Topic: WH40 calibration - controlled enviroment

[Rocketman]

If I take 2 litres of water and sit above the drip tray of the WH40 and see how much is measured ?
Would I expect 2000 mm to be measured ?

[Gyvate]

I don't think it is that simple.
The unit is mm/m² - the amount of rain falling one m² of surface. One tip of the WH40 rain gauge corresponds to 0.1022 mm
The funnel surface is not 1 m² but much less. You can calculate the surface by simple geometrical math(s) measuring its diameter.
But I'm not going to do the math work for you now 

EDIT:
I think, what you want to do is not see if two litres come out when you pour two litres in - that's trivial.
I think you want to know what your console shows as measured rainfall

[hiljo]

If I take 2 litres of water and sit above the drip tray of the WH40 and see how much is measured ?
Would I expect 2000 mm to be measured ?

Yes, because you drip it in a controlled environment, 2L is 2L. But the question is why would you want that?

[davidefa]

If I take 2 litres of water and sit above the drip tray of the WH40 and see how much is measured ?
Would I expect 2000 mm to be measured ?

Sorry, no, 2 liters of water in the wh40 funnel will not record 2000mm of rain.
'Build a cilinder with 2 liters volume' with the same area base as the aperture of the wh40, the height of the cilinder is the amount of rain that should be recorded.
Using cm as unit of measure ( assuming diameter of wh40 funnel=7", base area=248.16cm2, not sure this is correct/accurate, but it was reported on the forum ):

Code: [Select]

2000cm3/248.16cm2=8.059cm=80.6mm
P.S.
My math is not so good, had to edit the post a couple of times : - (

[Gyvate]

@davidefa
that's doing the math for the OP.
I would have wanted him to this himself 
see my edited post
it depends where he measures what:
if he puts a container under the WH40, he will measure 2 litres 
if he looks at the console, the meausred rainfall will of course be different as the funnel doesn't have 1 m² surface but only around a quarter of it.

(diametre)² x pi / 4 is the formula - so your calculation based on 7 inches = 17.78 cm is correct

[hiljo]

But if you take a measuring cup, fill it with exactly 2000mL of water (or another amount), and pour it in slowly so the cup has the time to flip, 2000mL should be measured right?

[Rover1822]

You will have measured 2000 ml. I'm being facetious here, because you are measuring 2000 ml and what it will produce as a reading.

You will not get 200O ml as and output from the sensor. As Gyvate explained, the units are totally different and depend on surface  area, which can be worked out to volume per surface area.

mm per meter squared, the area of the cone is no where near a meter squared, so you have to do some math for the actual area. Once you do that , also the volumetric portion, you will arrive at a calculation for volume to mm per meter squared, for the volume you dumped into the sensor.

Edit to maybe explain further: The sensor knows it doesn't have a 1 meter square cone, it does know the surface area it has, it can measure the volume of rain that past through the bucket. It then extrapolates the known volume, (based on mass to tip the bucket) , and then can build a number as if it collected that number as though it does have a 1 meter square cone.

[hiljo]

Ah now I get it. One tip of the WH40 isn't 1mm, but is extrapolated so it represents 1mm of rainfall (over 1m2).

I thought that 1 tip was really 1mm, not extrapolated 

[Gyvate]

Ah now I get it. One tip of the WH40 isn't 1mm, but is extrapolated so it represents 1mm of rainfall (over 1m2).

I thought that 1 tip was really 1mm, not extrapolated 

in fact one tip equals 0.102 mm/m², not 1 mm

[Rocketman]

So 2000 mils of water spread over 248.16 cm X 8.059cm ( measured height for that volume ) 80.59 mm