Keith Armstrong

Why EMC immunity testing is inadequate for functional safety

Safety-implicated, safety-related, and safety-critical systems are increasingly using electrical, electronic and programmable electronic devices. All such devices can suffer malfunctions or damage due to electromagnetic interference. Safety systems have safety integrity requirements (defined by IEC 61508) - but their EMC aspects are not adequately controlled by either safety or EMC standards. The paper describes the shortcomings in the way that the EMC immunity of such equipment is dealt with, and shows that the normal immunity testing approach is inadequate, on its own, as a means of verifying this aspect of safety integrity.

Why increasing immunity test levels is not sufficient for high-reliability and critical equipment

It is often assumed that passing an EM immunity test at 100% of the level of the worst-case disturbance that can occur over the lifecycle, and taking measurement uncertainties into account, will prove that the design of the tested equipment will almost never suffer from errors or malfunctions due to that dis-turbance in real life. Unfortunately, although the above is necessary when testing the EM immunity of equipment that must function with high relia-bility — such testing is insufficient to demonstrate that high-reliability, security, mission-critical or safety-critical equipment or systems will achieve tolerable failure levels over their life-cycles despite the EM disturbances in their environments. Part II of this paper explains why this is so, and Part III briefly introduces the techniques that are necessary for achieving sufficient confidence in EMC, when high reliability is required.

Review of progress with EMC-related functional safety

Developments in electronic technologies encourage the wide use of electronics, and there is a rapidly increasing use of mobile and portable radio communication. As a consequence, it is increasingly likely that errors in - and misoperation of - electronic devices due to inadequate EMC could increase the health and safety risks to users and third parties, and could also increase the risks of damage to property, liability claims and financial loss. A number of initiatives are presently underway to address the serious shortcomings in the way current regulations and standards address EMC-related functional safety - this paper briefly describes some of the developments.

Including EMC in risk assessments

The reliability of electronic technologies (including the software and firmware that runs on them) can become critical, when the consequences of errors, malfunctions or other types of failure include significant financial loss, mission loss, or harm to people, domestic animals or property (i.e. functional safety).

Opportunities in the Risk Management of EMC

It is not an exaggeration to say that we are witnessing the birth of a brand new industry Risk Management of electromagnetic compatibility (EMC) - which will be needed in most safety-related and high-reliability applications/industries. But at the moment there are (effectively) no resources available that can satisfy its requirements, either from EMC test laboratories or functional safety assessors. A great deal of work needs to be done to prepare manufacturing industry, test laboratories and safety assessors for these requirements, for which a large demand will build up by 2021. The new opportunities now available include: 1) Academic teaching at all levels 2) Academic research 3) Vocational training courses 4) Computer-aided simulation 5) Test methods and specialized test equipment 6) Verification/validation techniques other than testing 7) Development of policies and procedures 8) Safety Assessor services 9) Accreditation services. This paper briefly introduces the rapidly growing need for the above, and discusses each of these opportunities in turn.

Testing for immunity to simultaneous disturbances and similar issues for risk managing EMC

Where electronic equipment must function so as to maintain very low risk levels for safety, financial, or other reasons, it is not sufficient to only test it for immunity to electromagnetic (EM) disturbances, whatever the test levels used. However, where EM immunity tests are used as a part of such equipments verification or validation, for their results to be meaningful for the achievement of low risks, it is necessary to increase the test levels significantly above the levels of EM disturbances that could occur in the operational environment(s). This paper describes a number of reasons for increasing immunity test levels, gives some guidance on by how much, and discusses the problems that this approach can encounter.

Non-standardized immunity test techniques to help manage risks caused by EM disturbances

Where electronic equipment must achieve very low risks in Functional Safety or other applications, it is not practicable to rely solely on immunity testing, at whatever test levels, to demonstrate that risks caused by electromagnetic (EM) disturbances are low enough. However, immunity testing to the normal standards is an important part of such equipments verification and validation, and using non-standardized immunity testing can help make a good case that the risks caused by EM disturbances are low enough. This paper describes a number of ways in which the standard test methods can usefully be modified, for this purpose.

Why is the IEEE developing a standard on managing risks due to EM disturbances

The IEEE Standards Association is developing a standard to deal with the problem of managing risks that can be caused by electromagnetic (EM) disturbances, which will not rely solely on immunity testing, making it a new type of EMC standard. Where failures in electronic equipment can cause Functional Safety or other risks to be higher than considered acceptable at any time during its lifecycle, the proportion of those failures that could be caused by electromagnetic (EM) disturbances must be taken into account as part of the Risk Management process. However, immunity testing alone is incapable of providing sufficient design confidence, however much the test levels are increased, and this paper describes why and the reasons for this new IEEE standard.

PCB design techniques for the SI and EMC of Gb/s differential transmission lines

Differential transmission lines are increasingly employed to carry very high data rates in serial communications in printed circuit boards (PCBs). This paper provides an overview of a number of signal integrity (SI) and electromagnetic compatibility (EMC) problems with differential lines in PCBs. It also describes design techniques that can help achieve good SI and EMC

How to manage risks with regard to electromagnetic disturbances

When Functional Safety or other risks must be managed throughout the lifecycle of an electronic system, the acceptable levels for risks that could be caused by electromagnetic (EM) disturbances are so small that they are incapable of being verified or validated by using only immunity testing, even with increased test levels. After 2000, many safety standards were published that required a risk-based approach to electromagnetic interference (EMI), although until 2013 there were no publications providing any practical guidance on how this could realistically be achieved. The first practical guidance was published in 2013 and is now being incorporated into IEC, IET and IEEE standards, and is the subject of this paper.