[Nut-upsdev] belkin-hid:

Peter Selinger selinger at mathstat.dal.ca
Thu Aug 2 02:38:35 UTC 2007

Arjen de Korte wrote:
> Let me explain. Usually, if you perform a deep discharge test, you'd drain
> the batteries to the level where the low battery indicator hits. If we
> would indeed indicate 'OB' when running a battery test, it means that at
> that time, we would show 'OB LB'. Oops. If clients are looking over our
> shoulders, they might determine that it is time to shutdown at that time,
> if we're not quick enough to switch back to mains. I actually have a UPS
> that takes a couple of seconds to do that and indeed, the system rebooted
> at the end of a battery test until I masked this state out (which is not
> pretty either). Also, any 'upssched' that may be running (for people that
> shed part of the load if the systems are running on battery for a fixed
> time interval to maximize runtime or in case of shutdown sequences longer
> than the runtime available when the battery is low) might initiate a
> shutdown sequence if we would indicate 'OB' during battery tests.
> For the above reasons, during battery tests you should never show the 'OB'
> indication (although the load is powered by the inverter), but rather the
> 'OL' (to indicate the mains is present) status. The documentation we
> presently have is not very clear in this respect. I propose to change this
> and make clear that clients expect this to be an indication of the line
> status. So for systems that have an ACPresent indication should preferably
> be
>     OL = ACPresent
>     OB = !ACPresent

I agree that this makes sense, and that the documentation in
docs/new-drivers.txt should be updated to make this more clear. I am
not sure I want to see OB when the load is off, though. Many low-end
UPS's don't have separably switchable outlets. 

> Giving the fact that nowadays many UPSes have multiple switched outputs,
> the OFF status is probably too course to be of much value. I think that
> applications that need this, better look at the 'outlet.n.status' values.
> Short of the fact that this probably doesn't belong in the 'ups.status'
> anyway, since it doesn't require immediate action from clients (if they
> are powered by the UPS in question, they probably never see it).

The OFF flag could be of interest when monitoring a UPS that is not
powering the machine monitoring it. It may help a remote user trying
to see the power status of another machine. Not all drivers/devices
support outlet.n.status. 

-- Peter

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