Forum: Reliability & Maintainability Questions and Answers
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?
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.
Posted by: Leroy Meyers
Date posted: Mon Mar 5 15:54:19 US/Eastern 2007
Subject: Preventive Maintenance - - Reliability
I have a subcontractor that is providing an MTBF for a system. He is saying that since certain items will undergo preventive maintenance (ie. TWT, Motor), these items are not part of the reliability model (not included in the MTBF calculation). The subcontractor reasons that these items will be changed before they fail.
Am I correct or incorrect?
Posted by: Leroy Meyers
Date posted: Mon Mar 5 15:51:46 US/Eastern 2007
Subject: Field Data & MTBF
I have field data over a period of many years, and I want to calculate the MTBF with a confidence level. Would it be correct to use the Chi Square distribution? If so, would the Degrees of Freedom be 2n+2 (where n=number of failures)as if it were a time-truncated test?
I'm looking at page 38 of Practical Statistical Tools for the Reliability Engineer.
Posted by: Randolf
Date posted: Mon Mar 5 15:50:23 US/Eastern 2007
Subject: Failure Rate to Probability of Occurrence per Flight Hour Conversion
Can anybody tell me how to convert a failure rate (obtained from MIL-217 etc.) into a Probability of Occurrence per Flight Hour ?
Posted by: Vesna Borak
Date posted: Mon Mar 5 15:48:22 US/Eastern 2007
Subject: X5R capacitor burn-in at +125degC/168hrs
The X5R ceramic capacitor operating range is -55 to +85 degC. This relates to the capacitance value, as certain capacitance range (+/-15%)is guaranteed within the above temperature limits.