[Nut-upsuser] finding a common abstraction for reporting

[Jim Klimov]

Regarding VA/W conversion, keep in mind the power crest factor, and that it
is not always sqrt(2)/2 =~0.7

Some devices actually report theirs and I've seen the likes of 0.9 for
example.

On Mon, Mar 21, 2022, 14:36 Greg Troxel <gdt at lexort.com> wrote:

>
> [I was going to rely privately to reduce list traffic, but the list
> instructed me not to do that :-( ]
>
> Charles Lepple <clepple at gmail.com> writes:
>
> > On Mar 17, 2022, at 7:26 PM, Greg Troxel <gdt at lexort.com> wrote:
> >>
> >> My script is in the process of being extended to also deal with apcupsd
> >> and that seems to have different variables, like timeleft in minutes
> >> instead of runtime in seconds.  It seems obvious to me that I should
> >> bring things into a common schema, because the monitoring system doesn't
> >> care about UPS brand; it wants to know is utility power good enough, how
> >> many seconds left, etc.
> >
> > I am not necessarily recommending that you should use apcupsd-ups
> > (it's monitor-only and won't send the shutdown command[*], for one
> > thing); however, it's worth pointing out that a few of the conversion
> > factors are documented in that driver's source:
> >
> >
> https://github.com/networkupstools/nut/blob/v2.7.4/drivers/apcupsd-ups.h#L66
> >
> > [*] https://networkupstools.org/docs/man/apcupsd-ups.html#_limitations
>
> Thanks, that was useful.  The case that prompted me to ask was a UPS run
> by someone else that I think is using apcupsd and not nut.  I'm not
> responsible for the UPS; I just want to get power status.
>
> >> I wonder how much NUT does that by itself, or if it's more doing format
> >> translation of the individual units.  And I would appreciate comments on
> >> the wisdom/necessity of this approach.
> >
> > What Jim said about this is technically correct, but I would look at it
> another way:
> >
> > NUT defines standard units for variables (as long as the variables are
> > not marked as "opaque"), and the drivers map device-specific readings
> > to those standard units. (USB HID PDC tends to use seconds, as do most
> > SNMP MIBs, if I am not mistaken.)
> >
> > Units are in parentheses in the Description column:
> https://networkupstools.org/docs/user-manual.chunked/apcs02.html
>
> Thanks.  So most of what I was asking about is defined: there are a list
> of NUT variables, defined semantics, and units.
>
> The thing that's messy is power vs realpower (which is a bit funny
> because they are "apparent power" and "power").  It seems old Best units
> report in VA and some APC in W.   Whether to map them both into
> "power-ish" for the mqtt protocol is an interesting question, especially
> since I don't really believe either measurement without confirming it.
>
>
> To the extent my script supports apcupsd, it would make sense to do the
> same normalization.
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