A Primer On EMI/RFI Filters And Use

EMI or electromagnetic interference and RFI or radio frequency interference are two different sources of “noise” found in electronic equipment. As the names implies, EMI is from electromagnetic disturbances, which can occur in nature or be man-made. RFI is typically low frequency and impacts radio frequency transmission. Both can be corrected through the use of the right EMI/RFI filter.

The Reality of EMI and RFI

It is important to realize that both EMI and RFI can move through conduction, most commonly through cords, cables and signal and power lines. However, both can also be considered to spread or propagate through radiation, expanding their interference beyond moving directly through the power or signal sources.

The result of EMI and RFI will vary depending on the specific device. For a display on a television, the results will be what is most commonly known as “snow” or static. With a computer, the result is most commonly a degradation in the sending and receiving of data, often resulting in slow data transferal or problems with achieving and maintaining a solid wireless connection. This may be continuous or it may come and go based on the use of other electronics or electromagnetic radiation sources in use in the area.

Since radiated interference is the most difficult to control, providing EMI/RFI filter systems on the power and signal lines is seen as essential to prevent the radiation at those sources. However, the actual power cord into the device can be problematic when it comes to radiated noise.

Conducted interference can include the components within the device or electronics. This could include interference from microprocessors, motors and even the actual switching power supplies and fans used within the systems.

The Use of EMI/RFI Filter

Any EMI/RFI filter is a passive electronic component designed to suppress the interference with a power source or within a system. They can also be used to prevent radiated interference, which is essential in smaller electronic devices in use today.

It is critical to choose the correct EMI/RFI filter for the application. In the electronics industry, as well as in telecommunications, there will be specific requirements for the use of EMI/RFI filter models and designs for the various applications.

The most commonly considered issues when selecting the optimal EMI/RFI filter for the type of interference to suppress includes concerns with insertion loss, voltage and current, and the leakage current. The leakage current aspect is typically regulated by industry and will be an essential consideration in selecting the correct filter.

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