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Forum: Reliability & Maintainability Questions and Answers

Topic: Reliability & Maintainability Questions and Answers

Topic Posted by: Reliability & Maintainability Forum (src_forum@alionscience.com )
Organization: System Reliability Center
Date Posted: Mon Aug 31 12:47:36 US/Eastern 1998

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Original Message:

Posted by: Daniel Mahoney (dmahoney@draper.com )
Organization:Draper Laboratory
Date posted: Fri Aug 20 10:01:26 US/Eastern 1999
Subject: Turn on/turn of effects on parts
Message:
Greetings all, Can anyone supply some insight into the effects of turn on/turn off to electronic parts? Specifically, which is better? If I have some very low power electronics (1 millivolt level) should I turn them on for a tenth of a second, then off for 10 seconds or just leave them on (GB environment)?


Reply:

Subject: Turn On/Off Reliability
Reply Posted by: Bruce Dudley (bdudley@alionscience.com )
Organization: Reliability Analysis Center
Date Posted: Mon Aug 30 13:09:58 US/Eastern 1999
Message:
This problem revolves around the reliability factors of how failure prone the device(s) is with electrical stress applied, how good the reliability is without power applied and what is the effect of "thermal" stress cycling. If the number of thermal cycles (ON-OFF POWER) is moderate in comparision to the end of life expectations, then the cycling fatigue failure problem could be eliminated. An analysis of the cycles to failure due to thermal fatigue will resolve this situation. If it is high, then temperature fatigue will be the life limiting factor and the power cycling should be limited or left on to reduce this stress factor. Given that thermal cycling is not a problem due to ground benign environmental conditions (i.e. very low delta temperature changes), the problem resolves to the relative historical defect failure rates of the two conditions, power on and power off. In our experience, component failure data has consistently shown that most solid state electronic parts have less failures without electrical stress applied as less failure mechanisms are observed. So, the general conclusion is higher reliability should be obtained on solid state parts by turning the power on and off as needed. If the parts are electromechanical (relays or switches), on off cycling may cause wear or corriosion of the contacts. Then one should consider the application of power on only.


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