Sandaysoft

Hi
Looking at the top of the 8681 (series) rain detector the slope of the funnel looks to me a bit shallow. Light rain hardly slides down and heavy rain could bounce out. I was thinking of making a copper sleeve quite a lot higher with the same opening area but much steeper sides of the funnel. Worth doing ? Or is the detector fairly accurate anyway ? Thoughts please ?
Alan

Hello Alan,

I found that the rain gauge reports about 25% less than actual. I have a manual rain gauge next to the fine offset gauge and have been comparing readings and trying different size configurations and have managed to come within .5mm over about 10mm
The other day the station reported 8.1 and the manual gauge just under 8mm. I'm resonabilly happy with this reading.

Only this morning I created a pdf of what I have done for someone else and then I came across your post.

You can download the pdf or pps here
http://members.optusnet.com.au/gscvic/raingauge/

You'll need a 2 litre coke bottle as it has the right curves for the application and deforms and slides over the rain gauge.
Also another plastic bottle 1.5 litre and is vertically straight not curved about 95mm diameter.

Follow the pdf and you'll get the idea

I hope this helps.
Good luck!
Regards
Gerard

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http://members.optusnet.com.au/ktau/wws/

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Gerard



http://weather.gkt.net.au
Member of http://www.auweather.net/

Hi
Is the area of the opening the same as the original or does it by chance (or design) compensate for the underreading ?
Alan

Hello Alan,

The area is greater by design. The fine offset is 55cm2 (11cm X 5cm), and the mod is 70.9cm2 (9.5cm dia). As I was getting a 75% reading compared to the manual gauge I initially made the area 40% larger. I then slowly reduced the diameter of the opening until I got a good reading but it wasn’t consistent between light rain and windy rain and heavy rain. I then studied the design of the manual gauge which went vertically from the conical section up to the opening and emulated that geometry, and now it is reasonably consistent throughout the different types of rain. Unfortunately we are not getting much rain here so I have had few chances to adjust the dimensions. But I’m reasonably happy with it at the moment
I had considered offsetting the rain by 1.33 in the software but the fine offset design had the same inconsistency throughout the different types of rain and being rectangular I figured that rain from different directions may not be consistent.

I hope I’ve made sense

Regards
Gerard

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Gerard



http://weather.gkt.net.au
Member of http://www.auweather.net/

Got a decent dump of rain overnight, 32.4mm on the station and 26mm in the manual gauge. Have reduced the size of the station mod from 95mm dia to 86mm dia to correct the error.

Gerard

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Gerard



http://weather.gkt.net.au
Member of http://www.auweather.net/

Hi all,

My rain gauge too was very pessimistic by about 25%.
I've made a mod using a 9,5 cm in diameter kitchen funnel stuck on a ceramic cache pot.
So that I get 3 advantages:
1- as in your coca bottle mod, the collecting surface is increased and the slope is more vertical than the original design
2- the gauge is protected from wind
2- the gauge is protected from sun
http://aeropic.free.fr/meteo/img_8045.htm



bye
Alain

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weather station weatherwise WH1080
http://aeropic.free.fr/meteo

Alain,

I like your mod! When I get around to building my single stevenson screen I intend to place the rain gauge inside the screen and have a funnel similar to what you have used collecting rain from outside the screen.

I have the louvered pantry doors I found, have collected everything else required, but the time to build the screen.
Finding the time is what I'll have to work on.

Cheers
Gerard

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Gerard



http://weather.gkt.net.au
Member of http://www.auweather.net/

I like the rain fix aeropic - does it just drip from the funnel into the old one or is it sealed to it? You must have a big error on your temp though, surely, with the small shield exposed to the sun?

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Thanks for the info. After scouring a well known UK supermarket, I found that a large bottle of Capella apple juice had just the right dimensions to fit snugly over the unit, and an inverted bottle of Highland spring water provided the 86mm diameter dimension for the funnel. Stuck together with sticky tape (for now). I'll see how it gets on.
Andy

Had a fair amount of rain last night. My weather station says 16mm, but vertical sided tin says 10mm! Other local stations on WU say about 10mm as well, so I'm thinking 86mm diameter is too big? Slightly confusing though, as 58cm2 isn't that much bigger than the 55cm2 of the unit itself ?? Maybe the gauge is calibrated to have shallow sloping sides. Or the strong wind shook is back and forth (with the bottles increasing the drag of course) to similate more rain. Any thoughts?

Something wrong there - that amount of error with that mod suggests that you were OVER reporting to start with ?

Please define "vertical sided tin" - is that a real calibrated intrument or .......

and certainly, as you may have read elsewhere on the forum, Your rain bucket should be fixed securely (preferably NOT on a mast), and the drain holes shouldn't be exposed to any kind of updraft.

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......................Imagine, what you will KNOW tomorrow !

Hi Andy,
Where is the rain gauge located? When mine was on the pole it was reporting much rain when there was only wind. I took it off the pole and mounted it (With the stand off bracket), found it better but still got some phantom rain. I now have secured it by the base onto a solid mount for a number of months now and havent had any phantom readings since.

Just climbed up the ladder and checked the diameter of the funnel again and about 86mm dia is what I have, I am reasonablly happy with the reporting. Although I think it reads a little more in heavy rain and a little less in light rain. I guess that it is the nature of the construction and quality of the Fine Offset w8681 (1080/1) Rainfall detector.

Gerard

_________________
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Gerard



http://weather.gkt.net.au
Member of http://www.auweather.net/

Has anyone considered making the catchment area for the rain gauge 10 times the size of the original and modifying Cumulus to accomodate this so that you get .03mm increments instead of .3mm increments in rainfall?

or perhaps make it 3 tmes the size to get .1mm increments?

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Cheers

Phil

http://members.ozemail.com.au/~storerfamily/weather
http://www.seabreeze.com.au/graphs/sa.asp

The beteljuice modified his LaCrosse rain bucket to x10 so that he could tell very light rain (actually it doesn't quite work like that for reasons various).

You naturally have to inform Cumulus of what you have done, else all your totals are wrong !

BUT Cumulus still works (ie. rounds) to its 'normal' decimal point (0.1mm / 0.01in), You can see the difference on your station console and you should have improved any tolerance error, but you won't see that extra decimal point resoloution in Cumulus.

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......................Imagine, what you will KNOW tomorrow !

Ah ok. I assume my fine offset WH1091 registers .3mm each time the rain gauge empties as that's how much rain registered when I accidentally moved it the other day. Therefore I thought making it 3 times the size would make sense.

Anyway, as I live in the driest state in Australia, the driest continent on the planet, I probably won't get to test this for quite a while.

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Cheers

Phil

http://members.ozemail.com.au/~storerfamily/weather
http://www.seabreeze.com.au/graphs/sa.asp