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Electromagnetic Compatibility

 Electromagnetic Compatibility (EMC)

Electromagnetic Compatibility is defined as: -

�The ability of systems, equipment, and devices, that utilize the electromagnetic spectrum, to operate in their intended operational environments without suffering unacceptable degradation or causing unintentional degradation because of electromagnetic radiation or response. It involves the application of sound electromagnetic spectrum management; system, equipment, and device design configuration that ensures interference-free operation; and clear concepts and doctrines that maximize operational effectiveness.�

EMC Practices:-

           The purpose of EMC practices is to ensure system or subsystem compatibility. Control is achieved through the use of proven design techniques having a sound theoretical and practical basis, the correct use of which assures a system relatively free of EMI problems. Such standard practices have been found to be effective through theoretical analysis, laboratory measurements, and system performance checks.

            The analysis of an EMI problem may begin with categorizing the path between the source and the sensitive design as either a conductive or radiated one, or a combination of the two. Further categorization can be accomplished by observing the frequency spectrum commonality between the emitter and the susceptor, as well as the time domain commonality between them. Other factors are their location (distance and direction) relative to one another.

              One major question that arises when considering intersystem EMI is whether the emitter or the receptors are operating within specifications and regulations. If they do one seeks to determine the path between them. If the possibility exists that the source, susceptor or the path are not on at all times we may eliminate EMI via time-sharing or synchronization. Finally if the spacing between the source and the receptor can be increased EMI may be alleviated.

 PHENOMENA AND EFFECTS WHICH MAY BE REGARDED AS ELECTROMAGNETIC DISTURBANCE:-

                Without prejudice to the generality of regulation 4(1), and in addition to the phenomena regarded as electromagnetic disturbance pursuant to regulation 4(2) (being phenomena expressly stated to be such in Article 1.2 of the EMC Directive), the following phenomena and effects may be regarded as electromagnetic disturbance�

    1.    Conducted low-frequency phenomena

�harmonics, inter-harmonics;

�signalling voltages;

�voltage fluctuations;

�voltage dips and interruptions;

�voltage unbalance;

�power�frequency variations;

�induced low�frequency voltages;

�DC in AC networks; and

�DC ground circuits;

    2.    Radiated low-frequency phenomena�

�magnetic fields; and

�electric fields;

    3.    Conducted high-frequency phenomena�

�induced continuous wave (CW) voltages or currents;

�unidirectional transients; and

�oscillatory transients;

    4.    Radiated high frequency phenomena�

�magnetic fields;

�electric fields;

�electromagnetic fields;

�continuous waves; and

�transients; and

    5.    Electrostatic discharge phenomena (ESD)

THE CE MARK

In the EC mark, the symbol "CE" shall be set out in the form shown below and the figures of the year in which the mark was affixed.

�This mark should, where appropriate, be accompanied by the distinctive letters used by the notified body issuing the EC-type examination certificate.

The EMC Directive 89/336/EEC became mandatory on January 1, 1996, and it stands for Electromagnetic Compatibility. EU (European Union) defined EMC as the ability of a device, unit or equipment, or system to function satisfactorily in its electromagnetic environment without introducing intolerable electromagnetic disturbances to any devices in that environment. This encompasses both immunity to outside noise (function satisfactorily), and emission of noise (without introducing intolerable disturbances). For this reason CENELEC (European Committee for Electrotechnical Standardization) put out two different standards.

The Generic Immunity Standard EN 50082-1, and Generic Emission Standard EN 50081-1 from 1991 for Residential, Commercial, and Light Industrial environment. This has been harmonized in 1993 for Heavy Industrial environment becoming EN 50081-2 (Emission), and EN 50082-2 (Immunity). EN 50081-1:1991 Generic Emission Standard has two parts, Radiated Emission and Conducted Emission regulated by EN 55022, comparable to FCC part 15 in US.

EN 50082-1:1991 Generic Immunity Standard consist of Electro Static Discharge (ESD), Radio Frequency (RF) and Electric Fast-Transient Burst (EFT).

The Radiated Emission deals with the electromagnetic field emitted by any electronic circuit that performs a switching sequence, and this increases if an antenna, consisting of I/O cables, is present. The test is performed between 30 to 230 MHz with a limit of 30 dBuV/m from 10 meters distance, and followed by 230 to 1,000 MHz with a limit of 37 dBuV/m from 10 meters distance for Commercial environment.

For Heavy Industry environments the distance changes to 30 meters.

Conducted Emission refers to the noise that is generated into the power lines, and causes interference at frequencies, between 0.15 to 30 MHz with limits of 60-dBuV quasi peak.

Electro Static Discharge deals with the static charges that can build up in normal operation to several kilovolts and stresses the electronic components. The test is performed with 4 kV for Direct Discharge and 8 kV for Air Discharge.

The RF Immunity refers to the ability of the equipment to work undisturbed in a RF field (electromagnetic field) between 27 to 1,000 MHz, with 80% AM (amplitude modulation), and for Light industrial environments a 3 V/m Stress level is used, or 10 V/m for Heavy industrial environment.

In every day life any RF transmitter (2 way portable radio) that has a field higher than 1 or 10 V/m may disturb your device. If the power is known the field strength can be easily determined.