Conformity Magazine - November 2007 - (Page 35)

This issue is usually called “EMC for Functional Safety” – a very different discipline from compliance with EMC regulations, such as the European Union’s EMC Directive. (See references [1-5] for additional information on this topic.) The EM environment that such systems could experience over their lifetimes could be very different from that tested by standard “EMC compliance” immunity tests. Nuclear electromagnetic pulse (NEMP or HEMP) or Intentional EMI (IEMI) can be of significant concern in some applications. Physical and climatic environments, plus the wear and tear and misuse that systems can be subjected to over their lifetimes can cause circuit EM behavior to alter, and can degrade the performance of EM mitigation measures such as shielding, filtering, and transient suppression. The EM performances measured by the normal “EMC compliance” immunity tests are very poor indicators of reallife behavior, for reasons I’ve written about previously (see [6] and [7]). An EMC test plan that gave sufficient confidence for safety would be much too lengthy, and much too costly. Just as for safety-related software (Part 3 of IEC 61805), appropriate EMC design techniques are required, based on qualitative and quantitative assessments of the reasonably foreseeable worst-case EM and physical environments over the lifetime of the system. To achieve a suitable level of confidence in our equipment’s EM performance within a reasonable cost and time budget, we need to employ appropriate EMC design methods as well as appropriate validation and verification methods (which include EMC testing). IEC 61508 [8] is the basic IEC standard on Functional Safety, and applying it to safety systems tells us how to determine the safety integrity levels (SILs) we need for their safety functions, and then how we should design to achieve those SILs (e.g., how many redundant channels). But IEC 61508 does not tell us how to design or validate the EM performance. IEC CD 61000-1-2 [11] is intended to become the International Electrotechnical Commission’s basic standard on EMC for Functional Safety, to provide the “pilot function” for all IEC standards on that topic. IEC CD 61000-1-2 can be read as the “EMC Part” that is missing from IEC 61508, and includes validation and verification requirements, including testing. Validation and Verification Techniques A wide variety of validation and verification techniques can be used, including the following: Demonstrations—Such as demonstrating that the functional safety requirements have been correctly implemented. Checklists—For example, to ensure that EMC design measures have been observed, applied and implemented correctly. Inspections—For example, checking that the assembly and installation have followed the EMC requirements correctly. Reviews and Assessments—These ensure compliance with the objectives of each phase of the lifecycle. Usually performed by experts, on each phase of the lifecycle and the activities within them. High SILs require greater confidence, and this can mean using third-party experts. A benefit of using reviewers from outside an organization is that it helps avoid the problems of “institutional bias” or “corporate blind spots.” Even where the reviewers are not as expert as the designers, their different perspectives will help detect problems. Audits—These include checking that the correct specification, design, assembly, installation and verification processes have been followed. Audits can be seen as a quality assurance activity and it helps if designers do not carry them out. Instead, people familiar with QA auditing, who are less likely to be distracted by design issues, should carry them out. NOVEMBER 2007 CONfORMity 35 http://www.pseinc.com http://www.pseinc.com

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Conformity - November 2007 Contents Editor’s Note Commission Sets Date, Terms for 700 MHz Auction FCC Reaffirms Roaming Obligations Commission Moves to Improve USF Management FCC Proposes Fines for Violations of E911 Handset Requirements Commission Levies $1 Million Plus Fines for Unsolicited Fax Advertisements GR-3150 - Lithium Battery Certification Levels Based on Criteria for General Product, Safety, and Performance, Part 2 ESD Open Forum Machinery Field Evaluation for the United States Validation, Verification, and Immunity Testing Techniques for EMC for Functional Safety Thermal/EMC Simulation Addresses New Mechanical Design Challenges Product Safety Equipment Buyer’s Guide FCC Releases Report on Telephone Numbering Resource Utilization Canada Still Has PCS Spectrum to Assign Updated Standards List for the EU’s Medical Devices Directive Updated Standards List for EU Directive on Active Implantable Medical Devices Call for Papers for the 2008 EOS/ESD Symposium Announced Mobile Phone Use in Hospitals May Be Dangerous CPSC Actions in the News IEC Standards Update UL Standards Update Telcordia Standards Update From Our “You Can’t Make This Stuff Up” Department Product Reviews Looking Back: Items from Past Issues of Conformity Upcoming Events Advertisers

Conformity Magazine - November 2007

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