SRC Forum - Message Replies
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
Posted by: DP JOSHI
Date posted: Mon Mar 5 15:58:51 US/Eastern 2007
Subject: Reliability Apportment/Prediction
Dear Sir, If failure rate(hazard rate) for a non repairable complex mechatronics system is calculated based on total mission time and thereafter apportioned to the various sub systems in series and then predicted reliability for the individual subsystems is calculate on the individual subsystem mission times(certain subsystems are active standby and certain are passive standby-trigerred by certain inputs on certain times, t1, t2 etc..) - is this approach correct?
2.What apportionment techniques can be applied for series system comprising of 20-25 mechatronics system sub system in series to achieve mission target reliability of 0.99. Very little data is available.
3.How do one calculate the number of trials required for achieving certain target reliability figure if present reliability at certain confidence level has been calculated on limited apriori data and tests.
4.For a complex mechatronics system data with low population what model for reliability apportioment and calculation of number of future trials to increase reliability/reliability at higher confidence level is to be used.
Subject: Reliability Apportionment/Prediction
Reply Posted by: John Cloarec
Date Posted: Mon Mar 5 17:42:58 US/Eastern 2007
Your first point: using field data to estimate the global failure rate of your system is better than using only the total mission time, because this duration is not link to any failure. Unless you use Chi-Square distribution to find the failure rate based on assumptions on the expected number of failures and confidence level. After using prediction to check if target is met is normal practices. Your second point: for apportionment techniques have a look in MIL-HDBK-338. I wrote several papers on this subject but ... in French. Your third point: I think you can find useful information in MIL-STD-HDBK-781. Your fourth point: refer previous responses. Regards