Re: [weewx-user] WeeWx Calculations
Thank you for your precious answers and for the historical insight, always
useful to get the reason behind a choice
Il giorno domenica 17 luglio 2022 alle 19:53:31 UTC+2 tke...@gmail.com ha
scritto:
> Greg has it exactly right.
>
> Until the introduction of LOOP2 packets about 8 or 9 years ago, the
> Vantage stations behaved this way. They only published pressure reduced to
> sea-level (SLP), so station pressure (and altimeter pressure) had to be
> back calculated.
>
> -tk
>
> On Sun, Jul 17, 2022 at 7:56 AM Greg Troxel wrote:
>
>>
>> Andrea Di Saverio writes:
>>
>> > If, as stated
>> > here
>> https://github.com/weewx/weewx/wiki/Barometer,-pressure,-and-altimeter,
>> > the `pressure` is the raw value measured by the station, why is it in
>> the
>> > `Calculations` section in the configuration file
>> > (https://www.weewx.com/docs/usersguide.htm#[[Calculations]])?
>> > I expected it cannot be calculated, rather it is the starting point to
>> > calculate the `altimeter` and `barometer` values.
>>
>> There is a long chain of processing.
>>
>> Somewhere in the weather station (you didn't say which one) there is a
>> pressure sensor, and almost always these are measuring station pressure
>> (with some offest that may require calibration).
>>
>> Then, various weather stations process that pressure to form barometric
>> pressure or altimeter pressure, because that's what ~everybody wants to
>> see.
>>
>> The weather station communicates some kind of pressure information to
>> weewx, and that depends on at least the station type, and perhaps on how
>> it is connected.
>>
>> weewx then does some combination of:
>> - use values that are reported ("hardware" is the code word for this)
>> - calculate values, in the case that
>> * they are not reported
>> * config, or defaults, say that's better than using the reported value
>>
>> The following behavior would not be surprising at all:
>>
>> station has station_pressure sensor
>>
>> station applies some reduction to barometric pressure
>>
>> station UI displays only barometric pressure
>>
>> station reports only barometric pressure to weewx
>>
>> weewx calculates station pressure by essentially inverting the
>> station's reduction to barometric, using configured elevation and
>> temperature
>>
>> weewx calculates altimeter pressure from station pressure and
>> configured elevation
>>
>>
>> See:
>> https://www.weewx.com/docs/usersguide.htm#pressure_calibration
>>
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>> .
>>
>
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Re: [weewx-user] WeeWx Calculations
Greg has it exactly right.
Until the introduction of LOOP2 packets about 8 or 9 years ago, the Vantage
stations behaved this way. They only published pressure reduced to
sea-level (SLP), so station pressure (and altimeter pressure) had to be
back calculated.
-tk
On Sun, Jul 17, 2022 at 7:56 AM Greg Troxel wrote:
>
> Andrea Di Saverio writes:
>
> > If, as stated
> > here
> https://github.com/weewx/weewx/wiki/Barometer,-pressure,-and-altimeter,
> > the `pressure` is the raw value measured by the station, why is it in
> the
> > `Calculations` section in the configuration file
> > (https://www.weewx.com/docs/usersguide.htm#[[Calculations]])?
> > I expected it cannot be calculated, rather it is the starting point to
> > calculate the `altimeter` and `barometer` values.
>
> There is a long chain of processing.
>
> Somewhere in the weather station (you didn't say which one) there is a
> pressure sensor, and almost always these are measuring station pressure
> (with some offest that may require calibration).
>
> Then, various weather stations process that pressure to form barometric
> pressure or altimeter pressure, because that's what ~everybody wants to
> see.
>
> The weather station communicates some kind of pressure information to
> weewx, and that depends on at least the station type, and perhaps on how
> it is connected.
>
> weewx then does some combination of:
> - use values that are reported ("hardware" is the code word for this)
> - calculate values, in the case that
> * they are not reported
> * config, or defaults, say that's better than using the reported value
>
> The following behavior would not be surprising at all:
>
> station has station_pressure sensor
>
> station applies some reduction to barometric pressure
>
> station UI displays only barometric pressure
>
> station reports only barometric pressure to weewx
>
> weewx calculates station pressure by essentially inverting the
> station's reduction to barometric, using configured elevation and
> temperature
>
> weewx calculates altimeter pressure from station pressure and
> configured elevation
>
>
> See:
> https://www.weewx.com/docs/usersguide.htm#pressure_calibration
>
> --
> You received this message because you are subscribed to the Google Groups
> "weewx-user" group.
> To unsubscribe from this group and stop receiving emails from it, send an
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> To view this discussion on the web visit
> https://groups.google.com/d/msgid/weewx-user/rmiilnvvldj.fsf%40s1.lexort.com
> .
>
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Re: [weewx-user] WeeWx Calculations
Andrea Di Saverio writes:
> If, as stated
> here https://github.com/weewx/weewx/wiki/Barometer,-pressure,-and-altimeter,
> the `pressure` is the raw value measured by the station, why is it in the
> `Calculations` section in the configuration file
> (https://www.weewx.com/docs/usersguide.htm#[[Calculations]])?
> I expected it cannot be calculated, rather it is the starting point to
> calculate the `altimeter` and `barometer` values.
There is a long chain of processing.
Somewhere in the weather station (you didn't say which one) there is a
pressure sensor, and almost always these are measuring station pressure
(with some offest that may require calibration).
Then, various weather stations process that pressure to form barometric
pressure or altimeter pressure, because that's what ~everybody wants to
see.
The weather station communicates some kind of pressure information to
weewx, and that depends on at least the station type, and perhaps on how
it is connected.
weewx then does some combination of:
- use values that are reported ("hardware" is the code word for this)
- calculate values, in the case that
* they are not reported
* config, or defaults, say that's better than using the reported value
The following behavior would not be surprising at all:
station has station_pressure sensor
station applies some reduction to barometric pressure
station UI displays only barometric pressure
station reports only barometric pressure to weewx
weewx calculates station pressure by essentially inverting the
station's reduction to barometric, using configured elevation and
temperature
weewx calculates altimeter pressure from station pressure and
configured elevation
See:
https://www.weewx.com/docs/usersguide.htm#pressure_calibration
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