VP2 Pressure losing accuracy

[Ray Proudfoot]

Over the last few days I've noticed my VP2 barometric pressure is slightly lower than nearby stations and that reported by Manchester Airport - 3 miles away.

The difference is 0.02" (0.7hPa) which I appreciate isn't huge but it's consistently lower. The console is mains powered and hasn't moved location since I bought it over 3 years ago. I've checked the altitude and it's still correct at 261 feet.

Any ideas what the problem might be?

[G2003]

Funny you should mention this, I've been noticing the same thing with my VP2 lately.

[Ray Proudfoot]

Thanks. I'm glad I'm not imagining it. I've increased the altitude on the console by 10 feet and it's helped. But I cannot understand why it would start to drift. The barometer should be the instrument least likely to cause problems once correctly setup.

[DanS]

I'm not running a Davis but noticed on my console that a drop in supply power causes my barometric readings to drop slightly as well. This was noticed when I was on battery power only and after a few months when they started dropping off. When I'd replace them with fresh ones and the baro readings would return to proper readings. I've since added a wall wart supply.  I was wondering if your mains power has had an additional load added recently to lower it's level a little, bringing your wall adapter's output down slightly and having the same effect on your readings?  Maybe you could try just running on known good batteries for a day to see if it does have an effect.

[Ray Proudfoot]

I was wondering if your mains power has had an additional load added recently to lower it's level a little, bringing your wall adapter's output down slightly and having the same effect on your readings?  Maybe you could try just running on known good batteries for a day to see if it does have an effect.

I have added a sub-woofer but that's connected to another outlet in the same room but well away from the socket that feed the VP2. I'd be amazed if that was the cause. We're only talking a small discrepancy and I have managed to reduce the error by adding 10 feet to the console altitude.

I'll bear your suggestion in mind but my suspicions still point to the console. If the error rate increases then a email to Davis might be in order given everything has been fine for over 3 years.

[Ray Proudfoot]

Later... I've switched to battery power and no change was noted in the pressure. I've increased my console altitude by 20ft and that seems to have brought me in line with nearby stations. Unfortunately, Manchester Airport only reports pressure to the nearest millibar so it can't be used for precise readings.

Switching back to AC power now. Thanks all.

[SlowModem]

I'm not running a Davis but noticed on my console that a drop in supply power causes my barometric readings to drop slightly as well.

I have that same problem with my 968.

[LFWX]

Don't forget the VP2 reports a different "type" of pressure reading than many other weather stations, including airports and will seem to drift under certain types of weather or during certain times of the year.

[Ray Proudfoot]

Don't forget the VP2 reports a different "type" of pressure reading than many other weather stations, including airports and will seem to drift under certain types of weather or during certain times of the year.

Would you care to elaborate on that please? Pressure is pressure. Why would Davis operate on a different standard to all other stations? A source for your info would be helpful.

[LFWX]

Don't forget the VP2 reports a different "type" of pressure reading than many other weather stations, including airports and will seem to drift under certain types of weather or during certain times of the year.

Would you care to elaborate on that please? Pressure is pressure. Why would Davis operate on a different standard to all other stations? A source for your info would be helpful.

Sea Level Pressure vs Altimeter Pressure (two different methods of calculating Barometric Pressure)

http://www.wxforum.net/index.php?topic=12373.0

[Ray Proudfoot]

All stations reporting pressure must make adjustments for the altitude of the station. That's the only way you get meaningful pressure readings. I have made the necessary adjustment to my station altitude to compensate for my altitude. My readings are now similar to nearby stations.

Just to clarify. By adding 20 feet to my station altitude that has compensated for the Davis reduced sea-level pressure.

[beaudog]

Presure is not presure.

Airports as a general rule always report pressure altitude.

Tv stations and most other weather reporting agencies report sea level pressure.

The Davis console reports sealevel on its display.

If you are trying to match that to an airport it will in most cases be off by a small amount. Enough to account for the small error that you see.

Here is a chart of my station showing both sea level and altitude.   They are not he same.

[CorkHarbourWX]

Hi,

If you're noticing "drift" then in the first instance I'd check for something that might be causing a rise/fall in temperature near the console (computer monitor or other electronic device producing heat). If however you're satisfied that nothing in the locality of the console has changed, unfortunately your sensor may be showing early signs of failing... that's what happened to me - initially it was just small variations but over time they got larger and larger. Unfortunately I'm still in the wars trying to get my duff sensor sorted out (see post elsewhere on this forum).

I hope it settles down for you...

BR
Cormac (EI4HQ)
www.corkharbourweather.ie
Twitter: @CorkHarbourWX
[Cobh / UTC+1] NNNN++++

[Ray Proudfoot]

Hi BR,

The console does get direct sunshine late on summer evenings but only for a short while and it's not very strong as it's close to the horizon.

Since increasing the altitude setting by 20 feet it's now remaining close to other stations. The variation is quite small so I don't think it's failing just yet.

I have an aneroid barometer in the hall that's over 60 years old so if the Davis was to fail after 3 years I would be rightly indignant.