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Re: Barometric Pressure Reporting of Davis Vantage Pro 2

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  • wuhu_software
    Digitalhexcode, I believe your guess about the console being the source of this 15 minute delay in the pressure data. I cannot imagine why the Weatherlink DLL
    Message 1 of 4 , Sep 21, 2010
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      Digitalhexcode,

      I believe your guess about the console being the source of this 15 minute delay in the pressure data. I cannot imagine why the Weatherlink DLL would do this, but I suppose anything is possible with weather stations and software.

      Reading over the notes for the DLL, I may have found a way to force the reading to update when I choose. 

      There was another issue that cropped up with the Davis stations recently. In order to obtain the wind gust over the past 10 minutes, a new call is required to do this.

      When you retrieve the 10 minute gust value, or force the re-sampling of the relative pressure, this requires a bit of communication time with the console. Rather than to force the gust and relative pressure reads on every update (this would significantly affect the over all scan time), I am polling these variables at the following rates:

      Gust: 10 seconds
      Relative Pressure: 30 seconds

      While I did attempt to verify the forced pressure sampling rate, it appears that my readings are very stable right now. I did see one "blip" that lasted a couple of mins, but that was about it. 

      To see what is going on, you can open the log and check the check box labeled "Show Console Com. Errors". Normally this is used for debugging the communications but it will show you what is being polled and when. You will notice some of the lines that follow the retrieval of gust and pressure readings are following by either (cached) or (slow). The slow ones require a transaction with the console. You can notice the amount of time it takes to acquire this data by measuring how long the log is paused during the acquisition. On my system, these calls can take a good second or two to complete.

      Dan Brown (long time WUHU user) has been debugging some test versions for me and I believe that the Vue console actually responds much faster than the VP2 console from what I can see. I suppose I should verify with Dan that he has a USB data logger like the one I tested.

      The following version is available for testing that includes the above mentioned modifications.


      Feedback appreciated.


      --- In wuhu_software_group@yahoogroups.com, "Digitalhexcode" <digitalhexcode@...> wrote:
      >
      > It would seem that the console itself does some averaging according to a Google search "force vantage barometer update". The console does a 15 minute average which is why the peaks appear chopped off and the slopes are blocky on the pressure graph but not the temp as seen here on my station running WUHU.
      >
      > http://www.findu.com/cgi-bin/wxpage.cgi?call=NR6G-1&last=240
      >
      > For a comparison, here is a Davis Vantage Pro 2 with WeatherLink
      >
      > http://www.findu.com/cgi-bin/wxpage.cgi?call=DW0117&last=240
      >
      > It appears that the VPLive software and Cumulus have found a way to force the console to update the pressure readings as seen here.
      >
      > http://www.softwx.com/weather/vplive.html
      >
      > http://sandaysoft.com/cumulus-184-released
      >
      > But they don't mention how they were able to force the console to give instantantaneous pressure readings.
      >
      >
      >
      > --- In wuhu_software_group@yahoogroups.com, "wuhu_software" wuhu_software@ wrote:
      > >
      > >
      > > It may be that other software packages are performing averaging and / or have a longer sample time. I read somewhere that Weatherlink samples the pressure only every 15 mins. WUHU is simply reporting the value at the moment the sample is read.
      > >
      > > I am not sure why you would want to average the samples to smooth the curve rather than use the real sensor data, but who knows?
      > >
      > >
      > > --- In wuhu_software_group@yahoogroups.com, "Digitalhexcode" <digitalhexcode@> wrote:
      > > >
      > > > I have a Davis Vantage Pro 2 Plus and recently switched from WeatherLink to WUHU software. The one thing that stuck out at me from the start was that the barometric pressure readings went from a smooth slope on Weather Underground and CWOP to a stair step looking line graph. A friend of mine recently put his Vantage Pro 2 on WUHU and noticed the same thing. It is as though WUHU reports the pressure less often than the other sensors. Does anyone know if this is the case? Thanks for any help.
      > > >
      > > >
      > > > http://www.findu.com/cgi-bin/wxpage.cgi?call=NR6G-1&last=12
      > > >
      > > >
      > > > http://www.wunderground.com/weatherstation/WXDailyHistory.asp?ID=KCAVISAL6
      > > >
      > >
      >
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