[wxqc] Sensor drift

[spamfree]

Hi,

I'm not sure which is horse hocky; my post or Davis' claims. Anyway, if that is how you have your station set up (set to zero elevation and calibrated to a nearby source) I can tell you what drift you should expect over a range of pressure. The algorithm for calculating altimeter from sensor pressure is what it is, and it's not a fixed offset. For example, if you were at 4000 ft. the drift over an altimeter range of 30 mb would be about 3 mb. You can play around with the numbers at http://www.srh.noaa.gov/elp/wxcalc/stationpressure.shtml

It gets worse the higher the altitude. At 10,000 ft the you'd expect a 9 mb drift over the same 30mb range.

Steve
  
======= At 2006-05-23, 12:08:07 you wrote: =======

>Davis claims if you do not put in the elevation and cal to a local standard
>then all should be just fine. Horse hockey!!!
>N5IHE
>
>
>
>
>On 5/22/2006 10:25:27 AM, spamfree (spamfree at pensom.org) wrote:
>> Hi,
>> 
>> It will. The Vantage Pro console measures the actual pressure (sensor
>> pressure) internally, but calculates a sea level reduced pressure 
>> value which is what is displayed on the console, and passed on to 
>> connected weather programs. Their algorithm uses elevation as well as 
>> temperature and humidity in their calculation. The problem is that 
>> CWOP only wants altimeter for the pressure which is calculated from 
>> the sensor pressure and elevation only. The result is that if you are 
>> above around 500 ft elevation, your CWOP submitted pressure will 
>> appear to drift when compared to other non-vantage pro stations as the 
>> average temperature and humidity change. This is especially noticable 
>> after passage of a front and as the seasons change.
>> 
>> I wrote a freeware tool to address this called VPLive 
>> http://www.pensom. org/weather/vptools/vplive.html . VPLive reverses 
>> the VP barometer calculation to get the sensor pressure, and then 
>> calculates the altimeter from that and sends that to APRS/CWOP.
>> 
>> You can also play around with the whole pressure calculation issue 
>> with this other freeware tool http://www.pensom. 
>> org/weather/vptools/vppressurecalc.html
>> 
>> Steve
>> 
>> ======= At 2006-05-22, 10:12:44 you wrote: =======
>> 
>> >I am
>
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