Electromagnetic compatibility - AbsoluteAstronomy.com

Electromagnetic compatibility (EMC) is the branch of electrical sciences which studies the unintentional generation, propagation and reception of electromagnetic energy with reference to the unwanted effects (Electromagnetic interference

Electromagnetic interference

Electromagnetic interference is disturbance that affects an electrical circuit due to either electromagnetic induction or electromagnetic radiation emitted from an external source. The disturbance may interrupt, obstruct, or otherwise degrade or limit the effective performance of the circuit...

, or EMI) that such energy may induce. The goal of EMC is the correct operation, in the same electromagnetic environment, of different equipment which use electromagnetic phenomena, and the avoidance of any interference effects.

In order to achieve this, EMC pursues two different kinds of issues. Emission issues are related to the unwanted generation of electromagnetic energy by some source, and to the countermeasures which should be taken in order to reduce such generation and to avoid the escape of any remaining energies into the external environment. Susceptibility or Immunity issues, in contrast, refer to the correct operation of electrical equipment, referred to as the victim, in the presence of unplanned electromagnetic disturbances.

Interference mitigation and hence electromagnetic compatibility is achieved by addressing both emission and susceptibility issues, i.e., quieting the sources of interference and hardening the potential victims. The coupling path between source and victim may also be separately addressed to increase its attenuation.

Discussion

Based on the above definition, Electromagnetic Compatibility refers to the ability of an equipment or a system to perform satisfactorily in its electromagnetic environment without introducing intolerable interference into any thing in that environment. In other words, the equipment must have a certain level of "immunity" to the EMI present in its environment so that it is not "susceptible" to that EMI. Moreover, the equipment should not introduce "intolerable electromagnetic interference". This means that any "emission" of EMI by the equipment must be below certain level so that it can be tolerated by other equipment in its vicinity. Now, if an equipment has both -high immunity and low emissions, it will be compatible (in electromagnetic sense) with other equipment in its vicinity.

Since EMC and EMI are frequently referred to as a combined term "EMC/EMI", it is important to understand the differences between EMC and EMI . EMI is a phenomenon while EMC is an equipment characteristic or a property not to generate EMI above a certain limit AND not to be affected or disturbed by EMI. The statement "Live and let live" is the best way to describe EMC.

Types of interference

Electromagnetic interference

divides into several categories according to the source and signal characteristics.

The origin of noise can be man made or natural.

Continuous interference

Continuous, or Continuous Wave (CW), interference arises where the source regularly emits a given range of frequencies. This type is naturally divided into sub-categories according to frequency range, and as a whole is sometimes referred to as "DC to daylight".

Audio Frequency, from very low frequencies up to around 20 kHz. Frequencies up to 100 kHz may sometimes be classified as Audio. Sources include:
- Mains hum from power supply units, nearby power supply wiring, transmission lines and substations.
- Audio processing equipment, such as audio power amplifiers and loudspeaker
  Loudspeaker
  A loudspeaker is an electroacoustic transducer that produces sound in response to an electrical audio signal input. Non-electrical loudspeakers were developed as accessories to telephone systems, but electronic amplification by vacuum tube made loudspeakers more generally useful...
  
  s.
- Demodulation of a high-frequency carrier wave such as an FM radio transmission.
Radio Frequency Interference (RFI), from typically 20 kHz to an upper limit which constantly increases as technology pushes it higher. Sources include:
- Wireless and Radio Frequency Transmissions
- Television and Radio Receivers
- Industrial, scientific and medical equipment
- Digital processing circuitry (For example microcontroller
  Microcontroller
  A microcontroller is a small computer on a single integrated circuit containing a processor core, memory, and programmable input/output peripherals. Program memory in the form of NOR flash or OTP ROM is also often included on chip, as well as a typically small amount of RAM...
  
  s)
Broadband noise may be spread across parts of either or both frequency ranges, with no particular frequency accentuated. Sources include:
- Solar Activity
  Solar variation
  Solar variation is the change in the amount of radiation emitted by the Sun and in its spectral distribution over years to millennia. These variations have periodic components, the main one being the approximately 11-year solar cycle . The changes also have aperiodic fluctuations...
- Continuously operating spark gap
  Spark gap
  A spark gap consists of an arrangement of two conducting electrodes separated by a gap usually filled with a gas such as air, designed to allow an electric spark to pass between the conductors. When the voltage difference between the conductors exceeds the gap's breakdown voltage, a spark forms,...
  
  s such as arc welders
- CDMA mobile telephony

Pulse or transient interference

Electromagnetic Pulse, EMP, also sometimes called Transient disturbance, arises where the source emits a short-duration pulse of energy. The energy is usually broadband by nature, although it often excites a relatively narrow-band damped sine wave
Transient (oscillation)
A transient event is a short-lived burst of energy in a system caused by a sudden change of state.The source of the transient energy may be an internal event or a nearby event...

response in the victim.

Sources divide broadly into isolated and repetitive events.

Sources of isolated EMP events include:
- Switching action of electrical circuitry, including inductive loads such as relays, solenoids, or electric motors.
- Electrostatic Discharge
  Electrostatic discharge
  Electrostatic discharge is a serious issue in solid state electronics, such as integrated circuits. Integrated circuits are made from semiconductor materials such as silicon and insulating materials such as silicon dioxide...
  
  (ESD), as a result of two charged objects coming into close proximity or even contact.
- Lightning
  Lightning
  Lightning is an atmospheric electrostatic discharge accompanied by thunder, which typically occurs during thunderstorms, and sometimes during volcanic eruptions or dust storms...
  
  Electromagnetic Pulse
  Electromagnetic pulse
  An electromagnetic pulse is a burst of electromagnetic radiation. The abrupt pulse of electromagnetic radiation usually results from certain types of high energy explosions, especially a nuclear explosion, or from a suddenly fluctuating magnetic field...
  
  (LEMP), although typically a short series of pulses.
- Nuclear
  Atomic nucleus
  The nucleus is the very dense region consisting of protons and neutrons at the center of an atom. It was discovered in 1911, as a result of Ernest Rutherford's interpretation of the famous 1909 Rutherford experiment performed by Hans Geiger and Ernest Marsden, under the direction of Rutherford. The...
  
  Electromagnetic Pulse (NEMP), as a result of a nuclear explosion.
- Non-Nuclear Electromagnetic Pulse (NNEMP) weapons.
- Power Line
  Electric power transmission
  Electric-power transmission is the bulk transfer of electrical energy, from generating power plants to Electrical substations located near demand centers...
  
  Surges/Pulses

Sources of repetitive EMP events, sometimes as regular pulse
Voltage spike
In electrical engineering, spikes are fast, short duration electrical transients in voltage , current , or transferred energy in an electrical circuit....

trains, include:
- Electric Motors
  Electric motor
  An electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...
- Gasoline engine ignition systems
- Continual switching actions of digital electronic circuitry.

Coupling mechanisms

Some of the technical words employed can be used with differing meanings. These terms are used here in a widely accepted way which is consistent with other Wikipedia pages.

The basic arrangement of noise

Electronic noise

Electronic noise is a random fluctuation in an electrical signal, a characteristic of all electronic circuits. Noise generated by electronic devices varies greatly, as it can be produced by several different effects...

source, coupling

Coupling (physics)

In physics, two systems are coupled if they are interacting with each other. Of special interest is the coupling of two vibratory systems by means of springs or magnetic fields, etc...

path and victim, receptor

Receiver (radio)

A radio receiver converts signals from a radio antenna to a usable form. It uses electronic filters to separate a wanted radio frequency signal from all other signals, the electronic amplifier increases the level suitable for further processing, and finally recovers the desired information through...

or sink is shown in the figure below. Source and victim are usually electronic hardware

Electronic hardware

Electronic hardware refers to interconnected electronic components which perform analog and/or logic operations on received and locally stored information to produce as output and/or store resulting new information and/or to provide control for output actuator mechanisms.Electronic hardware can...

devices, though the source may be a natural phenomenon such as a lightning strike

Lightning strike

Lightning strikes are electrical discharges caused by lightning, typically during thunderstorms.Humans can be hit by lightning directly when outdoors. Contrary to popular notion, there is no 'safe' location outdoors. People have been struck in sheds and makeshift shelters...

, electrostatic discharge

Electrostatic discharge

Electrostatic discharge is a serious issue in solid state electronics, such as integrated circuits. Integrated circuits are made from semiconductor materials such as silicon and insulating materials such as silicon dioxide...

(ESD) or, in one famous case, the Big Bang

Big Bang

The Big Bang theory is the prevailing cosmological model that explains the early development of the Universe. According to the Big Bang theory, the Universe was once in an extremely hot and dense state which expanded rapidly. This rapid expansion caused the young Universe to cool and resulted in...

at the origin of the Universe.
There are four basic coupling mechanisms: conductive

Electrical conductor

In physics and electrical engineering, a conductor is a material which contains movable electric charges. In metallic conductors such as copper or aluminum, the movable charged particles are electrons...

, capacitive

Capacitor

A capacitor is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric ; for example, one common construction consists of metal foils separated...

, magnetic

Electromagnetic induction

Electromagnetic induction is the production of an electric current across a conductor moving through a magnetic field. It underlies the operation of generators, transformers, induction motors, electric motors, synchronous motors, and solenoids....

or inductive, and radiative

Electromagnetic radiation

Electromagnetic radiation is a form of energy that exhibits wave-like behavior as it travels through space...

. Any coupling path can be broken down into one or more of these coupling mechanisms working together. For example the lower path in the diagram involves inductive, conductive and capacitive modes.

Conductive coupling

Conductive coupling
Conductive coupling
Conductive coupling is the transfer of electrical energy by means of physical contact via a conductive medium, in contrast to inductive coupling and capacitive coupling...

occurs when the coupling path between the source and the receptor is formed by direct contact with a conducting body, for example a transmission line, wire, cable, PCB

Printed circuit board

A printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, tracks or signal traces etched from copper sheets laminated onto a non-conductive substrate. It is also referred to as printed wiring board or etched wiring...

trace or metal enclosure.

Conduction modes

Conducted noise is also characterised by the way it appears on different conductors:

Common-mode or 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.

Inductive coupling

Inductive coupling occurs where the source and receiver are separated by a short distance (typically less than a wavelength). Strictly, "Inductive coupling" can be of two kinds, electrical induction and magnetic induction. It is common to refer to electrical induction as capacitive coupling, and to magnetic induction as inductive coupling.

Capacitive coupling

Capacitive coupling
Capacitive coupling
In electronics, capacitive coupling is the transfer of energy within an electrical network by means of the capacitance between circuit nodes. This coupling can have an intentional or accidental effect...

occurs when a varying electrical field

Electric field

In physics, an electric field surrounds electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding...

exists between two adjacent conductors typically less than a wavelength

Wavelength

In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...

apart, inducing a change in voltage

Voltage

Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...

across the gap.

Magnetic coupling

Inductive coupling
Inductive coupling
In electrical engineering, two conductors are referred to as mutual-inductively coupled or magnetically coupled when they are configured such that change in current flow through one wire induces a voltage across the ends of the other wire through electromagnetic induction...

or magnetic coupling (MC) occurs when a varying magnetic field

Magnetic field

A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...

exists between two parallel conductors typically less than a wavelength

Wavelength

apart, inducing a change in voltage

Voltage

along the receiving conductor.

Radiative coupling

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

EMC control

The damaging effects of electromagnetic interference pose unacceptable risks in many areas of technology, and it is necessary to control such interference and reduce the risks to acceptable levels.

The control of electromagnetic interference (EMI) and assurance of EMC comprises a series of related disciplines:

Characterising the threat.
Setting standards for emission and susceptibility levels.
Design for standards compliance.
Testing for standards compliance.

For a complex piece of equipment, this may require the production of a dedicated EMC control plan summarizing the application of the above and specifying additional documents required.

Characterising the threat

Characterisation of the problem requires understanding of:

The interference source and signal.
The coupling path to the victim.
The nature of the victim both electrically and in terms of the significance of malfunction.

The risk posed by the threat is usually statistical in nature, so much of the work in threat characterisation and standards setting is based on reducing the probability of disruptive EMI to an acceptable level, rather than its assured elimination.

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:

International Electrotechnical Commission
International Electrotechnical Commission
The International Electrotechnical Commission is a non-profit, non-governmental international standards organization that prepares and publishes International Standards for all electrical, electronic and related technologies – collectively known as "electrotechnology"...

(IEC), which has several committees working full time on EMC issues. These are:
- Technical Committee 77 (TC77), working on electromagnetic compatibility between equipment including networks.
- Comité International Spécial des Perturbations Radioélectriques
  Comité International Spécial des Perturbations Radioélectriques
  The Comité International Spécial des Perturbations Radioélectriques was founded in 1934 to set standards for controlling electromagnetic interference in electrical and electronic devices, and is a part of the International Electrotechnical Commission .-Organization:CISPR's organization is divided...
  
  (CISPR), or International Special Committee on Radio Interference.
- The Advisory Committee on Electromagnetic Compatibility (ACEC) co-ordinates the IEC's work on EMC between these committees.
International Organization for Standardization
International Organization for Standardization
The International Organization for Standardization , widely known as ISO, is an international standard-setting body composed of representatives from various national standards organizations. Founded on February 23, 1947, the organization promulgates worldwide proprietary, industrial and commercial...

(ISO), which publishes standards for the automotive industry.

Among the more well known national organizations are:

Europe:
- Comité Européen de Normalisation
  European Committee for Standardization
  The European Committee for Standardization or Comité Européen de Normalisation , is a non-profit organisation whose mission is to foster the European economy in global trading, the welfare of European citizens and the environment by providing an efficient infrastructure to interested parties for...
  
  (CEN) or European Committee for Standardization).
- Comité Européen de Normalisation Electrotechniques (CENELEC) or European Committee for Electrotechnical Standardisation.
- European Telecommunications Standards Institute (ETSI).
United States:
- The Federal Communications Commission
  Federal Communications Commission
  The Federal Communications Commission is an independent agency of the United States government, created, Congressional statute , and with the majority of its commissioners appointed by the current President. The FCC works towards six goals in the areas of broadband, competition, the spectrum, the...
  
  (FCC).
- The Society of Automotive Engineers (SAE).
Britain: The British Standards Institution
British Standards
British Standards are the standards produced by BSI Group which is incorporated under a Royal Charter...

(BSI).
Germany: The Verband der Elektrotechnik, Elektronik und Informationstechnik
Verband der Elektrotechnik, Elektronik und Informationstechnik
The VDE Association for Electrical, Electronic and Information Technologies e.V. is one of Europe’s largest technical-scientific associations with 35,000 members, including 1,300 corporate and institutional members and 8,000 students.- Organization :...

(VDE) or Association for Electrical, Electronic and Information Technologies.

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

CE mark

CE marking is a mandatory conformity mark for products placed on the market in the European Economic Area . With the CE marking on a product the manufacturer ensures that the product conforms with the essential requirements of the applicable EC directives...

. Undisturbed usage of electric devices for all customers should be ensured and the electromagnetic field strength should be kept on a minimum level. EU directive 2004/108/CE (previously 89/336/EEC) on EMC announces the rules for the distribution of electric devices within the European Union

European Union

The European Union is an economic and political union of 27 independent member states which are located primarily in Europe. The EU traces its origins from the European Coal and Steel Community and the European Economic Community , formed by six countries in 1958...

. A good overview of EME limits and EMI demands is given in List of EMC directives.

EMC design

Electromagnetic noise

Electromagnetic interference

is produced in the source due to rapid current

Electric current

Electric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...

and voltage

Voltage

changes, and spread via the coupling mechanisms described earlier.

Since breaking a coupling path is equally effective at either the start or the end of the path, many aspects of good EMC design practice apply equally to potential emitters and to potential victims. Further, a circuit which easily couples energy to the outside world will equally easily couple energy in and will be susceptible. A single design improvement often reduces both emissions and susceptibility.

Grounding and shielding

Grounding and shielding aim to divert EMI away from the victim by providing an alternative, low-impedance path. Techniques include:

Shielded
Electromagnetic shielding
Electromagnetic shielding is the process of reducing the electromagnetic field in a space by blocking the field with barriers made of conductive and/or magnetic materials. Shielding is typically applied to enclosures to isolate electrical devices from the 'outside world' and to cables to isolate...

Housings.
Shielded Lines.
Grounding or earthing schemes such as Star Earthing for audio equipment, or Ground planes for RF.

Other general measures

Decoupled
Decoupling
The term "decoupling" is used in many different contexts.-Economic growth without environmental damage:In economic and environmental fields, decoupling is becoming increasingly used in the context of economic production and environmental quality. When used in this way, it refers to the ability of...

Cable Entries (Line filter, Signal filter) using RF chokes
Choke (electronics)
A choke is a coil of insulated wire, often wound on a magnetic core, used as a passive inductor which blocks higher-frequency alternating current in an electrical circuit while passing signals of much lower frequency and direct current by having an impedance largely determined by reactance, which...

, or RC elements
RC circuit
A resistor–capacitor circuit ', or RC filter or RC network, is an electric circuit composed of resistors and capacitors driven by a voltage or current source...

.
Transmission line techniques for cables and wiring, such as balanced differential signal and return paths, and impedance matching.
Avoidance of Antenna Structures, such as loops of circulating current, resonant mechanical structures, unbalanced cable impedances or poorly grounded shielding.

Emissions suppression

Additional measures to reduce emissions include:

Avoid unnecessary switch
Switch
In electronics, a switch is an electrical component that can break an electrical circuit, interrupting the current or diverting it from one conductor to another....

ing operations. Necessary switching should be done as slowly as technically possible.
Noisy circuits (with a lot of switching activity) should be physically separated from the rest of the design.
High peaks can be avoided by using the spread spectrum
Spread spectrum
Spread-spectrum techniques are methods by which a signal generated in a particular bandwidth is deliberately spread in the frequency domain, resulting in a signal with a wider bandwidth...

method.
Harmonic
Harmonic
A harmonic of a wave is a component frequency of the signal that is an integer multiple of the fundamental frequency, i.e. if the fundamental frequency is f, the harmonics have frequencies 2f, 3f, 4f, . . . etc. The harmonics have the property that they are all periodic at the fundamental...

Wave Filters.
Design for operation at lower signal levels, reducing the energy available for emission.

Susceptibility hardening

Additional measures to reduce susceptibility include:

Fuses, trip switches and circuit breakers.
Transient absorbers.
Design for operation at higher signal levels, reducing the relative noise level in comparison.

EMC testing

Testing is required to confirm that a particular device meets the required standards. It divides broadly into emissions testing and susceptibility testing.

RF testing of a physical prototype is most often carried out in a radio-frequency anechoic chamber.

Open-air test sites, or OATS, are the reference sites in most standards. They are especially useful for emissions testing of large equipment systems.

Sometimes computational electromagnetics

Computational electromagnetics

Computational electromagnetics, computational electrodynamics or electromagnetic modeling is the process of modeling the interaction of electromagnetic fields with physical objects and the environment....

simulations are used to test virtual models.

Like all compliance testing, it is important that the test equipment, including the test chamber or site and any software used, be properly calibrated and maintained.

Typically, a given run of tests for a particular piece of equipment will require an EMC test plan and follow-up Test report. The full test program may require the production of several such documents.

Susceptibility testing

Radiated field susceptibility testing typically involves a high-powered source of RF or EM pulse energy and a radiating antenna to direct the energy at the potential victim or device under test (DUT).

Conducted voltage and current susceptibility testing typically involves a high-powered signal or pulse generator, and a current clamp

Current clamp

In electrical and electronic engineering, a current clamp or current probe is an electrical device having two jaws which open to allow clamping around an electrical conductor. This allows properties of the electric current in the conductor to be measured, without having to make physical contact...

or other type of transformer

Transformer

A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...

to inject the test signal.

Transient immunity is used to test the immunity of the DUT against powerline disturbances including surges, lightning strikes and switching noise. In motor vehicles, similar tests are performed on battery and signal lines.

Electrostatic discharge

Electrostatic discharge

testing is typically performed with a piezo spark generator

Piezo ignition

Piezo ignition is a type of ignition that is used in portable camping stoves, gas grills and some lighters, and potato guns. It consists of a small, spring-loaded hammer which, when a button is pressed, hits a crystal of PZT or quartz crystal. Quartz is piezoelectric, which means that it creates a...

called an "ESD pistol". Higher energy pulses, such as lightning or nuclear EMP simulations, can require a large current clamp

Current clamp

or a large antenna which completely surrounds the DUT. Some antennas are so large that they are located outdoors, and care must be taken not to cause an EMP hazard to the surrounding environment.

Emissions testing

Emissions are typically measured for radiated field strength and where appropriate for conducted emissions along cables and wiring. Inductive (magnetic) and capacitive (electric) field strengths are near-field effects, and are only important if the device under test (DUT) is designed for location close to other electrical equipment.

Typically a spectrum analyzer

Spectrum analyzer

A spectrum analyzer measures the magnitude of an input signal versus frequency within the full frequency range of the instrument. The primary use is to measure the power of the spectrum of known and unknown signals...

is used to measure the emission levels of the DUT across a wide band of frequencies (frequency domain). Specialized spectrum analyzers for EMC testing are available, called EMI Test Receivers or EMI Analyzers. These incorporate bandwidths and detectors as specified by international EMC standards. EMI Receivers along with specified transducers can often be used for both conducted and radiated emissions. Pre-selector filters may also be used to reduce the effect of strong out-of-band signals on the front-end of the receiver.

For conducted emissions, typical transducers are the LISN (Line Impedance Stabilisation Network) also sometimes called as the AMN (Artificial Mains Network) and the RF current clamp

Current clamp

.

For radiated emission measurement, antennas are used as transducers. Typical antennas specified include dipole, biconical, log-periodic, double ridged guide and conical log-spiral designs. Radiated emissions must be measured in all directions around the DUT.

Some pulse emissions are more usefully characterized using an oscilloscope

Oscilloscope

An oscilloscope is a type of electronic test instrument that allows observation of constantly varying signal voltages, usually as a two-dimensional graph of one or more electrical potential differences using the vertical or 'Y' axis, plotted as a function of time,...

to capture the pulse waveform in the time domain.

History

The earliest EMC issue was lightning

Lightning

Lightning is an atmospheric electrostatic discharge accompanied by thunder, which typically occurs during thunderstorms, and sometimes during volcanic eruptions or dust storms...

strike (Lightning Electromagnetic Pulse

Electromagnetic pulse

An electromagnetic pulse is a burst of electromagnetic radiation. The abrupt pulse of electromagnetic radiation usually results from certain types of high energy explosions, especially a nuclear explosion, or from a suddenly fluctuating magnetic field...

, or LEMP) on buildings. Lightning rod

Lightning rod

A lightning rod or lightning conductor is a metal rod or conductor mounted on top of a building and electrically connected to the ground through a wire, to protect the building in the event of lightning...

s or lightning conductors began to appear in the mid-18th century. With the advent of widespread electricity generation

Electricity generation

Electricity generation is the process of generating electric energy from other forms of energy.The fundamental principles of electricity generation were discovered during the 1820s and early 1830s by the British scientist Michael Faraday...

and power supply lines from the late 19th century on, problems also arose with equipment short-circuit failure affecting the power supply, and with local fire and shock hazard when the power line was struck. Power stations were provided with output circuit breaker

Circuit breaker

A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow...

s. Buildings and appliances would soon be provided with input fuse

Fuse

The word fuse has several meanings:* Fuse , a device used in electrical systems to protect against excessive current....

s, and later in the 20th century miniature circuit breakers (MCB) would come into use.

As radio communications developed in the first half of the 20th century, interference between broadcast

Broadcast

Broadcast or Broadcasting may refer to:* Broadcasting, the transmission of audio and video signals* Broadcast, an individual television program or radio program* Broadcast , an English electronic music band...

radio signals began to occur and an international regulatory framework was set up to ensure interference-free communications.

As switching devices became commonplace, typically in petrol powered cars and motorcycles but also in domestic appliances such as thermostats and refrigerators, transient interference with domestic radio and (after World War II) TV reception became problematic, and in due course laws were passed requiring the suppression of such interference sources.

After World War II the military became increasingly concerned with the effects of nuclear electromagnetic pulse (NEMP), lightning strike, and even high-powered radar

Radar

Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...

beams, on mobile vehicles of all kinds, and especially aircraft electrical systems.

ESD problems first arose with accidental electric spark

Electric spark

An electric spark is a type of electrostatic discharge that occurs when an electric field creates an ionized electrically conductive channel in air producing a brief emission of light and sound. A spark is formed when the electric field strength exceeds the dielectric field strength of air...

discharges in hazardous environments such as coal mines and when refuelling aircraft or motor cars. Safe working practices had to be developed.

When high RF emission levels from other sources became a potential problem (such as with the advent of microwave oven

Microwave oven

A microwave oven is a kitchen appliance that heats food by dielectric heating, using microwave radiation to heat polarized molecules within the food...

s), certain frequency bands were designated for Industrial, Scientific and Medical (ISM) use, allowing unlimited emissions. A variety of issues such as sideband and harmonic emissions, broadband sources, and the increasing popularity of electrical switching devices and their victims, resulted in a steady development of standards and laws.

From the 1970s, the popularity of modern digital circuitry rapidly grew. As the technology developed, with faster switching speeds (increasing emissions) and lower circuit voltages (increasing susceptibility), EMC increasingly became a source of concern. Many more nations became aware of EMC as a growing problem and issued directives to the manufacturers of digital electronic equipment, which set out the essential manufacturer requirements before their equipment could be marketed or sold. Organizations in individual nations, across Europe and worldwide, were set up to maintain these directives and associated standards. This regulatory environment led to a growing EMC industry supplying specialist devices and equipment, analysis and design software, and testing and certification services.

Low-voltage digital circuits, especially CMOS transistors, became more susceptible to ESD damage as they were miniaturised, and a new ESD regulatory regime had to be developed.

From the 1980s, the ever-increasing use of mobile communications and broadcast media channels has put huge pressure on the available airspace. Regulatory authorities are squeezing band allocations closer and closer together, relying on increasingly sophisticated EMC design methods, especially in the digital communications arena, to keep cross-channel interference to acceptable levels. Digital systems are inherently less susceptible than the old analogue systems, and also offer far easier ways (such as software) to implement highly sophisticated protection measures.

Most recently, even the ISM bands are being used for low-power mobile digital communications. This approach relies on the intermittent nature of ISM interference and use of sophisticated error-correction methods to ensure lossless reception during the quiet gaps between bursts of interference.

EMC test equipment manufacturers (alphabetic)

Aaronia
Aaronia
Aaronia is a startup company based in Euscheid, Germany. Aaronia was founded in 2003 by Thorsten Chmielus and mainly produce spectrum analyzers which base on a patented spectrum analyzer process.In 2004 Aaronia shipped its first spectrum analyzer....
Aeroflex
Aeroflex
Aeroflex Inc. is an American company which produces and markets RF and microwave integrated circuits, components, and systems used for wireless communications. Aeroflex consists of Aeroflex Microelectronic Solutions , a fabless manufacturer of rad-hard and hi-rel semiconductor devices and...
Agilent (formerly the test and measurement division of Hewlett-Packard
Hewlett-Packard
Hewlett-Packard Company or HP is an American multinational information technology corporation headquartered in Palo Alto, California, USA that provides products, technologies, softwares, solutions and services to consumers, small- and medium-sized businesses and large enterprises, including...

)
Anritsu
Anritsu
is a Japanese corporation that is in the test and measurement market. Products include microwave, RF, and optical signal generators , spectrum analyzers, and network analyzers. It was formed with the merger of two companies, the Annaka Corporation and Kyoritsu Electric in Japan in 1931. In 1990...
MILMEGA
MILMEGA
MILMEGA is a company specializing in designing and manufacturing solid state, high power amplifiers for Electromagnetic compatibility testing...
National Instruments
National Instruments
National Instruments Corporation, or NI , is an American company with over 5,000 employees and direct operations in 41 countries. Headquartered in Austin, Texas, it is a producer of automated test equipment and virtual instrumentation software...
Rohde & Schwarz
Rohde & Schwarz
Rohde & Schwarz is an independent group of companies specializing in electronics. Well known as a manufacturer of electronic test equipment, they also manufacture equipment used for broadcasting, radiolocation, and radio communications...
Tektronix
Tektronix
Tektronix, Inc. is an American company best known for its test and measurement equipment such as oscilloscopes, logic analyzers, and video and mobile test protocol equipment. In November 2007, Tektronix became a subsidiary of Danaher Corporation....
Teseq
Teseq
Teseq AG, formerly Schaffner Test Systems is a supplier of Electromagnetic compatibility test solutions. They develop and manufacture instruments for EMC emissions and immunity testing both for radiated and conducted emissions and immunity...

(formerly Schaffner).
Würth
Würth
The Würth Group is a worldwide wholesaler of fasteners, screws and screw accessories, dowels, chemicals, furniture and construction fittings, tools, machines, installation material, automotive hardware, inventory management, storage and retrieval systems. Würth was founded in 1945 by Adolf Würth...

Discussion

Types of interference

Continuous interference

Pulse or transient interference

Coupling mechanisms

Conductive coupling

Conduction modes

Inductive coupling

Capacitive coupling

Magnetic coupling

Radiative coupling

EMC control

Characterising the threat

Regulatory and standards bodies

Laws

EMC design

Grounding and shielding

Other general measures

Emissions suppression

Susceptibility hardening

EMC testing

Susceptibility testing

Emissions testing

History

EMC test equipment manufacturers (alphabetic)

See also

Web sites

General introductions

Specific topics