How to resist power frequency magnetic field interference in I/O modules

Improving the immunity of I/O modules to power frequency magnetic fields requires addressing their low-frequency, high-penetration characteristics. For magnetic field-sensitive components such as Hall sensors, current transformers, or unshielded inductors, they should be kept as far away as possible from potential magnetic field sources such as transformers, motors, and high-current buses. If this is not possible, these components should be shielded with high-permeability metal covers, such as permalloy covers, which effectively shun magnetic lines of force. For signal loops, twisted-pair cables can cancel differential-mode voltage induced by magnetic fields. In circuit design, for analog signals that may induce power frequency interference, use instrumentation amplifiers with high common-mode rejection ratios, followed by 50/60Hz notch filtering using digital filters. For digital circuits, power frequency magnetic fields generally have a smaller impact, but interference may be induced through power lines; therefore, common-mode inductors should be used at the power input. During testing, according to IEC 61000-4-8 standards, the module should be placed in a power frequency magnetic field generating coil, and its functionality should be monitored, particularly the accuracy of analog measurements and the bit error rate of digital communication. For particularly sensitive applications, it may be necessary to use fluxgate or other sensors to replace devices that are susceptible to magnetic fields.