Electromagnetic Compatibility

In A Nutshell

Electromagnetic Compatibility (EMC) means that all electronic and electromechanical devices and machines run in their intended environment besides each other without interfering. In other words: each device must not be interfered by other devices and vice versa.
The following chapters are thought as free education for those of you out there who have to deal with EMC and product compliance.
 

1  Introduction to EMC

This chapter gives you an introduction to EMC and EMI. 

What is EMC?

EMC stands for Electromagnetic Compatibility. Every electronic device/machine on the market must be EMC compliant, meaning it must fulfill the EMC regulations and standards for the intended use of the product. Which EMC regulations and standards are applicable for which product is defined by the country where the product is sold (e.g. EU or USA etc.).

The expressions and definitions involved in EMC are explained in the picture below:

Depending on the regulatory requirements, an EMC compliant product must fulfill one or several of these points:

  1. Not interfere with other devices/machines in its environment (emission).

  2. Not be upset by other devices/machines in its environment (immunity).

  3. Not be upset or destroyed by an Electrostatic Discharge (ESD) event. Examples are:

    • Human body generated ESD pulses (personnel-borne ESD).

    • Aircraft charging due to precipitation static resulting from atmospheric conditions (p-static).

    • Electrostatic discharge during vertical replenishment by hovering aircraft (helicopter-borne ESD).

  4. Not be upset or destroyed by an Electromagnetic Pulse (EMP). EMP is a special topic e.g. for defense and military devices and infrastructure apparatuses. EMP is the umbrella term for:

    • Nuclear Electromagnetic Pulses (NEMP) generated by the detonation of a nuclear weapon.

    • High-altitude Electromagnetic Pulses (HEMP) generated by the detonation of a nuclear weapon at high altitudes (30km – 400km).

    • Non-Nuclear Electromagnetic Pulses (NNEMP) generated by payload of bombs, cruise missiles or drones, without the use of nuclear technology.

    • Lightning Electromagnetic Pulses (LEMP) caused by natural lightning strikes.

An additional point which can be mentioned here in this context: a product should not interfere with itself. This topic refers not particularly to EMC, it refers to signal integrity. However, signal integrity and EMC often goes hand in hand with each other.

In the following picture, you can see a machine (e.g. vending machine) which must have a certain immunity to ESD, radiated emission and conducted emission from other devices and machines. On the other hand, the machine itself must not upset the machines and devices in its environment (keep its emission low).

EMC vs. EMI.

EMI stands for Electromagnetic Interference and is often mixed up with EMC. EMI means that one electronic device/machine A is causing disturbance to another electronic device/machine B, which is in the surrounding of device/machine A.

What is the difference between EMC and EMI? Now, an EMC compliant product has to be tested on EMI during its development. For an EMC compliant product, EMI should not happen any more. This is due to the fact that EMC compliant products proved their electromagnetic immunity to be high enough and their electromagnetic emission to be low enough to work seamlessly in its predefined environment.

Coupling Paths

One important concept in EMC is the concept of coupling paths. To start off, let's see what parts are involved when Electromagnetic Interference (EMI) happens and why focusing on coupling paths is so important:

  1. Source: In real world, there are sources of unwanted electric or electromagnetic noise (during EMC testing, these sources of noise are artificial and as close as possible to the real world, e.g. ESD generators, burst generators, surge generators, antennas etc.).

  2. Coupling Path: The noise needs a path from the source to the victim to affect the victim. This path is called the coupling path or coupling channel.

  3. Victim: The victim is the receiver or receptor of the noise.

The picture above shows us, that if there are issues with EMI and EMC, you have the following three options:

  1. Lower the noise level of the noise source.

    • Emission testing: When testing the emission of your product (meaning: the product is the Source Of Noise) you have the possibility to lower the noise level by adding filters or apply the right guidelines to your electronics design (PCB, cables).

    • Immunity testing: When we talk about EMC immunity testing, it is not possible to influence the noise level, where the Source Of Noise is e.g. an ESD generator or a surge generator or an antenna radiating with a defined noise level (e.g. defined in the applicable EMC standard).

  2. Remove or make changes to the coupling path. This is where you usually have to focus if you do not pass EMC testing. Here you have the possibility to make changes and lower the emission or increase the immunity of your product, without redesigning the whole product (e.g. by improve shielding, add filters to cables and PCBs of your product).

  3. Increase the victim's immunity level with software. This may be realized with additional features in the software of your product, which make your product more robust. Examples could be software/digital filters (e.g. median), spike removers (remove spikes in signals) and sanity checks.

Let's have a closer look. There are different kind of coupling paths, some of them are conductive (galvanic) and some of them are non-conductive (radiated). The picture below shows you the four different types of coupling:

  1. Conductive or Common Impedance Coupling (galvanic)

  2. Capacitive Coupling (near-field)

  3. Inductive Coupling (near-field)

  4. Radiated Coupling (far-field)

If you don't want to go too much into detail, here the summary. If you would like to dig deeper into the topic: just continue reading.

Conductive Coupling / Common Impedance Coupling (galvanic coupling).

Conductive coupling happens e.g. when two circuits share a common path / trace to ground or to another reference plane. Why could this lead to EMC problems?
Here an example: If now one of these circuits experiences an ESD, burst or surge pulse, a high current may flow for a short time through this common PCB trace and introduce a noise voltage to the second circuit is introduced. This is the reason why it is important having low-impedance ground planes to earth / chassis. Because with low-impedance ground planes, the conductive coupling can be minimized.
The circumstance of common ground path or power supply path often leads to a bad signal integrity as well. Let's assume the first circuit drives some power electronics and the second is a sensitive measurement circuit. The high currents of the power electronics (noise currents) introduce a noise voltage in the said common path / trace and will lead to interference on the measurement circuit.

Capacitive Coupling (near-field coupling).

Capacitive coupling is a near field coupling, meaning: the noise source coupling structure and the victim receiving structure are somehow close together (on a PCB or in a cable harness) compared to the wavelength of the interference signal. The field of concern for capacitive near-field coupling is E-field (electric field). The energy of the radiated E-field noise typically falls off with 1/r^3 or 1/r^2 (1/r3 if the E-field is predominant, 1/r2 if the H-field is predominant) in the near-field area, where r is the distance between the emitting noise source structure (typically cables or metal plates) and the receiving structure (typically cables or PCB traces) of the victim.
Generally speaking, capacitive coupling is an issue where you have noise sources (typically cables or metal plates) with fast transient signals or high frequency signals and victims with high impedance circuits (e.g. Analog to Digital Conversion (ADC) inputs).
Why could capacitive coupling lead to problems during EMC testing? Here an example: several wires are together in the same cable which means that each wire is capacitively coupled to the other wires inside that cable (the capacitance is the bigger the longer the cable and the closer the wires to each other). One of the wires drives the reset signal of your controller system. During EMC testing, an ESD pulse happens to a connector pin which is connected to a wire in that cable. If there are no measures against ESD at the connector pin, this pulse may couple capacitively into the other wires in the same cable and potentially reset your controller (in case the controller reset signal is not filtered properly).
Capacitive coupling is also a topic when it comes to signal integrity: A typical example of capacitive coupling is a clock trace (noise source) laying parallel over e.g. several cm to a sensitive analog sensor signal trace (victim). The shorter the rise- and fall-time of the clock signal, the better (worse for your circuit) is the coupling.

Inductive Coupling (near-field coupling).

Inductive coupling is a near field coupling, meaning: the noise source coupling structure and the victim receiving structure are somehow located close together (on a PCB or in a cable harness) compared to the wavelength of the interference signal. The field of concern for inductive near-field coupling is H-field (magnetic field). The energy of the radiated H-field noise typically falls off with 1/r^3 or 1/r^2 (1/r3 if the H-field is predominant, 1/r2 if the E-field is predominant) in the near-filed area, where r is the distance between the emitting noise source structure (typically current loops, coils) and the receiving structure (typically loops) of the victim.
Generally speaking, inductive coupling is an issue where you have noise sources with high-current traces / wires or large loop areas and victims with low impedance or large loop area structures (e.g. sensor signal in a cable which builds a current loop with the chassis structure as the sensor signal cable is not laid close the chassis).
Inductive coupling could lead to issues during EMC testing, e.g. because of high currents flowing through cables and PCB traces during ESD testing or surge testing where currents up to several kA could occur.
Inductive coupling may also lead to bad signal integrity as well. A typical case is a high current Pulse Width Modulation (PWM) signal line (and therefore a high energy H-field), laid parallel to a sensor signal with 4...20mA-signaling, whereas the sensor signal and its return current path build a large loop structure (where the magnetic field of the PWM signal can couple into).

Radiated Coupling (far-field coupling).

Radiated coupling is a far field coupling, meaning: the noise source coupling structure and the victim receiving structure are located far away to each other compared to the wavelength. The field of concern for radiated coupling is the electromagnetic field (EM-field), where the H-field and the E-field energy both fall off with 1/r.
During radiated immunity / susceptibility EMC testing (IEC 61000-4-3), the testing equipment antenna radiates a predefined EM-field to the Equipment Under Test (EUT). When the EUT is tested regarding radiated emissions (CISPR 11, EN 55011), the EMC test equipment antenna is placed at a predefined distance (e.g. 3m, 10m) in order to measure radiated EM-field by the EUT.

Coupling paths overview and summary.

For the quick reader, here a summary about EMC coupling paths. Read more about near-field vs. far-field at our Knowledge Base.

 
 
 
 
 
 
 
 
 

2  EMC Compliance

EMC Compliance means that an electronic or electromechanical product is compliant to the laws, directives and regulations of the country where it is sold.

First, every government issues its own EMC regulations (laws, directives) for their country. Whereas these national regulations often refer to multi-national regulations (e.g. countries in the European Union refer to the EMC directive 2014/30/EU).

Second, the government usually builds, appoints or chooses an organization, commission or committee which is responsible for defining the applicable EMC Standards. Such organizations or committees define the applicable EMC standards in a way that products, which pass the tests defined in the applicable EMC standards, are then compliant to the EMC regulations (laws, directives).

Find out more about EMC compliance on our dedicated page: EMC Compliance.

 
 
 
 
 

EMC Standards

The following sections give you an introduction to EMC Standards and norms:

Find the applicable EMC Standards for your products on our dedicated page: EMC Standards.

What are EMC Standards?

EMC Standards and norms define terms, rules and test methods for EMC. Furthermore, they specify limits and minimum test levels for electric and electromagnetic emissions and immunity of electromechanical and electronic products.

 

Why do we need EMC Standards?

EMC Standards help to make measurements comparable and repeatable by defining the test methods and the test equipment and the test environment. And most important, EMC Standards have the purpose of bringing harmonization to EMC testing, in the best case: a global harmonization. This lowers trade barriers and as a most important consequence for the society: harmonized EMC Standards help to increase global prosperity and wealth.

Who writes EMC Standards?

Norms and standards in EMC are either defined and worded by international and national or regional organizations and committees on behalf of administrative bodies (like the EU delegates the wording of EMC Standards to CENELEC), or the administrative and/or regulatory bodies word the EMC Standards and regulations themselves.

What types of EMC Standards are there?

It is to be distinguished between the following classes or types of EMC Standards:

  • Basic EMC Publications. The Basic EMC Publications specify the general conditions, definitions and rules necessary for achieving electromagnetic compatibility. 

  • Basic EMC Standards. The Basic EMC Standards specify test methods (test setup, test equipment and environment) and are the EMC standards to which other EMC standards (EMC Product Standards, Generic EMC Standards etc.) refer to.

  • EMC Product Standards. The EMC Product Standards apply to particular products, such as electric road vehicles or coaxial cables. 

  • EMC Product Family Standards. The EMC Product Family Standards  apply to a group of products that have common general characteristics, that may operate in the same environment and have neighboring fields of application.

  • Generic EMC Standards. The Generic EMC Standards are for products operating in a particular EMC environment, and for this product does not exist a specific EMC Product (Family) Standards (yet).

 

4  Knowledge Base

We love spreading knowledge. We wrote down some of the most essential theoretical knowledge, which you need for mastering EMC. To read more, visit our Knowledge Base website.