Table of contents
- What does electromagnetic compatibility mean?
- Why is EMC important?
- What EMC standards and guidelines are there?
- When must the EMC directive be applied?
- What are EMC interferences?
- What causes electromagnetic interference?
- How can you shield electromagnetic radiation?
- How can I shield a cable?
- When is an EMC test necessary?
Electromagnetic compatibility - also known as EMC for short - encompasses all the abilities of an electrical device, tool or system not to impair the function of other devices through electromagnetic and electrical influences. The importance of EMC is enormous, as it is the only way to ensure that devices in industrial plants, test laboratories or buildings do not interfere with each other or even fail during operation.
The best way to answer the question "What does EMC stand for?" is to actively prevent electrical and/or electromagnetic emissions. At the same time, the definition of EMC also comes into play when it comes to passive immunity to this type of interference.
It is important to note that electromagnetic compatibility is not to be equated with the term EMI (electromagnetic interference), which refers to the fundamental ability of electrical devices to emit interference signals. EMC (Electromagnetic Compatibility) or EMC-compliant devices are usually labelled with an EMC symbol. We have summarised the most important EMC basics below.
What does electromagnetic compatibility mean?
The Electromagnetic Compatibility Directive (EMC Directive) for devices and systems specifies how EMC should be organised. Apart from a few exceptions, the EMC Compatibility Directive applies to all stationary equipment that can cause electrical or electromagnetic interference and/or can be affected by interference. In an EMC test carried out for this purpose, devices must therefore prove their functionality in electromagnetic environments without themselves releasing emissions that could affect other devices. These tests are usually carried out in a specialised EMC laboratory.
Why is EMC important?
Regardless of whether it is a question of EMC conformity in electrical engineering, vehicle or aircraft construction: Electrically or electromagnetically induced emissions can, in the worst case, lead to the failure of electronic devices, which makes EMC protection essential in both the industrial and private sectors. For this reason, the electromagnetic compatibility of systems and electrical devices must be confirmed in an EMC test so that EMC approval can be granted.
EMC-compliant enclosures
They form a shield against electrical, magnetic or electromagnetic fields. These interference fields arise, for example, during electrostatic discharges, switching operations, rapid changes in current or voltage, the operation of motors or high-frequency generators, etc. These enclosures are generally used with EMC cable glands.
EMC shielding
The homogeneous EMC shield is interrupted at the transitions from the cables to the cable glands, to the grommet housing, the add-on housing and into the control cabinet. For optimum EMC performance, these connections must be as overlapping as possible, with a large surface area, low resistance and 360° contact all round.
What EMC standards and directives are there?
The most important EMC requirements include immunity to interference and the strength of the emissions emitted by an electrical device itself. The following parameters, which can also be found in the EMC standard IEC 60939-1, are important for EMC calculations:
- Filter leakage current
- Rated frequency
- Rated voltage
- Rated capacitance to earth
The EMC limit values for the low and high frequency range can be found in the following table.
| Frequency range | Electric field strength in kV/m | Magnetic flux density μT/th> |
|---|---|---|
| 0 Hz | - | 500 |
| 1 Hz - 8 Hz | 5 | 40,000/f² |
| 8 Hz - 25 Hz | 5 | 5,000/f² |
| 25 Hz - 50 Hz | 5 | 200 |
| 50 Hz - 400 Hz | 250/f | 200 |
| 400 Hz - 3,000 Hz | 250/f | 80,000/f² |
| 3 GHz - 10 GHz | 0.083 | 27 |
| Frequency range | Electric field strength in kV/m | Magnetic flux density μT/th> |
|---|---|---|
| 0.1 MHz - 1 MHz | 87 | 0.73/f |
| 1 MHz - 10 MHz | 87/√f | 0.73/f |
| 10 MHz - 400 MHz | 28 | 0.73/f |
| 400 MHz - 2000 MHz | 1.375 √f | 0.0037/√f |
| 2000 MHz - 300 GHZ | 61 | 0.16 |
Download table
*quadratically averaged over 6-minute intervals
Depending on the type of device, it is assigned to the respective EMC class. According to EN IEC 61000-6-1:2019 and EN IEC 61000-6-2:2019, a distinction is made between two classes if radio frequency fields are unintentionally emvied in an EMC A or B environment:
- EMC class A: devices, systems, circuits, etc. designed for use in an industrial environment
- EMC class B: EMC level 1 devices, systems, circuits, etc. that are used in the immediate vicinity of residential, commercial and industrial areas
The EMC Machinery Directive (EMC Directive 2014/30/EU) applies to machines with electrical or electronic components that cause electromagnetic emissions or may themselves be affected by these interferences.
Overview of the most important EMC standards
- CB EMC certificate
- Pan-European CCA EMC
- China Compulsory Certification Mark (CCC)
- US Federal Communication Committee (FCC)
- Note: Information on the EMC Declaration of Conformity, details on the Electromagnetic Compatibility Ordinance in accordance with IEC 6060, as well as any changes to the EMC Directive on harmonised and internationally applicable standards, can also be found in the EMC guidelines of the responsible project group of the Federal Network Agency.
When must the EMC Directive be applied?
The EU EMC Directive 2014/30/EU applies to all end-user devices that generate electromagnetic interference themselves or can be affected by this interference during operation.
Depending on the EMC Directive, a distinction is made between different device classes and areas of application:
- EMC Directive 2014 30 EU: Applies to almost all electrical equipment in the European single market.
- EMC Directive 2014/35/EU: Low Voltage Directive for compliance with a high level of protection for electrical equipment. Devices and electrical equipment that are operated at a rated voltage of 50 to 1000 V (alternating current) or 75 to 1500 V (direct current) must not pose a risk to the health or safety of people, pets, livestock or goods.
- EMC Directive 2004 108 EC: Was replaced by the current EMC Directive 2014 30 EU on 19 April 2016
- EMC Directive 89/336/EEC: Was replaced by the EMC Directive 2004 108 EC
What are EMC interferences?
EMC radiation and the resulting EMC interference sources are induced by a large number of different devices and systems. In addition to smartphones, PCs, notebooks and tablets, this also includes WLAN devices and transmission masts for the 5G network. High and low-voltage power lines, underground cables, electric railway lines and electric cars are also sources of electromagnetic interference, which is why EMC protective measures are also essential in outdoor areas, depending on the type of EMC environment.
Due to the large number of interference factors, comprehensive EMC safety is also necessary for electrical equipment, which is ensured by the choice of materials and the design, among other things. This is the only way to ensure that devices, systems, circuits and tools themselves are immune to interference and that active interference emission is avoided as far as possible.
EMC interference examples at a glance:
A basic distinction is made between dynamic electromagnetic interference, i.e. interference that changes over time, and static, unchanging interference - usually due to magnetic and capacitive causes. The interference can be emitted via current or signal-carrying wires (conducted interference) or as an electromagnetic field (field-bound interference).
What causes electromagnetic interference?
In principle, electromagnetic interference (EMI) can be caused by any electrical device. One of the most common causes of electromagnetic interference (field-bound interference) is capacitive and inductive coupling. EMC radiation is mainly caused by electrostatic discharges (ESD), which pose a considerable danger in explosion-protected areas with highly flammable hazardous substances, for example. In addition to natural sources of EMC interference, e.g. lightning, a static charge between two bodies with different field strengths can also cause an electrical spark and destroy sensitive electronics through a skipping charge.
Various EMC protective measures can be taken to create an EMC environment. These include earthing devices, galvanic coupling, additional mains filters and shielding signal or current-carrying wires.
How can electromagnetic radiation be shielded?
Common EMC shielding is carried out using metal braided sleeves made of copper or stainless steel, which are routed over signalling and current-carrying wires. The following question often arises in this context: What is magnetic shielding? This type of EMC shielding is used when you want to avoid field-bound EMC interference. Before EMC shielding can be used in this case, it is important to measure the strength and frequency of the induced emission so that the EMC shielding is effective.
Which materials can shield magnetic fields?
Conductive metals such as copper, steel or silver are usually used as materials for EMC shielding. Aluminium strips are also used for EMC shielding if the respective EMC measures make it necessary - e.g. if the low weight of the shielding plays a major role.
What is an interference suppression filter intended for?
For EMC interference suppression, so-called interference suppression filters are often used, with which high-frequency interference can be filtered out using capacitors and resistors. The function that an EMC filter should fulfil depends on its design. For example, a mains filter reliably ensures that data lines are shielded from high-frequency interference.
Products for EMC protection
In addition to a special EMC housing for connectors from Harting, for example, there are also EMC shield clamps that can be used to implement uncomplicated shield earthing and dissipation of high-frequency interference on signal-carrying wires. In addition, EMC cable glands from WISKA and Lapp enable cables to be fed into an enclosure in an uncomplicated and shielded manner.
The most common products in the field of EMC protection also include
- EMC braided sleeving
- EMC protective conduit
- EMC cable entries
- EMC cable gland
When is an EMC test necessary?
EMC verification is always necessary if an electrical device is to receive a CE mark or an EMC certificate. This usually requires a corresponding EMC test to prove that the applicable EMC regulation regarding health protection is fulfilled and that no electromagnetic interference is caused or that the device itself is negatively affected by such interference.
The common EMC tests are differentiated according to their transmission path. In addition to galvanic, capacitive and inductive testing, the strength and frequency of the electromagnetic waves emitted by the respective device are also analysed. This "EMC law" is based on the EMC regulations set out in Directive 2014/30/EU, which also make EMC testing mandatory.
What does an EMC test cost?
Depending on whether a test laboratory carries out conducted or field-based EMC tests, the costs incurred also differ. A four-figure daily rate is not uncommon due to the effort involved in setting up the test, carrying out the test and the standardised test.
What is meant by the term interference sink?
The question often arises: What does immunity to interference mean? In simple terms, this refers to the ability of a device component to withstand the effects of an interference signal. The decisive factor here is always the so-called interference sink, which is particularly sensitive to electromagnetic and electrical influences.
Despite careful editing and checking of the content, Stecker Express assumes no liability for the topicality, correctness, completeness and quality of the information provided.
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