Author Topic: VP2 rain rate measuring  (Read 215 times)

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Offline bchwdlks

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VP2 rain rate measuring
« on: June 30, 2018, 02:46:11 PM »
What is the maximum rain rate that a VP2 tipping bucket will record? The user manual says that it is UP TO 96"/HR.

Earlier this week we had real downpour for a short period. I had checked the debris screen that morning so I am fairly certain that there was not any obstruction. Standing on the carport about 30 yards from the station, it looked like the bucket was overflowing. I was going to go check it, but got distracted - a six foot tall water stream where a downspout entered a 6" corrugated pipe. By the time I found out that the corrugated was not obstructed, the hardest rain had stopped. The pressure in the downspout was enough to blow out all the cracks where it transitioned to PVC.

The highest rain rate that the station recorded was 9.7"/hr. If the spec is correct, that means the gauge should record a rain 10 TIMES harder that what we experienced. Has anyone ever recorded a reading anywhere close to the upper limit?

Offline ocala

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Re: VP2 rain rate measuring
« Reply #1 on: July 01, 2018, 06:56:36 AM »
Just looked at 14 years worth of records in WL and the highest it recorded was 20 inches.
There was also an 18, 16, and many 12's and 10"s.
I don't know if it could record report up to 96 inches. I have stood by my gauge during very heavy rain and could hear it tip appx every 2 seconds. There is only so much water that can drain through the opening. I suppose that if the bucket were completely filled the pressure would be greater as opposed to if the outlet was just covered enough for a steady stream.

Offline archae86

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Possible protocol limit
« Reply #2 on: July 01, 2018, 08:24:51 AM »
I run both the Davis Vantage Pro 2 and a somewhat older RainWise standalone rain gauge.  The wireless protocol between the RainWise unit and its receiver can only record one tip every eight seconds. However I think there is some internal buffering, possibly of something like 128 tips. For the RainWise I think this means there is a sustained rate limitation arising directly from the reporting protocol.

I should mention that the only time I have actually noticed the RainWise operating above the short term limit has been when I deliberately poured water into it for testing purposes, or to get the annual total up-to-date. When I have done that, the RainWise hit the instantaneous limit from protocol without hitting a physical limit of flow rate.

I don't know the Davis protocol enough to guess whether there might be any similar issue there.

Offline Mattk

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Re: VP2 rain rate measuring
« Reply #3 on: July 01, 2018, 04:57:24 PM »
Davis VP2 rain rate is more of an instantaneous timed tipping of the bucket and is not the equiv of 1 or 10 or 60 minute interval type rates. The highest I have recorded is 1152mm/h resulting in an actual 33.2mm being recorded over the 10 minute archive interval which is serious rain. Anything approaching 2mm/minute is serious rain and 96"/HR (2438mm/HR or 40mm/min) would purely be a spec based on theoretical limitation of the coding and timing ability.