[wxqc] Barometric pressure errors

Sun May 13 13:57:37 CDT 2007

First of all my apologies to the group. I had intended to send my email to
John CW3212 and not everyone on this list. Sorry! John would have understood
my ramblings in that he had the same problem two years ago
http://server.gladstonefamily.net/pipermail/wxqc/2005-May/002898.html

"My QC reports have been showing that my barometric pressure readings drift 
to either 3 millibars too high, or 3 millibars too low, and then track at 
the same error."

I had initially set my up my barometer per Davis's manual using "Sea Level"
Pressure from the nearest airport. In my case KBJC 
http://www.met.utah.edu/cgi-bin/droman/meso_table_mesowest.cgi?stn=KBJC
<http://www.met.utah.edu/cgi-bin/droman/meso_table_mesowest.cgi?stn=KBJC&uni
t=0&time=GMT> &unit=0&time=GMT
I had assumed some internal calculations in the Vantage Pro 2 Console would
compensate for the large difference (Sea level and Altimeter).
This was shown to be incorrect after a few hours. I then used the proper
Altimeter reading. After a couple of days my readings would go up and then
down, following the pressure trend, but would be exaggerated by 3 or 4 mbs
in whatever direction the barometer was heading.
Having read that some barometer errors were corrected in the latest
firmware, I decided to try an upload to the latest version even though I may
have already had this. The upload caused my barometer to "stick" and not
change at all. Davis support was aware of the problem and instructed me to
set the elevation to zero and let it go over night. That did not work but by
deleting the zero and leaving it blank did un-stick the barometer. Two days
of observing the barometer, elevation at sea level and adding the aprox. 5.5
inches to compensate for 5454 feet seemed to work.
I have now started over with the correct elevation and correct Altitude
reading. Time will tell if this takes care of the problem. I did read where
one person had claimed he could tell who had a Vantage Pro by just looking
at the graphs of the various CWOP sites and observing this error. I hope
that is not the case.

Chris  AR893

  _____  

From: wxqc-bounces at lists.gladstonefamily.net
[mailto:wxqc-bounces at lists.gladstonefamily.net] On Behalf Of Don Jeerings
Sent: Saturday, May 12, 2007 8:12 PM
To: Discussion of weather data quality issues
Subject: [wxqc] Barometric pressure errors

Searching the "Net" to try to figure out why my brand new Vantage Pro 2
barometer tracks 3 or 4 mb's plus or minis over a period of a few days. I
ran across your inquire as to the same problem.  Notice your quality checks
are 2 thumbs up now. May I ask what did you finely do to correct this, set
to zero elevation? I am at 5454ft.

My old weather monitor II was just set to zero and I added 5.35 inches
through software for years with great results.

I found lots of references but no solutions.

I would greatly like to know what you ended up doing.

Chris 

AR893 (station off line because of the errors)

Chris 

There may be two different problems, Keep in mind that corrections can be
made in the Vantage Pro 2 (ISS) console  or sometimes in the associated
software. (like WD Display software by Brian Hamilton). 

It is best to program the Vantage Pro 2 equipment first.

You will need to first program in your altitude and since you are over 5,000
ft, this will make a significant correction. 

Once you have the altitude programmed in you can make small corrections by
using the BAR section.

If you have the Davis Console Manual I will refer to the page numbers. 

If you do not have the manual, E-mail me back and I will try and copy out
the pertinent information for you. 

 After you go into setup, look on Page 15  for the elevation correction
procedures,

 And look at the top of page 26 for making the barometer correction
procedures.. 

Note that if you use the Mill bar units for you're BAR settings, you will
obtain better resolution  and better accuracy. (also use Fahrenheit on your
temperature for better resolution)

After you make a calibration change you should wait at least 24 hours to
evaluate it. Make small changes and allow a day or so between calibration
corrections. KEEP A LOG of your corrections so you know where you are.

Let me know if this helps,. I can copy down in detail and send you more
information. 

Don Jeerings

Djeerings at tampabay.rr.com

Note also that the set up is for programming of many other important
variables for your system. 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://server.gladstonefamily.net/pipermail/wxqc/attachments/20070513/5b01520d/attachment.htm 