Fine-Offset Rain gauge

[wd40]

I have read all the threads about adding a funnel or sides to the rain sensor.
The other day the rain came down pretty hard. I had the chance to make an observation that I think is interesting and related to the fine offset rain sensor.

Just outside my window in the open yard are two 12" diameter clay saucers for the bottom of flower pots. One is upside-down so it want hold water and the other is right side up and will. The right side up one filled with water in a few minutes. I watched the splattering drops and noticed the splattering was much worse on the saucer collecting water compared to the one that water just ran off.

I recreated that inside dropping drops of water onto a small plate and watching for water splatter escaping the small plate to the counter top. Note: Wife was not home. As long as no puddles had formed, the escape was minimal. As soon as a puddle formed, the splatter escaping the small dish was much greater.

Laying on the sink was a green Scotch-Brite pad used to scrub pots. I laid that on the plate and did it gain. I noticed a reduction in splatter. i then tried a product you use under something to keep it from moving around. I tried it and that worked well.

My proposed mod will be to fit the top with these two products and test them to see if they help the gauge deal with heavy rain falls.

If it works, it will be a nice filter as well. I think the only problem is will it blow out in heavy winds.

[Ned]

While those products will reduce splatter, they'll also retain water and hinder the flow into the outlet and reduce or delay the measurement. So a short shower may not register at all, particularly if the sun comes out and dries it up
Building the sides up seems to be the best way to counter splatter.

[wd40]

Ned, you are surely right about the small amounts of rain want be detected. The sides are a better idea.

The splatter dampener is a wonderment so I have to try just to see what happens.

I am mostly interested in rain fall for my garden and small orchard.

Does anyone suspect the gauge is overflowing in heavy down pours or just the splatter?

[yv1hx]

Hi Weather enthusiasts!

Please try a look at the page 46 of the following document:

http://home.comcast.net/~dshelms/CWOP_Guide.pdf

They use wind shields to avoid the wind influence over the rain gauge.

I have plans to do some wind shielding to my rain gauge in the near future, using some acrylic plates.

[Gina]

I found with the standard gauge that brief showers were not registered - water remained on the funnel surface and dried up when the rain stopped and the sun came out. A larger funnel with steep sides and a top skirt not only stops rain drops bouncing out but they get into the gauge quicker, and with 3x the catchment area, the sensitivity/resolution is raised to 0.1mm. This means that many brief showers are now detected.

[wd40]

I had an opportunity to run a few test this morning.

The first was to check the accuracy of the tipping bucket to see if the resolution was indeed .01".

I used an eyedropper to count the number of drops to get a bucket tip. Then measured the weight of the drops. Then I compared that to the expected weight of .01" of water multiplied times the area of the opening.

Best I can tell the gauge is well within published specifications.
So that is good.

Next I did a drop test dropping the drops from several feet up to see if I could see a change in accuracy and I did not. Still, this was too vague to draw a conclusion since I have no comparison between my drop's velocity and a rain drop's velocity.

However, i did notice a repeat in my first observation in the first post where the splatter of a drop was minimal unless it struck a bead of water already on the surface of the gauge which in a rain storm would be quite common.

Into the house I went to drop water drops on the kitchen counter. Again, splatter was minimal unless I hit a drop beading on the counter top.

I then ran a drop test to simulate a light rain. I covered the gauge with a green scotchbrite pad. As Ned noted, it sucked up water like a sponge so that is out.

Then I used the anti slip padding. It did not soak up hardly any moisture and seemed to repel it. This looks like a good candidate for an insert to stop any splatter if the UVs don't get it.

I wonder too if a product we have in the US called RainX might work to reduce the surface tension of the water on the gauge to stop the water from beading on the gauge slopped walls. This might work on a funnel mod as well.

When all is said and done, I will probably add straight sides to the rain gauge as y'all suggested but I do enjoy a challenge to understand what is really happening.

[hills]

Very interesting thread and some great ideas there!!

I have read that some people use a product used for cleaing or waxing cars that repels water. I'll see if I can find that info, but I know there are plenty of car cleaning products out there that advertise their "water beading" qualities.

After having some heavy rain falls, I've continued to monitor the performance of my gauge since adding the high sides to the original collector and having my funnel feed into that.

Compared to 2 manual water gauges I have in the garden and I am very happy with its accuracy. It is within about 1-2% of each, infact my automatic gauge results are inbetween the 2 of their recordings and this remains consistent after heavy and light falls.

Unfortunatley I only empty the manual rain gauges at the beginning of each month to make it easier to compare with the monthly figures in Cumulus and due to this being such a wet month they have both overflowed. So I'll have to start my comparisons again.

[wd40]

Phil this RainX product normally goes on your car's windshield so water runs off and doesn't bead so the water runs off. It really has limited use since it has to be reapplied. Just interesting.

http://www.rainx.com/Products/Windshiel ... ginal.aspx

[dziedzicmj]

I would not worry too much about re-applying (RainX). On the windscreen it lasts for about 3 months in heavy use and up to 6 months you can still see a difference. So if it helps at all, applying it twice a year should not be a major issue.

Mdz

[wd40]

I have had two good test days. Both days have proven the accuracy of the Fine-offset style of rain gauge with a cushion material to stop the lost splatter. The material you see in the picture does not soak up water so it allowed the recording of a single .01" the first day of rain' Today it was accurate again with a rain rate of 1.3inch/Hr.

But it still hasn't seen a heavy rain so it is not fully tested.

[fadiaz]

Hi,

I am very interested in your experiments with the Fine Offset Rain Gauge. I do hope you can find good information on more ways to keep the accuracy of our rain gauges (yes, I also have a Fine Offset).

May I ask, what material are you using in that last experiment to prevent splatter?

Thanks


Francisco

[wd40]

It is a foam like material used to put under things to keep them from slipping around. If I find a name for it I will post that.

What I am not sure is how this stuff will stand up in the sun and if it will work in a heavy rain fall so for now I can not say it is a fix.

[Synewave]

When I first bought some of this material, it was marketed as a product that you placed a small square of on your car dashboard, then place your mobile phone on it and it would not slide off.

[philcdav]

Hi guys. interesting thread here.

I noted that 'normal' weather station rain gauges are ground mounted, usually a plastic funnel and measuring cylinder.

I have fitted a collar inside my rain collector. Its a 3" high ally strip, cut to fit tightly within the collector. It has 4 cut-outs which clip over the outside edge to secure it.

Its hard to see any effect, if any! But it certainly wont let drops bounce/spray out !