Author Topic: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements  (Read 15855 times)

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Offline George Richardson

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #50 on: April 29, 2016, 08:14:08 AM »
From Experience  :?, I would urge you not to adjust more than ONE (1) turn, then retest. I followed that method (think I made 3 turns) and got my VP2 way off in the other direction. Took nearly a year of back and forth but finally have mine consistently within about 1 - 2% difference to adjacent Stratus gauge.

Good Luck,

George

Offline WheatonRon

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #51 on: April 29, 2016, 08:16:31 AM »
Good suggestion. I thought 6 turns on an instrument made just a few months ago sounded too drastic.


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Davis VP2 with SHT31 (3 complete VP2 systemsó2 with a daytime fan and 1 that has a 24 hour fan); CWOP--CW5020, FW3075 and FW4350; WU--KILWHEAT17, KILWHEAT36 and KILWHEAT39; WeatherCloud.net; CoCoRaHS--IL-DP-132; and Weatherlink 2.0

Offline darkstarpa

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #52 on: April 30, 2016, 02:54:07 PM »
Quick update on my post #37.
We have had 2 very light rainfall events the past week  in NW NJ.
So far, my reporting seems to be in the accepted zone of 4 weather stations in a 1/2 to 2 mile sq mile radius.
I have been spot on with one station and slightly below with a 2 others by a few tenths of an inch of qpf. Positive step imop.
Cleaned the entire station out this afternoon as the forecast is for around a 1/2 inch of rain late tonight through tomorrow.

I did notice that the bubble level on the ISS set up is 1/2 way in and out of the circle.

Also, I have yet to purchase the CoCoRaHS rain set up to compare.

More news after this event.
« Last Edit: April 30, 2016, 03:01:28 PM by darkstarpa »

Offline darkstarpa

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #53 on: May 01, 2016, 06:27:57 PM »
The results are in with the most recent event.
My station recorded 0.13 inches of rain.
All other stations in the area were 0.33 to a high of 0.43 inches of rain.

At this point, i am frustrated as I paid decent money for the set up.

Not sure what my plan is exactly. Sorta of just want to toss it in the trash. :-x

I assume if I call Davis again, they will tell me that their systems rarely fail and rain totals vary across areas.

Offline WheatonRon

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #54 on: May 01, 2016, 07:09:09 PM »
My station is also under reporting rain when compared with Mr. CoCo. I will be trying to adjust my station by turning the screws under the two tipper buckets. Davis told me 1 counterclockwise turn for each 6% under reporting error. As suggested by George Richardson above, probably the best approach, which I am going to follow, is try one full turn and see what happens in the next few rainfalls. However, you really do need a reliable nearby source (a few feet away at most) to compare to and Mr. CoCo is perfect for that.
« Last Edit: May 01, 2016, 09:22:31 PM by WheatonRon »
Davis VP2 with SHT31 (3 complete VP2 systemsó2 with a daytime fan and 1 that has a 24 hour fan); CWOP--CW5020, FW3075 and FW4350; WU--KILWHEAT17, KILWHEAT36 and KILWHEAT39; WeatherCloud.net; CoCoRaHS--IL-DP-132; and Weatherlink 2.0

Offline CW2274

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #55 on: May 01, 2016, 07:09:48 PM »
I assume if I call Davis again, they will tell me that their systems rarely fail and rain totals vary across areas.
Don't know about the "rarely fail" part, but the "rain totals vary" statement is completely correct. You might as well compare high wind gust while you're at it.

Offline dalecoy

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #56 on: May 01, 2016, 09:16:12 PM »

Also, I have yet to purchase the CoCoRaHS rain set up to compare.

Offline ValentineWeather

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #57 on: May 01, 2016, 11:10:27 PM »
Using a medicine or eye dropper you can adjust the stops. The Davis 6" diameter should be close to Novalynx 6" which tips at 0.01" of water = 4.63 ml. If you fill dropper to 10 ml. and slowly drip into tipper it should tip at 5.73 water left in dropper.
This needs to be checked with gauge as level as possible. 
Randy

Offline CW2274

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #58 on: May 02, 2016, 01:33:51 AM »
Using a medicine or eye dropper you can adjust the stops. The Davis 6" diameter should be close to Novalynx 6" which tips at 0.01" of water = 4.63 ml. If you fill dropper to 10 ml. and slowly drip into tipper it should tip at 5.73 water left in dropper.
This needs to be checked with gauge as level as possible.
Randy, the Davis is 6.5" for 5.44ml per tip.

Offline ValentineWeather

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #59 on: May 02, 2016, 08:03:16 AM »
Using a medicine or eye dropper you can adjust the stops. The Davis 6" diameter should be close to Novalynx 6" which tips at 0.01" of water = 4.63 ml. If you fill dropper to 10 ml. and slowly drip into tipper it should tip at 5.73 water left in dropper.
This needs to be checked with gauge as level as possible.
Randy, the Davis is 6.5" for 5.44ml per tip.

(Thanks) Don't know why I was thinking 6". Same thing its an easy way to see how far off the stops are but use the 5.44ml. Someone reported a new unit came in unadjusted not long ago.
Randy

Offline Coolerman

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #60 on: May 02, 2016, 08:56:01 AM »
Well I got my CoCo gauge mounted on a 4x4 treated pole yesterday. Pole is 24" in the ground. Top of gauge is 2' above ground and 5" above the pole which was cut at a 45 degree angle. This was just in time for a brief, single cloud, shower that came through.

CoCo said .05" , Davis said .02" Not off to a good start...

The CoCo is about 40 feet from the Davis currently, so this data is probably meaningless but there it is.
Davis VP2 Pro Plus w/FARS, CoCoRaHS Station KY-GD-2

Offline Scotty51

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #61 on: May 02, 2016, 09:52:07 PM »
My station is also under reporting rain when compared with Mr. CoCo. I will be trying to adjust my station by turning the screws under the two tipper buckets. Davis told me 1 counterclockwise turn for each 6% under reporting error. As suggested by George Richardson above, probably the best approach, which I am going to follow, is try one full turn and see what happens in the next few rainfalls. However, you really do need a reliable nearby source (a few feet away at most) to compare to and Mr. CoCo is perfect for that.

Curious if your adjustments screws were all the way down from the factory ?
I posted about mine before, was under-reporting 40%-60%, lost count of how many turns I made to get it adjusted. After a few adjustments I've got it very close to the manual gauge, within 0.01".
 
The other thing you have to do is get the buckets tipping with an equal amount of water, the buckets are asymmetrically weighted so one screw will be a little higher than the other when properly adjusted.

Offline WheatonRon

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #62 on: May 02, 2016, 10:20:33 PM »
Haven't got around to opening the ISS again to tweak the tippers yet.  Will let you know what happens. Glad you were able to your rainfall gauge accurate, Scotty! But this surprises me. My new ISS was manufactured in January, four months ago. Why should we be having to recalibrate so soon? Damage in transit? :mad:
« Last Edit: May 02, 2016, 10:37:15 PM by WheatonRon »
Davis VP2 with SHT31 (3 complete VP2 systemsó2 with a daytime fan and 1 that has a 24 hour fan); CWOP--CW5020, FW3075 and FW4350; WU--KILWHEAT17, KILWHEAT36 and KILWHEAT39; WeatherCloud.net; CoCoRaHS--IL-DP-132; and Weatherlink 2.0

Offline SpartanWX

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #63 on: May 14, 2016, 03:46:08 PM »
At the end of the day, it is unfortunate to say a $30 rain gauge is more accurate than a $500+ Davis station! When I first got into weather as a hobby a decade or so ago, I thought spending the dollars on a Vantage Pro 2 would put me at the top of enthusiasts. Now I must conclude that the rain measurements being reported by my Pro 2 are only "directionally correct" and if rainfall is a critical measurement (generally not) I should rely on Mr. CoCo!
You are not paying for accuracy as much as you are paying for not having to go out in the middle of a torrential downpour to see how much it has/is raining, empty gauge, make recordings in your waterproof journal with your waterproof pen, etc. 

Offline Coolerman

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #64 on: May 16, 2016, 10:56:11 AM »
For the money that Davis charges they could get the darn tipping bucket calibrated properly BEFORE it gets into a consumers hands! I have two Davis rain gauges. One part of the 6163 ISS and a separate stand alone unit that has yet to be mounted. Once I get my pole installed and move the Davis ISS to that, AND get the separate Davis rain gauge mounted at the CoCoRaHS recommended height of 2', I will be able to do some comparisons between the two new Davis gauges, one at 5', and one at 2'. Those readings will be compared to Mr. CoCo. If they are off by a lot, (I understand about all the variables)  then Davis is going to re-calibrate them, not me.
Davis VP2 Pro Plus w/FARS, CoCoRaHS Station KY-GD-2

Offline zackdog

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #65 on: May 16, 2016, 11:15:28 AM »
I have been following this thread for quite a while and yesterday had a huge (for my location) precipitation event, actually an all-time record.  It started at noon with enough pea sized hail to turn the ground white, then turned to rain.  I fully expected a large difference between my VP2 and COCO rain collectors.  This morning when I took my COCO reading it was 0.82 inches.  I then checked the VP2 readings for the last 24 hour period and it was also 0.82 inches.  The high rain rate for yesterday was 1.35 "/hr.  I don't know why the two are identical, but maybe because the event started with a significant amount of hail that slowed the flow of heavy rain enough to get good readings from the tipping buckets.  It is also possible that the COCO did not catch as much of the hail.  I really don't know why, but they were identical.

Mark
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VP2 uploading via Vue console to CWOP, WU, PWS, and Weathercloud.


Offline dalecoy

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #66 on: May 16, 2016, 11:34:24 AM »
Once I get my pole installed and move the Davis ISS to that, AND get the separate Davis rain gauge mounted at the CoCoRaHS recommended height of 2', I will be able to do some comparisons between the two new Davis gauges, one at 5', and one at 2'. Those readings will be compared to Mr. CoCo.

We are all looking forward to your carefully-controlled comparisons.

Offline WheatonRon

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CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #67 on: May 19, 2016, 10:48:53 PM »
I replaced my 11 year old VP2 with a new ISS a few weeks ago. Subsequently, my location had a significant rain fall while I was away for a few days. Before leaving, I quickly looked at the rain collector and it was apparently clear. While away, I looked at my CWOP rainfall amounts and noted they were way off from nearby airports and fellow nearby reliable CWOP contributors. I was off by over 2 inches when I returned. Upon inspection, the rain collector was full of water. My guess it came from Davis with a partially blocked collector hole and some unknown substance completed the task of plugging the collector. Moral of the story? Ensure your new rain collector is clear of "stuff" including ensuring Davis original specs are present! For the rain collector, clean your new ISS with a pipe cleaner before relying on it!!!

This issue may have contributed to the difference I was experiencing (before this event), of under reporting rainfall when compared with my CoCo gauge discussed previously in this thread.
 :-)

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« Last Edit: May 19, 2016, 11:19:39 PM by WheatonRon »
Davis VP2 with SHT31 (3 complete VP2 systemsó2 with a daytime fan and 1 that has a 24 hour fan); CWOP--CW5020, FW3075 and FW4350; WU--KILWHEAT17, KILWHEAT36 and KILWHEAT39; WeatherCloud.net; CoCoRaHS--IL-DP-132; and Weatherlink 2.0

Offline mattgrahamca

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #68 on: May 27, 2016, 10:04:35 PM »
Well hello from rain drenched North Houston.

I wanted to give you update on the COCO vs Davis rain debate.

Thursday 7am-Friday 7am
COCO - 7.28 inches of rain
Davis - 6.40 inches of rain
12.1% off
Friday 7am to Friday 8pm
COCO - 4.90 inches of rain
Davis - 4.03 inches of rain
17% off

So i know the argument, A man with two watches never know the time.  However, this rain gauges are situated within 5 ft of each other with little difference in exposure to rain.



Offline WheatonRon

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #69 on: May 27, 2016, 10:16:05 PM »
Interesting. We had a bunch of rain this week and my results are as follows:

CoCo. 1.80 inches
DVP2.  2.10

Subsequent rainfall

Coco. .20
DVP2 .31


I think my VP2 was loose on my pole which may have resulted in more rain than my
Mr. CoCo. Will see after tonight after I tightened the pole supporting my PWS. Bottom line, there will always be differences, but they should be less than significant. In my case, the differences were more than significant.

Davis VP2 with SHT31 (3 complete VP2 systemsó2 with a daytime fan and 1 that has a 24 hour fan); CWOP--CW5020, FW3075 and FW4350; WU--KILWHEAT17, KILWHEAT36 and KILWHEAT39; WeatherCloud.net; CoCoRaHS--IL-DP-132; and Weatherlink 2.0

Offline ValentineWeather

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #70 on: May 27, 2016, 10:21:16 PM »
I have a Rainwise setup at one of my stations it follows the Cocorahs very closely.

Calibration means so much on these tipping bucket gauges. The Rainwise came calibrated at 5" per hour rate when I tested, instead of the 1" per hr. rate some tipping buckets are factory set.

My Texas Electronics was set at the 1" per hour rate and worked great for snow in the winter but can't keep up in a thunderstorm so I calibrated gauge at 3" per hr.  It recorded 4.31" and the 8" standard was 4.32" during our record rain last week.  The Cocorahs came up short at 4.21". This storm included hail which I'm sure bounced out of the Cocorahs.
Randy

Offline WheatonRon

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #71 on: May 27, 2016, 10:30:57 PM »
Agree. Since my VP2 ISS is brand new, I hope the difference can be attributed to me not properly securing my PWS to my fence post. I should not have to recalibrate a new ISS fresh from Davis via Scaled Instruments!  I hope I can get the two gauges reasonably close in rainfall totals before I die. Which Rainwise gauge do you use?
Davis VP2 with SHT31 (3 complete VP2 systemsó2 with a daytime fan and 1 that has a 24 hour fan); CWOP--CW5020, FW3075 and FW4350; WU--KILWHEAT17, KILWHEAT36 and KILWHEAT39; WeatherCloud.net; CoCoRaHS--IL-DP-132; and Weatherlink 2.0

Offline ValentineWeather

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #72 on: May 27, 2016, 10:38:30 PM »
Agree. Since my VP2 ISS is brand new, I hope the difference can be attributed to me not properly securing my PWS to my fence post. I should not have to recalibrate a new ISS fresh from Davis via Scaled Instruments!  I hope I can get the two gauges reasonably close in rainfall totals before I die. Which Rainwise gauge do you use?
This little jewel. Very well made I just remove the counter leave enough wire attached to counter for using for calibrator if needed and splice into the existing line from Davis gauge using same plug or get a new one if you don't want to cut into it. Believe those are 4 wire plugs.
 
http://www.rainwise.com/products/detail.php?ID=6697&Category=Rain_Gauges:Wired&pageNum_cart=/products/index.php
Randy

Offline CW2274

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #73 on: May 27, 2016, 11:12:50 PM »
Agree. Since my VP2 ISS is brand new, I hope the difference can be attributed to me not properly securing my PWS to my fence post. I should not have to recalibrate a new ISS fresh from Davis via Scaled Instruments!  I hope I can get the two gauges reasonably close in rainfall totals before I die. Which Rainwise gauge do you use?
This little jewel. Very well made I just remove the counter leave enough wire attached to counter for using for calibrator if needed and splice into the existing line from Davis gauge using same plug or get a new one if you don't want to cut into it. Believe those are 4 wire plugs.
 
http://www.rainwise.com/products/detail.php?ID=6697&Category=Rain_Gauges:Wired&pageNum_cart=/products/index.php
Ron, this is the exact same tipper I told you about 2 months ago in a PM. I have it wired as above and reports just as the Davis would.

Offline WheatonRon

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #74 on: May 27, 2016, 11:20:03 PM »
Thanks to both you (Jim) and Randy. Since the Blackhawks lost to St. Louis a few weeks ago, I have not been the same retired CPA as before. Now I must cheer for the PENS and wait til next year, but hopefully my rain gauge issue will be resolved by then. Fortunately, I am also a big Denver Broncos fan and they won the Super Bowl this year, so I am not totally wasted!
« Last Edit: May 27, 2016, 11:23:27 PM by WheatonRon »
Davis VP2 with SHT31 (3 complete VP2 systemsó2 with a daytime fan and 1 that has a 24 hour fan); CWOP--CW5020, FW3075 and FW4350; WU--KILWHEAT17, KILWHEAT36 and KILWHEAT39; WeatherCloud.net; CoCoRaHS--IL-DP-132; and Weatherlink 2.0