Electromagnetic compatibility

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Electromagnetic compatibility ( EMC ) describes the ability of a technical device not to interfere with other devices through unwanted electrical or electromagnetic effects or to be interfered with by other devices. In electrical engineering, unwanted reciprocal influencing is not just a question of technology, but also a question of law.

Demarcation from environmental compatibility

Electromagnetic waves, such as light or high-energy microwaves, also have an impact on living beings and nature . EMC is not to be confused with electromagnetic environmental compatibility (EMVU), which deals with the effects of non-ionizing electromagnetic radiation on the environment and people.


Electromagnetic compatibility means the lack of effects on other devices and facilities that could lead to unwanted or deliberate malfunctions in electrical or electronic equipment due to e.g. B. electrical, magnetic or electromagnetic fields and processes. This already includes influences from currents or voltages.

Correct construction and design are essential for ensuring that electrical equipment functions in an electromagnetically compatible manner. Evidence and confirmation of immunity to interference and sufficiently low interference emissions are regulated by EMC guidelines and EMC standards.

The European EMC Directive defines electromagnetic compatibility as follows:

"The ability of an apparatus, a plant or a system to work satisfactorily in the electromagnetic environment without itself causing electromagnetic interference which would be unacceptable for any apparatus, plant or system in this environment."

From this, the basic protection requirements are derived that every electrical equipment that is placed on the market must comply with. The protection requirements stipulate that on the one hand the interference emissions of the equipment must be so low that z. B. radio receivers or other equipment in the interference environment are not influenced in an impermissible manner. This is a limitation of the sources of interference (so-called radio interference suppression ). On the other hand, the expected disturbance variables (fields, disturbance currents or disturbance voltages) affecting the equipment should not impair its function. The equipment must therefore be set up sufficiently resistant to interference.

For equipment that complies with the relevant EMC standards, it can be assumed that the protection requirements are complied with. In Germany, the VDE or DKE is responsible for creating and editing the standards. Recently, the standards have been increasingly aligned on an international level. That is why international standardization organizations such as IEC , CENELEC and CISPR are playing an increasingly important role in Germany.


Different types of coupling

The usual interference coupling model is based on the terms interference source, coupling path and interference sink. The interference -generating apparatus is used as source of interference (engl. Source or culprit ), the resource is influenced as a noise receiver (engl. Victim or load ), respectively. So that the source can influence the sink, the disturbance must reach the sink so that it can act as a disturbance variable there . The path between source and sink is called coupling or coupling path . In EMC, the criterion for the quality of signal transmission is the signal-to-noise ratio .

A distinction is made between natural and technical sources of interference and interference sinks. An example of a natural source of interference is lightning , natural sinks can be living beings. Typical technical sources of interference are e.g. B. frequency converter , typical technical interference sinks are z. B. radio receivers.

When living beings are influenced by electrical, magnetic or electromagnetic variables, one also speaks of electromagnetic environmental compatibility or EMC . Protection against lightning is treated under the term lightning protection . Protection against electrostatic discharges is also often considered separately.

A distinction is made between the following coupling mechanisms:

  • The galvanic coupling , technically more precise impedance coupling , arises at the common impedances of the interference circuit with the circuit of the interference sink. This can be common components or line sections of both circuits, via the z. B. equalizing currents flow that couple voltages via the impedance of the common line section. In the case of printed circuit boards, impedance coupling may also arise via insufficiently dimensioned ground paths and support capacitors. Note: At this point at the latest, the term impedance coupling is technically preferable to the usual term galvanic coupling , since a capacitor does not provide a galvanic connection.
  • Capacitive coupling describes the influence of an electric field , e.g. B. Coupling to parallel conductors in a cable or cable duct or parallel conductors on a circuit board. This effect can e.g. B. occur between parallel lines with high-resistance terminating impedances.
  • Inductive coupling describes the influence of a magnetic field on an interference sink . The inductive coupling is created by magnetic field coupling, usually in conductor loops, e.g. B. between parallel conductor loops, each of which has low-resistance terminating impedances.
  • Of mutual coupling occurs when an electromagnetic field is applied to a noise receiver. Electrical conductors of a cable or on circuit boards can act as an antenna and z. B. receive radio or radio signals that arise on the conductor as interference signals.

Types of disorders

  • There are dynamic disturbances in current-carrying conductors, which change over time, and also static disturbances (especially magnetic and capacitive disturbances) which remain unchanged at all times.

The EMC is between wireline and field-bound distinguished disorders.

  • The conducted interference are the source of interference directly via supply or signal lines for susceptible equipment transferred.
A crackling sound on the radio can be caused, for example, by switching off a refrigerator, switching off the supply voltage with the help of a temperature switch generates voltage pulses with a spectrum from audio to radio frequency range. If, as a result of a change in current, these voltage pulses are fed to the radio via the supply line and demodulated there, a cracking noise occurs.
The only remedy is generally tailored filtering that does not distort the actual useful signal .
  • All capacitive and inductive influences on electrical or magnetic fields are referred to as field-related interference or interference fields for short .
The field- related interference is transmitted to the interference sink , for example as an electromagnetic field from a cable or a conductive surface as a source of interference , and received there, for example, by a conductor functioning as an antenna.
An example of a field-related disturbance is the coupling of a GSM - mobile phone transmission into an audio device, e.g. B. in a car radio or in a landline phone. The reason for this are radio waves from the mobile phone that penetrate the device, are demodulated (rectified) on the devices' semiconductor components and then, amplified with the useful signal, reach the loudspeaker.
The typical interfering noises arise because the radio telephones switch the HF carrier (GSM signal) on and off at a low frequency, i.e. in the audible frequency range, using a time division multiplex method.

Interference avoidance

An EMC-compliant design of systems or devices serves to avoid interference. One distinguishes

  1. Measures to avoid disruptions
  2. Avoid spreading from the source
  3. Avoidance of the effects of the disturbances

The measures have priority in their order, whereby the first two (active) measures concern the interference emission and the third the (passive) immunity or interference immunity.

Interference can be avoided by keeping the current and voltage rate of change sufficiently small so that no higher frequencies appear in the spectrum that spread unintentionally. However, this is often not possible:

  • Computers work with ever higher clock frequencies.
  • Switching power supplies have high operating frequencies in order to be able to make them smaller.
  • Power electronics have steep switching edges in order to be more efficient.

It is therefore necessary to prevent the occurrence and propagation of interference during the construction of the internal circuit (layout of the printed circuit board) by taking rapidly changing currents short and avoiding structures that act as antennas. Any disturbances that occur nevertheless are reduced in their propagation by shielding and filtering .

The twisting of symmetrical signals is an active as well as a passive protection, because capacitive and inductive radiation and influence cancel each other out.

Depending on the disturbance situation, either the interruption or the connection of electrical ground references is expedient:

  • So-called ground loops can be avoided by means of electrical isolation, or currents flowing in them can be reduced by using a sheath current filter .
  • Cable shields that are applied high-frequency-tight on both sides when entering a shielding housing can prevent high-frequency penetration and radiation.
  • Low-induction, wide ground connections can reduce potential differences between devices and thus make signal connections between them more secure.
  • Varistors , suppressor diodes and surge arresters divert voltage transients at the cable / device interfaces to earth if the voltage level exceeds a critical level for the following components.

Technical consequences

The electromagnetic waves can generate voltages or currents in circuits, for example . In the simplest case, these can lead to noise in the television , in the worst case to failure of the electronics.

The electromagnetic compatibility ensures that, for example, cardiac pacemakers or the control electronics of motor vehicles and aircraft do not fail at least up to a defined disturbance variable. The operation of cell phones in aircraft is possible under certain conditions, but is generally not yet permitted across the board (cf. LuftEBV ). One of the requirements in aviation is proof of the aircraft's electromagnetic compatibility with the mobile communications standard.

Electromagnetic compatibility also requires special attention in industrial machine and plant construction as well as in naval shipbuilding. Here, powerful electromechanical actuators and sensitive sensors often have to work together in a confined space without interference.

Statutory Regulations

The lawmakers write to the EU's commercialisers of electrical appliances before, in Germany by the Act on electromagnetic compatibility of equipment complied with the applicable safety requirements, by limiting values for immunity or for interference emission in relevant standards are laid down.

More on this topic can be found under the keyword CE marking with information on the EMC directive , which often has to be used together with the low-voltage directive .

As a rule, compliance with the protection requirements is assumed if the harmonized European standards applicable to the device are complied with in order to guarantee trouble-free operation of electrical devices for all customers and citizens. This often leads to the fact that the person who offers a device on the European market uses EMC tests or equivalent verification methods to prove the EMC. Depending on the complexity of the device, simple plausibility considerations are suitable as equivalent verification methods. For example, an incandescent lamp that does not contain any electrical or electronic components other than the filament will not, by itself, exceed any limit values ​​for high-frequency emissions during operation.

During the last few years, the requirements for many product areas have been harmonized within Europe, so the limit values ​​and framework conditions in different countries are the same, e.g. B. stipulated in the EMC directive.

In Germany, the Federal Network Agency (formerly the regulatory authority for telecommunications and post ), the Federal Office for Radiation Protection and the Federal Armed Forces are the authorities responsible for monitoring compliance with protection requirements or limit values within the framework of the ordinance on the verification procedure for limiting electromagnetic fields .

According to the EMC directive in the EU, aviation equipment is exempt from CE marking. It falls under Directive 216/2008 / EU. The aviation sector is supervised by EASA.


Generic standards theme
EN 61000-6-1: 2019 Interference immunity for residential areas, business and commercial areas as well as small businesses
EN 61000-6-2: 2019 Immunity for industrial areas
EN 61000-6-3: 2007 + A1: 2011 Emitted interference for living areas, business and commercial areas as well as small businesses
EN 61000-6-4: 2007 + A1: 2011 Emitted interference for industrial areas
Product standards (not exhaustive) theme
EN 50121-3-2: 2016 Railway vehicles - devices
EN 50130-4: 2011 Alarm systems, part 4: EMC product family standard, interference immunity for fire, intrusion and hold-up alarm systems as well as video surveillance, access control and personal call systems
EN 50370-1: 2005 Machine tools, part 1, emitted interference
EN 50370-2: 2003 Machine tools, part 2, immunity
EN 60601-1-2: 2015 Medical electrical equipment
EN 61800-3: 2018 Adjustable speed electrical power drive systems - Part 3: EMC product standard including special test methods
EN 61326-1: 2013 Electrical measuring, control, regulating and laboratory devices
EN 61326-2-3: 2013 Electrical measuring, control, regulating and laboratory devices - measuring transducers
EN 301 489-1 V2.2.3 Radio equipment - common technical requirements
DNVGL-CG-0339 Dec. 2019 Test requirements for electrical / electronic devices and systems on ships
Test standards: (not exhaustive) theme
EN 55011: 2016 + A1: 2017 Emitted interference: ISM devices - limit values ​​and measurement methods
EN 55014-1: 2017 Emitted interference: household appliances - u. Measurement of discontinuous disturbances (clicks)
EN 55014-2: 2015 Immunity: household appliances
EN 55015: 2013 + A1: 2015 Emitted interference: electrical lighting equipment
EN 55016-2-1: 2004 + A1: 2005 Emitted interference: interference voltage - measurement of conducted interference emission
EN 55016-2-3: 2006 Interference emission: Interference field strength - measurement of the radiated interference emission
EN 55032: 2015 Emitted interference: multimedia devices and devices
EN 55024: 2010 + A1: 2015 Immunity: Information technology equipment - limit values ​​and measurement methods
EN 61000-4-2: 2009 Immunity to static electricity discharge (ESD)
EN 61000-4-3: 2006 + A1: 2008 + A1: 2010 Immunity to high frequency electromagnetic fields
EN 61000-4-4: 2013 Immunity to fast transient electrical disturbances (burst)
EN 61000-4-5: 2014 + A1: 2017 Immunity to surge voltages
EN 61000-4-6: 2014 Immunity to conducted disturbances induced by high-frequency fields
EN 61000-4-8: 2010 Immunity to magnetic fields with energietechn. frequency
EN 61000-4-11: 2004 + A1: 2017 Immunity to voltage dips, short interruptions and voltage fluctuations
EN 61000-4-20: 2010 + Ber. 1: 2012 Immunity to high frequency electrom. Fields ( TEM )
EN 61000-4-21: 2011 Test and measurement procedures - procedure for testing in the ( mode swirl chamber )
Military norms theme
MIL-STD-461 Requirements for the electromagnetic compatibility of products for use in the military sector (US standard)
Aviation standards theme
EUROCAE ED-14 / RTCA DO-160 Requirements for the environmental compatibility of aviation equipment (identical European and US standards)


  • Adolf J. Schwab, Wolfgang Kürner: Electromagnetic Compatibility . 6., arr. and updated edition. Springer, Berlin 2011, ISBN 978-3-642-16609-9 .
  • Georg Durcansky: EMC-compliant device design . Franzis, Poing 1999, ISBN 978-3-7723-5385-7 .
  • Tim Williams: EMC guidelines and their implementation . Elektor, Aachen 2000, ISBN 3-89576-103-6 .
  • Joachim Franz: EMC, fail-safe construction of electronic circuits . Teubner, Stuttgart / Leipzig / Wiesbaden 2002, ISBN 3-519-00397-X .
  • Thomas Brander, Alexander Gerfer, Bernhard Rall, Heinz Zenker: Trilogy of inductive components - application manual for EMC filters, clocked power supplies and HF circuits, 4th revised and expanded edition . Würth Elektronik, Waldenburg 2008, ISBN 978-3-89929-151-3 .
  • Hasse, EU Landers, J. Wiesinger, P. Zahlmann: VDE series of publications Volume 185. EMC - lightning protection of electrical and electronic systems in buildings - risk management, planning and implementation according to the new standards of the series VDE 0185-305 . 2. completely revised and exp. Edition. VDE, Berlin 2007, ISBN 978-3-8007-3001-8 .
  • Ernst Habiger: EMC Lexicon 2011–2500 Terms and abbreviations from the world of EMC . 4th updated and expanded edition with CD-ROM. Weka, Kissing 2010, ISBN 978-3-8111-7895-3 .

Web links

Commons : Electromagnetic Compatibility  - Collection of images, videos, and audio files

Individual evidence

  1. European Standards. Harmonized Standards. European Commission website. Retrieved September 14, 2015.