Damjan Hajsek <hajsek.dam...@gmail.com> writes:
> So we can't do nothing to make UV index show right value, because with
> calibrating I can not get real data?
This can probably be solved, but "calibration" is very likely not the
approach.
Let me try to summarize what we know.
Your station seems to show reasonable UV values on the console.
Your station reports some encoded values that a weewx driver reads.
Currently, the bits for UV are extracted in some straightforward way
and assumed to be the UV index. This is leading to values that are
not even close to correct.
"Calibration", in weewx and generally, is a mechanism that makes small
changes to values to make them closer to the correct values.
Calibration is by definition a very minor change, like subtracting 0.7
hPa of pressure, or adding 0.5 C of temperature. Or perhaps 2 C, but
not 20 C. Calibration as a concept depends on having a close-to-right
value with a simple relationship, so that "V = R + c" holds fairly
closely for readings R, and calibration value c, and true value V.
So far, we have no reason to believe that attempting something like
calibration above with the values being read by weewx for your station
will give reasonably correct answers.
And then making assumptions:
Probably, the way the weather station sends UV index to the computer
is not just an integer in a field. We don't understand how that is
done yet.
So the path forward is, more or less:
1) Ensure (assume, and retry if not, because absent the manufacturer
documenting it, and documenting it correctly, we have to assume) that
the UV field really is the UV field.
2) Ensure that the path from bits in the UV field to the number that is
recorded is straightforward and reversible.
3) Keep records of pairs of displayed UV value and
reported/recorded-in-weewx UV values. A simple chart with two columns
would be fine (but I might add date/time in case it is useful).
4) Put this chart in a spreadsheet or csv format
5) Make a scatter plot of console vs weewx values, where each point is an
observation pair, with console on x axis and weewx-read value on y
axis.
6) Figure out if there is a clear relationship and what it is. Try to
come up with a formula, especially one that we can explain after we
create it how it works.
Change the driver to use the formula.
I am guessing these steps seem too complicated, but I expect others can
help.
So I would suggest that you do steps 3 and 4, for at least several days
and preferably a week, at night, and at various points during the day,
both sunny and cloudy days, and post a link to the spreadsheet, or
preferably mail csv format to the list.
Without steps 3 and 4, then I don't see a way to make progress.
Greg
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