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Rain gauge help
#11

For the opening;

Original rain gauge = 100mm .... A=7854 mm2


Modified (with funnel) = 215mm .... A=36305 mm2

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#12

Hi,

Yes, it is the area of the opening which is most relevant, although the "walls" may have some effect (particularly with the FO sensor) in preventing "splash out".  If both openings are circular then the calculation is very easy because the area is proportional to the square of the diameter.  Thus the increased area is 2.15 ^ 2 = 4.6225 and the sensitivity (or resolution) improved to 1 / 4.6...  = 0.2163..  of the original tip sensitivity.

I was also surprised by the suggested figure of 1mm / tip.  My understanding of German/Spanish/Dutch (???) is very poor, but the data sheet linked in #6 appears to describe the "resolution" as 1.0 mm per hour and perhaps refers to the (wireless) transmitted data, not to the raw tip count.  So I think a measurement of the real sensor (with synthetic rain) is necessary.  For example, drip > 78.65 cc of water (0.0786 litre) slowly through the original gauge and count the number of tips (which should correspond to 10mm of rain).

Cheers,  Alan.
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#13

OK so still not terribly scientific, but it looks like it's measuring 0.3mm per tip with the funnel on top. 

I bought a good quality garden rain gauge (it says professional but I have my doubts) . https://www.bunnings.co.nz/holman-rain-g..._p00278717

That gauge measured rain yesterday of 2.7mm, it has some very good 1mm graduations so I'm comfortable that's close. The station gauge read 1.8mm @ 0.2mm per tip that makes 9 tips. It should have read 2.7mm which divided by 9 tips is 0.3mm per tip. 

So for now I'll set it at that and continue to monitor the rainfall with both and see how I go. At some stage after Xmas I'll get a little more scientific about it.

Colin

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#14

So now don't forget to set properly the collector type on the TX software:

Code:
#define COLLECTOR_TYPE  0.300  // Please note: Values must be in metric units. Max. resolution: 3 decimal digits

Also de rain multiplier on the weather software should be adjusted properly:
Multiplier = COLLECTOR_TYPE / 0.2

in your case:
Multiplier = 0.3 / 0.2
Multiplier = 1.5

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#15

I assume the reference to the weather software multiplier is just for Cumulus? I don't think WeeWX needs that, but I'll double check

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#16

Well it appears that Weewx expects a tip to be 0.2mm, it was a fluke that I also initially selected the same amount in WeatherDuino so I hadn't seen this before.

In weewx.conf the StdCalibrate section will need an entry of rain = rain * 1.5 to bring it up to the correct amount for my gauge.

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#17

(22-12-2018, 00:58)41south Wrote:  I assume the reference to the weather software multiplier is just for Cumulus? I don't think WeeWX needs that, but I'll double check

(22-12-2018, 22:19)41south Wrote:  Well it appears that Weewx expects a tip to be 0.2mm, it was a fluke that I also initially selected the same amount in WeatherDuino so I hadn't seen this before.

In weewx.conf the StdCalibrate section will need an entry of rain = rain * 1.5 to bring it up to the correct amount for my gauge.

We had already talk about that. The multiplier is needed to any software whenever the rain gauge in use, have a tip bucket different than 0.2mm

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#18

Yeah, sorry, too many things going on and not enough memory left  Big Grin

Merry Xmas and thanks for all the help getting things going down here  Smile

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