EMI Filter Selection
EMI (Electro-Magnetic Interference) is unwanted electrical noise created by various AC sources such as motors, variable frequency drives (VFDs), solid-state and mechanical relays, but a major and common source is switched mode power supplies. EMI can wreak havoc on electrical systems compromising their safety and performance.
The propagation of EMI can take two forms, conducted and radiated.
Conducted EMI, whether sourced or created by an external device, travels through conductors, such as traces on PCB boards, electrical components, power line cords, and AC systems. If not attenuated, it can cause the electrical equipment to malfunction or behave erratically.
Radiated noise, aka RFI, is propagated through free space as radio waves. Much like conducted EMI, it can interfere with internal systems when absorbed. One of the most significant contributors to radiated RFI from electronic equipment is the AC power cord. The power cord is often an efficient antenna since its length approaches a quarter wavelength for the RFI frequencies present in digital equipment and switching power supplies.
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