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> Calibrating Davis Rain Collector
HoosierGuy
post Mar 14 2007, 11:41 PM
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Hello all! I just got a Davis VP2 a few weeks ago! It's my first weather station and I've been having fun tracking the weather speed and direction! I've had it outside now for about a week and half now. I've been waiting for it to rain here in Indiana now for the last ten days and finally it rained tonight and the Davis rain collector worked! lol 2.3 inches! I've been waiting impatiently for it to rain to see the rain collector in action.

Anyway, I donĺt want to mess with the calibration of the rain gauge right now but when summer gets here I want to make sure it's calibrated. Right now the bucket collector is about seven or eight feet up on a post.


So, I assume the easiest way to calibrate the Davis is to buy a regular
rain gauge to compare it to the Davis, yes? Do I need to buy a gauge
that meets the specifications of the United States Weather Bureau? Should I buy one of those gauges that has a tube inside another tube? I've found those on the net going for $33-$36.00 What's the minimum diameter the gauge should be?

Also, the gauge should be the same height as the Davis bucket, yes? What if it is not? Is there anything wrong with strapping the plastic rain gauge to the Davis bucket?

Right now I have a cheap plastic gauge by the Davis; it sites a few feet under the Davis and four feet over from it. So it is not even with the Davis.

Thanks!
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°rjan
post Mar 15 2007, 03:20 AM
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hi enthusiast!!!!!!!

believe me , calibration are needed, and you could use the cheap plastic, or you can make one yourself(ive got 4 next to the davis)........but most of all it is the positioning of the raincollector that is important.......it should be placed in an open but also shielded area, cause wind can for sure make the rain go horizontal......at 8 meter pr second they estimate 12 % catch of rain in the collector, so if youre a wind mate, do separate the anemometer, and seek a good place for the rain catch.......if adjusting the cal screws......you will need at least 3 heavy downpours of some length to verify the measurements, and this way you must adjust till you find the keyposition of the screws........do also go back in the forum archive, cause we've discussed this issue quite a lot in this forum..........

so go for it.......

°rjan
Norway


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HoosierGuy
post Mar 15 2007, 12:50 PM
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Is there anything wrong with strapping the gauge onto the bucket? Or would that mess them both up? It would seem to me that would be the perfect place to put a rain gauge to check the Davis.
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HoosierGuy
post Mar 15 2007, 01:07 PM
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It rained here - Wednesday night around 8pm to Thursday morning around 6am. My Davis picked up 3.46 inches of rain. The plastic gauge picked up 3.2

My plastic gauge is not completely round - it's flat on one side. It's half round half flat. I assume a gauge like this is not very accurate, correct? What diameter does the gauge need to be to be accurate?
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George Richardso...
post Mar 15 2007, 03:29 PM
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Is there anything wrong with strapping the gauge onto the bucket?
Not a good idea. Rain gages must be level. Manual rain gages must be emptied.
Reference other questions/statements: You will find that 93.7% of the birds in Indiana have been taught to light on the rim of your Davis rain bucket, facing out. and do their business where you will have the oportunity to properly dispose of their - whatever. This makes the mounting of the bucket at a 7 - 8 foot elevation difficult to maintain. You might look at a 6" SS screen filter. Davis recommends mounting at 5' el. Ambient has a 4" manual rain gage that a lot of folks seem to use for calibration. I've seen something about same elevation within 10' but same pole seems to be popular. From experience, perhaps the best advice I can give is compare the Davis to the manual gage for a good while before making any changes to the Davis. A lot of folks claim substantial calibration necessary and I thought I needed over 20% but when it all worked out it was under 10%. Good Luck, move slowly. Just think, why would a $5.00 drug store toy be more accurate than a $300 - 500 davis weather instrument? Also, this is a personal weather instrument: Why would a weather station a mile +/- away be more accurate for the conditions at your location than your station? Might be, but probably not.
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°rjan
post Mar 15 2007, 04:45 PM
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i still havent seen any bird-poop after having used the davis collector now for 7 yrs.......maybe its some kinda arab plot in the u.s of a, training the birds to drop..............polonium........ biggrin.gif

else you can strap it on the other side of your iss pole, and i guess youre so geared on this experiment that you check the rain fall every hour anyway and for sure empties it at observation time .....anyway.......good luck



°rjan
norway


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Removed_Member_Joseph Toubes_*
post Jul 16 2007, 09:52 AM
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I did one of those gut feeling turns of the screws of the rain collector. Last night it finally rained and the difference between the 4 inch gauge and the Davis was 0.01 inches, I think that is close enough.

The Davis registered 0.90 and the 4 inch 0.91. yep.. lucked out on this one.
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