Forum: Reliability & Maintainability Questions and Answers

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Posted 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 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.

Replies: (list all replies)
Reliability Apportionment/Prediction
John Cloarec Mon Mar 5 17:42:58 US/Eastern 2007
Oups I forget
John Cloarec Mon Mar 5 17:43:55 US/Eastern 2007

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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.


I say that this is not valid. Preventive maintenance has no affect on a reliability figure such as failure rate or MTBF. A failure rate for these items should be included.

Am I correct or incorrect?

Replies: (list all replies)
Reliability data
bwd Mon Mar 5 17:26:54 US/Eastern 2007
Maintenance versus Reliability
John M. Cloarec Mon Mar 5 17:37:56 US/Eastern 2007

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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 time-truncated test?

I'm looking at page 38 of Practical Statistical Tools for the Reliability Engineer.

Replies:
Field Data & MTBF
Rushabh Mon Mar 5 17:25:07 US/Eastern 2007

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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 MIL-217 etc.) into a Probability of Occurrence per Flight Hour ?

Replies:
Convert calendar failure rate to operating hour failure rate
Larry George Mon Mar 5 17:23:31 US/Eastern 2007

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Posted by: Vesna Borak
Organization:Cochlear Limited
Date posted: Mon Mar 5 15:48:22 US/Eastern 2007
Subject: X5R capacitor burn-in 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.


Would anyone be able to advise what happens if you burn-in the X5R capacitor at temperatures above +85degC, for example at +125degC for 168 hours - would there be any permanent damage (and which failure modes) or capacitor would recover once it cools down with no impact on reliability?

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