[Weather] termperature offset on Dalsemi station

[Rich Mulvey]

Ernie Oporto wrote:
>
> You can see at the link below that my Dalsemi station seems to send 
> data that is 7-10 degrees off from other stations around me.  Most of 
> the time this is because my station is in the shade due to my condo 
> complex's rules about where I can mount things.  Of course, at night, 
> we are all in the shade and the temperature difference is still 
> there.  This is one of the original dalsemi 1-wire stations. 
>
> http://www.findu.com/cgi-bin/wxnear.cgi?call=CW0861
>
> Surprisingly, the Trh in my humidity sensor (one of the original 
> humidity sensors that were sent out in samples) seems to show the 
> right temperature.  I'm sure I can fudge OWW to read the temp from the 
> humidity sensor for sending to findu.com <http://findu.com>, but I'd 
> like to see if I can get to the root of the problem and correct the 
> temp.  Is there any known issue I should be looking for that might 
> cause this?  Any recommendations?
>


   Is this the temperature sensor mounted in the DalSemi weather head?

   If so - you're *never* going to be able to get a reliable, consistent 
reading from it.  The problem is that the sensor is mounted in a sealed 
enclosure, and thus is not measuring the air temperature - it will be 
offset based on the amount of sunlight, cloudiness, how much heat is 
being absorbed by the weather head, etc.  So you'll generally see the 
temps running high in the daytime, and low at night.  You can't just 
apply an offset to the temps, because there are so many variables that 
will affect the measurement.

   The solution is to mount a completely separate temp sensor in a 
properly ventilated enclosure - google for "weather pagoda" or 
"stevenson screen" for many ideas in that regard.

- Rich