Rain gauge question / inches to mm

[david3]

I'm using a Vantage Vue with a .01" tipping spoon and the Console is set for imperial units / inches, and a 10 minute interval.

I installed Cumulus 1.9.4 B1061 a few days ago, so that's what I'm currently running.

I have Cumulus set to report in metric units (mm for rainfall), and my website reports metric data. There's no change made to the rainfall calibration in Cumulus (the multiplier is set to the default 1.000).

I started to take a closer look at the rain data and something looks odd.

On 3/11 we had .02" of rain. It was reported in Cumulus as .6mm, and when I look in the Mar13log.txt file, I can see the data in the 10th rain column as 0.3 at 02:50 and then 0.6 at 03:00:

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01:40 0.3
01:50 0.3
02:00 0.3
02:10 0.3
02:20 0.3
02:30 0.3
02:40 0.3
02:50 0.3
03:00 0.6
03:10 0.6
(continues)

It looks like it rounded each tip up from .254mm to .3mm and added the rounded data together. I would have expected .254mm x 2 = .508mm (.5mm rounded).

Now its raining again today on 3/12, and it looks like its doing the conversion correctly. So far we've had .15" of rain, and Cumulus reports it as 3.8mm (.254mm x 15 = 3.81mm). Looking in the Mar13log.txt file, the data looks good:

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19:10 0.2
19:20 0.7
19:30 0.7
19:40 1
19:50 2
20:00 3
20:10 3.8

Is there some reason for the different behavior; why sometimes it gets rounded before totaling and sometimes after?

[steve]

The Davis DLL does the conversion. Cumulus calculates the rainfall so far today using the annual rainfall counter; it subtracts the value as supplied by the Davis DLL at the start of the day from the current value supplied by the DLL, and then rounds to 0.1 mm. So what you are seeing is the result of the DLL conversion and rounding twice, and then Cumulus rounding the result. Sometimes the roundings will add and sometimes subtract.

If you look in the diags files, you can see the stored value from the start of day, and the current value as the day progresses, e.g

04/03/2013 08:55:00.444 : Writing today.ini, LastUpdateTime = 04/03/2013 08:55:00 raindaystart = 163.399993896484 rain counter = 163.800003051758

So for me (with a metric gauge and settings, that's 0.4 mm so far today at that point.

Note that the apparently spurious accuracy is because the values are in 'internal' format (i.e. decimal representations of the binary).

[david3]

Thanks Steve. So it's something with the way the Davis DLL does the conversion.

What's reported in Cumulus does match what's in the diag file:

Code: Select all

3/11/2013 00:00:00.507 : Raindaystart set to 31.2000007629395
3/11/2013 00:00:00.578 : Writing today.ini, LastUpdateTime = 3/10/2013 11:50:00 PM raindaystart = 31.2000007629395 rain counter = 31.2000007629395
3/11/2013 01:30:00.936 : Writing today.ini, LastUpdateTime = 3/11/2013 1:30:00 AM raindaystart = 31.2000007629395 rain counter = 31.2000007629395
3/11/2013 01:40:00.940 : Writing today.ini, LastUpdateTime = 3/11/2013 1:40:00 AM raindaystart = 31.2000007629395 rain counter = 31.5
3/11/2013 03:00:00.903 : Writing today.ini, LastUpdateTime = 3/11/2013 3:00:00 AM raindaystart = 31.2000007629395 rain counter = 31.7999992370605
3/12/2013 00:00:00.625 : Midnight rain reset, count = 31.80 time = 3/12/2013

3/12/2013 00:00:00.636 : Raindaystart set to 31.7999992370605
3/12/2013 00:00:00.707 : Writing today.ini, LastUpdateTime = 3/11/2013 11:50:00 PM raindaystart = 31.7999992370605 rain counter = 31.7999992370605
3/12/2013 19:10:00.132 : Writing today.ini, LastUpdateTime = 3/12/2013 7:10:00 PM raindaystart = 31.7999992370605 rain counter = 32
3/12/2013 19:20:00.369 : Writing today.ini, LastUpdateTime = 3/12/2013 7:20:00 PM raindaystart = 31.7999992370605 rain counter = 32.5
3/12/2013 19:30:00.324 : Writing today.ini, LastUpdateTime = 3/12/2013 7:30:00 PM raindaystart = 31.7999992370605 rain counter = 32.5
3/12/2013 19:40:00.393 : Writing today.ini, LastUpdateTime = 3/12/2013 7:40:00 PM raindaystart = 31.7999992370605 rain counter = 32.7999992370605
3/12/2013 19:50:00.833 : Writing today.ini, LastUpdateTime = 3/12/2013 7:50:00 PM raindaystart = 31.7999992370605 rain counter = 33.7999992370605
3/12/2013 20:00:00.294 : Writing today.ini, LastUpdateTime = 3/12/2013 8:00:00 PM raindaystart = 31.7999992370605 rain counter = 34.7999992370605
3/12/2013 20:10:00.411 : Writing today.ini, LastUpdateTime = 3/12/2013 8:10:00 PM raindaystart = 31.7999992370605 rain counter = 35.5999984741211