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Weather Station Hardware => Other Weather Station Hardware => Topic started by: Brian N8VHF on May 20, 2011, 10:26:57 PM
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I've been building my DIY weather station and as expected I ran into solar heating issues.
I mulled over several of the designs for radiation shields and not being one to use a proven design I finally decided to go off on my own and design something.
The design uses a few plumbing fittings and a PC case fan. Everything is press fit and no glue is used on the plumbing bits.
Air enters at the bottom and is pulled to the top by the fan and is then exhausted in the space between the pipe and pvc cap.
Sensor is placed about 2" up from the bottom.
So far it appears to by working very well. I'm within +/- 1 degree or so of the NJWxNet station run by Rutgers and other nearby stations.
My daughter called my attention to the fact that the temporary long bolts in the pic make it look like a space probe. I will be replacing those with 1/4"-20 stainless steel bolts that are about 3/4" long.
I still need to do a bit of cleanup and such to get the ink and dirt off of the pvc parts.
(http://n8vhf.com/wp-content/uploads/2011/05/wpid-2011-05-15-19.28.37.jpg) (http://n8vhf.com/wp-content/uploads/2011/05/2011-05-21-08.26.06-300x225.jpg)
Design docs (PDF) and more pics at my website. http://n8vhf.com/2011/05/21/fan-aspirated-radiation-shield/
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Good design! I also have been looking into this and realized, even though they're white, the PVC components will get warm from sunlight and the sensor can display this. The fact that you have your sensor down low in the tube (you mentioned about 2 inches up) is good as the sensor will "see" fresh outside air before it gets warmed from the PVC. I noticed this from seeing my inverted bowl type FARS reading slightly higher when the sun hit it because the fan was drawing air in through the warmed bowl gaps and across the sensor. I've since moved the fan to the bottom so it blows in fresh ambient temperature air, pass the sensor then out through the warmed bowls. This made a difference of several degrees during direct sun periods of the day.
I like your design.
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Thanks for the comments. Today was the first day we have had that had bright, direct sun on the FARS since I built it. it has been rainy and overcast for the last week. It performed perfectly. I was within +/- 1.5 degrees of the other local WX stations.
You mentioned having the fan at the bottom, blowing air over the sensor. I considered that but I was concerned that any heat generated by the fan could influence the metered temperature at my sensor. I don't have any evidence that it would cause problems, just a concern that it might.
I'm also considering adding a fan monitor to alert me if the fan fails. Since I used a PC case fan, it already has a fan speed monitor built in. I just need to hook it up to my CPU and program the monitor function.
-Brian
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I remember someone posting on here a year or two ago about a PVC FARS they built. It was several feet long, mounted vertically, painted all bright white except for a small portion at the upper end was painted flat black. The sensor was mounted at the bottom. No fan and used heat convection from the black paint absorbing the suns heat. The heated air current drew in the fresh ambient temp. air at the bottom. Pretty neat concept and never did hear any more about it or how it worked out.
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I might have to build a second one with the black paint at the top and put a sensor in it and compare the two.
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I might have to build a second one with the black paint at the top and put a sensor in it and compare the two.
Yeah, what you've done already has got me thinking/planning on some more experimenting as well. I'm happy with where I am now with the setup but it's interesting to try different things.
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Here is my 'version' of Brian N8VHF's PVC FARS, 1st I'd like to thank Brian for the idea, I've been wanting to do something along this line for a while and he gave me the push to the direction. I had to use 4" PVC because all I have are Davis fans and with a belt-sander and some s/s sheet metal screws, this is the finished product. I put a Davis Temp. sensor (6475) that I had in it and am waiting for the Davis ISS single solar panel to power the fan to show up. The Temp. sensor will get hooked to a Davis 6332 Anenometer Transmitter kit that is supposed to come with the panel. I'll post a picture of it installed once I figure out where it's going. Again THANKS to Brian for the great idea. Jack
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Is that a thermocouple at the end of those wires? Just curious if you were setup for testing with this.
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DanS....one is the plug for the Temp. sensor, the other is the leads for the fan. The wire for the fan is an extension cable piece that I took from an old WW III set-up I ran before the VP 2. The fan has been tested using a CR 123 battery and it 'pulls' REAL good. Jack
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I would put the fan at the bottom and the sensor below that. That way it pulls air past the sensor instead of blowing on it, no fan motor heat to deal with then.
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The fan pulls UP past the sensor. The sensor is about 2 1/2" up from the bottom with the fan at the junction of the 2 fittings under the cap. Jack
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Gotcha!
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How are you powering the fan? I just got my 40mm fans in and tested with my solar panel. Thought about putting in a battery for non-sunny days. Hopefully will have my FARS modified this weekend.
Todd
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I am using the solar panel that comes on the wireless Davis ISS, I ordered one off the 'net and it works pretty good. Similar to how you power the Davis DFARS kit. Forgot to mention that I am using the Davis fan.....Jack
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I finished setting it up on Saturday and it is working, even with over-cast skies for 2 days. The real test is today...real sunny and supposed to be low to mid 80's. Again, THANKS Brian for the great idea. Jack
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I just built a couple of these myself:
http://sandaysoft.com/forum/viewtopic.php?f=16&t=10609
I made a few design changes to allow my Fine Offset weather station sensor and my Sky Scan Atomic Clock temperature sensor to work:
- I made sure to get all of the PVC parts in bright white to reflect the sunshine so nothing would need to be painted on the outside. I did decide to paint the inside of the 4" cap and the inside of the 3" pipe flat/matte black which was a pain. The idea for doing this came from the Met Office (Fact Sheet 17 Page 7 (http://www.metoffice.gov.uk/media/pdf/k/5/Fact_sheet_No._17.pdf)) as they seem to think painting the inside of a Stevenson Screen flat/matte black may offer more accurate temperatures. It later turned out this was not necessary and probably made my temperatures higher. Unpainted and fully assembled, it is very dark on the inside even with the Sun shining on it.
- I cut the 3" pipe into 13" sections.
- Instead of two 3" drain inserts, I used one 4" drain insert on the bottom which slips over the 3" pipe nicely.
- I made a 9" stud and attached it to the bottom of the 4" drain insert then zip-tied my temperature sensor to that so it is in the middle of the pipe.
- I used 80 mm CPU fans after shaving down the corners with an electric work bench grinder and let the power cables come down to the drain insert and hooked up a 9 volt battery. It later turned out 9 volt batteries do not last that long so I ordered some solar-powered fans (http://www.ebay.com/sch/i.html?_odkw=Solar+Cell+Fan+Sun+Power+Energy&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR0.TRC0.XSolar+Cell+Fan+Sun+Power+Energy+Clip-On&_nkw=Solar+Cell+Fan+Sun+Power+Energy+Clip-On&_sacat=0) from an eBay seller in China. One of these fans should fit into the top of the 3" coupler.