Path: Xl.tags.giganews.com!local-2.nntp.ord.giganews.com!nntp.supernews.com!news.supernews.com.POSTED!not-for-mail NNTP-Posting-Date: Mon, 15 Apr 2024 23:26:36 +0000 From: john larkin Newsgroups: sci.electronics.design Subject: Re: Predictive failures Date: Mon, 15 Apr 2024 16:26:35 -0700 Message-ID: References: <0s1r1jhb5vfe7lvopuvfk4ndkbt54ud3d9@4ax.com> User-Agent: ForteAgent/8.00.32.1272 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Lines: 81 X-Trace: sv3-qw79UbpP5kauHZ+cPvuDMijERrZhHWfU3QBA1SmJgMi2alsRJNpReV3dTXBl8ZYwRr5MMVST5RKImZi!pU6fiNZAsBosDCaFbeGOrs6tNHyudA+tRaNxo3zda5oDAkNXYd6UZfh0tCiEp9tPfGyvGEDgQJy4!Fiv+Xg== 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: 4228 On Mon, 15 Apr 2024 18:03:23 -0400, Joe Gwinn wrote: >On Mon, 15 Apr 2024 13:05:40 -0700, john larkin wrote: > >>On Mon, 15 Apr 2024 15:41:57 -0400, Joe Gwinn >>wrote: >> >>>On Mon, 15 Apr 2024 10:13:02 -0700, Don Y >>> wrote: >>> >>>>Is there a general rule of thumb for signalling the likelihood of >>>>an "imminent" (for some value of "imminent") hardware failure? >>>> >>>>I suspect most would involve *relative* changes that would be >>>>suggestive of changing conditions in the components (and not >>>>directly related to environmental influences). >>>> >>>>So, perhaps, a good strategy is to just "watch" everything and >>>>notice the sorts of changes you "typically" encounter in the hope >>>>that something of greater magnitude would be a harbinger... >>> >>>There is a standard approach that may work: Measure the level and >>>trend of very low frequency (around a tenth of a Hertz) flicker noise. >>>When connections (perhaps within a package) start to fail, the flicker >>>level rises. The actual frequency monitored isn't all that critical. >>> >>>Joe Gwinn >> >>Do connections "start to fail" ? > >Yes, they do, in things like vias. I went through a big drama where a >critical bit of radar logic circuitry would slowly go nuts. > >It turned out that the copper plating on the walls of the vias was >suffering from low-cycle fatigue during temperature cycling and slowly >breaking, one little crack at a time, until it went open. If you >measured the resistance to parts per million (6.5 digit DMM), sampling >at 1 Hz, you could see the 1/f noise at 0.1 Hz rising. It's useful to >also measure a copper line, and divide the via-chain resistance by the >no-via resistance, to correct for temperature changes. But nobody is going to monitor every via on a PCB, even if it were possible. One could instrument a PCB fab test board, I guess. But DC tests would be fine. We have one board with over 4000 vias, but they are mostly in parallel. > >The solution was to redesign the vias, mainly to increase the critical >volume of copper. And modern SMD designs have less and less copper >volume. > >I bet precision resistors can also be measured this way. > > >>I don't think I've ever owned a piece of electronic equipment that >>warned me of an impending failure. > >Onset of smoke emission is a common sign. > > >>Cars do, for some failure modes, like low oil level. > >The industrial method for big stuff is accelerometers attached near >the bearings, and listen for excessive rotation-correlated (not >necessarily harmonic) noise. Big ships that I've worked on have a long propeller shaft in the shaft alley, a long tunnel where nobody often goes. They have magnetic shaft runout sensors and shaft bearing temperature monitors. They measure shaft torque and SHP too, from the shaft twist. I liked hiding out in the shaft alley. It was private and cool, that giant shaft slowly rotating.