Author Topic: Davis bucket calibration  (Read 4542 times)

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Offline Mattk

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Re: Davis bucket calibration
« Reply #50 on: July 22, 2017, 12:29:08 AM »
....So by your reasoning even if the tipper can handle 6" an hour just as accurately as 2"
Who said it can?
The people who do this as a profession and respected opinions to back it up. What is your basis?

An opinion doesn't back anything up. can you try and answer a question with an actual subjective answer.

A blanket calibration rate of 6"/hr just doesn't cut anything, some really need to be a little subjective here.
« Last Edit: July 22, 2017, 12:30:58 AM by Mattk »

Offline CW2274

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Re: Davis bucket calibration
« Reply #51 on: July 22, 2017, 12:46:31 AM »
....So by your reasoning even if the tipper can handle 6" an hour just as accurately as 2"
Who said it can?
The people who do this as a profession and respected opinions to back it up. What is your basis?

An opinion doesn't back anything up.
OK. We'll just stick with all your facts.
Davis Wireless VP2 SHT31 24hr 67CFM FARS
RW Tipper w/ CoCoRaHS

Offline Mattk

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Re: Davis bucket calibration
« Reply #52 on: July 22, 2017, 03:17:02 AM »
....So by your reasoning even if the tipper can handle 6" an hour just as accurately as 2"
Who said it can?
The people who do this as a profession and respected opinions to back it up. What is your basis?

An opinion doesn't back anything up.
OK. We'll just stick with all your facts.

Now don't be like that, all I want is your justification not some opinion that is third hand.

Offline CW2274

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Re: Davis bucket calibration
« Reply #53 on: July 22, 2017, 02:52:18 PM »
....So by your reasoning even if the tipper can handle 6" an hour just as accurately as 2"
Who said it can?
The people who do this as a profession and respected opinions to back it up. What is your basis?
A blanket calibration rate of 6"/hr just doesn't cut anything, some really need to be a little subjective here.
Seems to "cut it" for these guys...See 6.0, bold lettering too boot. http://novalynx.com/manuals/260-2595-manual.pdf
Davis Wireless VP2 SHT31 24hr 67CFM FARS
RW Tipper w/ CoCoRaHS

Offline JudinNorman

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Re: Davis bucket calibration
« Reply #54 on: July 22, 2017, 03:46:34 PM »
Quite the discussion on this subject so I will spew my 2 cents about the subject.

Lets be honest the Davis tipping bucket rain gauge is inconsistant, I threw mine in the trash a few years ago and have had a Rainwise which is not only more accurate as well as cheaper than a Davis with my Vantage Pro 2,  I wouldn't go back.  Had a deluge yesterday with Pro 2 console showing high rain rate of 6.62", this am my manual gauge showed 0.75" and the Rainwise recorded 0.76",  even in steady, light rains the gauges don't differ more than a couple 0.02". 

I can just guess at the problem with Davis tippers from the smaller collection area, different tipping bucket shape than most quality tipping gauges. 

Lots of mention sometimes of water loss with high rain rates which is true however I don't think there's a tipping bucket that all the water actually flows out of the bucket when tipped, surface friction, dirt etc can make water stick which increases the weight of the bucket and more water needed to tip the elevated bucket.  Maybe that's one reason Novalynx says the 6" hour rate for calibration gives good overall results along with most of the time rainfall rates are higher than 1-2" an hour across the country.

When I got my Rainwise I called Rainwise and spoke to Lonnie White about the accuracy.  He told me they calibrate their gauges which are 8" using 8 ml per tip which is very close to Novalynx's 7.95 ml per tip for 2" hr rain rate for 8" diameter.
 
I would trust what Novalynx manual says,  it's about the same as what Rainwise does to calibrate their gauges which perform great.

Did Davis release anything to back up their claim about the new Aerocone improving rain gauge accuracy in wind ? Or likely just another company trying to improve their bottom line by sucking in customers with no hard data to back up their claim. 

Offline Mattk

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Re: Davis bucket calibration
« Reply #55 on: July 22, 2017, 03:54:19 PM »
....So by your reasoning even if the tipper can handle 6" an hour just as accurately as 2"
Who said it can?
The people who do this as a profession and respected opinions to back it up. What is your basis?
A blanket calibration rate of 6"/hr just doesn't cut anything, some really need to be a little subjective here.
Seems to "cut it" for these guys...See 6.0, bold lettering too boot. http://novalynx.com/manuals/260-2595-manual.pdf

So they claim but don't be selective on this one as nobody else really does and typically the general average calibration rain rate that most use is 2"/hour and no doubt you have noted this in your "internet research" but fail to mention it as it doesn't fit with your thinking.

This concept that 6"/hour is somehow a common rain rate is a little flawed but yes you will see it at times but nothing like what some claim.

Offline CW2274

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Re: Davis bucket calibration
« Reply #56 on: July 22, 2017, 04:08:29 PM »
....So by your reasoning even if the tipper can handle 6" an hour just as accurately as 2"
Who said it can?
The people who do this as a profession and respected opinions to back it up. What is your basis?
A blanket calibration rate of 6"/hr just doesn't cut anything, some really need to be a little subjective here.
Seems to "cut it" for these guys...See 6.0, bold lettering too boot. http://novalynx.com/manuals/260-2595-manual.pdf

So they claim but don't be selective on this one as nobody else really does and typically the general average calibration rain rate that most use is 2"/hour and no doubt you have noted this in your "internet research" but fail to mention it as it doesn't fit with your thinking.

This concept that 6"/hour is somehow a common rain rate is a little flawed but yes you will see it at times but nothing like what some claim.
It NEVER ceases to amaze me how some people on this board ask for proof of something, it's supplied for them, but STILL want to argue about it. (I can't possibly be wrong syndrome). Do what you want, you obviously know better than the rest of us.
Davis Wireless VP2 SHT31 24hr 67CFM FARS
RW Tipper w/ CoCoRaHS

Offline WheatonRon

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Re: Davis bucket calibration
« Reply #57 on: July 22, 2017, 05:23:12 PM »
Quite the discussion on this subject so I will spew my 2 cents about the subject.

Lets be honest the Davis tipping bucket rain gauge is inconsistant, I threw mine in the trash a few years ago and have had a Rainwise which is not only more accurate as well as cheaper than a Davis with my Vantage Pro 2,  I wouldn't go back.  Had a deluge yesterday with Pro 2 console showing high rain rate of 6.62", this am my manual gauge showed 0.75" and the Rainwise recorded 0.76",  even in steady, light rains the gauges don't differ more than a couple 0.02". 

...

Did Davis release anything to back up their claim about the new Aerocone improving rain gauge accuracy in wind ? Or likely just another company trying to improve their bottom line by sucking in customers with no hard data to back up their claim.

I agree 100% with your comments about the accuracy of the VP2. I have two of them and they never read the same, and when compared to my CoCo guage and my Rainwise 111 they are off too--usually under reporting. And yes, I have the Aerocone on one of my VP2 ISS, and it adds no value to accuracy (wind or no wind) in my opinion. If I could hookup my Rainwise to my VP2 without creating an ugly visual mess (my wife is not happy with my current PWS setups, visually speaking) I would do it, as it always is very close to my CoCo guage.

And I have tried calibrating the VP2s (using the "correct" approach noted above) and the results remain inconsistent. I wonder if Davis reads this Forum, as the less than stellar accuracy of its VP2 rain guage has been discussed in numerous postings and threads and the best they can do is the Aerocone? Yet Davis enhances its product with the outstanding SHT31 sensor. Occasionally Davis does hit a home run!
« Last Edit: July 22, 2017, 05:55:33 PM by WheatonRon »
Davis VP2 with Daytime FARS, SHT31 (2 complete systems-1 for uploading to the internet, the other system for test and play); Rainwise 111; CWOP--CW5020; WU--KILWHEAT17; CoCoRaHS--IL-DP-132

Offline Mattk

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Re: Davis bucket calibration
« Reply #58 on: July 23, 2017, 04:48:14 AM »
On the subject of Davis rain collectors (as apparently Novalynx has the only right answer and every other calibrator and gauge manufacturer have it wrong, arh well) with the VP1 and certainly the VP2 these certainly were not up to the same standard as the original WMII versions. Quite a bit of time was spent at that time analysing and comparing the WMII, VP1 & VP2 against standard 8" gauges and most was done under actual rain conditions. The results could not be disputed and were also sent to Davis.

Out of the box VP2 collectors were/are always on the low side and no where near the standard of the WMII but they can be calibrated, but they do need to be properly setup and out of the box there is no levelling mechanism, which is a weak design point. Without being able to be levelled then don't waste your time, but then this is no different to any tipping gauge. How VP2's are calibrated (as such) before leaving the factory is rather obscure based on tipper angles but setup properly they do work as per the spec.       

Offline gvmelbrty

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Re: Davis bucket calibration
« Reply #59 on: July 23, 2017, 02:23:50 PM »
There is hope for the Davis gauge.. Three years ago, I had decided to give up on the Davis and switch to the Rainwise gauge, but thought I'd give Davis one more chance via calibration.

A member here loaned me his Novalynx calibrator. I marked the adjustment screws showing the factory settings before I made changes. After several hours of runs and many adjustments, the final screw turns ended up almost exactly where they were from the start. ?? It had been under reporting as compared to a 4" Stratus gauge, so this didn't make a lot of sense. ..

Anyway, I went with it and it's been within .02 of the Stratus ever since... I do gently clean dirt from the tippers and bucket every week or two.

Offline dalecoy

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Re: Davis bucket calibration
« Reply #60 on: July 25, 2017, 04:53:27 PM »

I do have one suggestion for "verification".  [Perhaps you have already done this]

Do the same test on your manual gauge.  Same bottle, same rate, etc.  [Since you're getting a new bottle, then repeat on your Davis].


Yes, i will try but not sure it will be possible, depends on if i can balance the bottle on it, I will video it next time just to show
whats what :)

Have you had a chance to try this verification (of course, with appropriate calculation for the different diameter [capture area] of the manual gauge)?

Offline Bashy

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Re: Davis bucket calibration
« Reply #61 on: July 26, 2017, 01:35:42 AM »
Not so sure i need to do it for the manual gauge, all i need to do is pour what ever the calculated amount is into the center tub and check the measurement on the side, its pointless doing it with a manual gauge, i know the manual gauge is accurate, it would be like you measuring a cochoras (spell check?) gauge, i see no gain from doing this?

If i just pour a measured out 5mm down the spout, that is what it will measure, no mater how slow or how fast its poured, its manual ;)

Kind regards
Bashy

Offline dalecoy

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Re: Davis bucket calibration
« Reply #62 on: July 26, 2017, 10:11:11 AM »
Not so sure i need to do it for the manual gauge, all i need to do is pour what ever the calculated amount is into the center tub and check the measurement on the side, its pointless doing it with a manual gauge, i know the manual gauge is accurate, it would be like you measuring a cochoras (spell check?) gauge, i see no gain from doing this?

If i just pour a measured out 5mm down the spout, that is what it will measure, no mater how slow or how fast its poured, its manual ;)

...unless there is some previously-undiscovered error in the actual method of dripping water into the Davis gauge. 

The purpose of doing the exact same test, using the same method and equipment, is verification of the end-to-end results.

For instance: there is some amount of evaporation of water that wets the funnel.  Maybe not significant in this case, but maybe it is significant.  And that's just one possibility.

Another instance: at the conclusion of the test, there will be some water left in the delivery equipment.  That would be different if you "pour into the manual gauge" and "drip into the Davis gauge".  Maybe not significant, maybe significant.

Etc.....
« Last Edit: July 26, 2017, 10:25:08 AM by dalecoy »

Offline ValentineWeather

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Re: Davis bucket calibration
« Reply #63 on: July 26, 2017, 10:27:15 AM »
Results of yesterdays rain 2 separate locations 2 miles apart. 2 tipping buckets both calibrated with Novalynx calibrator at recommended 6 inch/hr rate and it never went over 2" per/hr rate.

Results
TBRG1- .33 actual .32
TBRG2- .22 actual .22

It works, not sure why. I'm sticking with it after finding the slower calibration rates didn't.

Randy, the Aviator is my father in 1963 with his Indian bike

Offline Bashy

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Re: Davis bucket calibration
« Reply #64 on: July 26, 2017, 11:45:31 AM »
I have it at 24.8mm, I cant see me doing much better than that, going to see what the real rain ☔ says about it and go from there...
« Last Edit: August 05, 2017, 10:47:22 AM by Bashy »
Kind regards
Bashy

Offline Bashy

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Re: Davis bucket calibration
« Reply #65 on: August 05, 2017, 10:48:02 AM »
I have been tweaking over the last few weeks, just had a decent rain, 5.4mm in about an hour, the manual says 5.6mm, thats pretty good, i have just twiddled a wee bit more
hopefully that should do it.
Kind regards
Bashy

Offline dalecoy

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Re: Davis bucket calibration
« Reply #66 on: August 05, 2017, 11:20:23 AM »
I have been tweaking over the last few weeks, just had a decent rain, 5.4mm in about an hour, the manual says 5.6mm, thats pretty good, i have just twiddled a wee bit more
hopefully that should do it.

It would be interesting to now re-do the "drip" test.

Offline Mattk

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Re: Davis bucket calibration
« Reply #67 on: August 05, 2017, 05:25:55 PM »
I have been tweaking over the last few weeks, just had a decent rain, 5.4mm in about an hour, the manual says 5.6mm, thats pretty good, i have just twiddled a wee bit more
hopefully that should do it.

You will never get an exact match, every time, all the time anyway. If you are in the range +/- 4 to 5% +/- 1 tip then you are within the spec

Offline ValentineWeather

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Re: Davis bucket calibration
« Reply #68 on: August 05, 2017, 06:21:32 PM »
Today had a T/storm with pea size hail dropping .34" ( 8.6mm) in 13 minutes reaching 5.4" (137.1mm) per/hr rate at heaviest point.

Using the 6" (152mm) per/hr rate calibration the tipping bucket still came up short .01 (.33) (0.25mm) vs actual (.34) in 8" SRG. 
Randy, the Aviator is my father in 1963 with his Indian bike

Offline jgentry

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Re: Davis bucket calibration
« Reply #69 on: August 06, 2017, 04:59:41 PM »
So.... If I use the Novalynx rain gauge calibrator for my Davis VP2 rain gauge, would it improve the accuracy of the Davis gauge?
Davis Vantage Pro2. SHT 31. WU: KXALJEMI2 & KALTHORS2 CWOP: C6353 & C6358

Offline ValentineWeather

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Re: Davis bucket calibration
« Reply #70 on: August 06, 2017, 05:17:18 PM »
So.... If I use the Novalynx rain gauge calibrator for my Davis VP2 rain gauge, would it improve the accuracy of the Davis gauge?

I would think so. You would at least know if the gauge is capable of repeatability. If not and it's very possible if like my Davis gauge and all over the place replace with Rainwise 111 8". https://www.rainwise.com/products/detail.php?ID=6697
Randy, the Aviator is my father in 1963 with his Indian bike

Offline jgentry

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Re: Davis bucket calibration
« Reply #71 on: August 06, 2017, 05:20:18 PM »
So.... If I use the Novalynx rain gauge calibrator for my Davis VP2 rain gauge, would it improve the accuracy of the Davis gauge?

I would think so. You would at least know if the gauge is capable of repeatability. If not and it's very possible if like my Davis gauge and all over the place replace with Rainwise 111 8". https://www.rainwise.com/products/detail.php?ID=6697

Thanks! How do you get the RW gauge to report to the Davis console or to WeatherUnderground etc. in one piece?
Davis Vantage Pro2. SHT 31. WU: KXALJEMI2 & KALTHORS2 CWOP: C6353 & C6358

Offline ValentineWeather

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Re: Davis bucket calibration
« Reply #72 on: August 06, 2017, 05:27:34 PM »
So.... If I use the Novalynx rain gauge calibrator for my Davis VP2 rain gauge, would it improve the accuracy of the Davis gauge?

I would think so. You would at least know if the gauge is capable of repeatability. If not and it's very possible if like my Davis gauge and all over the place replace with Rainwise 111 8". https://www.rainwise.com/products/detail.php?ID=6697

Thanks! How do you get the RW gauge to report to the Davis console or to WeatherUnderground etc. in one piece?

rj11 phone line Green/yellow together go on 1 post and red on other rainbucket terminal. Black is not used.
Randy, the Aviator is my father in 1963 with his Indian bike

Offline jgentry

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Re: Davis bucket calibration
« Reply #73 on: August 06, 2017, 05:39:33 PM »
So.... If I use the Novalynx rain gauge calibrator for my Davis VP2 rain gauge, would it improve the accuracy of the Davis gauge?

I would think so. You would at least know if the gauge is capable of repeatability. If not and it's very possible if like my Davis gauge and all over the place replace with Rainwise 111 8". https://www.rainwise.com/products/detail.php?ID=6697

Thanks! How do you get the RW gauge to report to the Davis console or to WeatherUnderground etc. in one piece?

rj11 phone line Green/yellow together go on 1 post and red on other rainbucket terminal. Black is not used.

Thanks!
Davis Vantage Pro2. SHT 31. WU: KXALJEMI2 & KALTHORS2 CWOP: C6353 & C6358

Offline Phil23

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Re: Davis bucket calibration
« Reply #74 on: August 06, 2017, 06:10:48 PM »
While I haven't touched my own VP2 in regards to rain calibration, I'm curious about how others measure the bucket tips without upsetting their live data.

It would make simple sense to me to unplug the rain sensor from the ISS & patch it into a micro (Micromite, Arduino etc), and then log the tips in there.

Has anyone tried that sort of approach?

It would make it easy to log the bucket tips along with time stamps & compare results at different "Rain rates".

Phil.