Need clerification on how rain is measured... **solved**

[DAP]

I have been having trouble with my Davis ISS not reporting as much rain as my graduated cylinder rain gauge. Some times the measurement is off by as much as 50%.

I created a test fixture that consists of a push button switch attached to a few inches of phone cable as a fake rain gauge.

Today, I hooked this up to the davis transmitter instead of the rain gauge, and pressed the button 20 times. This should have registered as 0.2" of rain, but zero rain was transmitted to Weather Underground.

I looked at the history page, and it shows a significant spike in rain rate. Attached is a screen shot. So the ISS is detecting the button presses, and transmitting them, but somehow the meteobridge pro is not recognizing them as measurable rain.

What is the ISS transmitting, and what is the software doing to the data that it is dropping rain?

edit: Replaced screen shot because previous screen shot had a tool tip at an unfortunate location in the image.

[admin]

Do I get you right that MB PRO just records the rain rate and does not increase total rain amount?
Can you please show same screen dump for "rain0total"?

[DAP]

Attached is the rain0total for the same time period.
What I fear is that the meteobridge pro is doing some filtering on the data, and that there is an incorrect assumption about the maximum rain rate and/or an error in their math.

[Mattk]

That's certainly an abnormally high and probably unachievable rain rate in the real world and could very well be deemed an error and ignored. 20 times over what time frame? Normally calibrate at around 75-100 tips per hour

[DAP]

That's certainly an abnormally high and probably unachievable rain rate in the real world and could very well be deemed an error and ignored. 20 times over what time frame? Normally calibrate at around 75-100 tips per hour

In that experiment, I was pressing a button as fast as I could.

In earlier experiments, I had filled the funnel with a bucket of water (representing the fastest rate that the tipping bucket could be tipped in a heavy downpour), and the bucket was tipping about twice a second.
I also ran an experiment where I tipped the bucket once every 10 seconds. Neither experiment recorded any rainfall.

Being able to see a record of the actual tip counts received by the meteobridge would be a useful debugging tool.

[admin]

That's certainly an abnormally high and probably unachievable rain rate in the real world and could very well be deemed an error and ignored. 20 times over what time frame? Normally calibrate at around 75-100 tips per hour

Vantage also shows "abnormal" rain rates when two counter increases are close by. That is how it is supposed to work.

[admin]

@DAP: I don't understand why you don't get rain totals as this works with other MB PROs fine.
Could you please give me remote access as explained here:
viewtopic.php?f=57&t=9885

Please send URL and password to "info(at)meteobridge.com".

[DAP]

sent with same subject as this thread.

[DAP]

That's certainly an abnormally high and probably unachievable rain rate in the real world and could very well be deemed an error and ignored. 20 times over what time frame? Normally calibrate at around 75-100 tips per hour

Vantage also shows "abnormal" rain rates when two counter increases are close by. That is how it is supposed to work.

Define "close by". Less than 20 seconds? The maximum rate of my ISS seems to be about 1/2 second per tip, so the system should not report abnormal rates for 1/2 second or longer, or heavy rains will be improperly recorded.
It is easy to test the maximum rate of a rain gauge, dump a bucket of water in the funnel, and record the minimum time between tips. That or anything longer should be considered normal.

[miraculon]

The Davis VP2 rain gauge seems to have a history of a low "catch" compared with other gauges. This has been a well discussed issue on WxForum.
http://www.wxforum.net/index.php?topic= ... #msg268001
My "24 hour" totals from MP-Pro agree well with the console display when the time periods line up. My CoCoRaHS 4" manual gauge and 8" NovaLynx gauges always record higher totals than the VP2. Today the VP2 was -16% and the NovaLynx was +4% re: the manual gauge.

Greg

[Mattk]

Any gauge requires at least a calibration check when in final mount and yes Davis gauges are certainly no exception which can take quite some time to get right, accuracy is in the +/- 4% to +/-5%, however the issue here is no catch at all.

Can't say I have seen this issue so far, have MB pro RF from a Vue and MB linked via IP loggers to standard VP2 ISS. There is no logger on the Vue, the comparisons are not exact but then I have been experimenting with the MB Pro. In any case certainly seeing rain registration as in both rate and amount.

[DAP]

The issues as I see them:
The Davis Vantage Pro2 in combination with the Meteobridge pro is always reading low by a wildly varying amount, most of the time more than 10%, sometimes as high as 50%.
My attempts to debug this are stymied by the meteobridge pro not recording the raw data read, but instead the derivative and the integral of the data, and not documenting the algorithm they use to calculate those from the data.
Worse, the integral records zero when the derivative shows a massively high rate of rain, or a fast but plausible rate of rain.
I would like to be able to turn on some logging of raw data so I could verify that the ISS was not missing tips.
I would also like to have the algorithms to translate tips into the derivative and the integral explained so I could verify the results.

[DAP]

Since this line of debugging seems to have stalled, I have ordered a Davis base station so I can compare its results. I had hoped I would not need it, but apparently I do. I also ordered a second 4" rain gauge so I can mount it near the Davis rain gauge without disrupting the one I'm currently using for recording rainfall. This will eliminate the claims of "75 yards apart will cause wildly different rain readings".
There are only two more months of rain before it stops raining for the summer here. I want to get this working before the rain starts again next fall.

[Mattk]

I believe you will find the Davis ISS/Console/Envoy combination does not rely on or transmit individual measured tips but transmits a combined rain total from which rain increments can be derived which effectively maintains cumulative rainfall totals just in case there are any transmission issues etc.

In any case I would suggest you properly calibrate the Davis rain collector first and fully understand just how the Davis cumulative rain totals work.

[DAP]

I believe you will find the Davis ISS/Console/Envoy combination does not rely on or transmit individual measured tips but transmits a combined rain total from which rain increments can be derived which effectively maintains cumulative rainfall totals just in case there are any transmission issues etc.

In any case I would suggest you properly calibrate the Davis rain collector first and fully understand just how the Davis cumulative rain totals work.

Calibration of the rain gauge would be pointless until I can prove the meteobridge pro is recording tips properly. So far, the evidence I have shows the meteobridge pro is ignoring some tips of the bucket. Even if the gauge was out of calibration, it would at least be consistent in the size of its error.
So far, I have plenty of evidence that there is a problem, but not enough to identify what the problem is.