Forum: Reliability & Maintainability Questions and Answers
Posted by: Anil Date posted: Wed Jul 9 2:07:26 US/Eastern 2003 Subject: Reliability testing vs Durability testing Message: Could you please help me out in this? What is the difference between Reliability testing and Durability testing? Can you please give one automotive component example for both type of testings?
Posted by: Andrew Rowland (darowland@aep.com ) Date posted: Mon Jul 7 10:51:53 US/Eastern 2003 Subject: ALT Misunderstandings Message: Here's the scenario...electromechanical relays that are normally energized at ~262VDC except when charging the battery then they are exposed to ~277VDC. In one year these voltage levels are split about 8616/150 hours. The manufacturer rates the coil for 285VDC. Several of these relays have failed with open coils after about 12-14 years in service. Two were sent for FA to two different companies. Both found the same "body of evidence". First company concluded cause of failure was being continuously energized. Second lab concluded that wire opened due to stress cracking corrosion. In our attempt to determine the appropriate replacement periodicity, we "cooked" one relay at 300F, energized at ~260VDC for 480 hours and the relay DID NOT FAIL. From this we concluded that 4.7 years is the "right" periodicity. Normally energized relays is on our "Top 20" issues list, so we're going to spend about $175,000 every 4.5 years to replace normally energized relays. Before I rain on the plant's parade, I want to make sure I'm correct on a few points. First, the 300F test we did was based on the premise that the coil insulation would fail. This is not the failure mode/mechanism that we have experienced in the field. It seems to me than, this test was not applicable to what we know and the results cannot be used to determine an appropriate replacement periodicity to preclude open coils. Second, the Arrenhius model was used to determine usage time. Would a temperature-voltage model have been more appropriate? Third, since the relay we tested at 300F did not fail, I could reasonably argue that 6 years is also appropriate (or any other period of time). Fourth, with only one relay under test, the range would be so great at any reasonable confidence level that the results are essentially worthless. My opinion is that any replacement periodicity based on the work conducted to date would be based on poor engineering, at best. However, I would like the experts to weigh-in before I point this out. Thanks for reading my long-winded account.
Posted by: Mike Date posted: Wed Jul 2 20:22:48 US/Eastern 2003 Subject: Standard Download Message: Are there any webistes that I can download some standards, mil-std, etc? Thanks.
Posted by: C.P. Chuah (c.p.chuah@sheffield.ac.uk ) Organization:University of Sheffield Date posted: Tue Jul 1 10:29:56 US/Eastern 2003 Subject: reliability of electronics board Message: Can anybody tell me what is the best method and most representative to evaluate the reliability of an electronic boards assuming i have all the available failure rates of the components in use ? I have calculated it by just using the series model where it is assumed that one of the electronic component fails the board fails. But i am not sure if that represents a good reliability methodology as i am no expert in reliabilities. Thank you.
Posted by: Ela Date posted: Sat Jun 28 9:17:29 US/Eastern 2003 Subject: Reliability Evaluation Message: We are searching for a new methods of reliability evaluation based on field data instead of regular MTBF calculation.We found that this attitute is simple but not compatible with reality evidences.May be something like first/next failire or weakest link? Do you have any expearence in this field? Thank you,
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