How to ensure EMC (Electronic Performance Conformity) of current sampling in an electrical power measurement switch (PMS)?

The current sampling signal of a PMS (especially when using a shunt) is weak (millivolt level) and highly susceptible to electromagnetic interference. EMC protection requires comprehensive protection across the sensor, signal transmission, and processing links.

Sensor selection: Surface-mount shunt resistors are preferred due to their low parasitic inductance; if using a current transformer (CT), a shielded type should be selected.

Signal transmission: The sampling line must use twisted-pair or shielded twisted-pair cable, with the shield connected to analog ground at a single point on the PMS end.

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

Power supply: Provide independent analog power supplies for the amplifier and ADC, and use a PBZ1608E600Z0T ferrite bead and capacitors for filtering.

PCB layout: The sampling loop area should be completely covered by a ground plane and isolated from other circuits. In extremely harsh environments, consider using an isolated ADC (e.g., ADuM7701).

Through system design, the current sampling system can withstand IEC 61000-4-4 EFT level 4 interference, and the sampling accuracy is still better than 0.2% under full load conditions.