[wxqc] Barometer Errors

[rich.taft at att.net]

Yes this is true of VP & VP2 consoles. This issue has been brought to Davis’s attention by many people. Their claim is that the Temp/Humd corrected pressure is "More accurate" then simple elevation correction. My response was "Based on what?" since everyone else is using the elevation only method, then their statement can't be valid.  I have been told by Davis tech support that if enough people request that the pressure use the standard correction then it would be implemented in future releases. So unless the NWS is planning on changing the standards I would urge every VP & VP2 owner to contact Davis and ask for the "standardized pressure calculation"

On the same note, some of you may know that Davis issued a console firmware upgrade for all wired & wireless VP2 stations (No upgrade is being offered for VP stations) Aside from some bug fixes all this upgrade was to address was the new Daylight savings schedule to start in 2007. Unfortunately anyone who installed the November 28 2005 firmware will find that their Barometer readings will show sporadic spikes and the dew point calculation will be very erratic. I have been told by Davis that this is due to a timing issue between the console and some "third Party" (Read... Not weatherlink) software packages.  Davis has removed the Firmware update from their site with a "revisions pending" message. If you have already upgraded your console to the Nov 28 2005 firmware, then there is a Beta (April 5 2006) update available. This beta utilizes the new "No updater required" feature of the Nov 28 firmware, so you will have had to have installed the Nov 28 firmware with an updater, before up
grading to the April 5 2006 Firmware.

I have installed the Beta and found that it corrected the Dew point & spiky Barom data, but now my Barom is running 1.5 to 2 MB low.


Rich Taft
http://www.findu.com/cgi-bin/wxpage.cgi?call=CW3815
www.taftphoto.com

 -------------- Original message ----------------------
From: "spamfree" <spamfree at pensom.org>
> Hi,
> 
> If the times his barometer drifts off has a correlation with wide temperature 
> swings, and he is at altitude (say above 500ft), then the VP pressure issue 
> could explain it. The VP calculates a sea level reduced pressure from the sensor 
> pressure. Temperature and humidity is part of that calculation which is done in 
> the console. This is what WeatherLink sends to APRS/CWOP. But CWOP wants 
> altimeter, which is the sensor pressure adjusted only for elevation. There is a 
> difference between these two pressure representations, and the result is that 
> many VP stations have CWOP pressures values that drift in and out of the 
> expected norm. There are a couple of weather programs that calculate the correct 
> altimeter value from the VP pressure for submission to APRS/CWOP, but 
> WeatherLink currently isn't one of them. There has been talk that Davis may do 
> this in a future version.
> 
> Best regards,
> Steve