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A warning on the use of EN/IEC 61326-3-1 and -204 January 2012Keith Armstrong warns about misuse of these “EMC for Functional Safety” standardsThese EMC immunity test standards are intended to be used only within a functional safety process controlled by both IEC/EN 61508 and IEC TS 61000-1-2. But I keep on meeting people who incorrectly assume that all they need to do on EMC for functional safety is test to 61326-3-x and/or comply with the EMC Directive. This error is a very serious one, because it concerns safety-related systems, so the financial risks of getting it wrong are huge.
“Functional safety” concerns the malfunctions of machines and processes - a growing problem because we are increasingly controlling things with ever-more-complex electronics and software.
BS EN 61508 [4] is the BS version of IEC 61508, the IEC’s Basic Standard on the Functional Safety of safety-related systems that use electrical, electronic and/or programmable electronic (i.e. software, firmware) technologies.
We are probably more familiar with the functional safety Product Standards that have been developed from 61508: BS EN 62061 [5] and BS EN 61511 [6]. The rail and aviation industries use other functional safety Product Standards based on [4].
Because all electronics suffers from electromagnetic interference (EMI) and so must be designed to have adequate electromagnetic compatibility (EMC), since 2000 [4] has required that EMC be done in a way that helps ensure the achievement of acceptable levels of functional safety risk. But it has never said how to actually do EMC for functional safety.
Unfortunately, the usual approach to EMC – testing to EMC emissions and immunity standards – is inadequate for functional safety engineering. It can’t even provide sufficient confidence (that EMI won’t cause dangerous malfunction) to reach the lowest rung of compliance to 61508 – Safety Integrity Level 1 (SIL 1 for short), see [7] or [8].
However, since 2000 we have had IEC TS 61000-1-2 [9], the IEC’s Basic Publication on EMC for Functional Safety, which should be converted to a full International Standard sometime in 2012.
Despite being only a TS (Technical Specification), [9] is a mandatory requirement under 61508, and this should “flow down” to all Product Standards derived from 61508.
[9] employs a variety of design verification and validation techniques including (but not limited to) enhanced immunity testing, to achieve the levels of confidence in EMC required by any SIL. 61326-3-1 [2] and -2 [3] are being used incorrectly because they do not say anything about being part of a functional safety risk-control process under both [4] and [9].
Many years ago, the convener of the IEC team that produced [2] and [3] made clear to me that they were intended to be used as just a part of a process controlled by [4] and [9], and this is confirmed in the presentation that Dr Bernd Jaekel and Diethard Moehr gave jointly to the 100th Anniversary meeting of the IEC in Berlin on the 27th September 2006, as shown in the figure, which is taken from their presentation.
The convener assured me that the total lack of any information about this in [2] and [3] did not matter, because everyone involved with safety-related systems knew all about [4] and [9] and would naturally understand how to fit [2] and [3] into their functional safety compliance processes.
Sadly, he was wrong, because even now in 2011 it is commonplace to find the 61326-3 standards [2] and [3] being used on their own, without also complying with both IEC 61508 and IEC TS 61000-1-2.
The exact same problem also seems to afflict complying with 62016 [5] or 61511 [6], which the figure also shows should be part of a process controlled by both [4] and [9].
EMC for Functional Safety is a new field of standardisation that goes well beyond what can possibly be achieved by EMC immunity testing alone, so it will no doubt take a few years before the Independent Safety Assessors catch up with this new state of the art.
While waiting for the Safety Assessment industry to get up to speed, manufacturers and integrators of safety-related equipment and systems must still employ the state of the art in EMC and Functional Safety.
This is because huge penalties can be awarded in civil lawsuits under the Product Liability Directive. We can be fined up to 70 billion Euros without it even being proved that it was our equipment that caused the injuries, deaths or financial losses!
The risk of deviating from the state of the art in EMC for Functional safety is much greater than any Financial Director could ever accept, if anyone took the trouble to warn them about this situation.
PS: My series on EMC techniques for systems and installations will continue in the next issue.
References:
[1] Previous PSB columns in this series are archived (unfortunately without their graphics) at: www.psbonthenet.net/company.aspx?CompanyID=12242.
[2] BS EN 61326-3-1:2008, “Electrical equipment for measurement, control and laboratory use. EMC requirements. Immunity requirements for safety-related systems and for equipment intended to perform safety-related functions (functional safety). General industrial applications”
[3] BS EN 61326-3-2:2008, “Electrical equipment for measurement, control and laboratory use. EMC requirements. Immunity requirements for safety-related systems and for equipment intended to perform safety-related functions (functional safety). Industrial applications with specified electromagnetic environment”
[4] BS EN 61508 Ed.2:2010, “Functional safety of electrical/electronic/ programmable electronic safety-related systems”, in seven parts
[5] BS EN 62061 Ed.1:2005, “Safety of machinery. Functional safety of safety-related electrical, electronic and programmable electronic control systems”
[6] BS EN 61511-1:2004, “Functional safety. Safety instrumented systems for the process industry sector. Framework, definitions, system, hardware and software requirements”
[7] Keith Armstrong, “Including EMC in Risk Assessments,” 2010 IEEE International EMC Symposium Fort Lauderdale, FL (July 25-31, 2010), ISBN: 978-1-4244-6307-7 (CD-ROM).
[8] Keith Armstrong, “EMC Risk Analysis”, In Compliance magazine, August 2011, www.incompliancemag.com/index.php?option=com_content&view=article&id=761:emi-risk-analysis&catid=26:design&Itemid=130
[9] IEC TS 61000-1-2 Ed.2:2008, “Electromagnetic Compatibility (EMC) – Part 1-2: General – Methodology for the achievement of the functional safety of electrical and electronic equipment with regard to electromagnetic phenomena,” IEC Basic Safety Publication (2008), http://www.webstore.iec.ch
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