What is an EMI/RFI Filter?

EMI Filters, or electromagnetic interference filters, also called RFI Filters or radio-frequency interference filters, are an electrical device / circuit that mitigate the high frequency Electromagnetic noise present on the power and signal lines. The high frequency noise is generated by a variety of electrical and electronic devices such as motors, electronic controls, power supplies, inverters, clock circuits, microprocessors, appliances, electronic devices etc. This noise is typically in the 9KHz to 10GHz frequency range and it can degrade or prevent the signal transmissions and/or the intended performance of an electrical/electronic equipment. The lower frequency components of the EM noise can impact the power quality as well.

The Industrial EMI Filters provides a low impedance path to the high frequency noise and reduces it by either cancelling its line and neutral components or by grounding it. The effectiveness of an EMI/RFI filter measure as insertion loss (in dB over the frequency range). An EMI Filter is usually most useful for the Electromagnetic noise is 9KHz to 30MHz frequency range which is conducted through the wires. The frequencies beyond 30MHz are typically radiated (travel through the air) requiring shielding and input/output isolation. For radiated frequencies, the filter mounting is more critical than its insertion loss performance.