Ahne,

 Very good answer.

 But, If you do a test and have zero failures can't you still provide a MTBF based on a confidence level?

 I am not experienced in this area but I would think getting 0 failures should always give you a better confidence level than having one.

Thanks,
Bob K.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ahne Oosterhof
Sent: Thursday, April 11, 2013 11:26 PM
To: [log in to unmask]
Subject: Re: [TN] Reliability Predictions

Calculating a prediction of the MTBF by using failure predictions for each component is not a very precise method, or more accurately, a very imprecise method. The MTBF of any component is greatly affected by its power consumption and its resulting temperature rise and the temperature of the environment (and a few other things). But you get a number you can wow management (and customers) with. 
We did an actual life test on a number of instruments to determine MTBF. But I was told if no failure occurred they could not calculate a number. So I introduced one failure after the test was almost finished to at least get them to give me a number.

Ahne.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Blair Hogg
Sent: 08 April, 2013 13:10
To: [log in to unmask]
Subject: [TN] Reliability Predictions

This might be a little off-topic but does anyone out there in TechNet Land know if there is an IPC standard for reliability predictions, similar to Mil 217 or Telcordia? 

The process seems straightforward, grossly simplified you take a sum of the expected number of failures for all components on the BOM and take the inverse for MTBF. Haven't done enough research to determine the difference between the various standards used, it's a spare time project (whenever I get any).

Thanks,

Blair


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