How to select the power frequency magnetic field immunity test level for edge computing boxes?

Edge computing boxes used in substations or industrial sites need to withstand power frequency magnetic fields. According to the IEC61000-4-8 standard, the testing levels are divided into 1-5. Industrial environments typically use level 4 (30A/m) and level 5 (100A/m). For power system edge boxes, level 5 is often required for one minute of continuous operation. If the edge box uses a plastic shell, there is no attenuation of the magnetic field, so the internal design needs to be optimized:

1. Hall sensors and other magnetically sensitive devices should be kept away from the shell and a high-permeability alloy shielding cover should be added.

2. High-current circuits on the PCB should use a twisted-pair layout to reduce loop area.

3. The power module should use a semi-magnetic core, such as the PQ series, to reduce leakage flux.

4. The reset and sensitive signal lines are connected in series with a PBZ1608E600Z0T magnetic bead, whose 60Ω impedance suppresses induced electromotive force. This has been verified to pass the level 5 power frequency magnetic field test.

The edge box showed no display abnormalities and no communication errors, meeting the requirements of the DL/T 721 standard.