Author Topic: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements  (Read 15533 times)

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Offline WheatonRon

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #25 on: March 25, 2016, 10:55:16 PM »
The wind was not really a factor. I will check to ensure the VP2 is level and if so, I will try another heavy rain and see what happens.
Davis VP2 with SHT31 (3 complete VP2 systems—2 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 ocala

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #26 on: March 26, 2016, 07:15:17 AM »
Agree with Don in that the best comparison is having the gauges as close as possible. Preferably back to back.

Offline ValentineWeather

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #27 on: March 26, 2016, 08:17:52 AM »
Being close is good but careful you don't get splash from one gauge to the other.
 
The more I've calibrated TB's with a calibrator the more I understand the limitations of tipping buckets. The best accuracy is within the sweet zone of calibration. Outside this range the error factor increases without software correction.
 
The siphon type TB handles higher rain rates better with smaller error factors even with 20" per /hr rates but they don't do well with slower rates <1" per hour.  My understanding you won't get a first tip until .02 on the siphon gauge which is unacceptable for me and has reports of being erratic at slow rates.

Realistically the best rain gauge is the manual, preferably the US standard 8" diameter but the 4" will do being it only runs $35. Unfortunately they don't plug into the Davis ISS.  :-(
« Last Edit: March 26, 2016, 02:29:31 PM by ValentineWeather »
Randy

Offline Scotty51

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #28 on: March 26, 2016, 10:12:10 PM »
Don't feel bad, I got the same manual gauge a few weeks ago and my VP2 is not even close. The Davis is under reporting rain by 70% to 80%, this is with at least 0.15" of rain each day I compared. All the obvious things are not the problem, I just think it wasn't properly calibrated when leaving the factory, adjustment screws were basically screwed all the way down.

I've adjusted the screws, got the buckets tipping with an equal amount (roughly), and the last rain was Davis 0.18", manual 0.20", so it's a lot closer than it was. Going to rain tonight/tomorrow so I'll see how it does after that last reading.


Offline WheatonRon

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CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #29 on: March 26, 2016, 10:22:31 PM »
As I discussed in a separate thread, my 11 year old ISS was significantly under reporting rain fall. As a result, I purchased a new ISS and although the rain fall measurement is much better with the new ISS, it still seems off and may not be calibrated right. I checked whether the station is level or not and it is. Hopefully another storm will indicate the issue was isolated and not a calibration problem. That sounds hard to fix.
« Last Edit: March 26, 2016, 11:34:51 PM by WheatonRon »
Davis VP2 with SHT31 (3 complete VP2 systems—2 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 Scotty51

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #30 on: March 27, 2016, 12:22:11 PM »
As I discussed in a separate thread, my 11 year old ISS was significantly under reporting rain fall. As a result, I purchased a new ISS and although the rain fall measurement is much better with the new ISS, it still seems off and may not be calibrated right. I checked whether the station is level or not and it is. Hopefully another storm will indicate the issue was isolated and not a calibration problem. That sounds hard to fix.

It's been a somewhat easy fix for me, yesterday/today the rain total was Davis 0.16, manual 0.17.

Offline ValentineWeather

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #31 on: March 27, 2016, 12:38:20 PM »
Good job Scotty, surprised the gauge was sent out without the stops adjusted.

The Novalynx 6" gauge buckets are designed to tip 0.01" of water = 4.63 ml calibrated at 4" per hr rate. Using eye dropper you can adjust the stops and come close. The Davis tippers if gauge is true 6" should be very close.
Randy

Offline zackdog

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #32 on: April 17, 2016, 09:52:20 AM »
Just had a two day snow event and had the heater in the VP2 rain collector on the whole time.  Friday into Saturday was 6.6" of snow, Saturday into Sunday was 7.1".  Measurements were made at 7:00 am for CoCoRaHS. Following  are the SWEs.

Day             CCRHS            VP2           Snow
Sat 7:00         0.70"            0.63"           6.6"
Sun 7:00         0.59"            0.06"           7.1"

Mark 
"You don't need a weatherman to know which way the wind blows." - Dylan

Vantage Pro2 Plus w/ 24 hr FARS and (2) VantageVues

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


Offline ValentineWeather

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #33 on: April 17, 2016, 10:09:56 AM »
Just had a two day snow event and had the heater in the VP2 rain collector on the whole time.  Friday into Saturday was 6.6" of snow, Saturday into Sunday was 7.1".  Measurements were made at 7:00 am for CoCoRaHS. Following  are the SWEs.

Day             CCRHS            VP2           Snow
Sat 7:00         0.70"            0.63"           6.6"
Sun 7:00         0.59"            0.06"           7.1"

Mark

Ouch! that .06 hurts... :-(
Randy

Offline WheatonRon

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CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #34 on: April 17, 2016, 10:24:44 AM »
Just had a two day snow event and had the heater in the VP2 rain collector on the whole time.  Friday into Saturday was 6.6" of snow, Saturday into Sunday was 7.1".  Measurements were made at 7:00 am for CoCoRaHS. Following  are the SWEs.

Day             CCRHS            VP2           Snow
Sat 7:00         0.70"            0.63"           6.6"
Sun 7:00         0.59"            0.06"           7.1"

Mark

Please confirm that Sunday was not a typo! Surely, you meant .60 and not .06? If truly only .06, Davis should announce a recall!
Davis VP2 with SHT31 (3 complete VP2 systems—2 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 miraculon

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #35 on: April 17, 2016, 10:32:30 AM »
The heater seems to evaporate snowfall that is light. I have seen something similar with mine. If the snowfall is heavy, and the heater can keep up with it, then the error isn't as bad.

I have toyed with the idea of using some kind of proportional control with a low PWM duty cycle for light snow conditions.

When I first built my heater (a virtual "clone" of the Davis one), I had a 60°F bi-metal thermostat on the heater board. I might go back to it, since I seemed to have better results for the light snow conditions. I currently have a much higher temperature control inside, closer to the Davis one. This would be an easier thing to do than devising a new control system. I also bought a 75°F control which I haven't tried yet.

Greg H.


Blitzortung Stations #706 and #1682
CoCoRaHS: MI-PI-1
CWOP: CW4114 and KE8DAF-13
WU: KMIROGER7
Amateur Radio Callsign: KE8DAF

Offline ValentineWeather

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #36 on: April 17, 2016, 10:42:23 AM »
The heater seems to evaporate snowfall that is light. I have seen something similar with mine. If the snowfall is heavy, and the heater can keep up with it, then the error isn't as bad.


Greg H.

Even my fancy heater control in the Texas Electronics struggles with dry light snowfall. Nature of the beast I've decided. The only reliable way is manually.
Randy

Offline zackdog

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #37 on: April 17, 2016, 10:51:16 AM »
Okay, I jumped the gun. :oops:  I had no reason to believe anything had changed over night since we had had minimal wind.  Just shoveled the deck so I could get to rain collector and it was about a third full of water. ](*,) ](*,)Debris filter gone and opening plugged. Removed part of the plug and now have registered 0.28" for last hour and gauge is empty.  I am sure the reading is low, as it registered a rate of over 10"/hr.  Need to get a new debris filter.  I think I will just cover the rain collector next winter and rely on my CCRHS readings.

Mark
"You don't need a weatherman to know which way the wind blows." - Dylan

Vantage Pro2 Plus w/ 24 hr FARS and (2) VantageVues

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


Offline darkstarpa

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #38 on: April 18, 2016, 02:43:33 PM »
Figured that I would post my problem in this thread.
I purchased a Davis Vantage Pro 2 in early October as most reports indicated it was a superior package.

The rain measurements have never been right. Typically 50--65% off other weather stations in my area.
I decided to take on the problem after winter and the last snow. I have not purchased a CoCoRaHS rain collector yet to compare.
I have found numerous reports of problems with rain measurements on different web portals with the Davis Vantage Pro 2.

So I called Davis last week and was informed to try the following prior to sending back for possible repairs.
Did everything that was suggested.
Further I did the slow drip of a 1/4 cup of water that was suggested. The clicks that I heard, did match what was reported on the console.
Anyone else ever have this issue with a new station and reporting rain.

Troubleshooting steps:
 
1  Make sure there is no debris in the Rain Collector cone, preventing water from draining through to the tipping buckets.
 
2  Try pouring a small amount of water (1/4 cup) into the rain collector cone very slowly (should take at least 30 seconds).  Listen for and count the number of times you hear the tipping buckets tip.  You should see .01 in. of rain in the Daily Rain value on the console display for each tip of the buckets that you counted.
 
3  Try changing the Station ID # to something other than the default of Station # 1.  Remove the solar panel cover from the transmitter.  Locate the 4 DIP switches on the circuit board to the right of the battery chamber – almost to the right edge of the circuit board.  Using a ballpoint pen or similar small pointed object, flip the # 1 DIP switch Up/On.  You will now be transmitting as Station # 5.
 
3a  Put the console in the Setup mode (DONE button and minus ( - ) button at the same time.  You should see RECEIVING FROM… at the bottom of the display screen.  Wait until you see the number 5 appear above the line where it says Station No. and a slowly blinking X in the lower right-hand corner of the screen.  It can take anywhere from a few seconds to several minutes to establish communication between the transmitter and the console/receiver.  Once you see the X and the number 5, press and release the DONE button quickly.  Don’t hold it at all.  Just push it and let it go.  You should see the number 1 above the line, by itself and ON (ISS) in the lower left-hand corner.  Turn that OFF by pressing and releasing either the plus or minus button.  Press and release the right arrow ( > ) button to get to Station No. 2.  You should see the number 2 above the line and OFF below the line.  Continue with the right arrow button, making sure that 3 & 4 both say OFF.  When you get to number 5, it will say OFF.  Turn that on by pressing and releasing the plus or minus button.  It should say ON (ISS) below the line.  Check 6,7 and 8 and make sure they all say OFF below the line.  Press and release the DONE button quickly again and make sure RETRANSMIT is OFF.
 
That will eliminate the possibility that you may be picking up someone else’s station data.
 

Offline ValentineWeather

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #39 on: April 18, 2016, 02:59:33 PM »
If you look closely you will see me solution.
Randy

Offline mattgrahamca

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #40 on: April 18, 2016, 03:47:22 PM »
So I was in the huge Texas drenching last night.

I have found that my CoCoRaHs gauge measured 9.65 inches, while my VP2 measured 7.49 inches.

We had a couple hours of 1.6 to 2 inches an hour according to the VP2, but Mr CoCo can be compared well to other CoCos in the area.

I am happy the CoCoRaHS gauge is in my back yard

Offline ValentineWeather

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #41 on: April 18, 2016, 03:58:10 PM »
So I was in the huge Texas drenching last night.

I have found that my CoCoRaHs gauge measured 9.65 inches, while my VP2 measured 7.49 inches.

We had a couple hours of 1.6 to 2 inches an hour according to the VP2, but Mr CoCo can be compared well to other CoCos in the area.

I am happy the CoCoRaHS gauge is in my back yard

Hope your okay, that's a lot of rain. Daughter and brother in the Houston area also. 
Randy

Offline mattgrahamca

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #42 on: April 18, 2016, 04:03:01 PM »
Thanks, we are doing well.
Shocked the kids slept through it all!
I was upset that my internet went down too, so no logging on CWOP or WU

Offline ValentineWeather

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #43 on: April 18, 2016, 04:06:21 PM »
Try the cell service. My daughters okay also, haven't been able to speak with brother yet.
Randy

Offline mattgrahamca

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #44 on: April 18, 2016, 04:11:41 PM »
I did switch to cell, but since my internet was down, Meteobridge would not send my data to the web.

Do you have any good ways to tackle that?

Offline dalecoy

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #45 on: April 18, 2016, 04:15:39 PM »

The rain measurements have never been right. Typically 50--65% off other weather stations in my area.
I decided to take on the problem after winter and the last snow. I have not purchased a CoCoRaHS rain collector yet to compare.


You may have some local condition affecting your readings.  Until you purchase a CoCoRaHS (or similar) and mount it directly next to the VP2, you're guessing.

Offline ValentineWeather

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #46 on: April 18, 2016, 04:21:07 PM »
If you had phone tethering you could probably do it. Or a hot spot service possibly. Not 100% with meteobridge however.

I did switch to cell, but since my internet was down, Meteobridge would not send my data to the web.

Do you have any good ways to tackle that?
Randy

Offline WheatonRon

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #47 on: April 28, 2016, 09:20:03 PM »
I started this thread several weeks ago hoping my new VP2 ISS would more closely reflect the rainfall in my Mr. CoCo gauge. Since that time, very little rain fell here and very few additional posts were made to this thread. Last night we had a very gentle rain before midnight. I reported .23 in Mr. CoCo and .14 in the VP2. Early this morning we had a torrent of rain in a short period. Mr. CoCo reported .70 and the VP2 reported .45 during that time frame. Clearly, in heavy downpours, the tipper technology under reports rain. But I am surprised that during very light rain there was a fairly significant difference too. Mr. CoCo and the VP2 were near each other, level, and at the same height. Davis support provided me the technique to calibrate the gauge--determine error factor over three storms, average them, then turn the two screws at either end of the two buckets one full counterclockwise turn for each 6% error factor for under reporting rain. Has anybody calibrated his or her gauge using this technique and having success? Maybe a better answer as suggested previously in this thread is to purchase an add on gauge from Rainwise.


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Davis VP2 with SHT31 (3 complete VP2 systems—2 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 hankster

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Re: CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #48 on: April 28, 2016, 11:04:31 PM »
Considering your Davis is under reporting by about 40% (in both light and heavy rain) you have to turn the screws 6 turns. Is there even that much adjustment available?

Offline WheatonRon

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CoCoRaHS vs. Davis Vantage Pro 2 Rainfall Measurements
« Reply #49 on: April 28, 2016, 11:18:56 PM »
Six turns -- exactly what Davis support told me, and yes, the screws purportedly are long enough enabling this adjustment with "room to spare." But I find that tweaking a bit harsh for a rain gauge manufactured by Davis in January 2016, and on my fence only about a month!
« Last Edit: April 28, 2016, 11:40:41 PM by WheatonRon »
Davis VP2 with SHT31 (3 complete VP2 systems—2 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