"'Tomasz Lewicki' via weewx-user" <[email protected]> writes:
> Thank you for your reply and for your willingness to help. I've been a
> satisfied QGIS user for several years now; I manage a few stations, so I
> have a pretty good idea of how things work. I deliberately didn't provide
> details about the station model, console, etc., because I'd like the
> solution to be hardware agnostic. I'm familiar with the Wiki article, but
> unfortunately, it doesn't explain what I'm asking about. Or maybe I just
> can't read between the lines :)
I don't think it's reasonable to leave out relevant information on
purpose, and if you are asking a theoretical question that should be
separate.
> As for the barometer readings, I have two (WH25A and WN32P), and each shows
> a different value. Their readings differ by exactly 10 hPa. I have a Python
Something seems very wrong. I have never seen a pressure sensor that
far off. I suspect confusion between reduced and station pressures.
But maybe you just have bad hardware.
> script that retrieves the current METAR for a nearby airport, and based on
> the specified altitude above sea level and the entered pressure, it
> calculates the "correct" pressure and reports the offset of my barometer
> from the airport's.
It would be nice to publish that, so that you contribute to the commons.
> It saves the results to a file and calculates the mean
> and median from several measurements. That's why I wrote that I'm
> interested in a pressure correction of +6 hPa, because that's how much the
> WH25A sensor underreports (I borrowed a WN32P for verification only).
You said 10 earlier which is not 6. So please dig into your hardware
and debug logs and examine and then describe
- what the documentation (+ weewx wiki, internet) says it measures and reports
- what kind of calibration can be done on the hardware
- what values you have set for those calibrations
- how you determined your elevation and what your estimate of alitude
uncertainty is
- specific values reported by your hardware, your elevation, and
corresponding values/elevation from nearby official stations
> I'd simply like to understand how the correction calculation workflow
> works, as specified in the [StdCalibrate] / [[Corrections]] section of
> weewx.conf. At what point is this correction applied, and to which
> "measurement" method—only software? Only hardware? Both?
I suggest reading the source code. Also, in weewx.conf, services are
listed in order, and the standard approach is to do StdCalibrate before
StxWXCalculate. So *if* the console reports station pressure, and *if*
barometer is software instead of harder, then just adjusting station
pressure should be sufficient, because StdWXCalculate should see the
adjusted station pressure. But if the console is *also* reporting
barometric pressure, then StdWXCalculate will not be run for barometric
pressure.
You really need to understand what is being reported vs calculated, and
how weewx is choosing to calculate or use hardware for each item.
> My reasoning is as follows:
>
> 1. I set the pressure correction to pressure = pressure + 6.0 in
> weewx.conf; I don't change anything in the station console—no offsets, no
> entering "correct" ABS or REL pressure
>
> 2. After setting the pressure correction, should I set pressure =
> prefer_hardware or software?
You should understand what is going on with what's reported and what's
calculated.
> 3. What should I do with barometer then, to avoid applying a double
> correction or causing a calculation error?
You should understand what is going on with what's reported and what's
calculated.
If you don't want to try to understand that, then it's going to be much
<harder for you to get a good outcome.
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