Topic: Rain Gauge Calibration

[radioman61]

The rain gauge on my Atlas is reading low compared to other stations very near by and needs calibration. I reached out to Acurite to verify the procedure is the same as has been published for the 5 in 1. It is  not the same. Below is the reply I received from support. Thank you Acurite.

To calibrate the rain gauge on the AcuRite Atlas sensor:
First, make sure the rain collector is on a level surface.
Place the display unit close by so you can monitor it during the calibration process.
Make a pinhole in the bottom of a plastic cup. Hold the cup over the rain gauge and fill it with exactly 1 cup (8 oz.) of water, allowing the water to slowly drip into the rain gauge. You should hear the internal buckets tip and see the water drain through the rain gauge.
A few seconds after each bucket tip, the display console will display rainfall in approximately 0.01" or more increments.
The cup of water should take more than 20 minutes to empty; a quicker period will result in an inaccurate calibration. (We’re trying to simulate a normal steady rainfall.) When the cup is completely empty of water, the display console should register 0.61"
If the rain gauge doesn't register close to 0.61" after the cup is empty of water, then you should make an equal adjustment to the two calibration screws beneath the tipping lever. Be sure to adjust both screws the same amount. Turning screws clockwise will decrease rainfall amount. Turning screw counter clockwise will increase rainfall amount.
Adjustment:
To adjust the rainfall reading by 2.5% turn both screws 1/4  of a turn.
To adjust the rainfall reading by 5% turn both screws 1/2 of a turn.
To adjust the rainfall reading by 7.5% turn both screws 3/4 of a turn.
To adjust the rainfall reading by 10% turn both screws 1 full turn.
There should be nearly an equal number of water drops between bucket tips. If not, then adjust the calibration screws beneath the tipping lever until an equal number of water drops are tipping the buckets. Then, restart the calibration procedure.
If you don't hear the buckets tipping and see water dripping alternately out of each drain, there may be an issue with the rain gauge or its adjustment.


Thank you,

Meghan
AcuRite Customer Support

[MacGarage]

I had to turn the screws one full turn to get it in line with two other gauges I have on my property.

[radioman61]

I will add I’m impressed with the speed in which Acurite support got back to me as I had originally tried doing a chat session but my connection at work was flaky and I lost the chat box. Acurite emailed me to continue their assistance. Very well done.

[worachj]

Mine was under reporting too, needed to make a full turn of both screws to get it corrected.

[daman]

I will add I’m impressed with the speed in which Acurite support got back to me as I had originally tried doing a chat session but my connection at work was flaky and I lost the chat box. Acurite emailed me to continue their assistance. Very well done.

OT but I would like to add that also for me there live chat support was very speedy and helpful two days ago, it was very simple to do I did it at work on my phone, we had a short conversation and they got me going good job AcuRite! 

[radioman61]

I’m glad we now have a procedure to dial it in properly

[worachj]

I’m glad we now have a procedure to dial it in properly

Yeah, it nice to finally have a procedure, it only took me 6 guesstimate adjustments to get mine calibrated. 

Thanks for getting the calibration procedure from AcuRite!

[mcvoss]

My Atlas, which I've been watching for over a month ,is off by about <40%> compared to other stations and and my 5-1 which is on the same pole as the Atlas. Has anyone experienced that much of a difference?

[radioman61]

My Atlas, which I've been watching for over a month ,is off by about <40%> compared to other stations and and my 5-1 which is on the same pole as the Atlas. Has anyone experienced that much of a difference?

I’d say mine is close to that.  I still haven’t had a good weather day to get it down for calibration

[Neil_O]

My Atlas, which I've been watching for over a month ,is off by about <40%> compared to other stations and and my 5-1 which is on the same pole as the Atlas. Has anyone experienced that much of a difference?

The rain totals for my Atlas were roughly 20% - 25% low.  I moved the adjustments screws counterclockwise by 2 turns (theoretically a +20% correction), and my rain readings are now very close to a Davis Vantage Pro2 unit that's only about a mile or two from my house.

[nincehelser]

Rain calibration should be done in a controlled fashion, not to match distant stations.

If you want to check for "ground truth", use something like a well-mounted CoCoRaHS gauge near your station.

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[CW2274]

Rain calibration should be done in a controlled fashion, not to match distant stations.

If you want to check for "ground truth", use something like a well-mounted CoCoRaHS gauge near your station.

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Exactly. Besides, VP2's are notorious for being 'outta wack' too. Whether this VP2 is or not, who knows, you need something literally within feet of what you're comparing to, and preferably the same approximate height. Even after 'calibration', they can and will still differ, just not grossly.

[Neil_O]

Rain calibration should be done in a controlled fashion, not to match distant stations.

If you want to check for "ground truth", use something like a well-mounted CoCoRaHS gauge near your station.

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There are 4 fairly-high quality weather stations (2 Davis, 2 Ambient) within 1-2 miles of my house.  During a steady, fairly-gentle rain lasting hours over the entire area, these stations all agreed within 1% - 2% of one another.  At the same time, my Atlas was reading 25% lower than all 4.  Am I to believe that my Atlas is correct, and 4 other weather stations are incorrect by exactly the same amount???  Couple this with the fact that a good number of other Atlas owners have reported low rain totals with the Atlas, and it seemed pretty likely to me that the Atlas was reading low.  I don't really have the time to use the AcuRite 8-ounce, pin hole in a plastic cup calibration method.  Also, without using a calibrated graduated cylinder or volumetric flask, I question how close to "exactly 8 ounces" I could really get.  I made my re-calibration in the middle of the rainfall, so I was able to continue to monitor rainfall rates for the next 3-4 hours.  The other 4 weather stations continued to agree with on another extremely well, and my Atlas unit also agreed with them.  Is this perfect - no.  Is the calibration better than it was before I made the adjust, I'm quite confident of that.

[CW2274]

Rain calibration should be done in a controlled fashion, not to match distant stations.

If you want to check for "ground truth", use something like a well-mounted CoCoRaHS gauge near your station.

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  During a steady, fairly-gentle rain lasting hours over the entire area, these stations all agreed within 1% - 2% of one another. 

Sure, during an easy, area wide event, you'll more likely than not get some decent comparisons. That being said, if you want it done right, you'll compare with yourself. Granted, sucks that you may have to, sometimes it's part of PWS ownership. Should it be necessary, of course not, they ALL should be good outta the box, but....

BTW, I calibrated my tipper with a kitchen scale, 1ml syringe, and a gallon milk carton.

[Old Tele man]

Example of MICRO CLIMATE rain -- While on Guam, I was on the port wing fueling the wing-tip tank when a sudden squall blew across the island drenching me; however, 124 feet away the guy fueling the starboard wing-tip tank didn't get a drop! Something to remember when there are sudden down pours occurring within otherwise normal rain events.

[DoctorKnow]

My Beta Atlas read about 20% low. I adjusted and it now reads along with manual gauges and automated that I have used to compare.

Acurite never sent me a production unit, and I doubt they will now. Everyone else already has theirs from what I have heard, so I cannot tell you if it is a consistent pattern that they all read low out of the gate... I don't use facebook. The adjustment is very simple, so that is a good thing.

[rdelp68]

Has this procedure changed?  I got this one last week. Tested the rain gauge and it showed .51 I had to turn the screw a little over one full turn. got .61 and .62 with multiple tests.
Today its raining nearly every station nearby (yea its possible I got more rain) shows .52 to .70 and I have .83

Rob

[Neil_O]

The overall procedure is the same, but the percentage change per 1/4 turn was a lot more sensitive for my unit than what the procedure stated.  My unit originally read about 20% low for rainfall which should have correlated to about 2 counterclockwise turns for each screw.  When I made that adjustment, my unit read significantly high for rainfall.  I then turned each screw 1 turn clockwise and my unit is now close to spot-on against a rain gauge.  So, in the end, 1 full turn counterclockwise adjusted my rainfall readings by about +20%.