Wrong rain readings.

[Bojan Vidanovic]

Hi,

I can't find any solution that would explain this issue with rain data.

I'm using Davis VantagePro2 Plus, and it's set up with Metric units, also Weewx(2.4.0) is set up with Metric units and rain bucket is set on 0.2mm.

The problems is i have wrong rain readings on weewx and don't know why is stored in database like in example below:

Example with current readings:

On my console current readings are:

- Daily rain: 11.0 mm

- Rain rate: 0.8 mm/hr

On Weewx web page report is:

- Rain rate: 1.2 mm/hr

But in database they are stored as:

- Rain (Daily rain): 0.02000000005

- rainRate: 0.12000000003

All other readings are stored with appropriate values, except rain.

Any ideas?

Thanks in advance.

[mwall]

On Sunday, February 2, 2014 1:07:39 PM UTC-5, Bojan Vidanovic wrote:

All other readings are stored with appropriate values, except rain.

Any ideas?

the metric units for recording rain and rain rate in weewx are cm and cm/hr, respectively.

weewx 2.6 introduces another variation called 'METRICWX' that uses mm and mm/hr.  it also uses meter/second instead of km/hr.

it looks like you might need to add a calibration to make the weewx values match those of the console.  you might want to take some measurements with a another instrument to do the calibration properly.

m

[Bojan Vidanovic]

Didn't know that.

I guess i'll wait for Weewx 2.6

[Thomas Keffer]

This still doesn't add up. 

First, when you say, "I'm using Davis VantagePro2 Plus, and it's set up with Metric units," do you mean that it has a metric rain bucket in it? If so, you must tell the console that it has such a bucket. Otherwise, it assumes that you have the conventional, US 0.01" bucket. See the docs for information on how to do this.

Second, when you say, "weewx is set up for metric units," do you mean that you set the option target_unit in weewx.conf to

  target_unit = METRIC

right?

Finally, when you say that the "daily rain" stored in the database is 0.02", how do you know that? The column rain in the archive database shows only the rain that fell during the archive interval. You have to sum it since midnight to get the daily rain. Or, did you look in the stats database?

The new metric system METRICWX changes none of this. 

-tk

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[Bojan Vidanovic]

Sorry for misunderstaning,

1. Yes, it has a metric rain bucket and it's set in console to use 0.2 mm.

2.  Again yes, i meant on target_unit = METRIC
3. Ok, my mistake. So i need to calibrate it to get proper results on web page. If you look rainRate is 0.4mm higher than it should be.

[Thomas Keffer]

You should not have to calibrate it. Weewx should work just fine with a metric rain bucket. 

With a .2mm bucket, it should record .02 cm in the database with every tip.

With rainRate: weewx just returns whatever the console emits. There is nothing special about it.

To make sure your console is set up the way you think it is, run the utility wee_config_vantage with the option --info. If you used the setup.py installation, it would look like this:

cd /home/weewx

./bin/wee_config_vantage weewx.conf --info

Show us what the results are.

-tk

[Bojan Vidanovic]

Davis Vantage EEPROM settings:
    
    CONSOLE TYPE:                   VantagePro2
    
    CONSOLE FIRMWARE:
      Date:                         Apr 16 2012
      Version:                      3.00
    
    CONSOLE SETTINGS:
      Archive interval:             600 (seconds)
      Altitude:                     3 (meter)
      Wind cup type:                large
      Rain bucket type:             0.2 MM
      Rain year start:              10
      Onboard time:                 2014-02-03 20:08:00
      
    CONSOLE DISPLAY UNITS:
      Barometer:                    mbar
      Temperature:                  degree_10F
      Rain:                         mm
      Wind:                         km_per_hour
      
    CONSOLE STATION INFO:
      Latitude (onboard):           45.4
      Longitude (onboard):          12.5
      Use manual or auto DST?       AUTO
      DST setting:                  N/A
      Use GMT offset or zone code?  GMT_OFFSET
      Time zone code:               N/A
      GMT offset:                   +1.0 hours
        
    RECEPTION STATS:
      Total packets received:       8783
      Total packets missed:         49
      Number of resynchronizations: 0
      Longest good stretch:         550
      Number of CRC errors:         17
      
    BAROMETER CALIBRATION DATA:
      Current barometer reading:    29.933 inHg
      Altitude:                     3 feet
      Dew point:                    39 F
      Virtual temperature:          42 F
      Humidity correction factor:   15
      Correction ratio:             1.000
      Correction constant:          +0.000 inHg
      Gain:                         0.000
      Offset:                       -53.000

[Thomas Keffer]

Looks good. It confirms that it is expecting the 0.2mm rain bucket.

What is leading you to believe that rainRate is wrong? Are you saying that the value you are seeing on the console does not match what is on the webpage? If so, there can be a variety of reasons for this. 

The webpage information comes from the console's logger, which emits "the highest rainrate over the archive period." The documentation is a little vague about exactly what they mean by this, but it generally answers the question, "How  hard did it rain?"

The console shows the most recent rain rate, within the last LOOP period, which on the Vantage is 2.5 seconds. 

These numbers may or may not be the same.

-tk

[Bojan Vidanovic]

As i said, everthing is set up correctly, i have checked settings few times to get sure.

On webpage, the section "Current Conditions" is loaded from last record of archive database or consol's logger? Beacuse i've matched data with last archive record.

[Thomas Keffer]

The section "Current Conditions" comes from the last record in the archive database.

-tk