Author Topic: Problems calibrating barometer to pass MADIS and CWOP test  (Read 4736 times)

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Offline MatthewWeaver

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Problems calibrating barometer to pass MADIS and CWOP test
« on: December 27, 2009, 08:17:47 PM »
My barometer readings fail MADIS and CWOP (http://weather.gladstonefamily.net/site/C6998 [Corrected]).  I am not sure if I am calibrating correctly.

Can someone point me to simple step-by-step instructions to calibrate my reading?  Else, offer steps.

Here’s what I’ve done, but, again, not sure if this is correct and in either case I still get bad readings reported:

1.  Get readings from three nearby locations (within 30 miles and all at different altitudes)
2.  Take sea-level reading from each, calculate the difference (0.000838 for each foot of elevation change)
3.  Adjust my reading to reflect the average (and often matching) reading calculated for my altitude.  In making this adjustment, I enter the change directly on the WMR-968.

What is wrong?  Why do MADIS and CWOP continue to fail?  Am I doing the calculation correctly?  Am I making the change correctly?  How often should I have to recheck and update my calibration?
« Last Edit: December 27, 2009, 09:23:23 PM by MatthewWeaver »
Using Oregon Scientific WMR-968 with Virtual Weather Station and Win 7 x64.  Instruments include original sensors plus a THGN123N.
WeatherUnderground:  http://www.wunderground.com/cgi-bin/findweather/getForecast?query=12953
CWOP Info: http://weather.gladstonefamily.net/site/C6998

Offline kray1000

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Re: Problems calibrating barometer to pass MADIS and CWOP test
« Reply #1 on: December 27, 2009, 08:59:39 PM »
I do agree there is some issue with your barometer readings.

The difference between your station and the analysis has increased ("drifted") over the course of the last 24 hours.  Normally this happens at over 1000 feet elevation, during times of changing weather, using software that reports sea-level barometer to CWOP rather than altimeter.  What software are you using to report to CWOP (VWSAprs, VPLive, etc) and what version?

Based on your CWOP analysis, to start with, I would decrease your barometer reading by 0.15" inches.  Your reading will "drift" from that, I believe, until we update your software or find the real issue.
« Last Edit: December 27, 2009, 09:03:17 PM by kray1000 »

Offline Scalphunter

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Re: Problems calibrating barometer to pass MADIS and CWOP test
« Reply #2 on: December 27, 2009, 09:08:15 PM »
I would set your station console to your altitude to start. VWS is not the best software to adjust barometers. Let barometer settle in and then make slow adjustments from there. by the way your  link in test does not exist good thing you had the good  number in your signature.

John

Offline SlowModem

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Re: Problems calibrating barometer to pass MADIS and CWOP test
« Reply #3 on: December 27, 2009, 09:15:31 PM »
What is wrong?  Why do MADIS and CWOP continue to fail?  Am I doing the calculation correctly?  Am I making the change correctly?  How often should I have to recheck and update my calibration?

It looks like your barometer is trending correctly.  It looks like you've got it set too high.  Looking at surrounding stations your barometer should be set to 29.79 in. hg (or 1009 mb).  You will have to set this on the sea level setting.  You may also have to tweak this some over time.

Good luck!
Greg Whitehead
Ten Mile, TN USA

Offline MatthewWeaver

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Re: Problems calibrating barometer to pass MADIS and CWOP test
« Reply #4 on: December 27, 2009, 09:17:57 PM »
Kray1000, I am using VWS 14 p103 and VWSaprs 1.9.8.0.  Where should I make the adjustment?

Scalphunter, if making on console, via clicking Sealevel then Set?  Else, how?

Thanks both, I'd really like explicit instructions if possible as I'm seriously wondering if I'm making the right changes in the right place.

Thanks,
Matthew
Using Oregon Scientific WMR-968 with Virtual Weather Station and Win 7 x64.  Instruments include original sensors plus a THGN123N.
WeatherUnderground:  http://www.wunderground.com/cgi-bin/findweather/getForecast?query=12953
CWOP Info: http://weather.gladstonefamily.net/site/C6998

Offline Scalphunter

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Re: Problems calibrating barometer to pass MADIS and CWOP test
« Reply #5 on: December 27, 2009, 09:25:16 PM »
 I got an 200 you set barometer under barometer via  putting your altitude in that space. would have pull up an pfd here on your machine. But  your should be able to set it up for 700 feet or equival meters and then the machine should settle in for sea level reading. I use Wd here for reporting  so Barometer can be tweak with degree of control that VWS doesn't allow.

John

Offline MatthewWeaver

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Re: Problems calibrating barometer to pass MADIS and CWOP test
« Reply #6 on: December 27, 2009, 09:33:30 PM »
The WMR-968 does not have an altitude setting; for the moment, I've set sea-level to 29.79.  Slow Modem, how did you determine this value?  Likewise, Kray1000, how did you determine 0.15"?  BTW, why does the value "drift"?
Using Oregon Scientific WMR-968 with Virtual Weather Station and Win 7 x64.  Instruments include original sensors plus a THGN123N.
WeatherUnderground:  http://www.wunderground.com/cgi-bin/findweather/getForecast?query=12953
CWOP Info: http://weather.gladstonefamily.net/site/C6998

Offline kray1000

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Re: Problems calibrating barometer to pass MADIS and CWOP test
« Reply #7 on: December 27, 2009, 09:37:56 PM »
Maybe "Anthony" will chime in here, as I believe he has the same station you have.

I used the graphs in your CWOP analysis.  For the most recent readings, the blue line is (edit: about 3.5 millibars) above the red one.  One millibar is very close to 0.03".  (My eyes sometimes play tricks with my brain.)  

Lowering your barometer by about 0.10" or 0.11" should lower the blue line close to the red one, for the time being.
« Last Edit: December 27, 2009, 09:53:33 PM by kray1000 »

Offline SlowModem

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Re: Problems calibrating barometer to pass MADIS and CWOP test
« Reply #8 on: December 27, 2009, 09:45:41 PM »
The WMR-968 does not have an altitude setting; for the moment, I've set sea-level to 29.79.  Slow Modem, how did you determine this value?

I looked at stations close to you and took the average barometer reading and converted the millibars to inches mercury (well, google did the conversion).

Quote
  Likewise, Kray1000, how did you determine 0.15"?  BTW, why does the value "drift"?

I don't know why it's drifting.  I set mine and haven't touched it in a long time.  Perhaps your batteries are weak, but not weak enough to give the low battery alarm.
Greg Whitehead
Ten Mile, TN USA

Offline kray1000

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Re: Problems calibrating barometer to pass MADIS and CWOP test
« Reply #9 on: December 27, 2009, 09:52:25 PM »
Likewise, Kray1000, how did you determine 0.15"?  BTW, why does the value "drift"?

Sorry, I mis-read the vertical scale on the graph (see my edit above).  I would actually lower it about 0.10".

Since you're using the latest software versions, I suspect an elevation setting might be causing the drift.  But I agree with John's suggestion to set it and leave it for a few days.  I'd wait about three days, and check the CWOP page again, changing the analysis period to "3 Days".


Offline MatthewWeaver

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Re: Problems calibrating barometer to pass MADIS and CWOP test
« Reply #10 on: December 27, 2009, 09:54:21 PM »
Brand new lithium ultimate batteries.  But, that said, these were purchased quite a while ago.  I've got a ZTS Pulse Load Multi-Battery Tester that includes test of lithium batteries.  I'll pull and test them and all of my sensor batteries tomorrow.
Using Oregon Scientific WMR-968 with Virtual Weather Station and Win 7 x64.  Instruments include original sensors plus a THGN123N.
WeatherUnderground:  http://www.wunderground.com/cgi-bin/findweather/getForecast?query=12953
CWOP Info: http://weather.gladstonefamily.net/site/C6998

Offline SlowModem

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Re: Problems calibrating barometer to pass MADIS and CWOP test
« Reply #11 on: December 29, 2009, 11:00:53 AM »
I've been watching these trends for the past few days and things are looking a lot better now.  I think you've got it going in the right direction!   =D>
Greg Whitehead
Ten Mile, TN USA

 

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