[wxqc] CWOP Information for CW4490 (C4490) in Leander, TX US
Ted Lum
gladstonefamily.net at tedworld.com
Sun Jun 1 14:03:14 CDT 2008
Readme.txt (readme.wri) in WeatherLink root goes back as far as v5.6. I
do see this under 5.7:
"For Vantage Pro console, altimeter setting is reported instead of
barometer in the APRS string."
Maybe they didn't say what they mean. In any event, if you are seeing
temperature driven variation in APRS pressure then something is wrong.
The pressure sensor is indoors and cannot be affected by OAT. No OAT
correction should be happening in software for APRS pressure.
Victor Engel wrote:
> In a discussion dated April 10,11 of this year, it was mentioned that
> Weatherlink 5.7 resolved this problem. I looked but did not find a
> software release notes page anywhere -- at least for notes older than
> the current version.
>
> Victor
>
> On Sun, Jun 1, 2008 at 1:31 PM, Ted Lum <gladstonefamily.net
> <http://gladstonefamily.net>@tedworld.com <http://tedworld.com>> wrote:
>
> I don't know. That thread is more than two years old and I don't
> know if it was ever resolved. I have not been able to find
> anything in the Davis release notes that say they made a change,
> but that does not mean they didn't. Since the pressure sensor is
> located in the console, NOT the station, if you see a variation
> with OAT then almost certainly its coming from a software
> calculation and not a temperature affect on the sensor its self.
> This is only circumstantial, but your observations seem to imply
> they have air density in the calculation. We should find out for
> sure, I don't have first hand knowledge. As a Davis owner/operator
> I want to know.
>
>
> Victor Engel wrote:
>> OK. But I thought the latest version of Weatherlink was sending
>> altimeter -- and VWS as well. Do I have a wrong understanding there?
>>
>> Victor
>>
>> On Sun, Jun 1, 2008 at 12:37 PM, Ted Lum <gladstonefamily.net
>> <http://gladstonefamily.net>@tedworld.com <http://tedworld.com>>
>> wrote:
>>
>> You might want to re-check this thread.
>>
>> http://server.gladstonefamily.net/pipermail/wxqc/2005-November/003212.html
>>
>>
>>
>> Sam Drinkard wrote:
>>> Victor Engel wrote:
>>>
>>>> I'm going to answer your question specifically and then also raise a
>>>> more generic question.
>>>>
>>>> First, it looks like your pressure reading is too low. I believe if
>>>> your mean error exceeds 2 millibars, you will get the message. When I
>>>> first set up my stations (C6155) in 2006, I noticed it tracked another
>>>> stations AS425 very closely in all data points, including pressure.
>>>> Although we tracked closely, the analysis stated our readings were too
>>>> low, so I made an adjustment upwards. My stations has had good QC for
>>>> pressure ever since.
>>>>
>>>> I wonder, though, about something. All three of us use Davis Vantage
>>>> Pro hardware, and all three of us were too low by similar amounts. Do
>>>> these stations generally ship with a slight adjustment error? Could
>>>> there be an adjustment needed at the factory? Certainly, we can't
>>>> determine this from just three data points. I'm curious of others'
>>>> experiences around the country, though, with this hardware.
>>>>
>>>> An alternative, of course, is that our hardware is correct and the
>>>> analysis is wrong. Were that to be the case, though, the airport would
>>>> be too high. I think that's unlikely, since aircraft rely on accurate
>>>> altimeter readings to navigate.
>>>>
>>>> The other thing I've noticed but haven't spent time to check is that
>>>> it appears the error in my readings may be correlated to temperature
>>>> -- the higher the temperature the lower my reading with respect to the
>>>> analysis. I may just be imagining that, and the magnitude of the
>>>> effect certainly isn't large, if present. If this really is true,
>>>> though, I wonder what would cause it.
>>>>
>>>> Victor C6155
>>>>
>>>>
>>> Victor,
>>>
>>> I've noticed the same thing with my station, which is a Davis
>>> WM-II. If I look at the long term analysis of pressure, I can see a
>>> trend in the summer months that *seems* to degrade the sensor, but like
>>> you, I've not investigated this aspect. As most of us know, nearly all
>>> electronic components have some variant or change with changes in the
>>> component's temperature. Perhaps it would be a starting point to
>>> contact Davis and ask if there is any compensation built into the
>>> pressure sensor, or if ambient air temp changes would in fact, cause the
>>> sensor to not read in a non-linear fashion.
>>>
>>> Sam
>>>
>>>
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