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Fine Offset Rain Gauge
#1
It is a very wet and stormy night here tonight. While enjoying watching my WeatherDuino Pro2 weather station receive the ever increasing rain data and displaying it in my weather software, I had a though which I had not considered before - "How much rain can fall (rain rate) before a standard, unmodified Fine Offset Rain Gauge starts over flowing from the top because it can not process all the rain through the small hole in the bottom?"

Has anyone taken measurements of this before? Filling it to the top and seeing what it would equate to in a rain rate?

[attachment=622] [attachment=621]
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#2
See page 20


.pdf   Evaluation of Tipping Bucket Rain Gauge Performance and Data Quality.pdf (Size: 719,21 KB / Downloads: 86)
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#3
Hi,

I've not actually measured it, but I would not expect "overflowing" to be a significant problem. But with rain drops that dense (or large), I would expect "splash out" to give a considerable reduction in the measurement, since it's a known problem even with lesser rain (due to the low slope and small "walls" of the FO "funnel").

Another issue is the rate of tipping of the "see saw". The Fine Offset sensor/counter (i.e. in its T/H Transmitter) can handle an enormous speed (I don't know about the Weatherduino software) but some of the rainwater measurement will be "lost" whilst the see-saw tips.

Personally, I have experimented with adding a funnel (15 cms, 6 inches diameter) to the FO gauge to increase its sensitivity (by a factor of 2.5) and reduce splash-out. However, my first prototype showed that some form of surface treatment/paint is necessary: An off-the-shelf funnel didn't indicate the onset of rain any sooner (because beads of water collected in the funnel, even with its steeper sides) and now, after a few years, the plastic has "died" due to (UV) exposure, even in the UK.

Cheers, Alan.
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#4
(12-04-2016, 11:11)AllyCat Wrote: Another issue is the rate of tipping of the "see saw". The Fine Offset sensor/counter (i.e. in its T/H Transmitter) can handle an enormous speed (I don't know about the Weatherduino software) but some of the rainwater measurement will be "lost" whilst the see-saw tips.

As with the anemometer, each click of the rain gauge, calls and interrupt routine, so it can count very fast.
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