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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: Henry Davis ( )
Date posted: Mon Sep 18 19:11:53 US/Eastern 2000
Subject: Single Bit Error Rate
There is a requirement that the single bit error rate for memory shall not exceed 25 per one million hours. The SBE shall be calculated using MIL-HDBK-217F, CN2. I also have information re environments, etc. The operating environment is 1 hour/day at 60,000 feet and 23 hours/day at sea level. For sea level I calculated FR based upon 217 and used the Failure Mode Distribution (FMD-91)information for a factor for failures from data bitlosses. Does anyone have any suggestions for the SBE calculations/derrivations at 60,000 feet? If so I plan on taking a weighted average of the numbers for the final calcualtion.


Subject: Single Bit Error Rate
Reply Posted by: Bruce Dudley ( )
Organization: Reliability Analysis Center
Date Posted: Thu Sep 21 13:50:02 US/Eastern 2000
I would recommend calculating a new memory device failure rate using an airborne environment. Mil-Hdbk-217 has such factors which have a ratio of 4 to 1 for extreme uninhabited airborne conditions. I checked with our new PRISM reliability model and computed failure rates for stationary ground uncontrolled environment at 7 fits and at airborne uninhabited which was 30 fits. This is also roughly at a 4 to 1 ratio. If you use the failure modes as the factor for single bit error as you did for the ground condition, you will establish the airborne part of the operation. The two failure rates can be weighted by time of operation and combined to find the overall average error rate.

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