Drawbacks of conventional EMC testing
Electrical and electronic device compliance with Electromagnetic Compatibility (EMC) standards is a global requirement before those items can be commercialized, as EMC has become a critical factor for ensuring their performance, quality, and, in some situations, the safety of end users [1]. The ability to achieve and improve Electromagnetic Compatibility is a significant challenge now, due to the rapid development of new electronic products with evolving technologies and features.
It is commonly assumed that when a device has complied with its relevant EMC test limits, defined by standards, it is deemed to be the worst-case EM disturbance that the device will have to encounter in its lifecycle. Thus, it is presumed that the design will almost never suffer from malfunctions due to that disturbance in real life. This is not true in most cases and the device will have to deal with much worse Electromagnetic environments. Also, in most cases, the technology of the products advances at a faster rate than their corresponding EMC testing standard. This has given rise to a situation in which simply testing for immunity is no longer sufficient to ensure electromagnetic compatibility [2].
Although the conventional testing methodology specified in EMC test standards is considered necessary when testing the EM immunity of any Electrical/Electronic equipment, it is grossly inadequate to demonstrate that high reliability or safety-critical equipment or system will accomplish tolerable failure levels over their expected entire life cycle. The major drawbacks of conventional testing as stated in [2] are:
1) Only one EM disturbance at a time
2) Effects of the physical environment are not considered
3) Ageing is not considered
4) Lacking for future technologies
5) Doesn’t address Maintenance, repair, upgrades, etc.
General Aspects of ‘Risk-based’ approach
The technological advancements that have happened in the last few decades or so are immense.
It will be no exaggeration to say that this has caused the birth of a new industry that deals with
the Risk management of Electromagnetic Compatibility. Any equipment that is to be commercialized in the European Union should fulfill the essential requirements of the EMC Directive which states: “Equipment shall be designed and manufactured, having regards to the state-of-the-art, as to
ensure that:
a) The electromagnetic disturbance generated does not exceed the level above which radio and
telecommunication equipment or other equipment cannot operate as intended.
b) It has a level of immunity to the Electromagnetic Disturbance to be expected in its intended use
which allows it to operate without unacceptable degradation of its intended use.”
In [3], Prof. Frank Leferink iterates how not many Engineers read the Directives and the conventional approach is to follow the harmonized EN/IEC standards. In essence to that, some test laboratories tend to focus their efforts to get rid of the few exceeding dB above a limit in part of the frequency spectrum even though the equipment is not operating in its intended operating Environment.
The European Commission acknowledged that more and more companies are focusing their efforts to the bare minimum of adhering to harmonized standards to prove that they have achieved EMC. This led to the issuance of the Blue Guide [4], the RED Guide [5], and, most recently, the Guide for the EMC Directive [6], all of which emphasized the risk-based approach. What the above-mentioned guides state in relation to the “risk-based approach” can be summarized into the following points:
1) Harmonized standards never replace legally binding essential requirements.
2) Even when using harmonized standards, the manufacturer is fully responsible for
assessing the risk related to his product.
3) Conformity assessment requires technical documentation and shall include adequate
analysis of the risks.
4) If the EMC assessment determines that the equipment in question is naturally benign in terms of electromagnetic compatibility (both for emission and immunity), the apparatus is excluded from the scope of the EMCD, and no further action is required. It is, nevertheless, advised that the assessment’s results and conclusion be documented.
5) The EMC Assessment needs to take into account all normal intended operating conditions and configurations of the equipment.
From the above summary, it is clear that the “risk-based approach” should be in force by default. But this is not the case mainly because of another loophole from the legal aspect of conformity. After having identified the risks of the apparatus, the manufacturer can use 3 methods for EMC assessment and conformity. The manufacturer can apply a harmonized standard, an independent EMC assessment using his own methodology, or a mixed assessment comprising the former methods. Thus, the application of harmonized standards is considered adequate to show conformity from a legal perspective.
Adoption of the ‘risk-based’ approach
‘Good EMC Engineering’ requires much more than just a legal obligation to conform to the standards or guides and the need for a risk-based approach has already been acknowledged by several industries [3] [7]. This has prompted calls for a more sophisticated approach to EMC Engineering that is aligned more closely with Functional Safety. With the release of the IEC 60601-1-2 4 th edition [8], it was clear that more and more industries were racing towards the ‘risk-based- approach. Despite ongoing research aimed at facilitating the implementation of a risk-based EM approach, there are still obstacles to overcome. For example, owing to intellectual property rights and secrecy, the component/subsystem design, architecture, and other specific elements that may be necessary for risk estimation are normally not revealed [9].
Due to a lack of system understanding, implementing a risk-based approach at an early stage of system development is challenging in such instances. Nevertheless, more challenges are being acknowledged day-by-day as the approach is widely accepted and adopted throughout the industry.
References
[1] B. Audone, R. Paviolo and S. Fazari, “EMC testing of medical devices,” in Electromagnetic Compatibility (EMC EUROPE), 2013 International Symposium on, Bruges, 2013.
[2] K. Armstrong, “EMI and functional safety why traditional immunity testing is inadequate and what should be done instead”, Electromagnetic Compatibility 2006. EMC-Zurich 2006. 17th International Zurich Symposium on, pp. 469-472, 2006.
[3] F. Leferink, “Risk-based vs Rule-based Electromagnetic Compatibility in Large Installations,” 2018 IEEE 4th Global Electromagnetic Compatibility Conference (GEMCCON), 2018, pp. 1-4, doi: 10.1109/GEMCCON.2018.8628505.
[4] 2016/C 272/01 Commission Notice, The ‘Blue Guide’ on the implementation of EU product rules 2016, Official Journal of the European Union, Volume 59, C 272, Information and Notices, 26 July 2016
[5] The RED Guide, https://ec.europa.eu/docsroom/documents/29782
[6] Guide for the EMC Directive https://ec.europa.eu/docsroom/documents/28323
[7] A. R. Ruddle and A. J. M. Martin, “Adapting automotive EMC to meet the needs of the 21st century,” in IEEE Electromagnetic Compatibility Magazine, vol. 8, no. 3, pp. 75-85, 3rd Quarter 2019, doi: 10.1109/MEMC.2019.8878241.
[8] Medical electrical equipment – Part 1-2: General requirements for basic safety and essential performance – Collateral Standard: Electromagnetic disturbances – Requirements and tests
[9] Adopting a Risk-based EMC approach – ETN PETER Blog by Lokesh Devaraj – https://etn-
peter.eu/2021/03/08/adopting-a-risk-based-emc-approach/