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Weather Station Hardware => Other Weather Station Hardware => Topic started by: METARMan on June 12, 2009, 07:30:15 PM
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Does anyone have any experience with the SRS100 (passive) radiation shield from Ambient Weather?
http://www.ambientweather.com/amwesrpatera.html
Does the shield have a warm bias on high solar radiation days?
I'm wondering whether I should build a cotton region shelter/Stevenson screen instead.
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If your sensor(s) placement will be exposed to any direct sunlight I'd recommend either going aspirated with that shield or the aspirated stevenson as you mentioned. If your sensor(s) are shaded all the time then the mentioned SRS100 should be fine. A fan is needed to keep the ambient air flowing to cool the heated enclosure from the direct sun's effect. Shaded locations don't have this condition and the shielded enclosure is used to protect the sensors from indirect solar radiation. Hope this helps.
Dan
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I obtained the Radiation Shield from Ambient for my WMR968 sensor. In direct sunlight, where it was exposed to the Sun for more than 2 hrs, I still experienced
an elevated temperature reading. I would agree with Dan that if your sensor will be in direct sunlight you should go with the aspirated shield or the aspirated Stenvenson. Good luck,
Mark
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I have the SRS100LX which is just an extended version of the SRS100. It adds more baffle plates and longer screws.
I use it to experiment with temperature sensors. I measured daytime air flow vs nighttime air flow inside the shield. I used a hot wire anemometer to compare the day/night air flow. The day time air flow was measurably greater than night air flow inside the radiation shield. It has .6" separation between plates for air intake at the narrowest point.
The solar shield was mounted in direct sunlight.
I have used it to compare 1-wire digital temperature sensors with analog RTD temperature sensors. I never intended to make the shield fan aspirated.
In changing a sensors on a warm sunny day, the sensor was exposed to direct sun and partial shade for a few minutes. During that time, the measured temperature went from about 70º to 75º. As soon as the sensor was replaced inside the shield, the measured temperature went back to 70º.
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I also have one, and I do experience some "sun heating" in the morning. Therefore I put my temp/shield setup on the shady side of my vinyl fencing and it helped it some. But during the summer months the angle of the sun still gets it in the morning. I was looking at one time of constructing a modification to make it a solar FARS setup. I still need to do that. But I believe that would solve the problem you are concerned about.
I have some pics of the setup on my website, just scroll down on the left to the "Weather and Station Photos".
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It is interesting that so much emphasis has been placed on accurate instrumentation, yet the variations in radiation shields and thermometer shelters probably have more to do with representative temperature data than the accuracy of the instruments themselves. Although there are standards for thermometer instrumentation, there is no national or global standard for radiation shields/thermometer shelters (yet).
Even the standard cotton region shelters seem to give higher temperatures on sunny days (especially with snow cover) and lower temperatures at night compared to MMTS shelters.
Theoretically, even if instrumentation is extremely accurate and kept in the same place for decades, a change in shelter design or even a repaint can have an effect on temperature readings.
http://ams.confex.com/ams/pdfpapers/91613.pdf
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That is a very interesting paper. I think the question of a warm bias on sunny days for that radiation shield (or any shield) depends on the amount of wind you can expect in your location.
I've been comparing temperature readings from several nearby non-FARS VP2 ISSes to my 24 hr FARS ISS over the past six months to a year. I found during sunny mornings the non FARS units definitely heat up faster than mine. The morning heat up may extend into noon-early afternoon during the winter month's low sun angles. Once the sun is more directly overhead, the temperature differences tend to equalize so either the ISS radiation sheltering effect is better from the top than on the sides or the winds pick up here more later in the day. Probably the latter is the most important factor. On sunny, windy afternoons the non-FARS ISS that is mounted the closest to mine in height, will generally track right with my temperatures.
I find that there is much more of a difference in nighttime cooling temps than in daytime heating bias. On clear, windless nights (most nights here are like this), my temperatures are much cooler than the other two stations (3-10 degrees F). Partly this is due to their mounting heights AGL, one is mounted ~17-20 ft higher and the other maybe 4-6 ft higher than mine. The higher the ISS the warmer it is at night (and cooler during the day). However, I also think the nighttime temps drop so fast here due to radiation losses, that the fanless shields simply can't equilibate to the air temps as fast as mine.
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Does anybody have a Davis ISS (or other brand) mounted inside a cotton region shelter?
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It is interesting that so much emphasis has been placed on accurate instrumentation, yet the variations in radiation shields and thermometer shelters probably have more to do with representative temperature data than the accuracy of the instruments themselves.
I'm surprised that someone doesn't make a FARS model of the SRS100. Seems like it would be a great seller.
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I'll build you one. Want it 24 hours fan aspirated, solar powered?
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I'll build you one. Want it 24 hours fan aspirated, solar powered?
One of these days I'll probably get around to getting a high-classed setup, but I have higher priorities right now. I was just thinking about the free market economy, filling a need and making a buck, etc. I guess that's why I'm not a businessman.
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I'll build you one. Want it 24 hours fan aspirated, solar powered?
One of these days I'll probably get around to getting a high-classed setup, but I have higher priorities right now. I was just thinking about the free market economy, filling a need and making a buck, etc. I guess that's why I'm not a businessman.
I have the set-up. Problem is I don't have the motivation.
You could buy this kit of solar panel wire and fan and modify your SRS100.
http://www.goldmine-elec-products.com/prodinfo.asp?number=G17171 (http://www.goldmine-elec-products.com/prodinfo.asp?number=G17171)
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I have an SRS100 with no fan and it seems to keep temps just fine. No different than when I had a FARS in place....
Jim
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Jim,
When/why did you remove your FARS?
I was just going to install mine today/tomorrow. I still have to run some wire out to it, dont want to run my lights 24's a day light in winter for my rain gauge heater.
Andrew
I have an SRS100 with no fan and it seems to keep temps just fine. No different than when I had a FARS in place....
Jim
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Well it's like this:
My homemade FARS unit was had chipping paint and the fan was getting really gunk up. I saw the SRS100 on the ambient site and thought I'd give it a whirl..
The sensors fit right in there and it is easy to assemble. The unit is already molded in white so no pealing paint there. As I stated before, I am seeing very little/no difference in my readings in direct sunlight. I do have 12V DC running to my unit which I could modify to use a fan. I just haven't done it yet and right now, the readings are telling me i don't need to..
jim
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This is the most comprehensive study I've come across regarding different radiation shields:
http://www.knmi.nl/klimatologie/onderzoeksgegevens/homogeen_260/meulenbrandsma2007b.pdf
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Well written article describing a thorough test. The "microclimate that develops within the screen" and "thermal inertia" sections describe why mechanical aspiration may be needed when exposed to direct sunlight. I got it saved now and thank you for sharing.
Dan
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While a microclimate (raised temperatures) may develop inside a radiation shield that isn't aspirated, these studies seem to indicate that night aspiration cause a microclimate of their own by not allowing the air to become stratified (calm) and keeping the temperature inside the shield slightly elevated. So, perhaps daytime aspiration is best while at night fans should be off?
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Good question. From what I've been seeing, any shield that is subjected to solar radiation will absorb heat build up to some degree (material, color, amount of exposure, etc). The mechanical aspiration helps to remove this heat build up and maintain the inside temperature close to the outside surrounding air temperature. Running the fan at night would only give slightly faster response times to outside air temperature changes (if no breeze or wind). I also gather from the studies that a shield that is not exposed to direct solar radiation will follow the surrounding ambient air temperature without needing mechanical aspiration as the shield material doesn't need cooling. This can be seen on cloudy/overcast days.
I removed the fan from my radiation shield and I'm staying under 2F degree difference with the airport 1/2 mile away. Still experimenting to tighten that spec. down though.
Dan
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I just installed the Ambient Weather SRS 100 today. Noticed an initial temp drop of 4-5 degrees immediately after install. I'll keep track against local weather to compare.
I have a slight concern since it is mounted on the side of the house (20 ft. up), which is aluminum siding, although the house is light blue so I don't think i'm getitng much radient heat from the house. Anyone have any thoughts on this?
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I just installed the Ambient Weather SRS 100 today. Noticed an initial temp drop of 4-5 degrees immediately after install. I'll keep track against local weather to compare.
I have a slight concern since it is mounted on the side of the house (20 ft. up), which is aluminum siding, although the house is light blue so I don't think i'm getitng much radient heat from the house. Anyone have any thoughts on this?
You'll likely run into problems. What direction is it facing? Can you relocate to above the grass?
Many years ago I temporarily setup my temp/RH sensor (Davis WMII) inside the non-aspirated radiation shield on my TV tower located about 4 feet above ground. The tower was only about 4 feet from my house and was facing east. My house has a tan vinyl siding. In the morning when the sun was warming the house, the reflected heat caused the temp to read about 5 to 10 degrees higher than surrounding stations. The temp dropped to normal when the sun was no longer heating the side of the house.
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Thanks for the reply. It faces south east but since I live is a densely wooded area, it doesn't get much "direct" sunlight. I'll watch to see if I get spikes in late moring temp, then a drop when it crosses over the top of the house. If yes, I would still be getting solar heat readings. My larger concern is radient heat from the aluminum siding. I installed it on the top corner on the back side of a 2 story house.
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Hi guys,
First of all, I'm totally new to this hobby and I'm having a blast playing around.
My stations is a cheapo Zephyr/Watson/Fine Offset/ WH1081/Multi-branded model that sells for about $120.00 U.S..
My reason for posting is a recent discovery I've made with this station.
First off, this model does come with a radiation sheild although it's tiny compared to my dad's Davis VP2 (approx. 1-1/2" diameter).
Although this shield does block the direct sunlight, it also still shows up to 4 degrees F higher than other local stations that are mounted in the shade.
My station is mounted on a post setup approx. 5 foot above my garage roof. Early on I decided that my main problem was a lack of ventilation through the radiation sheild, but I really didn't know what to do about it.
After giving a lot of thought to building my own aspirated shield, I decided to play around with my mounting and came up with the following solution:
My Wind setup consists of a seperate directional sensor and speed sensor.
I moved the temp/humidity sensor to approx. 1", directly below the wind speed sensor, thinking that the movement from the speed sensor woudl provide some air flow across the temp sensor.
Well today I gave this setup it's first test and although it's not perfect, I was impressed with the results.
When the air movement was below 5 mph, I still got about a 1 - 2 degree F increase in temp readings above those of neighboring stations.
When the air movement was above 5 mph I was pretty much right on with my readings and anything over 6 mph air movement I was the same if not lower than my neighbor's readings.
I know that one day doesn't tell the story, but I did find these readings interesting.
If this continues to work out I might have found a solution that does not require an active solar radiation sheild.
I'll try to keep everyone updated with my results and I hope this helps someone out.
Dave
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Although this shield does block the direct sunlight, it also still shows up to 4 degrees F higher than other local stations that are mounted in the shade.
My station is mounted on a post setup approx. 5 foot above my garage roof.
That's probably a big part of your problem. There's a lot of heat that may be coming off the roof. If possible, I'd suggest putting the temp sensor closer to ground level.
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Although this shield does block the direct sunlight, it also still shows up to 4 degrees F higher than other local stations that are mounted in the shade.
My station is mounted on a post setup approx. 5 foot above my garage roof.
That's probably a big part of your problem. There's a lot of heat that may be coming off the roof. If possible, I'd suggest putting the temp sensor closer to ground level.
x2, about 6 feet above a grass surface away from heat radiating sources like the siding of your house.
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... also, if you can see your temp/humidity sensor through the sides of your radiation shield then your sensor can also "see", or detect, reflected solar radiation from nearby surfaces absorbing and emitting heat and give you higher readings. An example; Mine was showing around a 4 degree higher reading than actual temp. due to the sensor exposed to a reflection off the ground nearby. By blocking that source of reflection the temps read more accurately. I made a radiation shield that used bowls deep enough to block reflected radiation from below and still allows air to flow.
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Hey guys, thanks for the replies.....
I took your advice and totally re-worked my temp/humidity sensor mounting (for about the 5th time).
This time the sensor is inside the radiation shield mounted at about 7 foot above the ground (below the roof line).
Also, I extended the "arm" away from the garage sidewall by a little over 2.5 feet and am now getting my best readings yet.
I quickly found out that my mounting under the wind speed sensor worked really well on windy days and really poorly on calm days. Once the wind stopped blowing I was right back to 4 degrees higher than other nearby stations.
Now that I've addressed the reflected heat problem AND the solar problem (by spray painting the radiation shield bright white instead of the light gray that the manufacturers chose, I am now running neck and neck with my dad's Davis Vantage Pro 2.
Honestly I'm really impressed with the WH1081 for the price.
It only updates about every 48 seconds yet the range is fantastic and the sensors seem to be extremely accurate.
It will never compare to the Davis systems yet this was in my price range and the Davis wasn't. It might be cheap but it's been giving me a lot of pleasure playing around with it.
Thanks again for the suggestions/advice everyone. I really do appreciate the help.
Dave
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Great job. That's the benefit of everyone's info on the forum. With all the little hints, you can take a cheap unit like yours or mine, and produce a more accurate result, and get every ounce of usability out of it.
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Sam, thanks for the reply....
I just took a look at your web site and I'm impressed.
Could you please tell me how you added the local radar link to your site?
I'm probably going to get a site up and running in the near future but as yet I've not found how to add an animated radar screen.
Any help you can give me would be appreciated.
Dave
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Sam, thanks for the reply....
I just took a look at your web site and I'm impressed.
Could you please tell me how you added the local radar link to your site?
I'm probably going to get a site up and running in the near future but as yet I've not found how to add an animated radar screen.
Any help you can give me would be appreciated.
Dave
Go to wunderground.com>enter your zip code in the search box, hit enter>click on the radar map> using the cursor select or zoom in on your area of interest>Click on Animate Map in the upper left corner of image.>Adjust the settings at the bottom of the page to your desires, Click on Update Radar Map>Click on view/save this image in the lower left>copy the url appearing in your browser address bar>use that url to paste into your web editor as an image source.
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Sam,
I just gave it a test and it worked perfectly.
THANKS!
I'm the type of person that tries to juggle about a million hobbies at once and so far this one is rating right up there at the top of my list.
I can't believe how much I've learned about weather just over the last couple of weeks.
I plan to keep reading on this site to see just how much I can learn.
I really appreciate coming to a site that has such helpful and informative members.
Thanks again.
Dave
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no problem, we all need help sometimes.