[wxqc] Firmware Upgrade & Errors!

[Steve Hatchett]

The change Davis made has to do with how the sea level pressure (SLP) is
calculated. Their previous calculation would often show anomalous values the
top of each hour. This was related to how the mean temperature was
calculated (basically an average of the current temperature and the temp 12
hours before). They only stored hourly temperature data, so if there was a
big swing of temperature within the hour 12 hours before, it would cause a
jog in the SLP value when the algorithm switched from one 12 hour ago temp
to the next. This was most noticeable 12 hours after sunrise. It was
suggested to them that they either store and use more granular historical
temp data, or at least extrapolate the 12 hour ago temp so that the true
barometric trend would come through rather than hourly jogs.

 

When you make the firmware update, there is apparently an initial lack of
the extra temp data used in the calculation. So right after updating, the
displayed pressure jogs far from where it should be, and then over the next
12 hours homes back in to where it should be. If you are sending data during
this period, it could mess up your QC rating. If you calibrated your
barometer during that time to "fix" the apparent error, you'll have to
calibrate again to back that change out, because the apparent error fixes
itself within 12 hours.

 

I think the impact of this is relative to elevation. Those close to sea
level wouldn't have noticed the anomaly Davis was fixing, and probably
wouldn't notice the 12 hour issue after updating the firmware which I
described above. But those at elevation, and certainly those above 1000 ft.
likely will.

 

Steve Hatchett

SoftWx

 

 

  _____  

From: Bob Rathke [mailto:bob at ourfishadventures.com] 
Sent: Monday, April 02, 2007 4:09 AM
To: wxqc at lists.gladstonefamily.net
Subject: [wxqc] Firmware Upgrade & Errors!

 

Hi folks,

 

Recently upgraded my VP2 firmware, I am now getting consistent barometer
errors each day. I think I need to make an adjustment, but I am not sure
what the value should be. Could someone make a recommendation?

 

CW6551

Bob Rathke 

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