Conformity Magazine - September 2008 - (Page 26)

Risk Assessment and the Draft Combined EMC Performance and Safety Standard Risk assessment will be a normative requirement in the combined EMC performance and safety standard, and it aims to provide practical guidance on how to achieve this in its informative annexes. There are many issues to be considered when performing a risk assessment for the purposes of EMC for safety engineering. As [15] and [16] show, it is impossible, solely by EMC testing, to validate that acceptable levels of safety risks have been achieved. The current draft of Annex D accepts that, even though testing is a necessary technique, modern ME equipment in today’s complex EM environments cannot be thoroughly tested in a practical manner. Risk assessment can ensure good design practices, thereby increasing the likelihood of continuous functional safety over the lifetime of the equipment. The verification and validation of EMC as part of a risk-based approach to safety should use a number of techniques for verification and validation, including (from [18]): • Demonstrations • Checklists • Inspections • Reviews and assessments • Independent reviews • Audits (QA) • Non-standardised checks and tests • Individual and/or integrated hardware tests • Validated computer modelling • Testing (e.g., factory acceptance test or on-site testing) EM immunity testing is supplementary to the other verification and validation measures. Clause 9.1 of [10] says “In most cases there will be no simple or practicable way to verify by means of testing that EM immunity is achieved.” Many risk assessment methods are in current use, and listed by [2], but there is very little experience of applying them to EMC issues. Any employed method must take into account the fact that some failure modes caused by EMI (e.g., “latchup”) can cause some or all of a semiconductor’s output pins to change state at the same time, and “common-mode” EMI causes noise on many or all circuit nodes at the same time. Also, EMI and some types of faults can create noise that can be mistaken for valid signals. Also, it is generally assumed that two or more independent faults are so unlikely that only “single-fault” issues need be considered. But where the probability of a fault (or faults) is high enough (e.g., due to inadequate design for aging or corrosion), then two or more independent faults could occur 2 Conformity September 2008 with sufficient likelihood that they would cause excessive safety risks. Based on the work done on IEC 61000-1-2, the sort of guidance on risk management we should expect to see in the annexes should include the following issues: a) Design that takes into consideration: • The worst-case EM disturbances to which the ME equipment or ME system could be exposed throughout its lifecycle, including their levels, modulations, possibilities of simultaneous disturbances, etc. • The worst-case EM disturbances that the ME equipment or ME system could emit throughout its lifecycle • Environmental influences that could cause degradation of control measures for electromagnetic disturbances, including mechanical forces, shock and vibration, temperature extremes and cycling, humidity extremes and cycling, air pressure extremes and cycling, corrosion and aging of components and materials, etc. • Serviceability (maintainability) • Control of variability in EM characteristics in serial manufacture • Reasonably foreseeable use and misuse • Reasonably foreseeable faults b) Production aspects including • Counterfeit components • Purchased subassemblies that may not meet specifications • Semiconductor die shrinks (mask shrinks) • Manufacturing changes and variations c) Servicing and preventative maintenance d) Verification including • Initial type testing • Evaluation of manufacturing changes • EMC checks/tests of serially-manufactured units to apply QA to EM characteristics • EM checks/tests after servicing, repair, modification, upgrade, etc. • Evaluation using modulations, test levels, and test methods that have been determined by the risk assessment and EM environment assessment process

Table of Contents Feed for the Digital Edition of Conformity Magazine - September 2008

Conformity Magazine - September 2008 Contents Editor’s Note Commission Adopts Regulations for Internet-Based TRS Services Another Company Fined for Non-Compliance with HAC Requirements FCC Extends “Do-Not-Call” Registry Compliance Requirements Marketing Company Gets $1.4 Million Fine for Junk Faxes EU Commission Codifies Directive on TTE Market Competition EU Commission Releases Updated Standards List for the R&TTE Directive Updated Standards List for the “New” Low Voltage Directive Released New Standards List Released for the EU’s Machinery Directive The ESD Association: Voluntary Standards in Action ESD Open Forum Medical EMC Standards: Towards the 4th Edition of IEC 60601-1-2 iNARTE Informer Pre-Pulse Voltage in the HBM ESD Model Digital Interfaces and EMC Performance ESD Design Buyer’s Guide Product News Commission Publishes Updated Standards List for the EU’s Personal Protective Equipment Directive FDA Links “Human Factors” to Adverse Events with Medical Devices CPSC Actions in the News IEC Standards Update UL Standards Update Product Reviews Telcordia Standards Update From Our “You Can’t Make This Stuff Up” Department Looking Back: Items from Past Issues of Conformity Advertisers

Conformity Magazine - September 2008

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.