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Forum: Reliability & Maintainability Questions and Answers

Topic: Reliability & Maintainability Questions and Answers

Topic Posted by: Reliability & Maintainability Forum ( )
Organization: System Reliability Center
Date Posted: Mon Aug 31 12:47:36 US/Eastern 1998

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Posted by: Peet ( )
Organization:Grintek Electronic Systems
Date posted: Tue Jul 4 8:50:45 US/Eastern 2000
Subject: Reliability Prediction - Compensation for Shock Mountings
When performing a reliability prediction for a product being used in, for example, an airborne rotary wing environment (ARW). All available software packages that I know of does make provision for selection of the global environment, while in some cases you can select different environments for different products within a system. How would one distingiush between a product mounted directly into the cocpit of a chopper and one that is mounted onto a well designed shock obsorber that dimenishes the effect of vibrations and bumbs? Obviously, the product on the shock mount lives in a more friendly environment, but which of the available environments do you choose? Best Regards Peet


Subject: Product Use Environments
Reply Posted by: Jack Farrell ( )
Organization: Reliability Analysis Center
Date Posted: Thu Jul 6 16:12:21 US/Eastern 2000
The ARW use environment factor encompasses many environmental influence factors of which vibration (sine & random) is the most significant. One solution to your question would be to obtain a copy of RADC-TR-80-299 "Revision of Environmental Factors for MIL-HDBK-217B", review the technique used to arrive at the current ARW factor, and then adjust the factor based on your use environment. Of course you would need to be able to justify this new environmental factor to your customer. A second solution would be to develop a reliability prediction for your product using the PRISM software package. PRISM is a new systems reliability analysis tool developed by RAC as a replacement for MIL-HDBK-217. One of the many features of PRISM is the tailoring of the use environment based on vibration levels. Additional information, including a downloadable Demo is available at

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