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Classifying and Combating Electromagnetic Interference
By Derick Stevens, European FAE Manager, KEMET Corporation I
n today’s world, many pieces of electronic and electrical equip- ment operate in close proximity,
bringing with them the potential for each device to generate electromag- netic disturbances, interfering with those nearby. Equipment malfunc- tions caused by interference can have consequences that range from minor inconveniences, such as a dropped mobile phone call or WiFi connection, to serious disruptions of important services. Disturbances of safety-criti- cal systems could lead to injuries or even fatalities if precautions are not taken.
Regulations, such as the EU’s
recently-updated electromagnetic compatibility (EMC) directive, 2014/30/EU, provide a framework for ensuring coexistence between differ-
Disturbances of
safety-critical systems can lead to injuries or even fatalities if precautions are not taken.
ent pieces of equipment. New prod- ucts must be tested for compliance with the EMC directive before the
Frequency ranges for conducted and radiated noise.
encompasses the strength of the elec- tromagnetic signals emitted by equipment as well as immunity to interference from external sources. Different sets of regulations
apply to different types of equip- ment. Products marketed for use in commercial, industrial or business environments are classified as Class A, while products for use in residen-
ment are generally more strict. Electromagnetic interference
signals can exist across a wide fre- quency range. Generally, interfer- ence at 30 MHz tends to be conduct- ed through cables and current paths, or coupled between cables by induc- tive or capacitive mechanisms. Interference signals above 30 MHz are usually radiated by metallic
product can be marketed in EU coun- tries. The scope of the directive
tial environments are labeled Class B. The regulations for Class B equip-
parts, components, or cables acting as antennas.
Radiated Noise Shielding can be used to pre-
vent radiated signals from entering or leaving an enclosure. Designers have various shielding approaches to consider, including board-mounted shields that can be custom designed to shield a group of components or protect against a specific noise source. A metal enclosure or chassis
can be used to provide an overall shield, or a plastic enclosure may be metallized to create the continuous conductive surface needed to support shielding. Apertures, such as cut- outs for screens, or seams where enclosure halves join, represent dis- continuities in the shielding that can allow electromagnetic radiation to enter or to escape. Designs should minimize the size and number of any holes or seams. Designing a conduc- tive gasket or spring fingers to be inserted at joints between separate pieces of an enclosure can help to seal such breaches. If radiated EMC issues are dis-
Continued on next page
May, 2017
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Most problems
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