calculate MTBF
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From: Raveninghorde on 22 Jan 2010 07:47 On Thu, 21 Jan 2010 12:43:20 -0500, Rich Webb <bbew.ar(a)mapson.nozirev.ten> wrote: >On Thu, 21 Jan 2010 16:35:55 +0000, Raveninghorde ><raveninghorde(a)invalid> wrote: > >>On Thu, 21 Jan 2010 07:33:02 -0800, John Larkin >><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >> >>>On Thu, 21 Jan 2010 15:06:10 +0000, Raveninghorde >>><raveninghorde(a)invalid> wrote: >>> >>>> >>>>How do you calculate MTBF? >>> >>>Get the failure rate of each part (specified in FITS, failures per >>>billion hours), add them up, take the reciprocal, multiply by a >>>billion. >>> >>>John >> >>Thanks >> >>The National site is good and I found the info for the their parts. >> >>Microchip no luck, IR no luck. So where do you normally find the >>information? >> >>I suppose one also assumes perfect ESD procedures, and perfect lead >>free soldering. > >You're new at this so, even if you're not doing a MIL-STD prediction, >I'd strongly recommend downloading MIL-HDBK-217 from the online site ><https://assist.daps.dla.mil/quicksearch/> (search on MIL-HDBK-217 in >the Document ID field) and skimming though sections 3 and 4. The >Bellcore process is similar. > >John's basic equation is correct. You can use the tables in 217 to >estimate the reliability of items for which the manufacturer does not >provide the info. > >There are provisions to consider connections (e.g., "Quantity of Hand >Soldered PTHs [plated through holes]"). It's a hell of a lot of work to >do a full analysis. Given the customer I'll go with 217. I'm trying to avoid spending a week doing this so I'm looking at other solutions. I've seen a few websites that offer online calculation ($500) or send the BOM and results in 48 hours ($1500). I've also seen some programs that calculate MTBF. Anyone tried these options?
From: Raveninghorde on 22 Jan 2010 08:19 On Fri, 22 Jan 2010 02:02:42 -0800, Robert Baer <robertbaer(a)localnet.com> wrote: >Raveninghorde wrote: >> On Thu, 21 Jan 2010 10:24:29 -0500, Rich Webb >> <bbew.ar(a)mapson.nozirev.ten> wrote: >> >>> On Thu, 21 Jan 2010 15:06:10 +0000, Raveninghorde >>> <raveninghorde(a)invalid> wrote: >>> >>>> How do you calculate MTBF? >>> For a component? For an entire system? 217 or Bellcore/Telcordia or ... >>> >>> The Wikipedia article isn't a bad place to start. If you're tasked with >>> doing a full-up parts-stress reliability prediction analysis, good luck! >> >> For a lithium ion battery charger. >> >> My brief post was a cry of despair. I ship these by the hundred. Now a >> BIG US company wants them and I get asked for a bucket load of >> information. >..as long as they PAY for the info and time to compile it. Nope. They would prefer the BOM and do the calculation themselves. Since I won't give the BOM it's down to me sort it out.
From: Rich Webb on 22 Jan 2010 08:27 On Fri, 22 Jan 2010 12:47:25 +0000, Raveninghorde <raveninghorde(a)invalid> wrote: >Given the customer I'll go with 217. I'm trying to avoid spending a >week doing this so I'm looking at other solutions. > >I've seen a few websites that offer online calculation ($500) or send >the BOM and results in 48 hours ($1500). I've also seen some programs >that calculate MTBF. > >Anyone tried these options? When I got roped into doing one for a piece of shipboard equipment (nobody else would even admit to knowing how to spell "RM&A"), the company had a copy of Relex that I used for the crunching. Packages like that do save time, since they have the tables "built in" and one just needs to select the appropriate factors for each component. It can also make auditing a bit easier, as well as printing pretty reports. You might also want to start with the Appx A "Parts Count" method which is less detailed but does give you a ballpark figure (but one that tends to be more conservative). The intended use of either method is to establish an "apples to apples" comparison baseline, sort of like the EPA estimated MPG ratings. You don't expect to get exactly that MPG but you can have some reasonable expectations if one vehicle is rated 18 and another 32. The other big use is to help out the logistics chain in estimating the initial spare parts buy. The reliability prediction is paired with a FMECA (Failure Modes, Effects, and Criticality Analysis) to help decide which, how many, and where spares need to be stocked. Once the equipment has a field history, of course, the actual failure rates and spares usage drive the numbers. -- Rich Webb Norfolk, VA
From: John Larkin on 22 Jan 2010 10:04 On Fri, 22 Jan 2010 12:47:25 +0000, Raveninghorde <raveninghorde(a)invalid> wrote: >On Thu, 21 Jan 2010 12:43:20 -0500, Rich Webb ><bbew.ar(a)mapson.nozirev.ten> wrote: > >>On Thu, 21 Jan 2010 16:35:55 +0000, Raveninghorde >><raveninghorde(a)invalid> wrote: >> >>>On Thu, 21 Jan 2010 07:33:02 -0800, John Larkin >>><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >>> >>>>On Thu, 21 Jan 2010 15:06:10 +0000, Raveninghorde >>>><raveninghorde(a)invalid> wrote: >>>> >>>>> >>>>>How do you calculate MTBF? >>>> >>>>Get the failure rate of each part (specified in FITS, failures per >>>>billion hours), add them up, take the reciprocal, multiply by a >>>>billion. >>>> >>>>John >>> >>>Thanks >>> >>>The National site is good and I found the info for the their parts. >>> >>>Microchip no luck, IR no luck. So where do you normally find the >>>information? >>> >>>I suppose one also assumes perfect ESD procedures, and perfect lead >>>free soldering. >> >>You're new at this so, even if you're not doing a MIL-STD prediction, >>I'd strongly recommend downloading MIL-HDBK-217 from the online site >><https://assist.daps.dla.mil/quicksearch/> (search on MIL-HDBK-217 in >>the Document ID field) and skimming though sections 3 and 4. The >>Bellcore process is similar. >> >>John's basic equation is correct. You can use the tables in 217 to >>estimate the reliability of items for which the manufacturer does not >>provide the info. >> >>There are provisions to consider connections (e.g., "Quantity of Hand >>Soldered PTHs [plated through holes]"). It's a hell of a lot of work to >>do a full analysis. > >Given the customer I'll go with 217. I'm trying to avoid spending a >week doing this so I'm looking at other solutions. > >I've seen a few websites that offer online calculation ($500) or send >the BOM and results in 48 hours ($1500). I've also seen some programs >that calculate MTBF. > >Anyone tried these options? Given the FIT numbers, you can do a reasonable product by hand in a half hour maybe. John
From: mpm on 22 Jan 2010 10:51
On Jan 21, 10:06 am, Raveninghorde <raveninghorde(a)invalid> wrote: > How do you calculate MTBF? Easy! 1 - For consumer items not covered by a reasonble warranty period, Take the manufacturer's specified MTBF and divide by 1,000. 2 - For items covered under warranty, just add 30 minutes to the expiration date of same. 3 - And for cheap Chinese imports, just add up whatever time it takes you to open the packaging. OK -- I guess that was just a wee bit cynical. :) |