Path: ...!Xl.tags.giganews.com!local-1.nntp.ord.giganews.com!nntp.supernews.com!news.supernews.com.POSTED!not-for-mail NNTP-Posting-Date: Fri, 07 Jun 2024 22:19:50 +0000 From: john larkin Newsgroups: sci.electronics.design Subject: Re: Operating temperature derating Date: Fri, 07 Jun 2024 15:19:50 -0700 Message-ID: References: User-Agent: ForteAgent/8.00.32.1272 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Lines: 85 X-Trace: sv3-d23L/4BSE4vb2s54cauEa4k4lNi080RqLXiXUaqUTsRpEG0qwFyWJIHcy5TLPGU96HwdTZqfMyIEU7N!9GlJdgSKD4kQUoW+n5ejQUknVUkDpCIe1LCO1t/CUsZm31i6KsZ4uiXcqcvWwHZjH2oCWFTByStJ!mGuDvQ== X-Complaints-To: www.supernews.com/docs/abuse.html X-DMCA-Complaints-To: www.supernews.com/docs/dmca.html X-Abuse-and-DMCA-Info: Please be sure to forward a copy of ALL headers X-Abuse-and-DMCA-Info: Otherwise we will be unable to process your complaint properly X-Postfilter: 1.3.40 Bytes: 4607 On Fri, 07 Jun 2024 09:35:38 -0400, legg wrote: >On Thu, 6 Jun 2024 14:01:04 -0700, Don Y >wrote: > >>On 6/6/2024 10:45 AM, legg wrote: >>> On Mon, 3 Jun 2024 07:52:58 -0700, Don Y >>> wrote: >>> >>>> Presumably, one should feel comfortable using a device at the >>>> published operating temperature extremes "forever". >>>> >>>> But, what sort of derating likely went into that specification >>>> in the first place? Sad another way, how much *beyond* those >>>> limits might want suspect you could operate the device? >>> >>> There are two basic limits to operating environment temperatures. >>> >>> Junction temperature limits are usually proscribed below book >>> Tjmax for an agreed mtbf. Sometimes the environmental limits >>> can be extended under reduced performance guidelines, without >>> exceeding agreed Tj limits. >>> >>> For a whole product, there's usually other component limiting factors >>> that occur first - electrolytic and film capacitors, insulation system >>> ratings and surface touch restrictions. >>> >>> Performance is measured with these specified limits in mind. >>> >>> or not. >> >>Yes, but is it (measured)? Or, actively designed with as a target? >> >>Or, do you just use rules of thumb knowing that the typical *operating* >>environment is likely to be X and chose components specified for Y > X >>(but not necessarily Y >> X)? >> >>Note this iPhone claims a max operating of 93F and storage of 113F. >>It is now 108F outside -- does that mean I can't use it outdoors? >>And, when the temperature climbs to 115, I'll have to set it in an >>ice bath? (I'm being facetious, of course). >> >>I suspect there isn't a place in the lower 48 that doesn't >>see ambient temperatures above 93F at least part of the year. >> >>And, Apple isn't a garage shop with few design/test resources at >>its disposal. >> >>So, clearly there is margin in these specifications. Whether it >>is intended -- and to what extent -- is my point. >> >>When designing for industrial/commercial applications, we were always >>extremely careful to *ensure* our products would operate in the temperature >>ranges (and other environmental factors) that we specified. A fisherman >>out on the North Atlantic would be miffed if his kit stopped working >>because it was too cold or too hot (or, too much salt spray). A craftsman >>would be annoyed if the tip of his screwdriver sheared off from "excessive" >>torque. >> >>Similarly, a factory floor can't shut down because it's an unusually >>warm day in the shop... >> >>Consumer kit *seems* to have a far more cavalier attitude towards >>these things. And, one that doesn't really hold up to close inspection >>(e.g., the iPhone). >> >> >The guidelines are derived from empirical data and accelerating >factors are determined. The arrhenius equation comes to mind. > >Predictors determine the design guidelines, but, yes, varying >degrees of physical testing is a standard element in design and >product verification. > >Commercial considerations of free enterprise have always pushed >human behaviour towards banditry, so what can I tell you? > >RL That's entirely wrong. Whether you make spears or helicopters, you need repeat business. Communist thugs are the genocidal bandits. They have a captive market and no competition.