How to design power frequency magnetic field immunity for HMI (Human Machine Delivery) systems?

The primary goal of HMI power frequency magnetic field immunity design is to prevent interference voltages induced in the internal loops of 50/60Hz and its harmonics. Power frequency magnetic fields typically originate from nearby transformers, motors, or high-current buses. Design measures include: reducing the area of sensitive loops within the equipment, which is the most effective method. For analog input circuits, current sampling circuits, etc., twisted-pair or coaxial cables should be used to transmit signals, and signal lines should be routed as close as possible to the metal base plate to utilize the mirror effect to cancel out the magnetic field. During PCB layout, susceptible circuits (such as high-gain operational amplifiers and Hall sensors) should be kept away from the edges of the equipment and internal components that may generate magnetic fields (such as power transformers).

For unavoidable loops, magnetic shielding can be used, i.e., using high-permeability materials, such as permalloy or silicon steel sheets, to create a shielding cover to enclose the sensitive circuits, providing a low-resistance bypass path for the magnetic field. In circuit design, for voltages induced by low-frequency magnetic fields, band-stop filters can be used in the signal processing stage to filter out power frequency and its harmonic components. If the equipment casing is made of ferromagnetic material, it can also provide some magnetic shielding. By comprehensively utilizing techniques such as reducing loop area, magnetic shielding, and filtering, HMI products can meet the requirements of power frequency magnetic field immunity standards such as IEC 61000-4-8. E-Tech Electronics can provide guidance on the selection of magnetic shielding materials.