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07-10-2020, 22:24   #1
Oneiric 3
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V2 Pro Overestimating Rainfall Totals

I have noticed that my weather station, a V2 Pro, is obviously and seriously overestimating rainfall totals lately. For example, today, my manual gauge has recorded just under 8mm so far today, but the V2 is reading 23.4mm. Rainfall has been consistently light all afternoon and eving but is currently registering at rate of 10 to 12 mm/ph. Each registered tip is still the usual 0.2mm to 0.3mm each cycle etc but happening on a scale that is way too frequent for the type of rain that is falling.

I've read up on 'reed switches' etc, but it's all too complicated for my simple mind. Anybody any tips or suggestions as to what might be going wrong? And would it be expensive to fix? Thanks in advance.
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07-10-2020, 23:45   #2
axe2grind
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Take the bucket off and clean, could be simply a spider. Various bugs get into mine. Not often the bucket gets impacted, but it does happen.
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08-10-2020, 02:44   #3
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Clean the cups, also - what height is your gauge?
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08-10-2020, 13:44   #4
Oneiric 3
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Clean the cups, also - what height is your gauge?
Standard 1.5m height on a flat shed roof (which i have 'grassed up') that itself is around 9 ft above ground level. Not ideal but seems to work reasonably well.
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08-10-2020, 16:43   #5
Gaoth Laidir
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Standard 1.5m height on a flat shed roof (which i have 'grassed up') that itself is around 9 ft above ground level. Not ideal but seems to work reasonably well.
Rain gauges should be at ground level, with the top rim flush with the ground, but this is to reduce the chances of undersampling through blowover in windy conditions. If on a flat solid surface then over-reading due to splashing off the roof in heavy rain is possible, but not to the extent that you're seeing (and anyway you seem to have accounted for that by "grassing up" the roof. Does that mean you planted grass on it?).
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08-10-2020, 19:15   #6
Oneiric 3
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Does that mean you planted grass on it?).
Yes, to counteract any excess heating from what is a concrete roof. The rain gauge is attached to the complete system so not possible to place it in the ground. Spray at that height is not an issue though and in normal stratiform rainy conditions, wind or not, my Davis at least has constantly under-recorded rainfall by as much as 25/30% (checked against manual gauge and local Met station)

Checked bucket and tipper as advised. Bucket was clear but the tipper did have a lot of cobwebs covering it. Not sure if this created the problem (if anything, they would have prevented the spoons tipping rather than the other way around) but we'll see, as there is a forecast weak trough expected to move down later tonight so will check any rainfall totals that might come from it against the manual tomorrow.
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08-10-2020, 23:43   #7
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I had some very erratic rainfall readings for a time with my Davis V pro 2 some years ago. Cant remember exactly but I think I cleaned the connectors on the cables ( that fit into the sockets.....layman's terminology ) in the unit and the rain one was getting a bit rusty and I just happened to have the Broadband service man call and he was kind enough to snip off the old head and put on a new one. I have had to calibrate the gauge at times but it has been quite good this year. Would feel the need to check it regularly against a manual gauge for verification purposes.

By the way the Weather shop is showing some good special prices atm for anyone interested in getting one.

https://www.weathershop.co.uk/shop/b...ts/vantage-pro
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09-10-2020, 14:29   #8
Oneiric 3
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I had some very erratic rainfall readings for a time with my Davis V pro 2 some years ago. Cant remember exactly but I think I cleaned the connectors on the cables ( that fit into the sockets.....layman's terminology ) in the unit and the rain one was getting a bit rusty and I just happened to have the Broadband service man call and he was kind enough to snip off the old head and put on a new one. I have had to calibrate the gauge at times but it has been quite good this year.[/url]
For such an expensive machine though, rainfall readings ought to be more accurate.

I was in communication with Ryan Wilhour yesterday and he confirmed that something called a 'reed switch' is banjaxed. Going to go all out and purchase something called a 'single spoon' tipper, which is being sold as being more accurate than the original tipper that came with the Davis. Costs about 40 quid (including reed switch) and will probably take weeks to get here but might be just worth it. We'll see anyway.
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09-10-2020, 15:45   #9
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For such an expensive machine though, rainfall readings ought to be more accurate.

I was in communication with Ryan Wilhour yesterday and he confirmed that something called a 'reed switch' is banjaxed. Going to go all out and purchase something called a 'single spoon' tipper, which is being sold as being more accurate than the original tipper that came with the Davis. Costs about 40 quid (including reed switch) and will probably take weeks to get here but might be just worth it. We'll see anyway.
I'd be confident enough its the reed switch is the problem. Not a lot else can go wrong with rain gauges. I replaced a reed switch board on my Rainwise Gauge about a year ago and solved an issue i was having.
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09-10-2020, 18:47   #10
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Quote:
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Standard 1.5m height on a flat shed roof (which i have 'grassed up') that itself is around 9 ft above ground level. Not ideal but seems to work reasonably well.
Eeeek! That's 13ft and then some up in the air!

Is it possible the wind was causing false tips?

Quote:
Originally Posted by Oneiric 3 View Post
For such an expensive machine though, rainfall readings ought to be more accurate.

I was in communication with Ryan Wilhour yesterday and he confirmed that something called a 'reed switch' is banjaxed. Going to go all out and purchase something called a 'single spoon' tipper, which is being sold as being more accurate than the original tipper that came with the Davis. Costs about 40 quid (including reed switch) and will probably take weeks to get here but might be just worth it. We'll see anyway.
I had to change out mine a couple of year ago. Single spoon is alot more accurate, but still over records slightly, particularly in heavier rainfall and in showery conditions.

Ryan is very good to deal with and in fairness has keen prices on Davis stuff.

Edit: When you get the single spoon tipper and go to fit it, the unit goes in opposite to what you feel it should click in! Caught me out for a while!
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09-10-2020, 21:36   #11
Oneiric 3
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Eeeek! That's 13ft and then some up in the air!

Is it possible the wind was causing false tips?
Not at all. The 30mm + that I eventually recorded the other day occurred under flat calm conditions throughout. I really don't see wind being much of an issue anyway regarding the height of the gauge and anyway, I got my hands on this 'cone' back in 2017 that supposedly offsets, or at least reduces, any errors that might be created by excessive wind (which is rare enough around these parts anyway)

https://www.scaledinstruments.com/sh...ut-davis-logo/

The bird spikes are obscene though and I only use 4 of them and feel uncomfortable with even using that amount.

Cheers for the tips on the fittings. I am ordering reed switches and still have no clue what they are, where they are to be fitted and how they are to be fitted! but I'll figure it out when the challenge beckons.
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10-10-2020, 15:07   #12
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Not at all. The 30mm + that I eventually recorded the other day occurred under flat calm conditions throughout. I really don't see wind being much of an issue anyway regarding the height of the gauge and anyway, I got my hands on this 'cone' back in 2017 that supposedly offsets, or at least reduces, any errors that might be created by excessive wind (which is rare enough around these parts anyway)

https://www.scaledinstruments.com/sh...ut-davis-logo/

The bird spikes are obscene though and I only use 4 of them and feel uncomfortable with even using that amount.

Cheers for the tips on the fittings. I am ordering reed switches and still have no clue what they are, where they are to be fitted and how they are to be fitted! but I'll figure it out when the challenge beckons.
Reed switches are electrical components attached to a circuit board. The basics are when the bucket of a rain gauge tips a magnet passes the reed switch and causes two tiny pieces of metal to touch and make a circuit. Each pass is measured as 0.2mm or 0.1mm depending on what model rain gauge you have.
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