insane fan speed readings from lm_sensors

[Lonni J Friedman]

This isn't the CPU fan, its the chassis case fan. I'm already
capturing CPU activity, and its basically idle the entire time.  Keep
in mind, this starts happens in the early morning hours (4AM), when
the system isn't being actively used.  The exhaust fan on this system
is whisper quiet, even when running at nearly 1400RPM.

On Thu, Sep 12, 2019 at 9:21 AM Leon Goldstein via Linux-users
<linux-users at linux-sxs.org> wrote:
>
> Hi Lonni:
>
> All I can suggest is run System Monitor to see the CPU % activity when
> the fan speed rises.
>
> Can you hear the difference in fan speed?  I have a laptop that gets
> very conspicuously noisier when CPU capacity is peaking, as e.g. during
> an update kernel installation.  (I'm using Mint 18.3 Mate.)
>
> On 9/11/19 8:39 PM, Lonni J Friedman via Linux-users wrote:
> > Since its so quiet here (when is it not?), I'll drop a puzzle on you
> > fine folks to noodle on.
> >
> > I recently started monitoring my system exhaust fan speed (RPMs),
> > mostly out of curiosity.  What I discovered has exposed a mystery that
> > I'm struggling to explain.  Every day between 04:00 & 10:00, the fan
> > speed readings start to rapidly oscillate between sane numbers (under
> > 3000 RPM) and insane numbers (over 10,000 RPM).  For the rest of the
> > day, the readings are perfectly normal & reasonable.  Its always
> > during that same time window.  There's no way this exhaust fan is even
> > capable of spinning at the rate that is being reported.  This has to
> > be an erroneous reading.
> >
> > Here's a graph of what I'm talking about:
> > https://imgur.com/erXGz4J
> >
> > There's nothing in dmesg or /var/log/messages to explain this
> > behavior.  I've looked at every cronjob running on the system for some
> > bizarre correlation, and can't find anything.
> >
> > I'd like to think that if this was a flaky sensor, it wouldn't be so
> > reliable in when it happens.  So something else must explain the
> > weirdness.  Anyone have ideas/suggestions?
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> >
> --
> Leon A. Goldstein
> System L3
> Linux Mint 17.3
>
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