[wxqc] CWOP Information for CW4490 (C4490) in Leander, TX US

[Ted Lum]

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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