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BT's UGLY Fine Offset Rain Gauge Mod

For discussion of DIY weather equipment - sensors, accessories, improvements to existing kit etc
rich27gc
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Re: BT's UGLY Fine Offset Rain Gauge Mod

Post by rich27gc »

I can't really see from the picture, but that looks like a wide exit to the funnel, have you restricted it?
I found that I had to reduce the funnel exit to the same size as the original hole in the rain gauge or in heavy rain the buckets got over whelmed.
jim-easterbrook
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Re: BT's UGLY Fine Offset Rain Gauge Mod

Post by jim-easterbrook »

The original rain gauge hole is still there - the new funnel drips onto the original gauge which is unmodified apart from having this monstrosity glued on top. The collecting area has increased by a factor of 2.38 - I never recorded a rain rate anywhere near the claimed maximum so I don't expect any problems from the increased area.
Jim
rich27gc
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Re: BT's UGLY Fine Offset Rain Gauge Mod

Post by rich27gc »

I think the increased head of water caused my problem with the water flowing faster from the funnel.
Readings I took before the mod were around 25% under reading, after the mod I have achieved anywhere from 4 to 15% under reading, 15% usually after heavy rain.
Given the price of the whole station I'm quite pleased with the results. There is a Davis station in the same village and that isn't as accurate. :D
AllyCat
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Re: BT's UGLY Fine Offset Rain Gauge Mod

Post by AllyCat »

Hi Jim,
jim-easterbrook wrote:The collecting area has increased by a factor of 2.38
It looks exactly like the "14 cm" funnel that I used for my very similar "temporary" modification two years ago. I couldn't believe it was that far back until I checked my ebay purchase folder. :)

I wasn't sure how to handle the calculation for the flat rim at the top (which at 6 mm represents no less than 16% of the collection area) and I think decided to take the average diameter on the assumption that half the water would splash or drain each to the inside and outside. Is your 2.38 a calculated or calibrated value?

The modification certainly gives much smoother (step-free) rainfall graphs, but I was rather disappointed that it doesn't normally give any earlier warning of "it's raining" because the rain collects in droplets on the funnel (despite its much steeper sides than the FO) before eventually running into the gauge.

I wonder if we can find a paint to kill two (or even 3) birds with one stone? Protect against UV, "hydrophobic" and perhaps a little prettier?

Cheers, Alan.
jim-easterbrook
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Re: BT's UGLY Fine Offset Rain Gauge Mod

Post by jim-easterbrook »

AllyCat wrote:It looks exactly like the "14 cm" funnel that I used for my very similar "temporary" modification two years ago.
That's probably where and when I bought mine. It's been sitting around for a while.
I wasn't sure how to handle the calculation for the flat rim at the top (which at 6 mm represents no less than 16% of the collection area) and I think decided to take the average diameter on the assumption that half the water would splash or drain each to the inside and outside. Is your 2.38 a calculated or calibrated value?
I think I took the approximate inside diameter. The scale factor is a calculation. I don't expect much accuracy from the gauge, before or after fitting the funnel. 16% is neither here nor there.
Jim
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Buford T. Justice
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Re: BT's UGLY Fine Offset Rain Gauge Mod

Post by Buford T. Justice »

Cool. Please keep us posted how it works out. Your funnel looks kind of big though.

On the white one I used, I cut the rim off of it with a pair of scissors going down about 2-3 mm as it was catching too much rain. Now it usually agrees with my Stratus rain gauge, but I am still experimenting with the total size of it. Once I have it just right, I will post a before and after picture.
Last edited by Buford T. Justice on Fri 01 Nov 2013 8:57 pm, edited 2 times in total.
duke

Re: BT's UGLY Fine Offset Rain Gauge Mod

Post by duke »

@rich27gc
There is a Davis station in the same village and that isn't as accurate
I'm curious, compared to what???
rich27gc
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Re: BT's UGLY Fine Offset Rain Gauge Mod

Post by rich27gc »

I know you're going to tell me not to compare two different locations, but it's really isn't that far away from me so I'm comparing it with my ClimeMET manual gauge.
duke

Re: BT's UGLY Fine Offset Rain Gauge Mod

Post by duke »

I know you're going to tell me not to compare two different locations,
No actually, I was curious how you were measuring the accuracy of your modification and you answered that too.

As for comparing your station to another station, that 'cannot' be done in my opinion no matter how close. There are just two many variables other than the 'local (in your vicinity)' weather that everybody expects to be the same, it never is, you just don't know why the other station compared may appear more or less accurate, mounting restrictions, poor maintenance etc.....
jim-easterbrook
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Re: BT's UGLY Fine Offset Rain Gauge Mod

Post by jim-easterbrook »

Blooming thing has stopped registering any rain now. Investigation will have to wait until the weekend.
Jim
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nitrx
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Re: BT's UGLY Fine Offset Rain Gauge Mod

Post by nitrx »

I followed this discussion with interest but have some questions:

If I make the surface 3 times bigger for collecting the rain I should set the offset of cumulus by the fine offset for rain to 0.33 to get 0.1 mm rain ?

I want also register how long it has rained but I dont know exactly how these times are calculated I read something about it but there will be different methodes. One example was it rains when at least every 10 minutes 0.1 mm rain is registered. The longest raintime in the Netherlands is about 26 hours.

Ofcourse I know it's impossible to get exact values with a fine offset but 1 mm or 10 mm doesn't say all about the experience how wet a day was a strong thunderstom of 10 minutes can give 10 mm in 15 minutes and it can be nice waether for the rest of the day but a drizzle day can give 3 mm and will go in the books as a 'bad' day.
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Buford T. Justice
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Re: BT's UGLY Fine Offset Rain Gauge Mod

Post by Buford T. Justice »

I cannot answer all your questions. My entire goal with this mod was to get close to my Stratus rain gauge which the CoCoRaHS network observers use here in the USA without modifying Cumulus settings. I said in a few posts earlier I had cut down the funnel I am using. I am now a little under what the Stratus is showing so I need to get a new funnel, cut it down a little, and keep it bigger than what I have now slightly. I did figure out I got it from Walmart a long time ago. They still sell it along with a bigger funnel:

http://www.walmart.com/ip/Mainstays-2pc ... t/17188380

I think it is the smaller 8 oz. funnel I am using.
AllyCat
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Re: BT's UGLY Fine Offset Rain Gauge Mod

Post by AllyCat »

Hi Ron,
nitrx wrote:If I make the surface 3 times bigger for collecting the rain I should set the offset of cumulus by the fine offset for rain to 0.33 to get 0.1 mm rain ?
Not quite, you should set the multiplier in Cumulus calibration to 0.33. That will make each "tip" of the rain gauge show as 0.1 mm. One of the reasons for increasing the collection area is that I believe that less than 0.2 mm is considered as a "dry" day (or recorded as "trace"), so a 0.3 mm tip resolution is not really adequate.
nitrx wrote:...a strong thunderstom of 10 minutes can give 10 mm in 15 minutes and it can be nice waether for the rest of the day but a drizzle day can give 3 mm and will go in the books as a 'bad' day.
10 mm in 15 minutes will probably show as a "record" of 40 mm/hour rain rate in the Cumulus (all time) logs! But to check back for "unusual" data that is not normally reported by Cumulus, you could look at the "Select a Graph" for any period of time, or "post process" the Cumulus files with a Spreadsheet program such as Excel.

Cheers, Alan.
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nitrx
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Re: BT's UGLY Fine Offset Rain Gauge Mod

Post by nitrx »

Alan thank for pointing out the multiplier.

I've had pourdown of 111,6 mm/hr intensity but I'm interested in how long it has rained on a day I think a database or excel will help.

Ron
darren
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Re: BT's UGLY Fine Offset Rain Gauge Mod

Post by darren »

If you were bothered about making it prettier. How about using a plastic lid fromsomething, a piece of wood or upvc. Slightly larger all round, a hole in the middle for the pipe, sit it on top, turn it all over, hot glue or other adhesive all around the underside to attach it to the rain gauge, turn it back over then the same around the pipe where it sticks through?
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