Electronic and electrical safety related equipment must remain safe over its entire lifecycle.
Functional safety in an electromagnetic smog. IET principal policy advisor Graham Barber guides us through the haze.
The IET’s membership includes world-class expertise across many specialist technologies. Despite the wide range of volunteer committees and events which the IET operates it is regrettably not always possible to tap into this expertise. This may be for commercial reasons, or because individuals have not awoken to the societal benefit of sharing knowledge. However, when the IET does get a critical core of technology expertise together then the outcomes can be revolutionary. An example of this is the IET’s leadership on the design principles required for products and systems (equipment) which have to be functionally safe and not risk harm to humans, animals and the environment.
Engineers and technicians are familiar with the fact that to place products on the market in Europe they must be declared compliant with all relevant Conformité Européenne (CE) Directives and carry the ‘CE marking’. In the case of equipment which predominantly uses electricity this includes the need to comply with the Electromagnetic Compatibility (EMC) regulations (EMC Directive 2004/108/EC). In the UK this is currently implemented via the Electromagnetic Compatibility Regulations 2006. This Directive and its national regulations are meant to ensure that in the working environment for which they are intended products co-exist without susceptibility to electrical interference that impairs their functionality, nor do they cause interference to other equipment. These EMC regulations, in one form or another, in the UK have been in force since October 1992. Compliance with the EMC regulations is typically measured by testing to internationally harmonised equipment standards.
However, Provision 7 of the UK EMC regulations, by way of example, states: ‘Nothing in these Regulations shall affect the application of Community legislation and national legislation as regards the safety of equipment.’ This is more simply stated that these EMC regulations do not apply to equipment safety!
All electronic technologies are vulnerable to errors or malfunctions caused by electrical interference and intentional radiators e.g. the ubiquitous mobile phone and plethora of ‘smart’ wireless devices. There is increasing use of ever-more sophisticated electronic technologies; including wireless, computer and power conversion technologies in every sphere of human endeavour, including those where errors or malfunctions in the technology may have implications for what is known as functional safety. These errors, malfunctions or failures could lead to human, animal or environmental harm.
In circumstances where equipment has functional safety implications designing and testing for compliance with the normal EMC regulations cannot be sufficient to provide assurance that the equipment is indeed functionally safe. For functional safety a different approach is needed for electromagnetic compatibility.
Electronic and electrical safety related equipment must remain safe over its entire lifecycle despite foreseeable electromagnetic disturbances. Equipment designers must take into account reasonably foreseeable issues such as:
• A wide range of electromagnetic disturbances that may occur simultaneously e.g. a transient plus a continuous RF field.
• Electromagnetic disturbances combined with faults, misuse, wear, corrosion, aging etc.
Traditional EMC testing is based on applying a single disturbance at a time to a perfect item of equipment and so does not address these issues.
The Policy Department of the IET published in 2008 pioneering guidance on Electromagnetic Compatibility for Functional Safety which addressed this issue. The guidance was prepared and written by an ‘EMC for Functional Safety Working Group’, a committee of IET EMC volunteer expert members from a cross-section of UK industries who pooled their experience and expertise to give some structure for what they considered needed to be done when designing equipment that has to be functionally safe. The main body of the guide consists of ten steps (0-9) where steps 1-9 describes the revolutionary process which includes key stages, identifying the electromagnetic environment, equipment design, verification and validation with checklists for each step.
The Internet free-to-download guidance has had a constant interest level of around 800 visits a month. The guidance is also available in print from Nutwood UK Limited. Feedback from stakeholders about the published guidance included the need to describe how to deal with the interfering effects of electromagnetic disturbances that a safety-related system could experience over its complete lifecycle, and design to reduce as far as reasonably practicable any risk. This requirement was not trivial to fulfil as it needed EMC technical expertise, functional safety design experience, critical safety know-how, and detailed knowledge of software architecture design. Fortunately, as the IET’s membership breadth of disciplines is large, plus use could be made of personal contacts of the 2008 guide Working Group, it proved possible to build an enthusiastic team of volunteer professional people as a Policy Department committee which produced the ‘how to’ guidance over a period of 18 months.
As is always the case the successful achievement came from the drive, enthusiasm and dedication of the team of volunteers working with IET staff support. Something the IET relies upon for most of its work.
The ‘how to’ guidance has now been published for free download ‘Overview of techniques and measures related to EMC for Functional Safety’. It is written using language compatible with the basic international standard for Functional Safety IEC 61508.
Four members of the committee ran a workshop on this new guidance and the techniques and measures at EMC-Europe in Brugge on the 2 September 2013 and at EMC-UK in Newbury on the 8 October 2013. Both events were very well attended and gave encouragement to the hope that this IET revolutionary work might get taken forward to the international standards arena via a pre-existing appropriate British Standards Institution EMC committee. Again the volunteer groups’ personal contacts and committee involvements will be a vehicle for achieving this ambition.
|To start a discussion topic about this article, please log in or register.|