I have had Davis systems the past 10 years and always interested in weather but I am new to this board. I know this topic has been discussed many times before but here is my concern.
I realize that the CWOP analysis can be suspect due to the accuracy of the reporting stations but I am having major problems with my Davis Vantage Pro 2 agreeing with our local airports. (I am CW4900 elevation of 2736 verified in NW KS)
Oberlin KS municipal airport 15 miles SE elevation 2703
McCook NE Airport (Ben Nelson) 17 miles NE elevation 2583
CW4900 elevation 2736
Current barometer readings.
Oberlin 30.10
McCook 30.13
My Console 30.26
My Envoy 30.00
I sent the Envoy and the Console into Davis 4 months ago and spent nearly $200 to get them corrected and “rebuilt” so that they could stay within their advertised specification. Needless to say, they are not even close to the the surrounding airport reading nor are they even close to each other and the Console and the Envoy are within 20 feet of each other in the house. My conclusion is that the Davis equipment come no where near their advertised accuracy. Of course the CWOP analysis is way off target and off by .18" HG as I write this yet yesterday it was tracking along the same line.
After chasing the numbers for several months I am convinced the accuracy promised by Davis it just pie in the sky and not related to reality. I have conversed with them many times but nothing changes and the units are still inaccurate. Supposedly they checked them when they were rebuilt but I wonder.
Before I started checking my Vantage Pro 2 against other local readings I was wrongly assuming that they gave the correct barometric reading but I was badly mistaken all these years. I didn’t place much faith in the CWOP analysis as when I went through the list there were some reports that were obviously erroneous. I know the airport readings are checked regularly for accuracy by the FAA and NOAA and have very little tolerance for accuracy.
I am sure glad I don’t set my altimeter to the readings from my station!!
Has anyone else experienced this problem with the Davis Units? I am befuddled. Thanks
PS: all other readings for Temp etc are right on the money.
CWOP expects altimeter readings from your station. Make sure you tick that setting in the CWOP/APRS settings page on the Altimeter barometer tab. Just tick the top entry unless you want WD to use the altimeter reading on your WD console.
CWOP gets it data from my Davis Envoy that according to Davis is identical to the barometer in the Console. They should read the same.
My weather information on the computer screen is Virtual Weather for good visibility.
If I change the barometer setting on the Envoy, it shows up immediately in CWOP and on the Virtual Weather screen.
My data goes from the Station, to the Console and the Envoy but there is a barometer in the Envoy in case someone does not have a console. The Console information would be worse than the Envoy but neither are accurate.
Both the Envoy and Console are set to the proper elevation. (2736 ft) I just checked both.
Per the instructions for the Envoy and the Console, all data is converted to sea level or corrected altimeter by the elevation. Any fine tuning is by setting the barometer to a known reading, in this case the local airports.
The VWS sends the corrected sea level data as the CWOP, Envoy and VWS screen all match.
Looking at my records, I have adjusted the Envoy down a net of .35" HG since July 22 so that it now reads the same as the local airport. I started the records on July 22 the date the Davis Envoy and Console were returned to me from Davis and adjusted to match the current airport data. I have never had to adjust the Envoy up, just down
The Console has never been adjusted in that same period but it now reads .18" HG too high.
I’m still puzzled but thanks for the ideas on what to check on.
It is strange that the console and the envoy should be so far off if they are both set to the same elevation, esp since they have just been calibrated by Davis. I have personally had two consoles and an envoy in the same location and the three readings tracked nicely within the Davis spec.
If VWS is sending sea level corrected baro to CWOP then it’s logical that your data may not match other sites that are correctly sending the CWOP requested altimeter pressure.
Thanks niko,
I am no expert on CWOP but why would it receive anything but corrected to sea level barometer data? At our elevation of 2736 feet the raw barometer reading would be off by about 2-1/2" HG if the others used raw verses corrected data. As a rule of thumb from my puddle jumper aircraft experience the altimeter setting was about 1’" HG for ever 1000 ft change in elevation. (High to low, look out below)
Interesting that yours track consistently which leads me to believe there is still something wrong with my units. I sent another email to Davis a couple minutes ago so maybe they have some eureka information.
The data to CWOP is not raw but altimeter pressure. There can be a slight difference between altimeter pressure and pressure corrected to sea level based on std temps and atmosphere and actual temps and humidity but it is usually only about .02" HG max variation. I think that is why Davis specs show.01" HG accuracy for proper elevation and setup and only .03" HG accuracy for elevation only. Raw pressure or station pressure here is about 27.4" HG.
Here again I am trying to remember my pilot training but could be in error.
Supposedly the Davis WeatherLink is supplying the altimeter pressure to CWOP at least that is what the literature says. The Davis link then feeds the VWS that puts it out on the internet.
I am still mystified why the Console reading does not stay within tolerance.
Last time I worked this issue WL was not providing altimeter readings correctly. I worked with a handful of local station owners who were not aware of CWOP guidelines for reporting altimeter pressure. One of the stations was using WL and after troubleshooting found out that WL does not report altimeter readings. I do not know if Davis has fixed WL to correct the problem.
Thanks Dan,
I see there are a couple of new updates for WeatherLink that I do not have installed so will update this weekend. The last update was issued Nov 10 2011.
I don’t think that your problem is with the vantage pro. The pressure sent to the weather program is a corrected number. Most other stations do not use this correction.
the reason most people on this forum do not have this problem is that WD has a program in it that removes the correction.
Using weather link or VWS sends SLP corrected. The only that you can cure your problem is to use a program called VW live. I have a friend here that was having that problem.
after he started using VP live it fixed the trouble . The WD module that WD uses is the same program. If you wish to pm me then it can be done here .
Chuck
I was finally in the same place as the two consoles, the baro spec is +/-0.03’’ Hg, as you can see they are well within that. Note that I had just relocated the lower one from another part of the house for the pic so the indoor temp/hum values have not yet adjusted to the location.
