Jeff, I cannot claim to have done a reliability prediction on a medical product, nor to have done the same prediction using both MIL-HDBK-217 and Telcordia SR-332. However, I think one must remember that with all these predictive models, they are just that - models! You cannot compare the results from one model with the results from another; it just doesn't work. You might as well measure with a yardstick and a metre rule. What you can do, and what they primarily enable, is the comparison of one design with another using the same measuring device. Whether or not the results bear any relation to reality is a question that is unlikely to be answered until you have a lot of units in the field for a long time and sufficient field data to calculate a mean value that is stable. The model also enables you to examine the underlying data to identify the components and sub-assemblies that are having greatest impact on the whole system reliability. I think that this is probably the greatest benefit, as it identifies opportunities to simplify parts of the design or to take stress reduction measures. Remember also that these models are based on mature designs, where any systematic failure modes (design errors or oversights) have been eliminated such that only the underlying natural random failure rate remains. In my experience the early life of a product is usually dominated by systematic failure modes, and at that stage the random hardware failure rate is something dreams are made of. Some people may believe that certain models bear a closer resemblance to reality than others (and I can think of at least four other models beside 217 and 332) and consequently prefer those models to be used. There is an argument that a model designed for commercial equipment may be more realistic than one designed for the military, or that the individual component models and factors may be more up-to-date. At the end of the day, you get a different number, but what does it really mean? If using SR-332 makes your customer happier than using MIL-HDBK-217, then I'd use SR-332. Then, at least, he can't argue with the answer. Best regards
Neil R. Barker CEng MIET FSEE MIEEE Manager Quality Engineering e2v technologies (uk) ltd 106 Waterhouse Lane Chelmsford Essex CM1 2QU UK Tel: (+44) 1245 453616 Fax: (+44) 1245 453571 Mob: (+44) 7801 723735 P Please consider the environment before printing this email. From: jeff collins [mailto:[email protected]] Sent: 15 March 2007 19:46 To: [email protected] Subject: Medical Products: Telcorda SR-332 vs.Mil-HDBK-217 Group, For those of you who are involved with Medical products and MTBF Prediction, what reliability standard/method do you use? ( Telcordia SR-332 or MIL-HDBK-217) I normally use MIL-HDBK-217 for medical products and Telcordia SR-332 for Telecom or similar products. I'm working on a medical product where they have requested all of their MTBF Predictions to Telcordia SR-332. Thanks for any insight you may have on this topic. Regards, Jeff Collins ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________ Sent by E2V TECHNOLOGIES PLC or a member of the E2V group of companies. A company registered in England and Wales. Company number: 04439718. Registered address: 106 Waterhouse Lane, Chelmsford, Essex, CM1 2QU, UK. - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Jim Bacher: [email protected] David Heald: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
