How to ensure EMC of concentrator current sampling?

The current sampling signal from the concentrator (using a current transformer or shunt) is weak, requiring comprehensive EMC protection across the sensor, transmission, and processing links.

Sensor selection: Surface-mount shunt resistors (low parasitic inductance) or shielded current transformers are preferred.

Signal transmission: Twisted-pair or shielded twisted-pair cables must be used for sampling, with the shield connected to analog ground at a single point at the concentrator end.

Signal conditioning: A differential amplifier (e.g., INA188) is directly connected across the sampling resistor; its high CMRR (>120dB) is critical. The amplifier output is then filtered by an RC low-pass filter (1kΩ + 1nF) before being fed into the ADC.

Power supply: Independent analog power supplies are provided for the amplifier and ADC, using PBZ1608E600Z0T ferrite beads and capacitors for filtering.

PCB layout: The sampling loop area is completely covered by a ground plane and isolated from other circuits. For harsh environments, an isolated ADC can be used.

Through design, the current sampling system can withstand IEC 61000-4-4 EFT level 4 interference with an accuracy better than 0.2%.