBZ1608E600Z0T ferrite bead. Shielded twisted-pair cable is used for the transmission line, with the shield grounded at a single point at the concentrator end. On the PCB, the sampling circuit area is completely surrounded by a ground plane. This solution can attenuate high-frequency noise (>10kHz) in the acquisition circuit by more than 40dB, and the power frequency sampling accuracy error is less than 0.2%.