[wxqc] Barometer Errors

[spamfree]

Hi,

If the times his barometer drifts off has a correlation with wide temperature swings, and he is at altitude (say above 500ft), then the VP pressure issue could explain it. The VP calculates a sea level reduced pressure from the sensor pressure. Temperature and humidity is part of that calculation which is done in the console. This is what WeatherLink sends to APRS/CWOP. But CWOP wants altimeter, which is the sensor pressure adjusted only for elevation. There is a difference between these two pressure representations, and the result is that many VP stations have CWOP pressures values that drift in and out of the expected norm. There are a couple of weather programs that calculate the correct altimeter value from the VP pressure for submission to APRS/CWOP, but WeatherLink currently isn't one of them. There has been talk that Davis may do this in a future version.

Best regards,
Steve
  
======= At 2006-04-16, 19:43:33 you wrote: =======

>George,
>
>The URL 
>http://weather.gladstonefamily.net/cgi-bin/wxsite.pl?site=c1523;tile=10;baro_date=2006-04-07;days=91;fit=1;asosonly=1
>
>adds a couple of undocumented features. One of them only excludes the 
>CWOP stations from the comparisons stations at the bottom. The other 
>performs a lineat best fit analysis to see what the best fit function is 
>between your data and the analysis data. This can show up problems where 
>the error is not just a simple offset in the data, but also a scaling 
>factor as well.
>
>I think that this latter case is the issue in your case. Isn't there an 
>issue with weatherlink performing the wrong pressure reduction to get to 
>sea level pressure? [Someone more knowledgeable than me please chime in].
>
>Philip
>
>George Prevelige wrote:
>> I try not to take it personally when I receive a whole page of errors in my
>> daily Weather Quality Report. But this barometer issue is starting to bother
>> me.
>> 
>> 90% of the time, my report is error free. But, periodically, normally before
>> a front comes through, my barometer readings deviate above the margin of
>> error. I understand that a front can cause local anomalies, but what about
>> the times between fronts when I get these errors (like today - I had 51/96
>> barometer errors, 0/96 for all other readings)? 
>> 
>> Before I start tweaking my barometer, are there any other explanations for
>> my readings to be 2 to 3 MB (usually lower than sample) off the reference
>> data, only to be back in sync a day or two later?
>> 
>> Others have voiced concern about incorrect or absent comparison data near
>> their site. There are no sites within 10 miles of my station that have
>> consistent or even useable data.
>> 
>> George
>> CW1523
>> Vantage Pro
>> Weatherlink
>> 
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>> 
>
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