What is EMC?
Electromagnetic Compatibility (EMC) is defined by the International Electrotechnical Commission (IEC) as:
The ability of a device, equipment or system to function satisfactorily in its electromagnetic environment without introducing intolerable electromagnetic disturbances to anything in that environment.
There are therefore two aspects to EMC; firstly controlling the electromagnetic 'noise' produced, also known as electromagnetic interference (EMI) or emissions; and secondly designing equipment to be sufficiently immune to intentional and unintentional electromagnetic sources in the environment so that it continues to operate correctly and does not become 'susceptible' to interference.
The problems of interference range from nuisance (e.g. poor quality TV/Radio reception) to unreliability (e.g. computer crashing) to safety (e.g. railway signalling failure).
Within Europe, electrical equipment with CE Marking meets the EU Electromagnetic Compatibility (EMC) Directive. The Directive has essential protection requirements for emissions and immunity to ensure that, for example; broadcast radio and television reception is unaffected by interference and that equipment will continue to operate adequately in the vicinity of radio transmitters such as mobile phones.
For manufacturers and suppliers in Europe, as well as EMC testing equipment under the EMC Directive, it is necessary to compile Technical Documentation, make a Declaration of Conformity and apply CE Marking. An option is to use an EMC Notified Body to provide an assessment.
What are EMC Emissions?
Emissions are described as the unwanted generation of electromagnetic energy. Under the EMC Directive, the permitted levels of emissions are specified in Harmonised Standards for products, product families or generic environments. Usually it is necessary to perform EMC emission testing to demonstrate that the limits are met or if they are not met, to identify where design changes are required.
How can you prevent unwanted EMC Emissions?
The emissions can either be 'radiated' via electromagnetic fields that couple to other equipment or 'conducted' through wired connections such as the power cable. To prevent emissions it is possible to add filters and suppressors to cable interfaces, add cable or equipment shielding and grounding or change the circuit and PCB design.
What is EMC Immunity?
EMC Immunity (often called susceptibility) refers to the correct operation of electrical equipment in the presence of electromagnetic disturbances. Under the EMC Directive, the minimum levels of immunity are specified in Harmonised Standards. Usually it is necessary to perform EMC immunity testing to demonstrate that the limits are met or if they are not met, to identify where design changes are required.
What can be done to increase immunity?
Interference can couple into equipment by the same routes as emissions, i.e. 'radiated' or 'conducted' coupling and similar measures can be applied such as to add filters and suppressors to cable interfaces, add cable or equipment shielding and grounding or change the circuit and PCB design.
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