Forum: Reliability & Maintainability Questions and AnswersPosted by: DP JOSHI Date posted: Mon Mar 5 15:58:51 US/Eastern 2007 Subject: Reliability Apportment/Prediction Message: 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 standbytrigerred 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 Message: 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 Message: 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 timetruncated 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 Message: Can anybody tell me how to convert a failure rate (obtained from MIL217 etc.) into a Probability of Occurrence per Flight Hour ?
Posted by: Vesna Borak Organization:Cochlear Limited Date posted: Mon Mar 5 15:48:22 US/Eastern 2007 Subject: X5R capacitor burnin at +125degC/168hrs Message: 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.
