How to design power frequency magnetic field immunity for power FTU?

The power frequency magnetic field (50Hz) immunity design employs high permeability shielding and differential sampling. The chassis is made of electrical pure iron DT4C, 1mm thick, with a relative permeability of 5000 and a shielding effectiveness greater than 20dB. Current sampling uses a closed-loop Hall sensor, such as the ACS712, with internal differential cancellation of magnetic field interference. Voltage sampling uses a digital isolation amplifier ISO7240C. PCB layout: sensitive circuits are kept away from magnetic field sources, such as transformers and motors. Twisted-pair cables are used to reduce loop area. With this design, the FTU can pass the IEC 61000-4-8 power frequency magnetic field immunity test (100A/m, 50Hz) with a sampling error of less than 0.5%.