# WXforum.net

## Weather Station Hardware => Davis Instruments Weather Stations => Topic started by: StretchCT on August 18, 2019, 03:12:41 PM

Title: Converting CoCoRaHS 4" gauge to Davis 6.5"
Post by: StretchCT on August 18, 2019, 03:12:41 PM
I need another set of eyes on this....

I'm running really off with the Davis Vantage Pro2 gauge and was in the process of testing it.  Originally thinking a .5" of rain is a .5" of rain, another thread in here convinced me its not.  However it didn't go into much detail as to how to convert those volumes.

So if there is .53" of water in the 4" CoCoRaHS gauge..
4"*4"*.53"*pi=V which is 26.64
and to reverse to get height...
26.64/4"/4"/pi = h which is .2"

Thus if you put .53" of water from the CoCoRaHS gauge into the Davis 6.5" gauge, the Davis should give you 0.2".  (which mine is currently giving 0.06")

Yes?

PS if I tip it 20 times, it registers 0.2", so it seems the switch is ok.

Anyone know how to delete data from Wunderground now?  Seems I can no longer edit my info.
Title: Re: Converting CoCoRaHS 4" gauge to Davis 6.5"
Post by: CW2274 on August 18, 2019, 03:33:50 PM
No idea if your math is correct, however I can tell you that 544ml of water in a VP2 bucket equals 1" of rain (100 tips).
Title: Re: Converting CoCoRaHS 4" gauge to Davis 6.5"
Post by: nincehelser on August 18, 2019, 05:16:05 PM
Isn't the 4" a diameter and not the radius (2")?
Title: Re: Converting CoCoRaHS 4" gauge to Davis 6.5"
Post by: StretchCT on August 18, 2019, 08:10:23 PM
Crap  -see thats why I need a double check.

But it works out the same.  Different volume, but same height result.
Title: Re: Converting CoCoRaHS 4" gauge to Davis 6.5"
Post by: CW2274 on August 18, 2019, 09:01:10 PM
If you want to calibrate your VP2 properly, I'd forget using a Stratus gauge, use the 544ml measurement as there's no ambiguity, it's a known fact. Using your Stratus means just another variable to screw it up.
Title: Re: Converting CoCoRaHS 4" gauge to Davis 6.5"
Post by: StretchCT on August 19, 2019, 06:48:08 PM
Today's tstorm brought 0.2" in the Stratus. .05" in the Davis.  :-(  ](*,)

Title: Re: Converting CoCoRaHS 4" gauge to Davis 6.5"
Post by: CW2274 on August 19, 2019, 07:14:45 PM
Today's tstorm brought 0.2" in the Stratus. .05" in the Davis.  :-(  ](*,)
Obviously there's issues. If you don't want to mess with the Davis bucket (I didn't), do like some of us here and hook this up. It's works exactly the same and is very accurate, especially for a tipper, and a piece of cake to wire.

https://www.rainwise.com/products/detail.php?ID=6697
Title: Re: Converting CoCoRaHS 4" gauge to Davis 6.5"
Post by: klschmidt on August 20, 2019, 07:00:56 PM
As CW2274 pointed out, a 544ml calibrator will provide the greatest accuracy, but if you do not have a calibrator or laboratory glassware why not use the Stratus? It may be more accurate than kitchen measuring tools. My math comes out the same as yours. A second container with a small hole may be needed to provide flow control. I think I'd start by turning each calibration screw counterclockwise about three rounds (just a guess), verify that they are level, and commence to check calibration using .53" in the Stratus gauge. Whenever it's getting close I'd try a full inch in the Status gauge (should read .38" on the Davis). I think you can get the Davis really close without buying anything.
Title: Re: Converting CoCoRaHS 4" gauge to Davis 6.5"
Post by: CW2274 on August 20, 2019, 07:19:16 PM
As CW2274 pointed out, a 544ml calibrator will provide the greatest accuracy, but if you do not have a calibrator or laboratory glassware why not use the Stratus? It may be more accurate than kitchen measuring tools.
Maybe, if the Stratus is accurate, I've heard all are not created equally, so I elected to use the specific measurement alone. With that, I used a gallon milk jug, a plastic syringe, and a scale accurate to a gram. Works very well.
Title: Re: Converting CoCoRaHS 4" gauge to Davis 6.5"
Post by: klschmidt on August 20, 2019, 08:46:17 PM
As CW2274 pointed out, a 544ml calibrator will provide the greatest accuracy, but if you do not have a calibrator or laboratory glassware why not use the Stratus? It may be more accurate than kitchen measuring tools.
Maybe, if the Stratus is accurate, I've heard all are not created equally, so I elected to use the specific measurement alone. With that, I used a gallon milk jug, a plastic syringe, and a scale accurate to a gram. Works very well.
Since the tipping bucket rain gauge "weighs" the rainfall, calibrating with 544 grams of water is probably the best method.
Just in case the OP does not have a scale (and to satisfy my own curiosity) I checked my gauge. It took 105.97g of water to reach the .53" mark. When dumped, the gauge retained .46g (without shaking or slinging it). The water that was dumped out (105.51g) should tip the Davis bucket 19.4 times. 108.75g of water (.20" in Davis) is just short of .55" in my gauge.