Forum: Reliability & Maintainability Questions and Answers
Posted by: Julien Nico (ARZ_ST_ELB@compuserve.com )
Date posted: Wed Oct 20 9:53:56 US/Eastern 1999
Subject: Population sample number to perform endurance test
In order to improve reliability figure got by FMEA analysis on one of our new product, we will perform endurance tests.
We have to define number of product to test in order to have an MTBF with a known uncertainty. More over, due to the component high cost, it is not possible to have a high number of tested part. Statistics define applicable rules but we have to use standard deviation of the MTBF. As it is a new component, it is not possible to use existing data. We are looking for a data base of standard deviation for component used in aeronautical or another means to minimize number of test items. Many thanks for your help.
Posted by: T.R. Pilling (email@example.com )
Date posted: Sat Oct 9 22:35:27 US/Eastern 1999
Subject: Fault Isolation Requirement
We are currently writing operational requirements for a new fighter aircraft and have received a variety of feedback from contractors regarding a fault isolation requirement. The requirement is currently written as 90% automatic fault isolation to a single ambiguity group (LRU). We've been told that 90% should be easily achieved for avionics but not for hydro-mechanical systems. Is this true? If so, what do you think would be a reasonable requirement given emerging technology over the next 8-10 years?
Please respond at your earliest opportunity. Thanks
Posted by: Clay Davis
Date posted: Tue Oct 5 17:12:16 US/Eastern 1999
Subject: Reliability vs Availability Calculations
I am trying to determine the availability for a new design for a computer system. Since availability is highly dependent of the software and the MTTR, I have decided to focus only on the hardware at this point.
My question is, say for a system that has an MTBF of 10 yrs, is the availability (from a hardware standpoint) 0.9048 at the end of the first year? I calculated this number using the standard R=e(-lambda*t). Lambda = 1 / 87600 hours and t = 8760 hrs. This would lead me to believe the computer system is going to be un-available for more than 1 month during the first year, which cannot be correct. Any thought on what I am doing wrong? Thanks for your help. Clay Davis
Posted by: Floyd Kreuze (firstname.lastname@example.org )
Date posted: Tue Oct 5 13:18:26 US/Eastern 1999
Subject: EEPROM Failure Model
I have some questions concerning the MIL-HDBK-217F Notice 2 failure rate model for EEPROM's (Page 5-4) What happens to A1 and A2 when the total number of programming cycles over EEPROM life goes over 500K? Is it possible that these tables are out of date and that EEPROM's rated at 1000K programming cycles (over life) are now being used reliably? What is there in the technical literature on this topic?
Posted by: Gerd Jonas (email@example.com )
Date posted: Mon Oct 4 9:35:38 US/Eastern 1999
Subject: Non Operating prediction
Which tool is usefull to calculate the fpmh for electronic equipment in non operating condition? Thanks for your help. gerd