I’ve been monitoring the temperature reported by my station, and feel like it may be reading too high.  In the past, my reported temperature was frequently flagged by CWOP as being below the analysis value, typically at night.  I had checked it with another temperature sensor in the same location and the two had agreed,  This led me to the conclusion that I had a micro-climate in my back yard.  I presented my information on the weather quality mailing list and the experts there came to the same conclusion.

Temperatures with my revised FARS tended to read high in the day and as expected by the analysis at night.  Since this was different than what I had experienced in the past using the same sensor I began to suspect the readings I was getting.  CWOP even flagged me once or twice for possible solar heating.  But that was on days that were very overcast with no direct sunlight.  So I wasn’t totally convinced of the solar heating theory.

I had problems in the past with the voltage regulator on the sensor board causing some slight heating.  But I remedied that by moving the temperature sensor off of the board.  I began to suspect the fan I was using.  The new power supply was feeding it 20 VDC and it was spinning pretty fast due to the extra voltage.  I also didn’t feel much air exiting the FARS, although air was certainly being drawn in.  My theory was that the fan met with enough air resistance to heat it up due to insufficient exit air flow, and the air heated up by the fan was backing up over the temperature sensor.  So I drilled some new vents in the FARS to help the air escape.  Maybe this weekend I’ll add a resistor to slow down the fan as well.  But for now I will be keeping an eye on the temperature readings to see if this change had any effect.

I’ve also done some more work making the Web pages dynamic using AJAX.  I came up with a simple way to supply the data as XML by creating a new PHP page that returns the data needed to update the pages as an XML document.  Everything is calculated and formatted using my existing PHP code, converted to XML, and returned to the AJAX code via XMLHTTP calls.  The JavaScript code just has to extract the data it needs from the XML document and fill in the blanks on the Web page.  Simple enough, but a lot of tedious work to code the XML data for all the fields and to write the JavaScript code to fill in all of the fields on the Web pages.  But I’m making progress, and have some fields filled in dynamically on each page.  That will take me the better part of this week to complete, depending on how energetic I feel.  But I have a plan of attack that works.  Just need to do the grunt work now.