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Author Topic: Calibrating Davis VP2 rain gauge  (Read 13717 times)

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Offline niko

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Re: Calibrating Davis VP2 rain gauge
« Reply #15 on: February 26, 2016, 01:12:48 AM »
Hi...if someone could test...with a Davis VP2

how much reading will you have on the davis console  with a 5 ml test tube or 10 ml (emptyed drop by drop with a dropper)?

thanks

Just follow the calculation posted by N7XSQ at the start of this thread to get the volume in ml for 1 cm of rain, and then divide that amount by 5 or 10. But you won't get a reliable result with such a small amount of water, you need to put enough water through the gauge for maybe a hundred tips / 1 inch / 2.5 cm and average the result.

Offline steerage250

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Re: Calibrating Davis VP2 rain gauge
« Reply #16 on: June 30, 2018, 05:12:05 AM »
My Davis V2 rain gauge was reading 20% less than a 4" manual gauge placed beside it.  I checked the balance between the 2 buckets, and it was way out - 1 side tipped at about 48 drops, and the other about 83 drops!  I had to turn one screw 3 whole turns before they were about equal - and then proceeded to tweak both together to get the calibration about right (4.28ml/tip).

Offline FPGAgeek

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Re: Calibrating Davis VP2 rain gauge
« Reply #17 on: July 16, 2018, 07:31:06 PM »
It is on my to-do list to check my VP2 tipping bucket also, I will probably do this using a drip test. I have read a few forums that the VP2 can be very awkward to calibrate and may be best avoided unless absolutely necessary. I have also read (but can't find the source at the moment) that the VP2 tipping bucket is biased for some reason, I haven't found anything from Davis about this and what percentage it would need to be biased - 48-to-83 tips sounds high though.

I would be interested if anyone knows any more about this  :?

Online teal

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Re: Calibrating Davis VP2 rain gauge
« Reply #18 on: July 16, 2018, 08:04:38 PM »
  Be nice if we had some rain to test it with, 39 days without so far.

  teal.

Offline steerage250

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Re: Calibrating Davis VP2 rain gauge
« Reply #19 on: July 17, 2018, 12:25:43 AM »
I found that dripping water from an eye dropper into each side to compare was quite unreliable/variable - ie results did not have good repeatability (part of which is probably cause by losing count - any distractions and I was lost!).  I then calibrated it using the drip method recommended by Davis using 43ml of water.  However, that only represents 2mm of rainfall, and when each bucket holds 0.2mm - that's an error of 10%.

I am now comparing it to a manual gauge mounted right up against the Davis during good rainfall (and it's lucky we've had a bit of that recently).  I have checked the calibration of the manual gauge, and it seems good (Davis Australia were not happy that their gauge was being checked by a mass-produced item  :D).  I am gradually winding the adjustment screws up so my Davis readings are scattered each side of the manual gauge reading (rather than all on the "less" side).

Offline bitsostring

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Re: Calibrating Davis VP2 rain gauge
« Reply #20 on: July 17, 2018, 09:47:13 AM »
  Be nice if we had some rain to test it with, 39 days without so far.

And because it didn't rain on St Swithin's Day (15 July) you've probably got another 39 to go!
It's meant to be fun. . .

Offline aardvark

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Re: Calibrating Davis VP2 rain gauge
« Reply #21 on: July 17, 2018, 06:03:12 PM »
Perhaps someone could market a calibration kit.  Not knowing the sales on it, but  something for someone with knowledge .    For me I assume that that one tip is 0.01 inches, assuming that the rain unit is level and that the water drops into the pan, the tipper is not impeded.   
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Offline niko

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Offline aardvark

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Offline niko

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Re: Calibrating Davis VP2 rain gauge
« Reply #24 on: July 17, 2018, 07:35:25 PM »
Those two are probably pricey, there are others.

btw I enjoyed your post on a certain other forum today  :wink: