Conformity Magazine - February 2009 - (Page 18)

design, and assessment. Its basic features for an automotive application are described below. The approach described in [7] and [9] will require a significant learning curve for many manufacturers, functional safety assessors, and EMC test laboratories who want to develop the skills to assess a design’s EMC for functional safety. Manufacturers Need to be More Clever Using only EMC testing to demonstrate due diligence in achieving tolerable safety risks over a vehicle’s lifecycle, requires the twelve issues raised above – and their combinations (for example, an older vehicle with one or more faults, corroded metalwork and conductors, driven incorrectly, suffering multiple physical and EM disturbances simultaneously) – to be addressed by the test program. This would be so lengthy that no organization could possibly afford it. Manufacturers need to be cleverer, if they are to achieve tolerable functional safety risks with reasonable times and costs. One aspect of this cleverness is to use EM design techniques that ensure safety-related systems will maintain the necessary EM characteristics over their lifetime, taking the reasonably foreseeable EM and physical environments into account [27]. Another is to verify and validate these more robust designs, using a variety of methods (generally including some EMC testing) to achieve the necessary confidence without excessive timescales or costs. Assessing the Lifetime EM and Physical Environments An assessment of the reasonably foreseeable real-life possibilities over the vehicle lifetime [28] [29] should include: • EM disturbances in the near-field (e.g., crosstalk in cable bundles) and far-field (e.g., radio/radar transmitters); • Intra-system interference (between ESAs in a system); • Inter-system interference (between different systems in a vehicle, and a vehicle system and the world outside; also considering electronic devices carried by people); • Modulation types, and their frequencies or waveshapes; • Simultaneous EM and/or physical disturbances (including continuous, extremes, cycling and transients); • Possibilities for use and misuse; • Physical environment(s) (e.g., mechanical, climatic, biological, wear, etc.); • The effects of aging; • Future changes to the EM and physical environments; • Component tolerances, and future changes to components (e.g., obsolescence, die shrinks, etc.) It is usually only possible to establish the types of EM phenomena (see Figure 3), their modulations and worst-case levels, with any confidence. 18 Conformity february 2009 Standards from the IEC and military describe a variety of physical environments, but the compatibility levels (or test levels) they specify should not be applied unquestioningly, as they may not have been created for safety purposes. If a vehicle type is to be sold into an EM and/or physical environment not fully addressed during its original design, an assessment of the new EM and physical environments is required. To maintain tolerable risk levels could require design changes, reverification and revalidation. Good EM and Physical Design Engineering There are a great many publications on good EM design techniques that can be applied at different levels of assembly, from ICs to cabling and vehicle structures. Reference [27] discusses a number of well-proven, good EM and physical design techniques for controlling functional safety risks, which is greatly expanded upon in an Annex to [7] and Part 4 of [9]. Hazard Identification and Risk Assessment A documented hazard identification and risk assessment process is required that assesses how the reasonably foreseeable EM and physical environments over the lifecycle could possibly affect the ESA or vehicle, taking into account faults, misuse, etc. It should show how any excessive risks were reduced to an acceptable degree by design, and be a living document that guides the design process throughout. Inductive (or consequence) methods start with a low-level error or failure, and try to determine whether it could lead to a hazardous situation. They include failure mode effects analysis (FMEA) and event tree analysis [30]. Deductive (or causal) methods start with hazardous situations, and try to determine what could have caused them, and include fault tree analysis [30]. Brainstorming techniques identify any possibilities. They apply inductive methods to see if the possibilities could have hazardous consequences, and then apply deductive methods to discover what could cause them, and also their likely effects. It is usual to employ at least one inductive and at least one deductive method to improve the coverage of the risk assessment. Brainstorming is always required to foresee faults, use, misuse, etc., overlooked by standard methods. All of the above must take into account the EM and physical characteristics of the product and its reasonably foreseeable EM and physical environments over its lifetime. Many vehicle manufacturers and Tier 1 companies employ risk assessment methods, but they tend to do it by rote, which is not recommended by functional safety experts [31] [32]. Any risk assessment method must take into account the fact that some failure modes (e.g., latch-up) can cause some/all

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Conformity Magazine - February 2009 Contents Editor's Note FCC Clarifies Closed Captioning Requirements for DTV Receivers Commission Cracks Down (For the Fifth Time!) On Junk Fax Marketer FDA Requests Comments on Global Harmonization Documents Australia Now Requires Solar Panel Testing and Certification EU Drafting New Directive on Toy Safety EU Commission Revises Standards List for EMC, R&TTE Directives Additional Standards Published For the EU's Medical Devices Directive EU Commission Publishes Additional Standards for Directives on Active Implantable, In Vitro Medical Devices EMC For the Functional Safety of Automobiles ESD Open Forum The ILAC Arrangement: Facilitating Trade Efficient Methodology for the EMI Analysis of Optical Transceivers Including PCBs and/or Flex Circuits The EuP Directive - Implementation, Design Requirements and Issues Chambers, Shielding, and Accessories Buyer's Guide CPSIA Lead Requirements Apply to Existing Inventory, Says CPSC CPSC Clarifies Certifcation Requirements Other CPSC Actions in the News IEC Standards Update Product Reviews UL standards Update Telcordia Standards Update From Our "You Can't Make This Stuff Up" Department Looking Back: Items from Past Issues of Conformity Advertisers

Conformity Magazine - February 2009

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