Topic: FARS Comparison

[Aardvark]

I did a comparison between the FARS shield and the Passive Shield and there really isn't much difference between the temperatures.   I had replaced my ISS on the VP2 because of a corroded supercap and last summer replaced the supercap, decided I needed to do something with it and added another temp/humid sensor and a standard shield to compare the two.   I figured about a 1.3 F  difference in temperature between the two.

However, I am collecting data and hope to have a better comparison come next summer.   

[piconut]

I set up a temp/humid station on the same pole as a FARS ISS and found almost no difference in readings except for rate of change which was measured slightly slower (slower to change) on the temp/humid station.  I ran it that way for about 4 months from mid summer to mid fall.  I still like my FARS though.

[miraculon]

Maybe you have already seen it, but there was a study that Davis did back in '99 comparing several passive/FARS shields. (AN-24)

http://www.davisnet.com/product_documents/weather/app_notes/AN_24-temp-radiation-shield-comparison.pdf

Greg

[Old Tele man]

The PROBLEM between normal & aspirated tempature shields comes during HOT summers, when solar loading is highest. That's when I clearly found a 3-5ºF difference between the two different shields during A-B-A tests. At night both traces almost always overlapped one another, but come sunrise the normal (non-aspirated) shielded sensor would rise faster & higher than the aspirated sensor. Swap the sensors and get an almost perfect mirror-image reversal of their plots.

[Aardvark]

The PROBLEM between normal & aspirated tempature shields comes during HOT summers, when solar loading is highest. That's when I clearly found a 3-5ºF difference between the two different shields during A-B-A tests. At night both traces almost always overlapped one another, but come sunrise the normal (non-aspirated) shielded sensor would rise faster & higher than the aspirated sensor. Swap the sensors and get an almost perfect mirror-image reversal of their plots.

I went back as far as I could with the sensor and found this data, still not that significant.

[DanS]

I'm not sure this would be relevant in this FARS thread but I'll pop it in here anyway. I ran a test of an unaspirated shield on a clear sunny day. The sun was shining directly on the shield and surrounding ground. I took a temperature probe and placed it near the top then the bottom of the shield. I let the probe sit in each place (not touching any part of the shield) for around 30 minutes before recording the temperature. This showed me the importance of sensor placement inside without a using some kind of aspiration.