Topic: Rain gauge out of Tilt

[azchrisf]

Hey guys,

I've run into an issue with my Davis (now about a year old). The rain gauge is under-reporting by approx. 15% compared to my CocoRahs gauge. I got 0.89 in yesterday vs 0.75 recorded by the Davis. I've noticed the discrepancy for some time. I know most will say "well that's the difference between the two" but both are mounted on the same pole, the CocoRahs being behind the Davis and down about 4 feet, so the difference should be negligible.

I checked level on the Davis and while it's not perfectly centered in the bubble, it's still within the center circle of the bubble, just leaning a little to one side. Nothing I can really do with this since it's on a pole.

With 15%, I'm going to assume that the problem has little to do with perfect level and more to do with calibration.
Any opinions?

[johnd]

A difference of 4 feet in height is not necessarily negligible and could well account for at least part of the discrepancy. Depending on how much it troubles you, might be worth eg getting a second CoCoRaHS and mounting it with the opening at the same height as the VP2 gauge and as close to the VP2 as possible.

(Not saying that this will necessarily resolve the problem, but at least it will give a proper like-for-like comparison between the two - rain catch can be surprisingly sensitive to height and exact exposure.)

[ocala]

Several threads on this same issue in regards to the Davis under reporting. You'll never get it to be exact but you can get it close.
Try this.
Turn each screw 1/4 of a turn. You'll see a diagram with a + or -. Turn it to the plus side which I think is clockwise. 
Wait for your next rain event and check the difference.
Just keep adjusting after each rain event until you get it where you're satisfied.
Also as John mentioned above putting the Davis and Coco at the same level would help  for accuracy issues.

[CW2274]

If you have WL, you can adjust down to a single percent through that instead of screwing (pun intended) with the ISS if you prefer.

[ocala]

If you have WL, you can adjust down to a single percent through that instead of screwing (pun intended) with the ISS if you prefer.

I know Cumulus you can calibrate rain fall but I didn't know it was available in WL.
Where is that setting?

[CW2274]

You'll need to close Bulletin if open, then upper left corner select Setup, then Set Rain Calibration.

[ocala]

You'll need to close Bulletin if open, then upper left corner select Setup, then Set Rain Calibration.

Count me as schooled.
I always thought that was a inches or mm calibration.
Cool. Something else to play with.

[CW2274]

As convenient as it is, I always do the screw tuning til I get it right, electronically seems like cheating...

[azchrisf]

Well there's a screw on each side, one looks a tad higher than the other so I'm not sure which to adjust. Is there any way to do this with certainty your calibrating accurately?

I may need to take it down and send it back to Davis for calibration...

Sent from my Pixel using Tapatalk

[CW2274]

Well there's a screw on each side, one looks a tad higher than the other so I'm not sure which to adjust. Is there any way to do this with certainty your calibrating accurately?

I'd try it myself first, at least you'll know when it's right.
I first use a 1ml syringe to try to equal the spoons capacity as much as possible first, so gently drop water into each spoon until they tip at the same amount at 5.4ml by adjusting the screws up or down. After they both are as equal as you can get them, the you can use a much larger amount to fine tune by turning both screw the exact same amount in the same direction. 1 inch of rain for the VP2 is 544ml.
I hope this makes sense....

[CW2274]

BTW, for the best possible accuracy, have it as level as you can get it.

[azchrisf]

Well there's a screw on each side, one looks a tad higher than the other so I'm not sure which to adjust. Is there any way to do this with certainty your calibrating accurately?

I'd try it myself first, at least you'll know when it's right.
I first use a 1ml syringe to try to equal the spoons capacity as much as possible first, so gently drop water into each spoon until they tip at the same amount at 5.4ml by adjusting the screws up or down. After they both are as equal as you can get them, the you can use a much larger amount to fine tune by turning both screw the exact same amount in the same direction. 1 inch of rain for the VP2 is 544ml.
I hope this makes sense....

Sounds like you're going to need some time and a lot of patience

Sent from my Pixel using Tapatalk

[CW2274]

Well there's a screw on each side, one looks a tad higher than the other so I'm not sure which to adjust. Is there any way to do this with certainty your calibrating accurately?

I'd try it myself first, at least you'll know when it's right.
I first use a 1ml syringe to try to equal the spoons capacity as much as possible first, so gently drop water into each spoon until they tip at the same amount at 5.4ml by adjusting the screws up or down. After they both are as equal as you can get them, the you can use a much larger amount to fine tune by turning both screw the exact same amount in the same direction. 1 inch of rain for the VP2 is 544ml.
I hope this makes sense....

Sounds like you're going to need some time and a lot of patience

Sent from my Pixel using Tapatalk

Yes, it's very time consuming, but I like tinkering. You can always do the WL thing, if you're able.

[azchrisf]

Well there's a screw on each side, one looks a tad higher than the other so I'm not sure which to adjust. Is there any way to do this with certainty your calibrating accurately?

I'd try it myself first, at least you'll know when it's right.
I first use a 1ml syringe to try to equal the spoons capacity as much as possible first, so gently drop water into each spoon until they tip at the same amount at 5.4ml by adjusting the screws up or down. After they both are as equal as you can get them, the you can use a much larger amount to fine tune by turning both screw the exact same amount in the same direction. 1 inch of rain for the VP2 is 544ml.
I hope this makes sense....

Sounds like you're going to need some time and a lot of patience

Sent from my Pixel using Tapatalk

Yes, it's very time consuming, but I like tinkering. You can always do the WL thing, if your able.

I'll take the time to adjust the buckets, my way of doing things too

Sent from my Pixel using Tapatalk