EMC电磁兼容

The problems associated with electromagnetic (radio)interference are not new and have plagued designersand users of equipment for many years, not only withradiated but also conducted interference. In order tominimise these problems some countries haveimposed various regulations and standards, notablyGermany and the USA. German regulations aredrafted, validated and enforced by the FTZ and VDEauthorities and have been mandatory since 1969. In theUSA the standards are enforced by the FCC and havebeen mandatory since 1980. Other countries haveapplied various types of government legislation.

Where standards differ between countries the recentremoval of trade barriers can actually cause technicalbarriers. With the drive to create a single market andhence the free movement of goods there is a need toharmonise technical standards to overcome thetechnical barrier problem.

The Directive

The Electromagnetic Compatibility Directive(/336/EEC) encompasses in its scope, apparatusliable to cause electromagnetic disturbance or theperformance of which is liable to be affected by suchdisturbances. 'Apparatus' is defined as all electrical orelectronic appliances together with equipment andinstallations containing electrical and or electroniccomponents. 'Electromagnetic disturbance' is definedas any electro-magnetic phenomenon which maydegrade the performance of a device, unit or system.Excluded from the Directive is apparatus subject toother directives containing EMC requirements. Atpresent this comprises only motor vehicles sparkignition systems, non-automatic weighing instruments,agricultural and forestry tractors, active implantiblemedical devices and certain electricity tariff meters.Amateur radio apparatus which is not commerciallyavailable is also specifically excluded.The Directive has two basic requirements:(i) Equipment shall not cause interference.

(ii) Equipment shall be immune from interference.

This creates two basis protection requirements whichmust be fulfilled by manufacturers.

1.Apparatus must be constructed to ensure that anydisturbance it generates allows radio andtelecommunications equipment and otherapparatus to operate as intended.

2.Apparatus must be constructed to provide anadequate level of protection against disturbances(ie. 'immunity' - the ability of apparatus to function inthe presence of an electromagnetic disturbancewithout loss of performance).

(EMC)Formal title

Council Directive /336/EEC of 3 May 19 on theapproximation of the laws of the Member Statesrelating to electromagnetic compatibility (EMC) asamended by Directive 92/31/EEC of 28 April 1992.Timetable

The implementation was effective 1 January 1992,however, transitional arrangements exist until 31December 1995. Member States must continue toallow to be placed on the market or to be put intoservice apparatus that conforms to the nationalregulations in force in their territory on 30 June 1992.Full implementation will be effective 1 January 1996.Failure to comply with these requirements will bemade a criminal offence.

Coverage

The Directive applies to individual items of apparatusfirst placed on the Community market or first taken intoservice in the Community on or after 1 January 1992even if other items of the same design have beenplaced on the market or taken into service before thatdate.

The European Commission (DTI in the UK) hasproduced an informal explanatory document on theDirective.

Components, according to the document, are outsidethe scope of the Directive. This applies both to simplecomponents and to more complex items, so long as theitem in question does not have an intrinsic function andits only purpose is to be incorporated inside theapparatus.

The document also states that systems must meet therequirements of the Directive, a system being definedas 'several items of apparatus combined to fulfil aspecific objective and intended to be placed on themarket as a single functional unit'.

The explanatory document defines an installation asseveral combined items of apparatus or systems puttogether in a given place to fulfil a specific objectivebut not intended to be placed on the market as a singlefunctional unit. It goes on to state that each apparatus orsystem used in an installation is subject to theprovisions of the Directive and that each apparatus orsystem must comply with the installations laid down bytheir manufacturer in order to ensure the properoperation of the installation itself.

1502323995RequirementsManufacturers and distributors of imports from outsidethe Community are required to provide a statementthat their equipment complies with the objectives of theDirective. However, they have three choices wherebythe compliance can be demonstrated. The simplestmethod is 'self certification'. This is achieved bysatisfying relevant standards either by in-house tests orcontracting the tests to an independent test house. TheDirective delegates responsibility for standards toCENELEC, the European electrotechnical standardsbody, which is required to produce harmonisedstandards in the form of European Standards (EN).These generally follow the recommendations of CISPR,a committee of the International ElectrotechnicalCommission (IEC) concerned with radio interference.The alternative method is to keep a 'technical file', thismust be available for inspection by the national bodyor bodies responsible for policing the Directive. Thisform of certification implies that the technical file shoulddemonstrate compliance with the objectives of theDirective. Achievement may be by setting out thedesign procedures used to ensure EMC performanceof the equipment and/or appropriate tests and mustinclude a technical report from a 'competent body'.One of the qualifications for competent body status is tobe a National Accreditation and Measurement Service(NAMAS) accredited laboratory. After 1 January 1996this method of claiming compliance will be obligatory ifthere is no appropriate relevant standard.The third method of demonstrating compliance onlyapplies to telecommunications transmitting andreceiving equipment which requires an EC typeexamination certificate to be obtained from a notifiedbody. The draft legislation identifies three such bodiesin the UK; the Radiocommunications Agency (RA) of theDTI, the Civil Aviation Authority (CAA) and the DefenceResearch Agency (DRA).A declaration of conformity can be made once thecompliance has been demonstrated. This declarationmust contain a description of the apparatus to which itrefers, referenced to the specifications under whichconformity is declared, identification of the signatoryempowered to bind the manufacturer, and whereappropriate, reference to the 'EC type - examinationcertificate' issued by a 'notified' body.Having made a declaration of conformity, the ECconformity mark CE (Communauté Européene), maybe affixed to the product or be included in theoperating instructions, on the guarantee certificate oron its packaging. The EC conformity mark shall consistof the letters CE as set out at the top of the next columnand the figures of the year in which the mark wasaffixed.2

EC conformity markLegislationApparatus which complies with the objectives of theDirective may not be impeded from being placed onthe market. However, if a 'competent authority' findsthat the apparatus does not conform, then theapparatus must be prohibited from the market and itsmovement restricted. The European Commission mustbe informed, which in turn will inform all theadministrations of the national competent authorities.Effectively this will 'ban' the equipment throughoutEurope including, for UK manufacturers anddistributors, the UK.The draft UK regulations are arranged in eight parts:Part IPreliminaryPart IIApplicationPart IIIGeneral RequirementsPart IVThe Standards Route to CompliancePart VThe Technical Construction File Route toCompliancePart VIThe EC Type Examination Route toCompliance for RadiocommunicationsTransmission ApparatusPart VIIEnforcementPart VIIIMiscellaneous and Supplemental.UK enforcement

This relates to Part VII and details how the EMCDirective is to be enforced within the UK. It defines theenforcement authorities, procurement of testpurchases, the powers granted to an enforcementofficer (search, seizure of apparatus), prohibition andsuspension notices, offences, misuse of the CE mark,penalties, power of the court and recovery ofenforcement expenses.

Enforcement authorities come under two groups:

Group 1 - enforcement for specific apparatuscomprise;1.the RA2.the DRA3.the CAA

4.the Director General of Electricity Supply for

electricity meters.

Group 2 - enforcement authorities for relevantapparatus other than that defined under Group 1comprise;

1.the Secretary of State

2.in Great Britain the weights and measures

authorities

3.in Northern Ireland the district councils.

The Directive requires member states to take 'allappropriate measures' to ensure compliant apparatusis placed on the market or taken into service. This hasbeen interpreted as requiring national legislationhaving adequate sanctions for breaches of theDirective's EMC requirements.

The following offences are included in the draftregulations:

1.Knowingly supplying, or taking into service

relevant apparatus contravening the regulations.2.Knowingly affixing the CE mark to non-compliant

apparatus and/or issuing a declaration ofconformity for that apparatus.

3.Contravention of a prohibition or suspension

notice.

4.Provision of false or misleading information in the

required documentation.

5.Affixing the CE mark or an inscription which may

be confused with it on non-compliant apparatus.6.Failure to assist an enforcement officer

(obstruction)

7. Failure to retain the full documentation.

Penalties

A person found guilty of offences 1 to 4 is liable uponconviction to; imprisonment for up to 3 months, or a fineup to level 5 on the standard scale (£5000 on 1 July1992), or both. A person guilty of offences 5 to 7 isliable to a fine up to level 5 only.

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Remedial action

Where a person is convicted of offences 1 or 2 and it isin the court's opinion that the person can take remedialaction in order for equipment to become compliant, thecourt may order the person to take remedial actionwithin a specified period of time. This period may beextended by order of the court.

Forfeiture

An enforcement authority may apply under thisregulation for the forfeiture of any relevant apparatuscontravening the regulations. An application may bemade to a magistrates court where proceedings havebeen brought against a person committing eitheroffences 1, 2 or 3. The application for forfeiture may befor some or all of the apparatus. The magistrates courtwill only grant a forfeiture order if it is satisfied that theequipment does not satisfy the protectionrequirements. Forfeited apparatus will either bedestroyed, disposed of for reconditioning or disposedof for scrap as directed by the court.

Conclusions

Despite the transitional period up to 31 December1995 the EMC Directive became effective on 1 January1992. Particularly concerning is the fact that productspecific standards and primarily immunity standardsare still lacking. However, the onus is upon companiesto describe the electromagnetic performance of theirproducts correctly and additional costs will inevitablybe incurred. The time to consider EMC is during theinitial design phase and not as an afterthought, goodpractices at the pcb level will pay dividends later.

The information contained within this data sheet wasextracted from the DTI Draft United KingdomRegulations dated July 1992 and was correct at time ofgoing to press.

Further information is available from:DTI,

Third Floor, Room 112 Grey,151 Buckingham Palace Road,London,SW1W 9SS

Tel: 071-215 1408Fax: 071-215 1529.

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The information provided in RStechnical literature is believed to be accurate and reliable; however, RS Components assumes no responsibility for inaccuraciesor omissions, or for the use of this information, and all use of such information shall be entirely at the user’s own risk.

No responsibility is assumed by RS Components for any infringements of patents or other rights of third parties which may result from its use.Specifications shown in RS Components technical literature are subject to change without notice.

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An Electrocomponents CompanyTelephone: 01536 201234© RS Components 1997