Re: Predictive failures

On Mon, 15 Apr 2024 18:03:23 -0400, Joe Gwinn <joegwinn@comcast.net>
wrote:

On Mon, 15 Apr 2024 13:05:40 -0700, john larkin <jl@650pot.com> wrote:
>

On Mon, 15 Apr 2024 15:41:57 -0400, Joe Gwinn <joegwinn@comcast.net>
wrote:
>

On Mon, 15 Apr 2024 10:13:02 -0700, Don Y
<blockedofcourse@foo.invalid> 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.