How to use the I/O module magnetic ring optimally

The optimal use of ferrite rings requires selection and installation based on the type and frequency band of noise to be suppressed. First, determine whether the noise is common-mode or differential-mode. For common-mode noise, use single or multiple turns through the ferrite ring; for differential-mode noise, twist the signal lines together before passing them through. Select the ferrite ring material according to the noise frequency; for example, manganese-zinc ferrite is suitable for frequencies below 1MHz, while nickel-zinc ferrite is suitable for frequencies above 1MHz. The impedance-frequency curve of the ferrite ring should have a peak within the noise frequency band.

The installation location should be as close as possible to the interference source or sensitive port, such as at the output line of a switching power supply, motor drive line, or the entrance of a long signal line. The number of turns wound on the ferrite ring increases the inductance but also the inter-turn capacitance; the optimal number of turns needs to be determined experimentally. The ferrite ring should be tightly closed to prevent air gaps from affecting the magnetic circuit. For radiated noise escaping from chassis openings, multiple ferrite rings can be installed on the cable to form a ferrite bead array. After use, the effectiveness should be verified by comparing conducted or radiated emission test results. Note that ferrite rings may saturate under DC or high current; models with high saturation magnetic flux density should be selected.