RFI and EMI Filters – in Preventing Electrical Circuit Performance
In this article, you will learn about the RFI filter (RFI stands for radio frequency interference) and EMI filter (electromagnetic interference filter) – aka RF interference filter. EMI, or radio frequency interference, is a type of electrical or electronic emission that may damage, impair, or prevent electrical circuit performance. Both natural and manmade emissions are responsible for these emissions. The EMI and RFI can either be conducted, meaning they are sent along power and signal lines, or they can be radiated, meaning they move in free space. Due to the fact that EMI and RFI can damage many important applications, such as hospital equipment and military devices, it’s usually important to implement methods to reduce their impact.
Radio Frequency Interference Filter: EMI Filter/RFI Filter
A good solution to prevent EMI/RFI is to use a filter. This passive electronic device suppresses conducted EMI/RFI emissions from power and signal lines but does not suppress radiated emissions. Filters may also be attached to specific devices to limit or suppress their EMI/RFI output, or to inhibit their susceptibility to EMI/RFI emissions from other devices. Since there is a lot to consider when selecting an EMI/RFI filter, it’s important to know the characteristics and features of both the device being protected and the filter that should be used together.
Passing of Frequency
Most filters pass only a certain range of frequencies through, meaning that an electronic device being protected will be exposed to a specific range of EMI/RFI emissions. As a result, certain EMI/RFI emissions, within a defined range, will not interfere with the performance frequencies of different electric and electronic devices. Unlike radio waves, cable television operates at a different frequency, so they don’t interfere with one another. A frequency pass can be set to one of four main settings:
- Low-pass filters allow low-level frequencies below a certain cut off point to pass through.
- High-pass filters allow high-level frequencies above a certain cut-off point to pass.
- In a Band Pass filter, frequencies within a given range pass through.
- The Band Stop or Band Reject filter allows frequencies outside a specified range to pass through.
The Insertion Loss
Measured in decibels (dB), the insertion loss of EMI/RFI filters proves their general effectiveness. This is calculated by comparing the strength of a signal on a low-performance (v1) application to a high-performance (v2) application after installing or not installing the filter. In the past, the industry-standard insertion loss figure was 50 Ohms; while this measurement is still common today, recommended insertion loss figures are much less rigidly applied.
Radio Frequency Power Line Filter
The power lines are typically divided into different phase sections, with neutral lines also attached. Each phase needs its own filter, as well as the neutral line. Attaching a filter to the power line is not enough; each phase also requires its own filter.
Considerations when Choosing a Size
Size and weight are also important factors to consider when choosing an EMI/RFI filter, particularly if space is limited. EMI/RFI filters are available in many sizes, but their range and effectiveness can be compromised if they are too large for an application. Additionally, portable applications, for example, those found on aircraft, may be hindered by weight factors, which may prevent their proper installation and use.
If you need help with choosing the right RFI/EMI Filters for your equipment, you are in the right place! EP-Power, together with Astrodyne TDI is known for its ability to produce highly reliable and durable power supplies and EMI/EMC/RF filters for a variety of markets, including Aerospace, Industrial, Medical, Military, and Semiconductor Manufacturing. With more than 60 years of experience as a custom Power Supply and EMI/EMC/RF Filter manufacturer, we produce for some of the most demanding industries and end markets.
For enquires, please send us an email at: sales@edac.com.sg
