DPM to MTBF conversion

Six Sigma – iSixSigma Forums Old Forums General DPM to MTBF conversion

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• #38652

Steven
Member

I need to convert Defects per Million to MTBF. Does anyone know of a correct formula?Steven

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#116018

Dayton
Member

Steven,
Why do you want to do that?   Mean Time Between Failures and Defects Per Million are both perfectly acceptable stand-alone metrics.   Are you trying to establish a correlation between the two?  That might be interesting, but what are you trying to accomplish with a clunky conversion like that?  A comparison which would certainly be prone to inconsistencies because of the variables at play in both separate calculations.
Please explain more what you are working on/with and what you are responding to.  Are to talking about MTBF of your process/equipment or your product?  MTBF calculations can be tricky for complex systems – the best way of which to calculate is still the old Mil.Std. way of determining the MTBF of each of the subassemblies separately and then determining the reciprocal of each MTBF and adding the reciprocals of all subassemblies together and taking the reciprocal of the summation – which gives you the compounded MTBF of the system.
Please explain in order to get some real help.
Vinny

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#116019

Bob J
Participant

Steven,
DPM in the traditional sense does not convert to MTBF…  DPM is defects/defectives per million opportunities….  MTBF is  failures in time at a point where you have a constant failure rate (not infant mortality or wearout ends of the bathtub curve)….
Give me a better sense on what you are trying to do and I’ll see if I can help….
Best Regards,
Bob J

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