[41south]

Hi all

I am trying to work out what the correct setting for my rain gauge is, but I just seem to end up confusing myself 

I purchased an Oregon Scientific PCR800 as per here https://www.oregonscientificstore.com/p-...tions.aspx

It comes as a wireless unit but I've just converted it to wired by soldering across the reed switch - this works fine and records bucket tips as expected.

As far as I can work out it's 1mm per tip - does that sound right? My intention is mod it with a 20cm funnel on top which - again if I haven't confused myself - will make it a 0.2mm per tip unit

Can anyone help confirm my assumptions and math please 

[engolling]

To prevent wrong assumptions - do you have a circular or a rectangular funnel?
I assume you have a circular one, since you only have one number given.
The area of a circle is A= r^2*pi, this would give you an area of 314cm^2.

But I can't bring my thoughts to an end since I can not find the area of the PCR800 sensor and the resolution of one tip on the webpage. Do you have further information?

Regards,
engolling

[41south]

Hi engolling

Yes I struggle with the same lack of information I think. 

For your first question, yes it is a round gauge and a round funnel

The measured diameter of the PCR800 is 100mm/10cm. The only info I have found seems to point to a 1mm tip - but this seems large I think?

Edit: I have found a quote which says "The bucket tips every 0.04" of rain that accumulates" - that does equate to 1.02mm per tip

[uncle_bob]

Maybe get an analogue gauge and run some comparisons to calibrate it.
Since you're in Wellington you won't have to wait too long for it to rain :p
(I'm from HB  )

[41south]

Well ...... funny you should say that   Yes I was thinking the same thing, might drop into Bunnings and grab one. I'm pretty sure the math is right on this but just thought somebody could confirm it

[engolling]

I can confirm a resolution of 1mm/tip
http://global.oregonscientific.com/manual/PCR800.pdf

The ratio between a diameter of 100mm and 200mm is 7850mm²/31400mm² = 1/4
So it should be 0,25mm/tip with the 20cm diameter funnel, if I am not wrong.

engolling

[JT118]

Here is how to calibrate a Rain Gauge of any description.

https://www.meteocercal.info/forum/Threa...07#pid2607

and here:

https://www.meteocercal.info/forum/Threa...alibration

The simplest and best way to do this is to measure the cross sectional area of the rain collector of your gauge and then do the arithmetic and calibration outlined in posts above. It is unlikely to be 1mm per tip. Most gauges run between FO gauges at .280mm/tip to Davis and a multitude of others at at 0.254 and 0.200 mm per tip depending on the buckets used. The amount of water in the bucket at the point of tip is related to the amount of rainfall only through the maths in the links above.

Interesting numbers 1mm of rain over 1 sq.metre = 1 litre of water, and 1mm rain over a hectare = 10 cubic m. of water.

[41south]

JT

I knew somebody with all the math knowledge would jump in here

When you say measure the the cross section area of the rain collector - do you mean the actual tipping bucket or the opening/funnel?

[werk_ag]

JT

I knew somebody with all the math knowledge would jump in here

When you say measure the the cross section area of the rain collector - do you mean the actual tipping bucket or the opening/funnel?

I think its the opening/funnel, but better will be wait for the answer from JT118, that for sure will come shortly.

...
It is unlikely to be 1mm per tip. Most gauges run between FO gauges at .280mm/tip to Davis and a multitude of others at at 0.254 and 0.200 mm per tip depending on the buckets used.

I was also quite surprised by an 1mm resolution, as you said it isn't usual even among low cost rain gauges like FO. I did some research on the Oregon Scientific PCR800 rain gauge and all that I found points to a 1mm resolution. Its strange, but seems to be true.

[werk_ag]

...
When you say measure the the cross section area of the rain collector - do you mean the actual tipping bucket or the opening/funnel?

I think its the opening/funnel, however it will be better waiting for the answer from JT118, that for sure will come shortly.

...
It is unlikely to be 1mm per tip. Most gauges run between FO gauges at .280mm/tip to Davis and a multitude of others at at 0.254 and 0.200 mm per tip depending on the buckets used.

JT118
I was also quite surprised by an 1mm resolution, As you said it isn't usual even among low cost rain gauges like FO. I did some research on the Oregon Scientific PCR800 rain gauge and all that I found points to a 1mm resolution. Its strange,  but seems to be true.