Davis Vantage: new rain collector

[marc@geissmann.org]

Hi

Davis Vantage issued a new rain collector that has another shape to the previous one. I would like to ask members about their experience they made with the new rain collector. I am asking me whether this is indeed an improved shape to measure rain fall more accurately during heavy wind conditions? Or is it just part of a "marketing story" to sell their components?

Would be interested in your opinion.

Thanks, Marc

[Luc]

Since half july I have two Vantage pro2 stations with both old and new rain cones next to each other.
My first observations are the new cone always measures more rain than the old one.
See: http://www.lucdesign.nl/data/weewx/mstk/index.html
Davis is new station read by the weewx vantage driver
Mstk is old station read by the weewx meteostick driver

[iatros]

read PM pls !

[Luc]

Not sure who has to read his PM, but I haven't got one from you, iatros.

[iatros]

sorry Luc and all; I sent it to Marc...
Martin

[wx_jon]

Luc, I don't see very much in the plots you linked to there, but I am quite interested in this comparison (my station is very vulnerable to wind). Do you have graphs of accumulated rain over the time period of comparison? Have you tried swapping the cones on the tipping bucket bases?
Thanks.

[Luc]

Hi Jon,
It is the dry season here currently. Last month and the upcoming three months I expect 'only' 400 mm rain. Swapping of the cones is an excellent idea! Never thought about it. Will do it today.
I will try to compose a cumulative weewx plot.
During a big rain shower the rain blows at an angle of about 45 degrees. Has already destroyed one of my PI cameras.

[bianco57]

What is most interesting is to be able to separate the rain gauge from the shelter.

As for the shape, it is probable (I trust Davis for that!) That the flow of the wind is improved.

On the other hand the diagram is very badly done by trying to make believe that the wind that circulates above the cone carries the rain next door! ...

It is possible that the turbulence above the cone is improved (reduced), but this is not at all what the diagram indicates! (and this discredit a little Davis ...).

In any case, the reference manual rain gauges (standards) all have an external conical shape, so it is preferable that the automatic rain gauges also have this shape

[georg]

I got the barrel type rain bucket, and i wonder if the new one has room for the heating element, used for melting the snow in the winter. (Luc i do not think you have that in your barrels).
Have been testing the accuracy of the rain collector over a whole winter period using 3 old fashioned manually collectors, in different shapes and different heights around my DV, and it is definitely measuring on the low side, which support what Luc is telling.

[iatros]

Hi Georg
no, there is no space for the heater in the AeroCone. Davis offers a "Rain collector cone and heater replacement kit for Vantage Pro2 rain collectors with AeroCone" (https://www.davisnet.com/product/rain-c ... ng-heater/). But you still have the "traditional bucket" for cold danish winters...
Best regards, Martin

[georg]

Thanks for the information Iatros.
Think i will keep the one i have for the moment.

[marc@geissmann.org]

Hi

Right, for those of us having snow (at least sometime) it is of an important disadvantage that the new rain cone does not have a suitable heating element.
Having the "normal" rain cone I am comparing rain quantity against Hellmann and it seems that my davis is reporting at the lower end (compared to the hellmann). But I need more rain dates to perform significant analysis. I will be interesting to follow Luc's comparison b/w the two cones (old and the new one).

Hellmann cone, pls see:
http://www.ugt-online.de/en/products/me ... -hellmann/

Marc

[dmgould]

Hi All:

I installed the new collector cone on my Pro 2 a couple of months ago. I also have an Ambient Weather station setup that the Pro 2 actually replaced about a year ago. Using the old cone the Davis measured rain consistently a bit lower than the Ambient station. Using the new cone both stations agree, or very closely agree on rain most of time.

My house in the mountains is located high on a hillside with breeze and wind common. I believe in my situation that the new cone is probably more accurate.

Dave

[Lespius]

Hi Everyone,

Not directly linked to the new shaped rain collector...

I had a couple of years ago an information about the calibration of the classic collector, from an association called Romma http://www.romma.fr/ (I used to be a member before I moved).
After some tests and comparisons with top collectors like the Speia, they have recommanded the following: 0.2 mm of rain = 3.7 ml, instead of the classic 4.2 mm.

I must say that since i did the modification my measurements are more i line with the Meteosuisse website.

But... what about this calibration with the new collector ??

Alain

[iatros]

Salut Alain

very Interesting.
Just as a matter of understanding:

0.2 mm of rain = 3.7 ml, instead of the classic 4.2 mm.

should it be: 0.2 ml (1 collector's spoonful) = 3.7 mm instead of 4.2 mm ?

That means, in Meteobridge -> weather station/local settings I set "Rain multiplier" to 4.2/3.7, i.e. 1.135 , right?

Martin

[Lespius]

Salut Martin !

Let me be more explicit.
In our metric system the buckets are supposed to overbalance for every 0.2 mm of rain. That is 0.2 l/m2. That is 4.2mm collected by the cone.
So if you pour 4.2mm in one bucket, it must overbalance. This is the theory. The VP2, as we know, underestimate the quantity of rain. According to Romma and their tests, a more accurate result can be obtain if the buckets overbalance for every 3.7mm, instead of 4.2mm, meaning that they will overbalance more often.
The best is to set this manually on the rain cone base (with the screws). But the same result can be reach through Meteobridge as you said, but then you will have cumulative rain as multiple of 1.135 x 0.2mm = 0.227mm
I have a document explaining this, but cannot attached it. Tell me if you want it..

Please apologize if you were already familiar with all this stuff

Alain

[iatros]

like this?:

meteobridge.jpg (44.57 KiB) Viewed 15000 times

(To attach a document: while writing your reply, look below the textbox, you'll find there a tab "Attachments" , and yes I'd be very interested in your doc!)
Thank you

[georg]

Hi to all
A bit confused over the dimensions used in this discussion.
-
The tip of the spoon is indicating 0,2 mm (not ml) rain registered.
In order to tip, there must theoretically be 4,2 ml in the spon.
(radius at the top of the cone app 82 mm, gives an area of 21.124 mm2 x 0,2 mm = 4.225 mm3 = 4,224 ml)
-

IMG_20170920_230741.jpg (21.8 KiB) Viewed 14978 times

-
Tested it with a syringe, and it is exactly what makes it tip.
-
To make it match the real world (the normal old fashioned gauge),
i have adjusted the calibrating bolts, situated under the spoons, so it tips on 3,7 ml.
Tested it over several month and results are more realistic.

[iatros]

Thank you Georg for your clarification! This was very helpful for me.

btw Very nice, your display of the Console! I wonder how you managed this..... (Don't explain me if it is too complicated )

[Lespius]

Thanks Georg. Thats exactly that.
Iatros, personnaly I would choose to calibrate the adjusting bolts instead of applying a correction in Meteobridge.
Cheers
Alain

[georg]

Hi iatros
-
That is the purpose of the forum, ping ponging for a solution.
-
You must have been exploring intensive, since you found the console.
http://arloese.dk/index.php/vejret-nu/d ... ntage-pro2
It is an ancient php script (2011 i think),
yeah it looks good, and very impressive, when you press the light button and turn on the light. .
-
It is still out there
https://silveracorn.nz/weather/wxscripts.php
I do not know whether, it will work with meteobridge.
I have tried to make it to a block but irfanview is not allowed in the template.
But as it is a simple php script it should be possible.
-
Greetings georg

[iatros]

You must have been exploring intensive, since you found the console.

..... link on your MT-homepage.....

And thank you for the script, I see it is written for Cumulus which I do not use; transcribing it to Meteobridge would (if even possible) be clearly beyond my possibilities.

[Luc]

I have two Davis Vantage pro2 stations mounted next to each other.

My new ISS with the new rain cone measured 18.4 % more rain than the old station in a period of 51 days.
On september 1st I changed the rain cones with each other.
In September my new ISS with the old rain cone measured 20.7 % more rain than the old station with the new rain cone in a period of 27 days.

My conclusions:
1. The main differences in rain are a result of the adjustment of the tipping mechanisms and not of the rain cone itself.
2. The effects of the rain cone shape (with max wind gusts of 30-35 km/h) are low.

My data:

Period 12-jul - 31-aug
ISS-1 with old rain cone: 304.2 mm rain
ISS-2 with new rain cone: 360.2 mm rain

Period 1-sep - 27-sep
ISS-1 with new rain cone: 96.6 mm rain
ISS-2 with old rain cone: 116.6 mm rain

[georg]

Thanks for the information Luc.
Yes, the tipping is essential for the result,
the bottom has to be absolutely level, (or the adjustment bolt has to be level)
to make the spoons tip at the same amount of water.
Also good to know that the old shape with my heating element is still ok.

[wx_jon]

Luc, that's quite disappointing, I have to say. I hoped it would help. My ISS is located on the roof of a 7-story building, so for me, the effect might be more dramatic. But I was hoping you would find an improvement with the new cone so that I could justify buying one...