Conformity Magazine - February 2009 - (Page 15)

by people working in the most hazardous occupations (e.g., oil industry divers). If there were 100,000 such vehicles on the roads for similar periods, we could expect 120 deaths from these overlapping transients every year. In this example, to be sure of experiencing just one overlapping pulse, a test vehicle would need to be driven 24/7 for 19 weeks. The likelihood of this discovering a significant safety problem is extremely remote, and even then it would almost certainly be diagnosed as something else. Were a customer to complain to his car dealer of a malfunction (that was due to these overlapping transients), the likelihood of the dealer experiencing the problem by test-driving the vehicle for a full eight hours would be very small indeed. Most likely the dealer would assume the driver had simply made a mistake. 5. Only One Port is Tested at a Time When an ESA is subjected to a radiated RF field, all of its interconnecting cables pick up RF voltages, but with phase differences between them. But traditional EMC conducted immunity tests intended to simulate the effects of radiated fields only test one cable at a time. Qinetiq PLC has injected RF into all of an ESA’s conductors simultaneously, with phase shifts to match what would be expected in real life. They discovered that the immunity could be significantly worse than that experienced when one cable was tested at a time. 6. EMC Tests Ignore the Physical Environment ESAs that are involved in safety-related activities must maintain certain EM characteristics over their life-cycles, despite the effects of the physical environment, including the following: • Mechanical (static forces, shock, vibration, etc.) • Climatic (temperature, humidity, air pressure, etc. – both extremes and cycling effects) • Chemical (oxidation, galvanic corrosion, conductive dusts, condensation, drips, spray, immersion, icing, etc.) • Biological (e.g., mould growth, etc.) • Operational wear and tear over the lifetime (friction, fretting, repetitive cleaning, grease build-up, etc.) Effects vary from immediate (e.g., non-flat mounting opening a gap and degrading shielding) to long-term (e.g., corrosion of a shield joint or filter ground bond). Reference [25] describes a number of real-life problems of this nature. Reference [26] shows that a filter can suffer up to 20dB degradation in its attenuation due to a combination of ambient 901 Sheldon Dr., RTP (Cary), NC 27513 USA february 2009 Conformity 15 http://www.ProductSafeT.com http://www.ProductSafeT.com

Table of Contents Feed for the Digital Edition of Conformity Magazine - February 2009

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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