modify bucket to 0.1mm

[Bashy]

Yeah that makes more sense lol, told you i was a thicket pmsl...

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

[niko]

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:

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.

[Meerkat]

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

[niko]

Better 

But:

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.

[Meerkat]

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.

[niko]

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.

[Meerkat]

Aha, I get it
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?

[Bashy]

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 ?

[SandhurstWX]

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

[niko]

I agree 

[Bashy]

Thanks  a lot Ian, so glad i rechecked it, that will explain why the rain amounts were off

Thanks for the concurrence Niko