cloudy cloudy

Author Topic: Simple Barometer adjustment help needed  (Read 5027 times)

0 Members and 1 Guest are viewing this topic.

Offline wc4r

  • Posts: 85
  • Williamsburg, VA
    • Williamsburg Weather
Simple Barometer adjustment help needed
« on: October 16, 2011, 01:08:00 PM »
According to the CWOP at http://weather.gladstonefamily.net/site/AP696 my barometer is off a bit. Now it may be due to my elevation setting being incorrect a little on my Davis Vantage Pro2 or maybe I need to make a correction in the WD software. What is recommended and which direction/amount should I adjust?
Joe

Offline NorCal Dan

  • Dan - KJ6RGX
  • Posts: 10,554
  • Davis Vue/Win10
  • Ocean Park, WA.
    • Traveling RV Weather
Re: Simple Barometer adjustment help needed
« Reply #1 on: October 16, 2011, 03:44:44 PM »
Argh...never adjust your readings just to match up with what CWOP shows...

Second, CWOP is expecting altimeter readings from your station...make sure WD is set to send altimeter in the CWOP setup section.

Offline wc4r

  • Posts: 85
  • Williamsburg, VA
    • Williamsburg Weather
Re: Simple Barometer adjustment help needed
« Reply #2 on: October 16, 2011, 04:47:53 PM »
Thanks Dan. Altimeter was net set. I'll see how it goes now.
73
Joe

Offline NorCal Dan

  • Dan - KJ6RGX
  • Posts: 10,554
  • Davis Vue/Win10
  • Ocean Park, WA.
    • Traveling RV Weather
Re: Simple Barometer adjustment help needed
« Reply #3 on: October 16, 2011, 06:43:03 PM »
After looking into this a little more I see your altitude is only 33' above sea level.  The altimeter setting should not be used at this low of altitude according to Windy.

The best answer to the problem is to calibrate your barometer.  You can either send it in to Davis to have it NIST certified, or you acquire a NIST certified barometer that you can use as a reference to calibrate your barometer.

Now since most of us here do this as a hobby you probably don't want to spend a couple hundred dollars to calibrate your barometer.  So what you could do is set an offset in WD to match up with the closest METAR or airport to your location.  The down side to using WD to apply the offset is that it only works on live data.  If you need to import data from the datalogger it will not have the offset applied.

Or you could do what I did...contact Davis and ask them for the key sequence to calibrate your barometer.  Once you have the steps,  wait for a time when the pressure is fairly stable and not changing for your area, then adjust your barometer to match the local airport barometer.

Once you make any changes it will take 28 days before you should re-check CWOP analysis to see if your readings are passing MADIS.


add:  Here is the sequence for the Vue barometer adjustment, I don't know if it's the same for the VP2:

Quote
First confirm the elevation is set correctly within the setup of the console.  Press & release the 2nd key.  Press & release the <done> key.  Press the <Bar> key nine times to display the current Elevation.  Use the +/- , </> to set.  Press and hold <done> for two seconds to exit setup.  To calibrate your Barometer press the <bar> key.  Press and release the <2nd> key.  Press & hold the <graph> (set) key and after the 4th flash of the current barometer reading release the key and you then manually set the barometer.  When finished press and release the <done> key to get back to the main weather screen. 
« Last Edit: October 16, 2011, 06:45:49 PM by NorCal Dan »

Offline Weather Display

  • Posts: 87,238
  • Davis VP2
  • New Zealand
    • Weather Display
Re: Simple Barometer adjustment help needed
« Reply #4 on: October 16, 2011, 06:44:20 PM »
not just according to me....not sure what that is all about...

Offline NorCal Dan

  • Dan - KJ6RGX
  • Posts: 10,554
  • Davis Vue/Win10
  • Ocean Park, WA.
    • Traveling RV Weather
Re: Simple Barometer adjustment help needed
« Reply #5 on: October 16, 2011, 06:49:58 PM »
not just according to me....not sure what that is all about...

Because you told me not to use the altimeter setting when at or near sea level.

Offline Budgie

  • Martin
  • Global Moderator
  • Posts: 6,022
  • CWOP: CW7959
  • Lochaber, Scotland
    • Lochaber-Weather
Re: Simple Barometer adjustment help needed
« Reply #6 on: October 16, 2011, 07:20:53 PM »
I used to do the met obs for the UK Met Office at the Coastguard station where I used to work.
We were on the first floor of a building right by the sea, at about 40' ASL, and we had to do the sea level correction for that location before sending the ob.  :wink:

The VP2 requires that the height ASL be set so that it will display your pressure above sea level.
In the VP2 console manual it says:
"Meteorologists standardize barometric pressure data to sea level so that surface readings are comparable, whether they are taken on a mountainside or by the ocean. To make this same standardization and ensure consistent readings, enter your elevation in this screen."

The manual states that you can also set your height below sea level.  :wink:

Offline NorCal Dan

  • Dan - KJ6RGX
  • Posts: 10,554
  • Davis Vue/Win10
  • Ocean Park, WA.
    • Traveling RV Weather
Re: Simple Barometer adjustment help needed
« Reply #7 on: October 16, 2011, 11:17:30 PM »
Curious, how much is the sea level correction is for 40' altitude?

Offline Budgie

  • Martin
  • Global Moderator
  • Posts: 6,022
  • CWOP: CW7959
  • Lochaber, Scotland
    • Lochaber-Weather
Re: Simple Barometer adjustment help needed
« Reply #8 on: October 16, 2011, 11:26:00 PM »
We're talking about 14 years ago now but I think it was something like 1.4mb (0.04 inches).
I found a calculator: http://www.csgnetwork.com/barcorrecthcalc.html  :D

Offline niko

  • syzygy
  • Global Moderator
  • Posts: 28,176
  • Crystal Ball broken! Please post the URL.
  • Northern California, U.S.A.
Re: Simple Barometer adjustment help needed
« Reply #9 on: October 17, 2011, 12:22:47 AM »
The manual states that you can also set your height below sea level.  :wink:

That's for the station in Death Valley  :lol:

Offline NigelS

  • Posts: 336
  • NW Leicestershire, UK
    • GablesEnd Weather
Re: Simple Barometer adjustment help needed
« Reply #10 on: November 21, 2011, 05:12:14 PM »
Can I just ask, to confirm.

In the VP Pro2 console setup, you enter an altitude and that makes the console display the baro pressure @ SL and this adjusted value is what WD gets from the datalogger.  So you dont need to set any offset in WD for SL Adjustment?  
(I assume the only time you'd need to set an offset would be if calibration of the barometer showed some offset was necessary).

Just want to check that I understand it properly!
« Last Edit: November 21, 2011, 05:37:31 PM by NigelS »
GablesEnd Weather - http://www.nrms.info

Offline Budgie

  • Martin
  • Global Moderator
  • Posts: 6,022
  • CWOP: CW7959
  • Lochaber, Scotland
    • Lochaber-Weather
Re: Simple Barometer adjustment help needed
« Reply #11 on: November 21, 2011, 05:17:53 PM »
Yep, that's about it.  :D

Offline NigelS

  • Posts: 336
  • NW Leicestershire, UK
    • GablesEnd Weather
Re: Simple Barometer adjustment help needed
« Reply #12 on: November 21, 2011, 05:38:08 PM »
Yep, that's about it.  :D

that's great, thanks

NigelS
GablesEnd Weather - http://www.nrms.info