Topic: 2018 Davis tipping bucket 28% error

[WXgeek]

in a recent rainfall event lasting 3 days my coco gauge measured 5.87" while my old Davis gauge read 4.25, these gauges are about 10 feet apart with the Davis gauge about 6 feet above the ground and the coco gauge at 2 feet, do you think the Davis gauge would benefit being upgraded to the tipping spoon?

[Mattk]

Has this always been the case? 28% is close enough to being a configuration error, metric v imperial cross contamination which can result in a 27% error

[WXgeek]

tbh I just recently got this Coco gauge because I was doubting the data so i'm not sure.

[PaulMy]

these gauges are about 10 feet apart with the Davis gauge about 6 feet above the ground and the coco gauge at 2 feet, do you think the Davis gauge would benefit being upgraded to the tipping spoon?

Measuring at 6 ft vs 2 ft above the ground can make a big difference in rain amount.
In my experience, with CoCoRaHS and VP2 being about the same height my original tipping bucket was usually higher. With about 3 years of the new tipping spoon it is usually right on or very close to the CoCoRaHS, and with a high rain rate the tipping spoon registering slightly higher.

Enjoy,
Paul

[Mattk]

You probably need to confirm if you have an imperial (0.01") tipper or a metric (0.2mm) tipper then confirm the the Weatherlink configuration matches the installed gauage.

[WXgeek]

these gauges are about 10 feet apart with the Davis gauge about 6 feet above the ground and the coco gauge at 2 feet, do you think the Davis gauge would benefit being upgraded to the tipping spoon?

Measuring at 6 ft vs 2 ft above the ground can make a big difference in rain amount.
In my experience, with CoCoRaHS and VP2 being about the same height my original tipping bucket was usually higher. With about 3 years of the new tipping spoon it is usually right on or very close to the CoCoRaHS, and with a high rain rate the tipping spoon registering slightly higher.

Enjoy,
Paul

Thank you for the info! I will upgrade from the old tipping bucket to the spoon.

[Mattk]

these gauges are about 10 feet apart with the Davis gauge about 6 feet above the ground and the coco gauge at 2 feet, do you think the Davis gauge would benefit being upgraded to the tipping spoon?

Measuring at 6 ft vs 2 ft above the ground can make a big difference in rain amount.
In my experience, with CoCoRaHS and VP2 being about the same height my original tipping bucket was usually higher. With about 3 years of the new tipping spoon it is usually right on or very close to the CoCoRaHS, and with a high rain rate the tipping spoon registering slightly higher.

Enjoy,
Paul

Thank you for the info! I will upgrade from the old tipping bucket to the spoon.

Doing that will not change the equation if you continue to have a metric/imperial miss match.

[weatherdoc]

I compared my Davis VP2 to my CoCoRaHS gauge (mounted on a 4x4 post a few inches apart at 5ft above ground) for several years (2008-2011) while I lived in Florida and consistently during heavy rain events (Florida thunderstorms and tropical cyclones), the Davis measured 15% less. During light and moderate rain they compared typically within 0.01". This is a well-documented issue with tipping rain gauges - they just can't tip fast enough in during heavy rain. I have done some casual comparisons in Virginia (since 2018) and now in North Carolina (since June) with similar results. Yesterday we had one of the heaviest rain events I've seen in years - leftover moisture from Helene, and my Davis measured 16% less than my CoCoRaHS. Davis reported (via WD) up to 6.8" per hour nearly instantaneous rainfall rates for several minutes.

[johnd]

@weatherdoc But the point is that the modern single tipping spoon is different in this respect from the older so-called tipping buckets. So it's important to know whether your VP2 was using spoon or buckets. Your old data was obviously buckets, but unsure about the recent data.

That said, a rate of 6.8"/hour is pretty intense at roughly 1 tip/5 seconds, but which should be OK for the spoon albeit maybe with minor errors, so maybe the max rate was actually higher still.

[Mattk]

Davis VP2 tipping buckets with correct configuration were renown for measuring under even up to 30% but have not seen a VP2 spoon out of spec as yet. With proper matching configurations the VP2 tipper could be adjusted even down from 30%, not so easy with the spoon. Confirming the configuration is the very first thing required in identifying rain anomalies.   

[weatherdoc]

@jonhnd - yes, even my 2018 VP2 has the "old" tipper, not the spoon. I had thought about switching but I've seen many complaints about the new spoon on the forum as well! At least I know my tipper is spot-on with my CoCoRaHS gauge for most precipitation and consistently 15% low with very heavy rain.

I agree with your assessment about the rate - maybe it would've been higher with the spoon.

[johnd]

@jonhnd - yes, even my 2018 VP2 has the "old" tipper, not the spoon. I had thought about switching but I've seen many complaints about the new spoon on the forum as well!

I do think this is a case where sampling a few forum posts or perhaps undue stress on negative posts can be misleading. In my experience (and that of many others, as I think mattk will probably confirm) the spoon offers a genuine improvement in accuracy over the old tipper. To what extent the spoon may still under report in very heavy rain is unclear, but the spoon rather than tipper mechanism should intrinsically ensure that performance is significantly better than the tipper.

Criticism of the spoon has I think often focused on the fact that trying to adjust/calibrate the spoon is not recommended by Davis because (a) unlike the tipper, the spoon mechanism is not really designed for easy adjustment; and (b) the response is very nonlinear which makes exact adjustment difficult. But other than this aspect, reports of measurement errors with the spoon are often traced back to familiar causes like using a reference gauge at a markedly different height or location from the ISS or mistakes in setting the gauge increment correctly on console or software. (It's possible also that there was a limited early batch of spoon mechanisms released with an incorrect adjustment.)

[Mapantz]

I absolutely detest these Davis-ass-licking posts, suggesting that some members that have expressed their dismay at the newer Davis spoon tippers are somehow wrong to criticise them.

The posts I see on here are so patronising, and come across that Davis products are exceptionally good and that no one should dare to argue against them.

Three spoon tippers I had in a year were all crap.

There's been plenty of reports about them across many forums. Coincidence? I think not.

[Mattk]

What I find is a waste of space is trying to establish what is wrong but all queries attempting to eliminate some times the bleeding obvious go unanswered.
 
And Yes there was obvious issues with the tipping buckets which I have raised over many years, And No I have not found a VP2 spoon as yet that is out of spec, that is a fact but if anybody has a VP2 spoon and especially multiple VP2 spoons that are duds then sent them my way and lets actually see what is the issue. There is no point whinging about the issue and not doing anything about it. 

[Mapantz]

I did do something about it.. I sent them back for a refund and stuck to the trusty see-saw tipper.

One retailer tested a unit I sent back and claimed it was actually reading low. There was absolutely no way in blue hell that was happening to me. I can't remember the percentage that I was told, but I remember working it out that it would have meant that 10mm rain events would be showing as 20mm on the spoon tipper.

I even recorded a rain rate of 414mm/hr on it once. It was very heavy rain, but there was no way that it was that high.

UK rain radars tend to max out at around 250mm/hr, and any radar returns showing those sorts of amounts are usually found in thunderstorms with hail in them, and they're not very frequent either. There was no thunderstorm occurring that day either.

[Mattk]

.... I even recorded a rain rate of 414mm/hr on it once. It was very heavy rain, but there was no way that it was that high.....

That is definatley possible when you understand just how the Davis rain rate is calculated as opposed to straight amount after an hour   

[Mapantz]

That is definatley possible when you understand just how the Davis rain rate is calculated as opposed to straight amount after an hour   

Maybe in a tropical climate, hurricane, or supercell thunderstorm..

That's more than double of what my see-saw tipper has ever recorded. It would also point straight toward the excessive rainfall totals that were being recorded, it was tipping too fast.

[Mattk]

That is definatley possible when you understand just how the Davis rain rate is calculated as opposed to straight amount after an hour   

Maybe in a tropical climate, hurricane, or supercell thunderstorm..

That's more than double of what my see-saw tipper has ever recorded. It would also point straight toward the excessive rainfall totals that were being recorded, it was tipping too fast.

No, not at all.

As I mentioned the only way to actually get a handle on these Spoons that supposedly have an issue is to properly analyze them, sending them back to a dealer will typically achieve nothing.

Like the Vue ISS spoon mechanism it was not to bad either but what could and did happen with the Vue if the debris screen went missing which it often did and with the quite large open hole just above the spoon then in heavy large droplet rainfall the spoon often took direct hits which caused the spoon to stutter hence overly record. Generally the comment was, rain gauge is stuffed, simple problem was, maintenance was stuffed. Anyway this scenario doesn't occur with the VP2 spoon.

And frankly the first of the VP/VP2 tippers were bad compared to the original WMII tipper design, the so called silver coated tippers were even worse and there were lots of thoughts based on the factory calibration method being used.

The VP2 spoon is greatly improved over the mid term tippers and until I actually have one in my hands that highlights the issue then I will have to always ask the relevant questions.   

[Mapantz]

sending them back to a dealer will typically achieve nothing.

You're kidding, right?

You think I am going to pay £90 for something that isn't working right, and keep it?

[Mattk]

Lets face it until the issue can be properly confirmed then the issue has also to be questioned. 

But lets get back to this actual issue which is an apparent 28% error?

Difference between a 0.2mm and 0.01" tipper or spoon is 27% so one should easily be able to see what the initial question should be and why?

So at this point have no idea why this query has been ignored?

[ocala]

I have had the the new spoon tipper roughly a year and a half.
After several tropical storms and summer rain events I can say the new tipper has never under reported. But during heavy rain events it almost always over reports. Been that way since it was installed. By the way this is comparing it to a coco gauge mounted at the same height on a 4x4 6ft high with their respective openings about 11 inches apart.
Really, even during light to moderate events the two gauges rarely match up exactly. But the new gauge performs much better then the old one for sure so it's a definite improvement.
I wish someone could come out with a gauge that could weigh the actual water. Now that would be something that could be a game changer. I talking about something like a coco cylinder that could be weighed as it fills up. Don't think you could establish a rain rate with something like that though .
Just my 2 cents

[Mattk]

Weighing type rain gauges are out there, Darrera, Kisters, Topac apogee are a few but probably not something everybody could afford in their backyard? Weighing gauges can handle like up to 120mm per minute, yes that's 7200 mm/hour. Many of the upper end tippers and due to the nature of tippers across different intensities can also store what enters the cone and be remeasured as if it was a simply open funnel conventional standard gauge. 

[ConligWX]

in a recent rainfall event lasting 3 days my coco gauge measured 5.87" while my old Davis gauge read 4.25, these gauges are about 10 feet apart with the Davis gauge about 6 feet above the ground and the coco gauge at 2 feet, do you think the Davis gauge would benefit being upgraded to the tipping spoon?

I personally upgraded to the tipping spoon since my tipping bucket was going faulty a few years back.  I ran a Cocorahs close by, to measure what output the new tipping spoon was, and it was better than the bucket setup I had.  the spoon was straight out of the box.  I did post some stats a while back.

https://www.wxforum.net/index.php?topic=37647.msg390167#msg390167

https://www.wxforum.net/index.php?topic=37647.msg391822#msg391822

I can only say in my opinion the upgrade worked for me.  though for others it would appear this is not the case.

[archae86]

For several years I ran a decade old Davis VP2 with tipping bucket, a Rainwise, and a CocoRahs-type analog gauge.  On average they were pretty close, but particular rain rates and wind conditions pushed them quite a bit away from each other, so I'm always sceptical of single-incident comparisons from other people posting.

More recently my Rainwise failed, and a pattern developed that my VP2 tipping bucket was averaging considerably lower than my analog gauge.  I imagined that my failure to clean or otherwise maintain it had given some loss, somehow.  Since I had to take it apart anyway, I decided to just buy and install a new tipping spoon.  I have about eight months of comparison now, and it is definitely reading much closer (actually so far on average slightly higher) to the CocoRahs.

When I took out the old bucket, I could not see obvious crud adequate to explain my previous problems, so I won't pretend to understand just what was wrong, but I'm happy I made the swap, which for me was clearly an upgrade.

Actually getting the old one out was a bit of trouble, and plastic retainer bits fractured (the whole ISS had spent over a decade out in New Mexico, so perhaps the plastic was more fragile than when new).  Also packing the full set of connecting wires (I have both solar and UV, so more wires than minimum) was again a pain.  So not quite a trivial task, but rewarding when done.

[havtrail]

I more interested in how your Rainwise rain gauge worked, if you have any info on that.

Rich K.