Sandaysoft

Support forum for Cumulus weather station software
It is currently Sun Dec 21, 2014 1:23 pm
Please click here before posting. Help me to help you!
Useful Links: Cumulus FAQ • Enhancement requests • Wiki (documentation) • Downloads
Please put your approximate location into your profile • Add your personal web site to the Cumulus user map
Read the Announcements and News section regularly!
Do not allow your PC to go into standby mode while Cumulus is running - read the readme.txt!
If you find Cumulus useful, please make a donation -

All times are UTC




Post new topic Reply to topic  [ 15 posts ] 
Author Message
 Post subject: Barometer calibration
PostPosted: Sun Dec 18, 2011 2:37 pm 
Offline

Joined: Sat Nov 26, 2011 1:35 pm
Posts: 10
Location: Bucks
Weather Station: WMR88
Operating System: Vista/W7
I'm not sure if my baromoetric sensor is off, or I'm failing to allow for altitude etc

The figures I'm seeing are always lower than the isobars on the met office website.

We're at about 700 feet asl.

If the difference ISN'T just down to the altitude, can I insert a correcting factor (presuming I can work it out) in the config? I don't fancy my chances of getting Oregon to replace it with one working any better.

And if I can correct it should I correct to the sea-level pressure or the local altitude pressure?


Top
 Profile  
 
 Post subject: Re: Barometer calibration
PostPosted: Sun Dec 18, 2011 4:10 pm 
Offline
User avatar

Joined: Mon Dec 20, 2010 12:12 pm
Posts: 469
Location: Palmerston, NT, Australia
Weather Station: WS-1081 with rain gauge mod
Operating System: Windows 7 & 1.9.3 b1059
ccomley wrote:
I'm not sure if my baromoetric sensor is off, or I'm failing to allow for altitude etc

The figures I'm seeing are always lower than the isobars on the met office website.

We're at about 700 feet asl.

If the difference ISN'T just down to the altitude, can I insert a correcting factor (presuming I can work it out) in the config? I don't fancy my chances of getting Oregon to replace it with one working any better.

And if I can correct it should I correct to the sea-level pressure or the local altitude pressure?


Yes it is due to altitude (mostly :? ), if your close enough to a Met office to consider that their data should be the same as yours, then you can use it. Wait for the pressure to even out, find the difference between Met and you and apply the difference in the Configer/Calibration in Cumulus.
While I'm at it, my (Fine Offset) keeps dropping roughly 2hPa every couple of months, and I have to keep calibrating. I feel one day it's going to die :o (thanks for correcting my spelling Dylan **13yo son**)

_________________
Michael, Palmerston, NT Australia www.Palmerston-WeatherImageNo image? I'm offline!
ImageImage


Last edited by MickinMoulden on Wed Dec 21, 2011 5:40 am, edited 1 time in total.

Top
 Profile  
 
 Post subject: Re: Barometer calibration
PostPosted: Sun Dec 18, 2011 5:07 pm 
Offline

Joined: Sat Feb 26, 2011 1:58 pm
Posts: 732
Location: SE London
Weather Station: Fine Offset 1080/1 & 3080
Operating System: Windows XP SP3
Hi,

Each 30 feet of altitude reduces the pressure by about 1 mb/hpa, so you should be seeing a pressure of almost 25 mb/hpa less that the Met office reports. Barometric pressure should always be corrected to sea level to be of any value to other users.

Cheers, Alan.


Top
 Profile  
 
 Post subject: Re: Barometer calibration
PostPosted: Sun Dec 18, 2011 6:34 pm 
Offline

Joined: Wed May 06, 2009 6:29 pm
Posts: 2047
Location: Cheadle Hulme, Cheshire, England
Weather Station: Davis VP2 with Daytime FARS
Operating System: Windows XP SP3
ccomley wrote:
I'm not sure if my baromoetric sensor is off, or I'm failing to allow for altitude etc

The figures I'm seeing are always lower than the isobars on the met office website.

We're at about 700 feet asl.

If the difference ISN'T just down to the altitude, can I insert a correcting factor (presuming I can work it out) in the config? I don't fancy my chances of getting Oregon to replace it with one working any better.

And if I can correct it should I correct to the sea-level pressure or the local altitude pressure?

You need to enter your altitude into the station which will then show the sea-level equivalent pressure. No further corrections should be necessary and it's very unlikely your station is faulty.

I found the manual here http://uk.oregonscientific.com/ulimages ... /WMR88.pdf

Go to Page 8 and at the bottom it tells you how to enter your altitude. 700ft is 214 meters. You should then see the same pressure as nearby Met Office stations.

If you're uploading to a website a link is often useful.

_________________
Cheers,
Ray, Cheshire.

Image


Top
 Profile  
 
 Post subject: Re: Barometer calibration
PostPosted: Sun Dec 18, 2011 9:16 pm 
Offline

Joined: Mon Nov 28, 2011 2:13 am
Posts: 375
Location: Brisbane, Australia
Weather Station: La Crosse WS 2306
Operating System: Windows 7 64 Bit
Hi

Its best to enter your height above sea level or your relative pressure value on your station which adjusts the absolute station level pressure to sea level, as sea level is standard on the weather charts and with other stations. All weather stations allow for your air pressure setting to be adjusted and much easier as no conversion is needed because it is sea level. Both my LaCrosse barometers stay on track with the local offical readings but I do own a basic Oregon Scientific and the reading on that are not as accurate as my La Crosse's.

_________________
Regards, Matt of Brisbane, Australia
Ferny Grove Weather


Top
 Profile  
 
 Post subject: Re: Barometer calibration
PostPosted: Mon Dec 19, 2011 11:16 pm 
Offline

Joined: Tue Aug 03, 2010 6:23 am
Posts: 484
Location: Ferntree Gully, VIC, Oz
Weather Station: WM918
Operating System: Win Server 2008 R2
The bottom line with any corrections is NOT to make assumptions and do it on your own.

In particular with pressure, contact your nearest Met office and have THEM provide you with current pressures and they will, if you are talking to anyolne competent, then be able to provide you with a corrected pressure for YOUR site (providing of course you know your exact altitude and not simply a guess).

Remember that Met Offices don;t only take pressure from statically placed instruments - aerial soundings are still done around the world and these, together with ground based instruments, allow any Met Office to provide corrected pressures anywhere between ground level and the stratosphere (well, maybe not quite that high...)

But - either way - contact your nearest met office and get them to help you. From that point on you shouldn;t have to touch your instrument again :)

_________________
Punctuation is the difference between 'Let's eat, grandma' and 'Let's eat grandma'


Top
 Profile  
 
 Post subject: Re: Barometer calibration
PostPosted: Mon Dec 19, 2011 11:33 pm 
Offline
User avatar

Joined: Mon Dec 20, 2010 12:12 pm
Posts: 469
Location: Palmerston, NT, Australia
Weather Station: WS-1081 with rain gauge mod
Operating System: Windows 7 & 1.9.3 b1059
There is a link (the last one) on my site that will show you your elevation. It uses Google maps and works very well. Also there is a webtag, <#altimeterpressure> Altimeter pressure. Pressure corrected to sea level using altitude only. Same as sea-level pressure for non-Davis stations. Once you've established your altitude and put this into Cumulus, you can work out your Sea Level pressure. I've never used it though. :)

_________________
Michael, Palmerston, NT Australia www.Palmerston-WeatherImageNo image? I'm offline!
ImageImage


Top
 Profile  
 
 Post subject: Re: Barometer calibration
PostPosted: Tue Dec 20, 2011 6:13 pm 
Offline

Joined: Sat Nov 26, 2011 1:35 pm
Posts: 10
Location: Bucks
Weather Station: WMR88
Operating System: Vista/W7
Thanks for the input guys

I *do* know the asl for the location.

I have told Cumulus this - I assumed it would correct for it given the datum.


Top
 Profile  
 
 Post subject: Re: Barometer calibration
PostPosted: Tue Dec 20, 2011 6:16 pm 
Offline
Cumulus Author
User avatar

Joined: Mon Jun 02, 2008 6:49 pm
Posts: 20768
Location: Sanday, Orkney
Weather Station: Davis VP2
Operating System: Windows Home Server 2011
ccomley wrote:
I have told Cumulus this - I assumed it would correct for it given the datum.

Cumulus does very little with the supplied altitude. It assumes the station has been set up correctly for SLP and reads it directly from the station.

_________________
Steve
Sanday Weather
----------------------------------------------------------------------------------------------------------------------------------
Like Cumulus and want to support it? Please donate! Image


Top
 Profile  
 
 Post subject: Re: Barometer calibration
PostPosted: Tue Dec 20, 2011 6:18 pm 
Offline

Joined: Wed May 06, 2009 6:29 pm
Posts: 2047
Location: Cheadle Hulme, Cheshire, England
Weather Station: Davis VP2 with Daytime FARS
Operating System: Windows XP SP3
ccomley wrote:
Thanks for the input guys

I *do* know the asl for the location.

I have told Cumulus this - I assumed it would correct for it given the datum.


You don't tell Cumulus. You enter it into the console using the instructions I provided. Don't make any changes in Cumulus.

_________________
Cheers,
Ray, Cheshire.

Image


Top
 Profile  
 
 Post subject: Re: Barometer calibration
PostPosted: Wed Dec 21, 2011 1:09 am 
Offline
User avatar

Joined: Mon Dec 20, 2010 12:12 pm
Posts: 469
Location: Palmerston, NT, Australia
Weather Station: WS-1081 with rain gauge mod
Operating System: Windows 7 & 1.9.3 b1059
steve wrote:
Cumulus does very little with the supplied altitude. It assumes the station has been set up correctly for SLP and reads it directly from the station.

What's this do then? <#altimeterpressure>

_________________
Michael, Palmerston, NT Australia www.Palmerston-WeatherImageNo image? I'm offline!
ImageImage


Top
 Profile  
 
 Post subject: Re: Barometer calibration
PostPosted: Wed Dec 21, 2011 8:37 am 
Offline
Cumulus Author
User avatar

Joined: Mon Jun 02, 2008 6:49 pm
Posts: 20768
Location: Sanday, Orkney
Weather Station: Davis VP2
Operating System: Windows Home Server 2011
MickinMoulden wrote:
What's this do then? <#altimeterpressure>

It gives the station pressure corrected to sea level using the altitude of the station only (rather than taking other factors such as temperature into account).

On non-Davis stations, it's exactly the same as sea-level pressure, because those stations only do the simple correction anyway. On Davis stations, which do a more complicated calculation for SLP, it's calculated from various bits of data supplied by the station.

_________________
Steve
Sanday Weather
----------------------------------------------------------------------------------------------------------------------------------
Like Cumulus and want to support it? Please donate! Image


Top
 Profile  
 
 Post subject: Re: Barometer calibration
PostPosted: Mon Jul 01, 2013 6:10 am 
Offline
User avatar

Joined: Tue Apr 14, 2009 10:21 am
Posts: 10
Location: Moutiers, Savoie, France
Weather Station: Freetec (Fine Offset WH1080)
Operating System: Windows 7/2003/2011
Just a small problem, maybe someone has an idea?
I installed a Fine Offset station at a local small airfield, so barometric pressure is a good thing to have!
When I look at the station's screen it tells me QFE (local pressure). Field is at 1033 feet, so the offset in pressure (at 27.6 feet per hPa) should be some 37 hPA to give QNH (pressure at see level).
If I take the QFE and add the 37hPa I get exactly the same value as in an aircraft's altimeter so things match up (and I know the altimeters are correct).
However, Cumulus consistently displays the the QNH 12 hPa low. I don't mind calibrating it up with the 12hPa, but maybe there is something more to it?
The sensors are some 8 meters above the ground so that should account for 1 hPa.
Any thoughts appreciated.


Top
 Profile  
 
 Post subject: Re: Barometer calibration
PostPosted: Mon Jul 01, 2013 7:05 am 
Offline
Cumulus Author
User avatar

Joined: Mon Jun 02, 2008 6:49 pm
Posts: 20768
Location: Sanday, Orkney
Weather Station: Davis VP2
Operating System: Windows Home Server 2011
Have you set the 'relative' pressure on the console to match your QNH value? That's the value which Cumulus displays. Instructions are in the manual- if you have one, if not there's a 'generic' one in the wiki.

_________________
Steve
Sanday Weather
----------------------------------------------------------------------------------------------------------------------------------
Like Cumulus and want to support it? Please donate! Image


Top
 Profile  
 
 Post subject: Re: Barometer calibration
PostPosted: Mon Jul 01, 2013 2:34 pm 
Offline
User avatar

Joined: Tue Apr 14, 2009 10:21 am
Posts: 10
Location: Moutiers, Savoie, France
Weather Station: Freetec (Fine Offset WH1080)
Operating System: Windows 7/2003/2011
Brilliant thinking! That was it. Working fine now.
Thanks!


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 15 posts ] 

All times are UTC


Who is online

Users browsing this forum: No registered users and 2 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  

Protected by Anti-Spam ACP Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group