Author Topic: Incorrect CWOP barometer with Davis Vue ***RESOLVED***  (Read 12256 times)

0 Members and 1 Guest are viewing this topic.

Offline LittletonCOwx

  • Senior Member
  • **
  • Posts: 78
  • Droplet
Incorrect CWOP barometer with Davis Vue ***RESOLVED***
« on: February 13, 2014, 02:33:03 AM »
***RESOLVED***  See post #44 and #45

Just got my Davis Vantage Vue online tonight through the TL-MR3020 Meteobridge once my USB logger arrived.   \:D/  So far from what I can tell, it is working great, with the exception of barometric pressure reported to CWOP.  From what I can tell here, it appears to be reporting about 13-14 millibars low compared to what is reported elsewhere.  The "live data" tab in the Meteobridge shows the correct number for the corrected SLP too.  Note, I'm at ~5630 feet, so absolute pressure is WAY lower than the reported difference, so I don't *think* that has anything to do with it.

Any ideas?  I don't understand why it would be right everywhere but CWOP.  I've done a little bit of researching so far, but haven't come up with an answer yet.  Does CWOP do some kind of offset once they've received the reported data?  Obviously I don't want to go chasing this problem by adjusted my barometer offset if it is only being reported incorrectly in one place.  Don't have any more time to chase this tonight as I need to get to bed, so I thought I'd ask here.  Thanks in advance!
« Last Edit: March 08, 2014, 07:32:35 PM by LittletonCOwx »
"Engineers don't idle well."     EW4560

Davis Vantage Vue | Belfryboy Clone USB Logger (fw v3.0 compatible :cool:) | MeteoBridge



Offline ValentineWeather

  • Forecaster
  • *****
  • Posts: 6364
    • Valentine Nebraska's Real-Time Weather
Re: Incorrect CWOP barometer with Davis Vue
« Reply #2 on: February 13, 2014, 09:32:14 AM »
Just got my Davis Vantage Vue online tonight through the TL-MR3020 Meteobridge once my USB logger arrived.   \:D/  So far from what I can tell, it is working great, with the exception of barometric pressure reported to CWOP.  From what I can tell here, it appears to be reporting about 13-14 millibars low compared to what is reported elsewhere.  The "live data" tab in the Meteobridge shows the correct number for the corrected SLP too.  Note, I'm at ~5630 feet, so absolute pressure is WAY lower than the reported difference, so I don't *think* that has anything to do with it.

Any ideas?  I don't understand why it would be right everywhere but CWOP.  I've done a little bit of researching so far, but haven't come up with an answer yet.  Does CWOP do some kind of offset once they've received the reported data?  Obviously I don't want to go chasing this problem by adjusted my barometer offset if it is only being reported incorrectly in one place.  Don't have any more time to chase this tonight as I need to get to bed, so I thought I'd ask here.  Thanks in advance!

WU takes the direct reading off the console so 29.93" is correct. Cwop wants altimeter so is making adjustments from station pressure.
What I've done is set console elevation 0' and adjust console pressure to nearby airport altimeter. Problem solved both CWOP and console will be correct. 
Randy

Offline LittletonCOwx

  • Senior Member
  • **
  • Posts: 78
  • Droplet
Re: Incorrect CWOP barometer with Davis Vue
« Reply #3 on: February 13, 2014, 11:29:31 AM »
Read this thread.

http://www.wxforum.net/index.php?topic=19787.0

Wow.   #-o  What a pain in the behind.  Thank you Davis...   :roll:

I've only looked at the first post so far, and it just should NOT be this difficult!    ](*,)


WU takes the direct reading off the console so 29.93" is correct. Cwop wants altimeter so is making adjustments from station pressure.
What I've done is set console elevation 0' and adjust console pressure to nearby airport altimeter. Problem solved both CWOP and console will be correct. 

Interesting workaround.  Do the other reports to places like WU still show up correctly?  I would think if the console shows the correct SLP, reports to WU and the like would be OK (hard to say with Meteobridge though; I might just have to try this tonight and see what happens).

----------------------------------------------------------------------------

Interesting aside:

My Dad is a longtime pilot (CFII) and I've done some flying myself, so I fully understand what is going on here.  What I find strange; I have an altimeter that my Dad got from a friend at one of the Metrology labs out at the airport.  It is about 20 years old, and didn't quite pass muster when it was in for calibration a few years back.  While it may not be good enough for a plane anymore (was off by about as much as 10 feet over its range), it is still plenty good for my living room shelf as a unique pressure display!  8-)

I can display altimeter setting on my Vue console by pressing the "Bar" button, then repeatedly pressing the "WxCntr" button.  So far for the past couple of months since I've had my Davis Vue up and running, the altimeter display on the console has shown the correct setting according to my altimeter (which gave me confidence in my +.02" barometer adjustment).  Just like when you're flying, you take that number and dial it into the altimeter with the adjustment knob, and it should correctly display your current altitude (lest you may crash whilst flying).  Hasn't been off more than 10 feet any time I've checked it.  :-k

Thanks for the replies so far!
UU
"Engineers don't idle well."     EW4560

Davis Vantage Vue | Belfryboy Clone USB Logger (fw v3.0 compatible :cool:) | MeteoBridge



Offline LittletonCOwx

  • Senior Member
  • **
  • Posts: 78
  • Droplet
Re: Incorrect CWOP barometer with Davis Vue
« Reply #5 on: February 13, 2014, 01:33:01 PM »
Ugh.  This is just STUPID! :roll:  To make matters worse, NONE of the correction methods are exact either!!!  #-o  Every single one makes an assumption or approximates some variable in the calculation.  Any time you have to interpolate and/or extrapolate data (i.e. table look up, like an atmosphere table), you are not getting an exact answer.  Close, maybe (and likely close enough for most purposes), but not exact.

While I fully understand everything that is going on (I deal with this kind of stuff ALL the time as an aerospace engineer launching rockets; we kind of HAVE to know this stuff...), I find it pretty pathetic that all of these organizations can't just agree on one pressure "standard" and go with it.  I can't believe there isn't some kind of working group or standards association for this.   :-&

The average person just trying to upload their weather data is NEVER going to go through this much effort to verify their pressure data are correct. (Though the average person probably won't go beyond uploading to WU either...)
"Engineers don't idle well."     EW4560

Davis Vantage Vue | Belfryboy Clone USB Logger (fw v3.0 compatible :cool:) | MeteoBridge


Offline LittletonCOwx

  • Senior Member
  • **
  • Posts: 78
  • Droplet
Re: Incorrect CWOP barometer with Davis Vue
« Reply #6 on: February 15, 2014, 12:41:54 AM »
Was playing around with this today.  Turns out, when using Meteobridge, it doesn't really matter what settings you have on the Vue console, so long as the displayed pressure is correct, as Meteobridge uses that final corrected SLP as a starting place for its reporting.  Apparently, the SLP / Altimeter adjusted barometric pressure sent out to the world is done inside the Meteobridge software, so I just zeroed out the altitude correction there, and now my CWOP data looks correct (or at least really close).

I actually like it this way, as I can still view the correct actual station pressure and the altimeter setting for my location through the Vue console.  Just got set up through MADIS this evening, so hopefully I can check out my data quality analysis soon.

Thanks for the help!

^^^ So, based on following posts, this "understanding" I had was not quite correct.  The adjusted pressure sent to places like WU has nothing to do with the raw pressure Meteobridge uses to make the CWOP pressure calculation.  Noting this for posterity's sake.
« Last Edit: February 27, 2014, 08:00:18 PM by LittletonCOwx »
"Engineers don't idle well."     EW4560

Davis Vantage Vue | Belfryboy Clone USB Logger (fw v3.0 compatible :cool:) | MeteoBridge


Offline docbee

  • Moderator
  • Forecaster
  • *****
  • Posts: 853
    • smartbedded
Re: Incorrect CWOP barometer with Davis Vue
« Reply #7 on: February 16, 2014, 01:27:27 PM »
Was playing around with this today.  Turns out, when using Meteobridge, it doesn't really matter what settings you have on the Vue console, so long as the displayed pressure is correct, as Meteobridge uses that final corrected SLP as a starting place for its reporting.

When you have an older console firmware version that does not support LOOP2 packets, then you are right. If it supports LOOP2, Meteobridge takes the raw pressure from LOOP2 and starts computing from that which is much better than reconstruction station pressure from Vantage's sealevel and then going forward to compute altimeter pressure from that. Too make things annoying, LOOP2 does not contain all you need, so SW has to toggle between LOOP and LOOP2 requests. However, all this is a pain in the ... and I am happy it now works for you ok.
founder of smartbedded.com - home of meteohub, meteoplug, meteobridge, meteostick

Offline LittletonCOwx

  • Senior Member
  • **
  • Posts: 78
  • Droplet
Re: Incorrect CWOP barometer with Davis Vue
« Reply #8 on: February 16, 2014, 08:02:55 PM »
Thank you for the follow-up on this topic Boris!   =D>  It is REALLY helpful to know that!

I do have the most recent Davis firmware on my Vue, so the readings that initially went to CWOP were strange.  I played around with the console and Meteobridge settings (methodically) until I figured out where the corrections were taking place, and from there, figured out what I had to do to get the correct data to both WU and CWOP.

I think your Meteobridge product is excellent!  :cool:  Much better than having to have a computer running 24/7, while also being a lot smaller physically and using only about 3 watts of power.  Bravo!  UU  The iPhone graphs are icing on the cake!   \:D/  Thank you!
"Engineers don't idle well."     EW4560

Davis Vantage Vue | Belfryboy Clone USB Logger (fw v3.0 compatible :cool:) | MeteoBridge


Offline LittletonCOwx

  • Senior Member
  • **
  • Posts: 78
  • Droplet
Re: Incorrect CWOP barometer with Davis Vue
« Reply #9 on: February 27, 2014, 07:57:17 PM »
Was playing around with this today.  Turns out, when using Meteobridge, it doesn't really matter what settings you have on the Vue console, so long as the displayed pressure is correct, as Meteobridge uses that final corrected SLP as a starting place for its reporting.

When you have an older console firmware version that does not support LOOP2 packets, then you are right. If it supports LOOP2, Meteobridge takes the raw pressure from LOOP2 and starts computing from that which is much better than reconstruction station pressure from Vantage's sealevel and then going forward to compute altimeter pressure from that. Too make things annoying, LOOP2 does not contain all you need, so SW has to toggle between LOOP and LOOP2 requests. However, all this is a pain in the ... and I am happy it now works for you ok.

So, we've had some pretty wild swings in pressure the past week or so here (about 995mbar to 1035mbar). The past 36 hours especially, we have gone from about 1035mbar down to 1000mbar and still dropping fast!   :shock:

I thought I had my barometer issue solved, but according to my CWOP analysis (and a couple other Davis stations near me), I am still showing much larger variations in pressure than they think I should be.  It is especially bad  at the lowest and highest pressures I've seen (+5mbar down around 995mbar, and -10mbar up at about  1035mbar).   ](*,)  When things aren't changing much and are between about 1010mb and 1020mbar, I seem to be within the CWOP acceptable +/- 2mbar error.

To complicate matters, there is another station less than 3 miles away from me, also a Davis Vantage Vue but using different software (Cumulus), where our pressure charts on WU are nearly carbon copies of each other.  However, his CWOP pressure chart follows the "analysis" line MUCH, MUCH more closely than mine!   #-o  This indicates to me that there is still something not quite right with how the Meteobridge software is reporting my "Altimeter" pressure to CWOP.

Without insight to the calculations, I have NO WAY of analyzing this any further, and am REALLY hoping for some additional help!  I am at a complete loss as to what else that I can do to fix the CWOP reporting without messing up my WU reports in the process.  I don't think that I should have to choose one to be correct over the other, and I would really like to get to the bottom of this!

My gut is telling me that part of the problem is my high altitude (5,629ft. or 1,716m), and the larger pressure correction necessary for that.

PLEASE HELP!!!   [-o<

Thanks in advance!!!
 UU
« Last Edit: February 27, 2014, 08:01:59 PM by LittletonCOwx »
"Engineers don't idle well."     EW4560

Davis Vantage Vue | Belfryboy Clone USB Logger (fw v3.0 compatible :cool:) | MeteoBridge


Offline LittletonCOwx

  • Senior Member
  • **
  • Posts: 78
  • Droplet
Re: Incorrect CWOP barometer with Davis Vue
« Reply #10 on: March 05, 2014, 02:24:53 AM »
OK, I think I've figured it out, unfortunately.   :-(

Meteobridge IS NOT SENDING CWOP THE ALTIMETER BAROMETER!!!  #-o

We've had some further pressure swings along with some pretty good temperature swings lately as well.  The "altimeter" barometric pressure has been off by as much as 0.35 inHg versus the SLP (confirmed by my actual aircraft altimeter).

Boris, how can I send SLP to Weather Underground while sending Altimeter to CWOP?   ](*,)
"Engineers don't idle well."     EW4560

Davis Vantage Vue | Belfryboy Clone USB Logger (fw v3.0 compatible :cool:) | MeteoBridge


Offline George Richardson

  • WxElement panel
  • Forecaster
  • *****
  • Posts: 1391
    • Smith Mountain Lake Weather
Re: Incorrect CWOP barometer with Davis Vue
« Reply #11 on: March 05, 2014, 09:56:40 AM »
"Boris, how can I send SLP to Weather Underground while sending Altimeter to CWOP?"

VPLive will do that very nicely!

Offline LittletonCOwx

  • Senior Member
  • **
  • Posts: 78
  • Droplet
Re: Incorrect CWOP barometer with Davis Vue
« Reply #12 on: March 05, 2014, 10:17:33 AM »
"Boris, how can I send SLP to Weather Underground while sending Altimeter to CWOP?"

VPLive will do that very nicely!

*deleted* Sorry George, my bad.   :oops:

I don't want to run a computer 24/7, and I already invested in the Meteobridge product.
« Last Edit: March 06, 2014, 01:46:43 PM by LittletonCOwx »
"Engineers don't idle well."     EW4560

Davis Vantage Vue | Belfryboy Clone USB Logger (fw v3.0 compatible :cool:) | MeteoBridge


Offline George Richardson

  • WxElement panel
  • Forecaster
  • *****
  • Posts: 1391
    • Smith Mountain Lake Weather
Re: Incorrect CWOP barometer with Davis Vue
« Reply #13 on: March 05, 2014, 10:44:22 AM »
LittletonCOwx,

"how can I send SLP to Weather Underground while sending Altimeter to CWOP?

VPLive will do that very nicely!"

"NOT helping...  I really don't appreciate the snarky response either."

I don't consider my response "snarky".

BTW, is your name William? (Now that's Snarky)

George

Offline Beaudog

  • Forecaster
  • *****
  • Posts: 1217
Re: Incorrect CWOP barometer with Davis Vue
« Reply #14 on: March 05, 2014, 11:00:44 AM »
I have already gone thru this.     It is indeed the altitude that aggravates the problem. I am at 5000ft also.

You are kinda falling into the CWOP trap. They warn not to try and match the analysis line exactly and to just use it for a guide. And, to try and match valid local stations even if they don't match the red line.

Your chart does not look that far off to me.   The spacial thing can be caused just by that one big blip.   I have never figured out exactly what causes those but I get them also when I am trying to tweak the barometer.  You are pretty close to most of the local stations, less that 8 miles.

You say you don't want to hear it but, the only way I ever got it correct was to use one program for everything except CWOP and then to use VP LIVE for CWOP.

If you figure out how to get it right be sure to let us know.




Offline LittletonCOwx

  • Senior Member
  • **
  • Posts: 78
  • Droplet
Re: Incorrect CWOP barometer with Davis Vue
« Reply #15 on: March 05, 2014, 11:02:03 AM »
*deleted*  Sorry George, my bad.   :oops:
« Last Edit: March 06, 2014, 01:46:29 PM by LittletonCOwx »
"Engineers don't idle well."     EW4560

Davis Vantage Vue | Belfryboy Clone USB Logger (fw v3.0 compatible :cool:) | MeteoBridge


Offline LittletonCOwx

  • Senior Member
  • **
  • Posts: 78
  • Droplet
Re: Incorrect CWOP barometer with Davis Vue
« Reply #16 on: March 05, 2014, 11:11:22 AM »
I have already gone thru this.     It is indeed the altitude that aggravates the problem. I am at 5000ft also.

You are kinda falling into the CWOP trap. They warn not to try and match the analysis line exactly and to just use it for a guide. And, to try and match valid local stations even if they don't match the red line.

Your chart does not look that far off to me.   The spacial thing can be caused just by that one big blip.   I have never figured out exactly what causes those but I get them also when I am trying to tweak the barometer.  You are pretty close to most of the local stations, less that 8 miles.

You say you don't want to hear it but, the only way I ever got it correct was to use one program for everything except CWOP and then to use VP LIVE for CWOP.

If you figure out how to get it right be sure to let us know.





To be clear, I am NOT trying to match the red line. However, in my case, the red line is usually almost right on what the altimeter pressure should be.  I just want my altimeter pressure sent to CWOP, correctly, as it is supposed to be.  My pressure (SLP) is not that far off from the analysis right now, but it has been WAY off recently (10 -12 mbar).

I KNOW for a fact that my altimeter pressure is not being sent to CWOP.  It's right there on the console display!

I am not going to leave a computer running 24/7, so that eliminates most all of the other software out there.  Meteobridge should be able to get this right, and I do not understand why it isn't.  Something appears to be wrong.

I've sent Boris another PM.  I've provided him with a lot of information, and I'm hoping he'll be more responsive this time around.
"Engineers don't idle well."     EW4560

Davis Vantage Vue | Belfryboy Clone USB Logger (fw v3.0 compatible :cool:) | MeteoBridge


Offline PaulMy

  • Forecaster
  • *****
  • Posts: 5509
    • KomokaWeather
Re: Incorrect CWOP barometer with Davis Vue
« Reply #17 on: March 05, 2014, 11:40:52 AM »
Quote
Wow man, are you always like this?  Thanks for not helping...
Sorry I can't help with your problem but that response to George is uncalled for as well as your previous comment.  George is a long-time good example of the many people on this forum that are or try to be helpful and making this the great forum it is.
 
Paul
 
 

Offline LittletonCOwx

  • Senior Member
  • **
  • Posts: 78
  • Droplet
Re: Incorrect CWOP barometer with Davis Vue
« Reply #18 on: March 05, 2014, 11:48:27 AM »
Paul,
This is not the first time George has rubbed me the wrong way.  He also seems to have the (rather poor) habit of recommending someone else's software/hardware in any given forum.

When asking for help with my Meteobridge, how is it helpful to say, "Get something different".

Forum veteran or not, poor form is uncalled for imo.
"Engineers don't idle well."     EW4560

Davis Vantage Vue | Belfryboy Clone USB Logger (fw v3.0 compatible :cool:) | MeteoBridge


Offline capeweather

  • Global Moderator
  • Forecaster
  • *****
  • Posts: 1309
    • http://www.capeweather.com
Re: Incorrect CWOP barometer with Davis Vue
« Reply #19 on: March 05, 2014, 12:57:23 PM »
This topic has been reported. Please stop and stay on topic. Thanks.

Chris
Cape Coral, Florida
Website: http://www.capeweather.com
Website: http://www.fortmyersweather.net

Offline ValentineWeather

  • Forecaster
  • *****
  • Posts: 6364
    • Valentine Nebraska's Real-Time Weather
Re: Incorrect CWOP barometer with Davis Vue
« Reply #20 on: March 05, 2014, 03:10:11 PM »
LittletonCOwx did you try setting console to 0' elevation including metrobridge software. Then adjusting console pressure to nearby airport altimeter. If everything is sea level there should be no corrections made by metrobridge.
Randy

Offline LittletonCOwx

  • Senior Member
  • **
  • Posts: 78
  • Droplet
Re: Incorrect CWOP barometer with Davis Vue
« Reply #21 on: March 05, 2014, 04:29:06 PM »
LittletonCOwx did you try setting console to 0' elevation including metrobridge software. Then adjusting console pressure to nearby airport altimeter. If everything is sea level there should be no corrections made by metrobridge.

Meteobridge is currently set to 0 ft (the blip in my CWOP data last night is when I set Meteobridge to my actual altitude of 5,629 ft).  However, currently the Vue console is not set to 0 ft (though I have tried that).  I do not want to be sending altimeter pressure to Weather Underground, and I would like my console to show SLP, so setting it to 0 isn't going to help.  It shouldn't matter anyway, as Boris said above that Meteobridge uses raw pressure and calculates everything from there.

The LOOP2 packets do have an "Altimeter Setting" entry (offset #69), but I have no idea if Meteobridge is using that.  If that is the same as the "Altimeter Pressure" which can be displayed on the console (by pressing "Bar", then "WxCntr" repeatedly), then it is exactly what I would want sent to CWOP, as it matches my airplane altimeter (as it should).
"Engineers don't idle well."     EW4560

Davis Vantage Vue | Belfryboy Clone USB Logger (fw v3.0 compatible :cool:) | MeteoBridge


Offline ValentineWeather

  • Forecaster
  • *****
  • Posts: 6364
    • Valentine Nebraska's Real-Time Weather
Re: Incorrect CWOP barometer with Davis Vue
« Reply #22 on: March 05, 2014, 04:55:32 PM »
Most everyone uses the altimeter which is the simple adjusted pressure for elevation. I use altimeter for all my pressure readings, including console plus what I send to CWOP and WU. From there they can calculate station pressure sea level pressure. MesoWest takes the altimeter data from CWOP and calculates it because they know the true elevation 4,170. If you know your CWOP station ID you can go to MesoWest and get the calculated station pressure, sea level pressure.

http://mesowest.utah.edu/cgi-bin/droman/meso_base.cgi?stn=C1122&unit=0&time=LOCAL&product=&year1=2014&month1=2&day1=14&hour1=8&hours=&past=0&graph=0

Nearby airport 1.7 miles different elevation.
http://mesowest.utah.edu/cgi-bin/droman/meso_base.cgi?stn=KPGA
« Last Edit: March 05, 2014, 04:59:09 PM by RMC »
Randy

Offline ValentineWeather

  • Forecaster
  • *****
  • Posts: 6364
    • Valentine Nebraska's Real-Time Weather
« Last Edit: March 05, 2014, 05:32:39 PM by RMC »
Randy

Offline LittletonCOwx

  • Senior Member
  • **
  • Posts: 78
  • Droplet
Re: Incorrect CWOP barometer with Davis Vue
« Reply #24 on: March 05, 2014, 05:48:51 PM »
Randy, I appreciate that.  Unfortunately, right now is the worst possible time to look at my data as altimeter pressure and SLP are nearly identical, so the problem is almost completely absent.  A couple of days ago that was not the case.  Note that since CWOP is being sent SLP by Meteobridge, MesoWest thinks is it altimeter, when it is not.  Thus, they're back-correcting my SLP from that, so that's even further off than it should be.  Ugh.

PS - I'm looking at Centennial airport (KAPA) out my office window just over 1 mile away.  My dad flies out of there (and sometimes I do too).
« Last Edit: March 05, 2014, 05:51:07 PM by LittletonCOwx »
"Engineers don't idle well."     EW4560

Davis Vantage Vue | Belfryboy Clone USB Logger (fw v3.0 compatible :cool:) | MeteoBridge