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RG11 Accuracy

Discussion of this sensor and its uses
apenwith
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RG11 Accuracy

Postby apenwith » Fri Jul 06, 2012 2:15 pm

Hi
It has just started to rain a little and it was noticeable that on dry concrete the drops were spaced quite well apart (it's also stopped me from mowing the grass).
The RG11 diameter is only about 60mm so I wonder if it is 'finding the holes between the drops'. What would happen if the RG is set to 0.01 mm and mounted under a funnel. By my sums the funnel should be around 150mm diameter to give a 0.2mm equivalent.
Regards
Alan

bruce45
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Re: RG11 Accuracy

Postby bruce45 » Fri Jul 06, 2012 2:27 pm

if the forcast in an other post about the weather is correct we should have something to compare. i think we need to see that the rg11 is reading before looking at further mods. just of the short showers that i have had i was not that happy about the low count with light rain compared to the tip bucket. heavier showers could give clearer results.

i do understand your logic but its early days.

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Re: RG11 Accuracy

Postby apenwith » Sat Jul 07, 2012 7:51 am

Hi
Last night we had 44mm rain according to my manual gauge (the Cumulus Bucket said 40.6mm and the local weather station 15 miles away had 38mm) but both the rg11's were just over 15mm - not very promising.
Regards
Alan

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Re: RG11 Accuracy

Postby bruce45 » Sat Jul 07, 2012 10:24 am

this is from hydreon site




What is the accuracy of the RG-11 Rain Gauge?

The Hydreon Rain Gauge is not as accurate as a properly maintained Tipping Bucket in ideal conditions.
We do not claim an accuracy specification for the RG-11 Rain Gauge. The RG-11 is very repeatable, and over a variety of conditions will yield an average result that is reasonably close to that of a tipping bucket. But, for any given rainstorm the result can be off by as much as 2:1 in either direction. Even this is not an upper limit.

The strength of the RG-11 is that it works in many situations where a tipping bucket simply does not. That is, the Rain Sensor is vastly more accurate than a tipping bucket that has ceased to work properly due to dirt or mineral deposit or mechanical difficulty, or a tipping bucket in a mobile application that is constantly giving false indications due to motion. The RG-11 is more accurate for a small (but in some applications, meaningful) amount of rain, such as 0.01", that will simply not register in a tipping bucket.

This said, if you do not need the ruggedness of the Hydreon Rain Gauge, and maintaining the tipping bucket is not a problem, use a tipping bucket.


as i said in the other post seems to be size of rain drop related together with the rain rate.

bruce45
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Re: RG11 Accuracy

Postby bruce45 » Sat Jul 07, 2012 11:10 am

just had a thought

to try and understand how the rg11 is recording for those who have two units could one not be set up for the rate of rainfall and the other for the total amount? that could then be compared to the tip bucket and cumulus.

not sure if this is possable but in theory if you have two stations close to each other replacing the tip bucket on one with the rg11 should record the rate.

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Re: RG11 Accuracy

Postby apenwith » Sat Jul 07, 2012 11:48 am

Hi
As Bruce said earlier - maybe it is too soon to think of mods but I am fairly sure that the catchment area has someting to do with the accuracy. So I shall still jump in with an idea.
The picture is supposed to be a funnel with the top tilted away so the base shows. The base has four equal holes so that to a large extent it will produce equal sized drops - hopefully giving the Hydreon algorithm an easier life and making rate comparisons more accurate.
funnel.jpg


Regards
Alan
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duke
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Re: RG11 Accuracy

Postby duke » Sat Jul 07, 2012 12:07 pm

Here's another idea (probably not a good one). How do you think the RG would cope / record rain from a standard funnel?

For example, simply removing the tipping bucket mechanism and mounting the RG in it's place.
Duke

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bruce45
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Re: RG11 Accuracy

Postby bruce45 » Sat Jul 07, 2012 2:55 pm

question for Steve

if i was to increase the sensitivity from 0.01 inches to 0.001 inches on the rg11 and change the tip size to the same would cumulus read each tip or just record the 0.001 tip as 0.01 if so could i set the multiplier to 0.1 so it would have to see 10 tips before recording?

we are just starting the have some very light rain with a light breeze.

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Re: RG11 Accuracy

Postby beteljuice » Sat Jul 07, 2012 3:01 pm

It would seem the unit is a drop detector / counter. If that is the case too many drops or a 'flow' of water is exactly what it can't cope with. That may go someway to explain under counting in heavy rain.

@ apenwith:
hmm ....... If the above musing is true you would be encouraging a 'flow' of water with your few output holes.

How about a small mesh with a few panel pins in to produced 'spaced' and directed drops ?
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bruce45
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Re: RG11 Accuracy

Postby bruce45 » Sat Jul 07, 2012 3:06 pm

hi dont no if this will help its from there site as to how the rg11 works


The RG-11 bounces beams of light within the lens. When drops hit the outside surface, it allows some of the beams to escape. The RG-11 detects the change in beam intensity, and determines the size of the rain drop that caused the change.

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Re: RG11 Accuracy

Postby steve » Sat Jul 07, 2012 3:32 pm

bruce45 wrote:if i was to increase the sensitivity from 0.01 inches to 0.001 inches on the rg11 and change the tip size to the same would cumulus read each tip or just record the 0.001 tip as 0.01 if so could i set the multiplier to 0.1 so it would have to see 10 tips before recording?
If you set the tip size in Cumulus to 0.001, then for each 'tip' that it gets it will increase the RG11 rain total by 0.001 of whatever units you are using in Cumulus.
Steve
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bruce45
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Re: RG11 Accuracy

Postby bruce45 » Sat Jul 07, 2012 3:37 pm

hi Steve

thats what i thought but the display is only 0.00 should it take 10 tips when set at 0.001 before cumulus would then record 0.01

if that is true then there might be a bug as i have only had one tip of 0.001 showing in the debug log but cumulus shows 0.01 recorded

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steve
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Re: RG11 Accuracy

Postby steve » Sat Jul 07, 2012 4:42 pm

Are you using "RG-11 No.2" on the settings screen? It's ignoring the tip size setting for that and using the tip size for No.1, so as a work around you'll need to set the tip size in the setting for No.1. I wonder if this is the bug that Alan saw where it seemed not to be saving the setting?
Steve
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bruce45
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Re: RG11 Accuracy

Postby bruce45 » Sat Jul 07, 2012 4:52 pm

ok that explains it just wanted to try it without changing the rg11 no1 setting as it was working.
have changed to the rg11 no1 port and changed the tip size and noticed in the today.ini file that it is increasing at the correct rate.

now it seems to be working ill delete the debug and clear the today file and let it run to see what happends

thanks Steve

bruce

apenwith
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Re: RG11 Accuracy

Postby apenwith » Sat Jul 07, 2012 4:53 pm

Hi
It would seem the unit is a drop detector / counter. If that is the case too many drops or a 'flow' of water is exactly what it can't cope with

I think that was what I thought a funnel with holes might achieve - a more standard drop size scattered over the surface of the RG. It would need a bit of experimentation to get the hole size right and maybe some drip points or panel pins as you say. And enough dripping that the funnel doesn't over fill. I think it is worth a try - what's to lose?
Alan


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