Hi Generally it's the magnetic stuff (like disk drives, not much core memory in use anymore ...) that limits your upper temperature in a given installation. I've lost far more disks to high temperature issues than just about everything else combined. Number two on the list would be power supplies in my case. I suspect that lightning may be involved in some of those.
Bob On Nov 19, 2009, at 11:23 AM, Mark Spencer wrote: > With regards to the MTBF for internet equipment the air temperature will play > a large role in determining the life span of equipment in data centers. > There is a lot of discussion in the IT world now about raising the typical > temperatures in data centers to save energy and the resulting decrease in > equipment life is generally accepted. As IT equipment is often able to be > duplicated the consequences of a single piece of equipment failing may not be > very severe and it may be replaced under a maintenance contract in any event. > > The equipment vendors typically specify operating temperatures that are > considerably higher than room temperature. > > > > > ----- Original Message ---- > From: Bob Camp <[email protected]> > To: Discussion of precise time and frequency measurement <[email protected]> > Sent: Thu, November 19, 2009 4:56:27 AM > Subject: Re: [time-nuts] Rubidium standard / MTBF > > Hi > > Just to put some numbers on this stuff: > > A typical TV has a design goal of a > 5 year lifetime. A "premium" TV has a > design goal of a > 10 year lifetime. The theory is that if it doesn't last > that long, the customer will not buy another one from your brand. > > Here in the US, most cell phones get swapped at the end of the two year > contract. It's a real good bet that they are designed to have a 2 year > lifespan at around the 90 to 95% level. Again, same theory, if it dies we > won't sell another one. I suspect the return rate also gets written into the > contracts with the carriers. > > There are a whole lot of normal use assumptions in their calculations. You > could debate the details for a *long* time. > > The one that I find the most shocking is the very major internet hardware > company that considers 5 years of continuos use to be the goal. The logic - > we want them to swap out the gear regularly.... > > Bottom line - your TV may be more reliable than your internet connection ... > > Crazy stuff > > Bob > > > On Nov 19, 2009, at 4:09 AM, Steve Rooke wrote: > >> 2009/11/19 Mike S <[email protected]>: >>> At 05:22 AM 11/18/2009, Steve Rooke wrote... >>>> >>>> The point I should have made is that most quoted MTBF figures have a >>>> reasonable bearing on the lifetime of the item, >>> >>> But your point would then be almost perfectly incorrect. MTBFs are not meant >>> to, nor do they, predict product lifetimes. They are measures/predictions of >>> product reliability. >> >> OK, I agree, the term is mean time between failures but the question >> is what is the lifetime of something. This is the point we are >> discussing and we really need to understand what this means. I'm not >> going to quote a number of web searches, this means different things >> to different people but this matter is not quite as black and while as >> you think. >> >> The lifetimes of any thing can be broadly split into two groups, there >> are things that have a predetermined lifespan, like lifeforms, and >> those that have no fixed lifespan. Let's look at the second broad >> category, as this is what we are really talking about. So what is the >> lifetime of an item in this category, is it related to MTBF or not. >> Well, lets see, take some items, like consumer goods, these are >> frequently thrown away when they fail as it is generally expensive to >> fix them and newer models are more attractive. Now, do all consumers >> wait till an item fails before they throw it away, well no, it depends >> on the culture but I bet a large proportion of consumers probably do >> wait till it fails. So in this case, quite a large section of what we >> are talking about, the lifetime of the item is related to the time it >> fails. Infant failures are obviously covered by initial warranty but >> this seems to indicate that for a large sample size, the products >> lifetime would be related to the MTBF. Agreed there are some >> assumptions there, I expect the MTBF of a cellphone is a reasonable >> amount but if you live in California and are seen with one over 6 >> months old you would die of embarrassment. So the lifespan of a >> cellphone in California is significanly shorter than the MTBF, the >> factor here is the MTBE (mean time before embarrassment). >> >> No lets look at the corporate environment. In this environment, >> failure of equipment can be very costly to a company so, if they have >> any sense, they will arange to upgrade equipment well inside the time >> that the item is expected to fail. Now, you may say that companies do >> this well inside a shorter cycle than this as they can amortise the >> cost off on tax release over a few years but I've worked in this >> industry long enough to know that budgets don't work that way in the >> real world and items get replaced when they fail. Again, with a large >> sample size, this equates the lifetime of an item with the MTBF. >> >> Now, there are those industries that do upgrade their things before >> they fail and including those things that have actually failed and >> been replaced, these things become available to people like us. Now, >> for us, the MTBF is not the relevant factor here as we will repair the >> thing, over and over again so it has a lifetime far in excess of it's >> MTBF. >> >> So, for the majority of cases in consumer an corporate usage, the >> lifespan of any thing is related to the MTBF. For the smart set with >> enough dosh, the lifespan of any thing is shorter than the MTBF, and >> for the poor buggers like, at least, some of us, the lifespan is >> greater then the MTBF. The point being that for the majority of cases, >> the lifespan of any item is related to it's MTBF for equivalent sample >> size. >> >> Now, I know that MTBF is related to the failure rate but failures >> determine the lifespan of any thing in the majority of cases. >> >> The guys that put people into space have to really understand that >> well. It's no good putting people into space for a 2 week mission in >> equipment that has an expected MTBF of 1 week unless you wish the >> mission to be only half completed given a sufficient sample size. It >> also causes a lot of paper work and hot air to be blown which is >> generally undesireable. >> >>> "What does MTBF have to do with lifetime? Nothing at all!" - >>> http://www.ece.cmu.edu/~ganger/ece546.spring02/readings/mtbf.description >>> >>> "MTBF represents the statistical approximation of how long a number of units >>> should operate before a failure can be expected. It is expressed in hours >>> and does not represent how long the unit will last." - Learn (or review) the >>> difference between MTBF and lifetime, Control Engineering, 9/24/2008; >>> http://www.controleng.com/article/312365-Learn_or_review_the_difference_between_MTBF_and_lifetime.php >> >> But all this means on whether you consider the lifespan of any item to >> be greater than the MTBF, IE. you don't mind the possibility of having >> to fix it a few times, or if you throw it out as soon as it fails, IE >> lifespan is related to MTBF. This, of course, does not cover instances >> for when there is a planned obsolescence of the item, then the >> lifespan is shorter than the MTBF but the swap out cycle has probably >> been planned from the MTBF in the first place. >> >>> I don't grant Wikipedia strong authority, but it is useful, and has this to >>> say: "MTBF is commonly confused with a component's useful life, even though >>> the two concepts are not related in any way. For example a battery may have >>> a useful life of four hours, and an MTBF of 100,000 hours. These figures >>> indicate that in a population of 100,000 batteries, there will be >>> approximately one battery failure every hour during a single battery's >>> four-hour life span." >> >> This is an example of an item with a specific lifespan and therefore >> MTBF is not related to a single items lifespan. In this case it >> determines the probability of failure of any item. Comparing the >> lifespan of items having a specific lifespan with their MTBF is like >> comparing apples with oranges. This is a bad example of what we were >> talking about. I agree that rb lamps do have a limited life but they >> can be replaced as they are just a component that fails in the actual >> whole item and this is just one failure in the terms of MTBF. >> >>> There's much more out there, if you make the effort. >> >> And there is much more in you if you logically think about it instead >> of just accepting things on the web without really thinking what we >> are relating to here. >> >>>> I felt that an example based on humans was not really applicable to >>>> the real world of electronic items but that is my own opinion and I'm >>>> happy if you disagree with me. >>> >>> MTBFs are not exclusive to electronics. Statistics, math and MTBFs are >>> objective matters, so your opinion really doesn't make any difference. >> >> Certainly statistics, math and MTBFs are objective and they have a >> specific bearing on this matter. Along with this, you need to add >> policy, as to how the entity using an item sees about its lifetime >> related to those objectives, IE. they are related. The lifetime of >> anything is a policy decision based on the items failure rate. >> >> Steve >> -- >> Steve Rooke - ZL3TUV & G8KVD >> A man with one clock knows what time it is; >> A man with two clocks is never quite sure. >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > > > __________________________________________________________________ > Make your browsing faster, safer, and easier with the new Internet Explorer® > 8. Optimized for Yahoo! 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