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Author Topic: modify bucket to 0.1mm  (Read 70605 times)

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Bashy

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Re: modify bucket to 0.1mm
« Reply #90 on: November 01, 2008, 10:41:06 PM »
Yeah that makes more sense lol, told you i was a thicket pmsl...

Baffling on the all time record though, another gremlin me thinks?

Offline niko

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Re: modify bucket to 0.1mm
« Reply #91 on: February 08, 2009, 05:09:29 PM »
You can't calculate the funnel diameter for a particular tip size without referencing the original tip size in the calculation.

The math is incorrect:
Quote
For a 0.1mm tip resolution(ROC) your Funnel Size(MFS) would be:
    = 1000 mm (100cm funnel diameter)

--------------------------------------------------------------------------------
For a 0.2mm tip resolution(ROC) your Funnel Size(MFS) would be:
    = 500 mm (50 cm funnel diameter)

The tip size depends on the area of the funnel, not the diameter. If the diameter is halved, the area is reduced to one quarter of the original area / or the tip size increased to four times the original.

« Last Edit: February 08, 2009, 05:12:35 PM by niko »

Offline Meerkat

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Re: modify bucket to 0.1mm
« Reply #92 on: February 09, 2009, 10:33:44 AM »
Hmmm ... now what on earth was I thinking there?
Must be the late nights that got to me.
Any case here is the corrected version (I've deleted the old).

I think a good starting point for determining the funnel size for your rain gauge  would be to first look
up your all-time recorded mm/h Rain Rate. Then you can calculate your max bucket/funnel size as follows:

ASSUMPTIONS (WMR200):
RGR = 999 mm/h ... rain gauge  max resolution = 39" (3.6sec between tips = 16 tips/min)
MRR = 333 mm/h ... max expected rain rate (5.55 mm/min x 60 = 333 mm/h)
RGD = 100 mm ..... current rain gauge diameter (4")
MFS = ? .......... max funnel size
ROC = ? .......... rain offset correction in WD


FORMULAS:
ROC = MRR / RGR
ROC =(RGD / MFS)^2
MFS = RGD / sqrt(ROC)
MFS = RGD / sqrt(MRR / RGR)
MRR = RGR * ROC
MRR = RGR * (RGD / MFS)^2


Your Max Funnel Size(MFS) for a Max Rain Rate(MRR) of 333mm/h would be as follows:
MFS = RGD / sqrt(MRR / RGR)
    = 100 / sqrt(333 / 999)
    = 100 / sqrt(0.3333333)
    = 100 / 0.5773502663029
    = 173.2 mm (max funnel diameter)


Your Rain Offset Correction(ROC) for a funnel size of 173mm (333mm/h) in WD is as follows:
ROC = (RGD / MFS)^2
    = (100 / 173)^2
    = 0.33412409369 (i.e. each original 1.0mm now = 0.33412409369 mm)


If you found a Funnel Size(MFS) of 200mm(8") and your Rain Gauge Diameter(RGD) is 100mm(4")
the Rain Offset Correction(ROC) in WD would be as follows:

ROC = (RGD / MFS)^2
    = (100 / 200)^2
    = 0.25


That would give you a Max Rain Rate(MRR) of:
MRR = RGR * ROC
    = 999 * 0.25
    =250 mm/h


If you found a Funnel Size(MFS) of 12" and your Rain Gauge Diameter(RGD) is 4"
the Rain Offset Correction(ROC) in WD would be as follows:

ROC = (RGD / MFS)^2
    = ( 4  / 12 )^2
    = 0.11111111111


That would give you a Max Rain Rate(MRR) of:
MRR = RGR * ROC
    = 999 * 0.11111111111
    =111 mm/h (appr. 4 3/8"/hr)


For a 0.1mm tip resolution(ROC) your Funnel Size(MFS) would be:
MFS = RGD / sqrt(ROC)
    = 100 / sqrt(0.1)
    = 100 / 0.3162278
    = 316.23 mm


That would give you a Max Rain Rate(MRR) of:
MRR = RGR * ROC
    = 999 * 0.1
    =100 mm/h


For a 0.5mm tip resolution(ROC) your Funnel Size(MFS) would be:
MFS = RGD / sqrt(ROC)
    = 100 / sqrt(0.5)
    = 100 / 0.707107
    = 141.42 mm


That would give you a Max Rain Rate(MRR) of:
MRR = RGR * ROC
    = 999 * 0.5
    =500 mm/h


METRIC TABLE (approximate values):
ROC     MRR    FUNNEL
---   -------  ------
0.1   100mm/h   316mm
0.2   200mm/h   224mm
0.3   300mm/h   183mm
0.4   400mm/h   158mm
0.5   500mm/h   141mm
0.6   600mm/h   129mm
0.7   700mm/h   120mm
0.8   800mm/h   112mm
0.9   900mm/h   105mm
1.0   999mm/h   100mm


IMPERIAL TABLE (approximate values):
ROC     MRR    FUNNEL
---  --------  ------
0.1   3.94"/h  12.44"
0.2   7.87"/h   8.82"
0.3  11.81"/h   7.20"
0.4  15.75"/h   6.22"
0.5  19.69"/h   5.55"
0.6  23.62"/h   5.08"
0.7  27.56"/h   4.72"
0.8  31.50"/h   4.41"
0.9  35.43"/h   4.13"
1.0  39.33"/h   3.94"


1 mm = 0.03937 inches
1 in = 25.4 mm
Cheers,
Rainer

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Script download links always available on the first page of my threads

Offline niko

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Re: modify bucket to 0.1mm
« Reply #93 on: February 09, 2009, 02:41:25 PM »
Better  :D

But:
Quote
For a 0.1mm tip resolution(ROC) your Funnel Size(MFS) would be:
MFS = RGD / sqrt(ROC)
    = 100 / sqrt(0.1)
    = 100 / 0.3162278
    = 316.23 mm

That's only valid if the original tip size is 1mm.

Or you could just use my online calculator.
« Last Edit: February 09, 2009, 02:48:46 PM by niko »

Offline Meerkat

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Re: modify bucket to 0.1mm
« Reply #94 on: February 09, 2009, 04:21:18 PM »
Isn't the tip(per) size (tipper quantity) irrelevant?
If I double the surface area on the rain gauge then sure I get double the water pouring through the funnel.
In other words it'll tip twice instead of once for the same rain rate.
if 1mm of rain falls over a surface area of 100mm2 that would be: 100*1 = 100ml
if 1mm of rain falls over a surface area of 200mm2 that would be: 200*1 = 200ml
So I would have to adjust the WD resolution to 0.5 i.e. for every tip only count half the quantity.
That's how I understand it from the WD setup below:

So if my tipper catches 2ml per tip and I double the surface area on the rain guage
the tipper is catching double the amount of water i.e. it will tip twice: 2*2ml = 4ml.
Therefore WD must only record half of it (4ml*0.5 = 2ml).

Am I missing something here?

By the way I did some tipping on my rain guage (WMR200) and I'm get conflicting reports from the console, the WMR gatherer and WD logs.
------------  -----  -----  -----  -----
Time of tip>  14h30  15h16  17h30  TOTAL
------------  -----  -----  -----  -----
WMR Console   1.1mm  1.0mm  1.1mm  3.2mm
WMR Gatherer  9.7    10.8   11.8   ?
WD Log        1.3mm  1.1mm  1.0mm  3.4mm

------------  ------  ------  -----  ------
The previous record in the log on the  4Feb2009 @ 16h55 recoded 0.7mm.
No other rain for the day. I also see some tips of 0.8mm in the logs.

Now I wonder what my tip size is.
Is WD making it's own rain or did I mess up a configuration somewhere.
Cheers,
Rainer

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Script download links always available on the first page of my threads

Offline niko

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Re: modify bucket to 0.1mm
« Reply #95 on: February 09, 2009, 04:34:55 PM »
The relationship is correct, if you increase the area 10x, you will reduce the tip to 1/10 of the original value - no argument there. But what you are missing is that you would only end up with a 0.1 mm tip, if you start with a gauge with a 1 mm tip and different brands and models of gauges have different tip sizes. If you 10x'd the area of a standard Davis gauge (which I wouldn'r recommend) you would end up with a 0.001 inch tip for instance.

Offline Meerkat

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Re: modify bucket to 0.1mm
« Reply #96 on: February 09, 2009, 04:36:30 PM »
Aha, I get it :D
If your tip size is 2ml and you want to bring it down to 0.5ml per tip then it would be 4x more accurate.
Which means a correction of 0.25 in WD.

Do you really get inaccurate rain gauges like that?
Cheers,
Rainer

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Script download links always available on the first page of my threads

Bashy

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Re: modify bucket to 0.1mm
« Reply #97 on: December 06, 2011, 04:25:11 PM »
Hi guys, i have had to add a new funnel @ 280mm diameter i think i got the correct setting for WD but could someone
please confirm it is 0.032 please cause i aint sure if it is recording the rain correctly?

Or is it 0.128 ?
« Last Edit: December 06, 2011, 06:42:57 PM by Bashy »

Offline SandhurstWX

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Re: modify bucket to 0.1mm
« Reply #98 on: December 06, 2011, 06:46:51 PM »
According to my calculations, the new setting in WD will be 0.128 mm for a funnel of diameter 280mm.

I use the calculations:-

   OSI Rain Gauge I/D =   100mm   Area =  7853.981   mm2
                  
   New funnel I/D =   280mm   Area =   61575.216   mm2
                  
   Area increase =   7.84   (New funnel area / original area)
                  
   Rain gauge original tip =    1   mm
                  
   So new tip =  0.12755102   mm   (original tip / area increase)


Hope it helps,
Ian

Offline niko

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Re: modify bucket to 0.1mm
« Reply #99 on: December 06, 2011, 06:49:27 PM »
I agree  :D

Bashy

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Re: modify bucket to 0.1mm
« Reply #100 on: December 06, 2011, 07:23:43 PM »
Thanks  a lot Ian, so glad i rechecked it, that will explain why the rain amounts were off

Thanks for the concurrence Niko ;)

Bashy

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Re: modify bucket to 0.1mm
« Reply #101 on: December 09, 2016, 02:02:26 PM »
Just my personal opinion but I think that's an unreasonable decrease in tip size. I wouldn't be trying to push that amount of water through that coffee mug sized OS rain gauge.

Hey Niko, just to let you know, i have been using the 0.1mm for years now with no issues at all, never hit the limit on the console
I have even had torrential rain a good few times, it works flawlessly :) I was surprised that it worked so well, like ya said, i have gone
from a larger coffee mug to a reasonable sized kitchen bowl lol :)

Offline bitsostring

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Re: modify bucket to 0.1mm
« Reply #102 on: May 20, 2017, 06:45:16 PM »
Thanks to all the above: required reading for those who are fed up with 1 mm tip on 100 mm gauge.

I went for a 200 mm funnel to bring the modified tip down to 0.25 mm (cp European Davis 0.2 mm) and it worked beautifully today: OS console 44.2 mm, WD shows 11.1 mm, CoCoRaHS 11.2 mm. (Good vertical rain for checking, not much wind.)

P.S. OS WMR200 manual says the rain gauge can handle 9999 mm/hr: I make that 2.78 tips/second (and I don't believe it - I think they mean the console display!).
It's meant to be fun. . .

 

cumulus