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Electromagnetic Compatibility (EMC)


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EMC stands for Electromagnetic Compatibility. In basic terms, EMC is the ability of a device, equipment or system to function satisfactorily in its electromagnetic environment, without introducing intolerable electromagnetic disturbance to anything in that environment.

The goal of EMC is to create a situation of functional and safe operation, in a common electromagnetic environment, of different equipment and the avoidance of any interference effects.





A characteristic and a discipline

EMC is a characteristic of equipment or system that mutually withstand their respective electromagnetic emissions.

EMC is now also a discipline aimed at achieving the 'peaceful' coexistence of equipment sensitive to electromagnetic disturbances (considered as the "victim") alongside equipment emitting such disturbances (considered as the "source").
 
This discipline investigates the unwanted radio interferences emitted (emissions), and unwanted susceptibility of equipment (immunity) against electromagnetic fields.



Today, EMC is indispensable

Equipment and systems are always subjected to electromagnetic disturbance, and any electrical / electronic device is, itself,  more or less an electromagnetic disturbance generator.

These disturbances are generated in many ways. However, the main underlying causes are sudden variations in current or voltage.

These disturbances can be propagated by conduction along wires or cables or by radiation in the form of electromagnetic waves.

Interference or noise mitigation and hence Electromagnetic Compatibility is achieved by addressing both emission and immunity issues.

 
                                        Electromagnetic Compatibility (EMC) Concept Overview
 
 
 
Why do we need EMC?

Disturbances cause undesirable phenomena. Two examples are radio wave interference and interference with communication, navigation, control and monitoring systems caused by electromagnetic emissions. These may cause device or equipment suffering from loss of functionality or even induce potential safety hazard to the users.

In recent years, several trends have together made EMC more important than ever:
  • Disturbances are becoming stronger with increasing voltage and current values.
  • Electronics circuits are becoming increasingly sensitive.
  • Distances between sensitive circuits (often electronic) and disturbing circuits (power circuits) are becoming smaller.

EMC is therefore a fundamental criterion that must be respected in all phases of product development and manufacturing, as well as during installation and wiring.

Moreover, EMC is now included in standards and is becoming a legal requirement. Within the European community, EMC is part of the essential safety properties, every electronic and electronic device has to meet essential requirements and brought under the CE marking regime. Aspects of safety are governed by Directives.

 
What is Emission? 

Emission is also known as EMI, which stands for Electromagnetic Interference.

Electromagnetic emissions relate to the unwanted electromagnetic energy emitted from one device which may interfere with the effective performance of another device.

The "Source" generates emissions. Sources of EMI can either be Natural or Man-made, Intentional or Unintentional. 

Natural: Sources associated with natural phenomena, such as electrostatic discharge, lightning, etc.
Man-made: Sources associated with man-made phenomena, such as fault surges, switching transients, local oscillators, harmonic outputs of communication transmitters, etc.
Intentional: Emitters whose primary function depends on radiated emitters. Examples include electronic licensed communication systems such as communication, navigation, and radar systems.
Unintentional:Devices that radiate radio frequencies but is not considered their primary function.


Electromagnetic Emission: The Source
 
 

What is Immunity? 

Immunity is also known as EMS, which stands for Electromagnetic Susceptibility.

Electromagnetic Immunity relates to the ability of a device to function satisfactorily in its intended electromagnetic environment.

Unintentional: The "Victim" is required to be able to withstand emissions generated by other "Sources".


Electromagnetic Emission: The Victim


EMC Testing


EMC Testing is necessary in ensuring that a device, equipment or system does not emit electromagnetic disturbances more than the levels determined in limits established by regulatory / standard bodies, and at the same time it is able to withstand an expected level of electromagnetic disturbances from various sources of transient phenomena and continuous radio frequency phenomena that are present in its intended electromagnetic environment. 

EMC testing are often carried out in validated test sites including OATS (Open Area Test Site), Fully Anechoic Chamber, Semi-Anehoic Chamber, Reverberating Chamber, Shielded Enclosures, etc.


Semi-Anechoic Chamber control room


Types of Measurement
 
IEV (International Electrotechnical Vocabulary) defines EMC as "The ability of a device, equipment or system to function satisfactorily in its electromagnetic environment, without introducing intolerable electromagnetic disturbance to anything in that environment."

Therefore, EMC deals with two things: Interference and Susceptibility, which are also known as Emissions and Immunity. Interference is about the unwanted radio interferences emitted (emissions), while susceptibility is about the unwanted susceptibility of equipment (immunity) against electromagnetic fields.

Interference and susceptibility are classified into two main categories: Radiated and Conducted. Electromagnetic Interference (EMI) is caused by undesirable radiated electromagnetic fields or conducted voltages and currents. The interference is produced by a source emitter and is detected by a susceptible victim via a coupling path. The coupling path may involve one or more of the following 4 basic coupling mechanisms.

1. Radiated:
  •     Radiative - Electromagnetic Field
  •     Capacitive - Electric Field (E Field)
  •     Inductive - Magnetic Field (H Field)
2. Conducted:
  •     Conductive - Electric Current

Radiated electromagnetic field coupling may be treated as two cases. In the near field, E and H field coupling are treated separately. In the far field, coupling is treated as a plane wave coupling.

Radiative coupling occurs when source and victim are separated by a large distance (far field), typically more than a wavelength. Source and victim act as radio antennas: The source emits or radiates an electromagnetic wave which propagates across the free space in between and is picked up or received by the victim.

Capacitive coupling occurs when there is a voltage difference between conductors, or when an electric field exists between two adjacent conductors typically less than a wavelength apart (near field). The coupling mechanism may be modeled by a capacitor.

Inductive coupling occurs when there is current flows in conductors, or when a magnetic field exists between two adjacent conductors typically less than a wavelength apart (near field). The coupling mechanism may be modeled by a transformer.

Conductive coupling occurs when electromagnetic energy propagates along a conductor in direct contact, such as power leads, transmission lines, wires, interconnecting cables, PCB traces, metal enclosures, etc.


Conducted noise is also characterized by the way it appears on different conductors:
  • Common-Mode Coupling: Also known as common-impedance coupling. Noise appears in phase (in the same direction) on two conductors.
  • Differential-Mode Coupling: Noise appears out of phase (in opposite directions) on two conductors.

The following is an overview of types of EMC measurements based on EN standards.


EMC Types of Measurement: EN Standards



Regulatory and Standards Bodies

Several international organizations work to promote international co-operation on standardization (harmonization), including publishing various EMC standards. Where possible, a standard developed by one organization may be adopted with little or no change by others. This helps for example to harmonize national standards across Europe. Standards organizations include:

1)  IEC (International Electrotechnical Commission)
     It has several committees working full time on EMC issues. These are:

  • TC77 (Technical Committee 77), working on electromagnetic compatibility between equipment including networks.
  • CISPR (International Special Committee on Radio Interference)
  • ACEC (The Advisory Committee on Electromagnetic Compatibility), co-ordinating the IEC's work on EMC between these committees.


2)  ISO (International Organization for Standardization)
     It publishes standards for the automotive industry.


The following are some of the national organizations:

1)  Europe

  •      CEN (European Committee for Standardisation)
  •      CENELEC (European Committee for Electrotechnical Standardisation)
  •      ETSI (European Telecommunications Standards Institute)


2) United States

  •     FCC (The Federal Communications Commission)
  •     SAE (The Society of Automotive Engineers)
  •     ANSI (American National Standards Institute)
  •     TIA (Telecommunications Industry Association)


3) Britain

  •     BSI (The British Standards Institution)


4) Germany

  •     VDE (Association for Electrical, Electronic and Information Technologies)


5) Japan

  •      JISC (Japanese Industrial Standards Committee)
  •      VCCI (Voluntary Control Council for Interference by Information Technology Equipment)

6) Korea

  •     KATS (Korea Agency for Technology and Standards)


7) China

  •     SAC (Standardization Administration of China)


8) Malaysia

  •     MCMC (Malaysian Communications and Multimedia Commission)
  •     DSM (Department of Standards Malaysia)



Regulatory and Standards Bodies


 

Laws

Compliance with national or international standards is usually required by laws passed by individual nations. Different nations can require compliance with different standards.

By European law, manufacturers of electronic devices are advised to run EMC tests in order to comply with compulsory CE-labeling. Undisturbed usage of electrical / electronic devices for all customers should be ensured and the electromagnetic field strength should be kept on a minimum level. EU directive 2004/108/EC (previously 89/336/EEC) on EMC announces the rules for the distribution of electrical / electronic devices within the European Union. A good overview of EMC limits and demands is given in the list of EMC directives.





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