EMC
Electro Magnetic Compatibility
EMC stands for Electro Magnetic Compatibility, and describes the way electric or electronic apparatus behave (regarding Electro Magnetic aspects) in the presence of other equipment. This discipline investigates the unwantedly emitted radio interferences (emissions), and unwanted susceptibility of electronics against Electro Magnetic fields and a number of associated phenomena , known to interfere with electronics in a similar way.
The goal of EMC is to create a situation of functional and/or safe operation, in a common electromagnetic environment, of different equipment and the avoidance of any interference effects.
- Electro Magnetic fields (radio waves)
- Electrostatic Discharges
- Fast impulses on supply and other leads
- Lightning pulses on supply and other leads
- Magnetic fields and their impact on electronic components
- Common Mode Voltages and Currents on all cabling
- Mains Fluctuation and Harmonic Currents effects
Interference, or noise mitigation and hence ElectroMagnetic Compatibility is achieved by addressing both emission and susceptibility issues. Limitation of emissions of all equipment, so as to enable communication receivers to operate in their vicinity, and limitation of the susceptability of all equipment, so as to enable communication devices (transmitters) in their immediate vicinity.
Within the European community, EMC is part of the so called essential safety properties, every electronic or electroinic device has to meet essential requiremenbts and brought under the ce marking regime. Aspects of safety are governed by directives.
The EMC-directive (2004/108/EEC)
The introduction of the ce mark has lead to a number of so-called New Approach directives, one of which is the EMC-directive.
The technical goal of this directive is two-way:
- Protect the radio spectrum against interfering equipment
- Protect equipment from common interference
All this within the higher goal of preventing trade barriers between the member states of the European Community as introduced the treaty of Rome (1957).
The EMC directive is part of the Framework of New Approach Directives governed by the CE marking directive.
As all ce related directives this is a New Approach Directive, which means that legal requirements to your equipment regarding EMC are described in global terms, called Essential Requirements, where the technical requirements are created and maintained by the market, -currently by mandate of the European Commission- by bodies such as ISO, IEC, CENELEC and ETSI, in the form of technical standards.
The assessment of compliance with the directive is being governed by two articles in the EMC-directive:
- Manufacturers Declaration (route acc. art. 10.1)
- Type testing using a Technical Construction File (TCF) (route acc. to art. 10.2)
Article 10.1 Manufacturers declaration
The manufacturers declaration consists of a liability statement from the manufacturer or importing agent in which he accepts the legal consequences (liability) for conformity of its equipment to the EMC directives essential requirements. The manufacturer is granted permission to do the assessment himself, or to outsource it to any test-house. Using this route the manufacturer is however, bounded to apply the so called Harmonized Standards for "type testing". These standards are created and listed for this purpose and published in the official news-letter of the EC (OJEC), and in the official journals of all EC-members.
Type testing is the term reserved within the "New Approach" for verifying and proving the compliance of production numbers of equipment by verifying only one (1) sample, assisted by an optional statistical analysis.
Following the provisions of a suitable Harmonized Standard, one obtains the so-called Presumption of Conformity with the directive.
Any New Approach directive has its own list of harmonized standards, describing the technical tests and - requirements (also documentation) a sample of equipment has to comply with in order to merit the "Presumption of Compliance".
A new requirement of the latest EMC-directive is that proof of compliance need to be provided to the authoritie on request in addition to the Declaration of Conformity. This means that a suitable test report needs to be available.
Article 10.2 Type testing using Technical Construction File (TCF).
Type testing using a TCF is done when no suitable Harmonized Standard exists, or if the manufacturer prefers other ways of showing compliance. This route is often used for new developments or in case of "families" of related equipment. In the latter case the application of a harmonized standard becomes too costly if a large number of closely related samples is to be investigated. Test are carried out on representative set of samples, and by technical investigation declared valid for an entire family or strongly related products.
Harmonized standards for the EMC-directive
This list of standards is an ever increasing subset of world-wide existing EMC-standards, that due to its way of defining test-methods, limits and susceptibility criteria, are very well suited for testing by the manufacturer himself, or by a suitable EMC test house.
Compliance to a Harmonized standard creates a full presumption of compliance with the essential requirements of the directive; in contrary to the TCF route, where a technical justification is required.
Harmonized standards define limits and criteria equipment should comply but refer to Basic Standards for testing methods.
This list of Harmonized Standards is published at least once a year in he Official Journal of the EC.
By following this link you may obtain a list of European Harmonized Standards concerning EMC.
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