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Old July 8th, 2012, 03:24 AM   #1 (permalink)
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Default Barometer question

I have a question about the S3's barometer capabilities. I installed Samsung's S Baro app (available through the More Services option in the app drawer), and this shows the barometric pressure and altitude above sea level. However I am not sure that the barometer sensor is working correctly. I live very close to a major UK airport and am familiar with aviation weather issues because of my involvement with flight simulators. S Baro is currently giving me a pressure reading of 994 hPa. However the current pressure report from the airport (less than 5 miles away) is 1004. So I have tried another barometer app from the Play Store, and this too is giving me a reading of 994. The error is clearly not coming from the app.

Does anybody know how the phone's barometer sensor can be calibrated? There are no options for this in the S Baro app.

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Old July 8th, 2012, 03:31 AM   #2 (permalink)
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As far as I know the barometer reading is (at least partly) based on a calculation . I think I saw a warning about this in S Baro..
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Old July 8th, 2012, 06:14 AM   #3 (permalink)
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A difference of 1004 to 994 is roughly 1%. I'd expect an airport to have the latest high tech equipment but I would say that if the barometer on a smartphone differs by only 1% that is pretty good?
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Old July 8th, 2012, 07:46 AM   #4 (permalink)
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Quote:
Originally Posted by Ballymoss View Post
A difference of 1004 to 994 is roughly 1%. I'd expect an airport to have the latest high tech equipment but I would say that if the barometer on a smartphone differs by only 1% that is pretty good?
It may be 1% if you base it on a range of atmospheric pressure starting at zero (presumably a vacuum?!!). However such conditions do not exist on this planet, and the standard range would be roughly 950 to 1050 hPa (even Hurricane Katrina had a pressure of only 920 hPa). This means that a difference of 10 hPa would equate to an error of around 10% which is rather less acceptable. A difference of 10 hPa makes a huge difference in the weather and has a big impact on the altitude readings - it suggests that you are nearly 300 ft higher above sea level than you really are. Obviously this app would not be used for serious navigation, but you ask any pilot would he would think about having his altimeter incorrectly set when he is trying to land his plane!!

I have now found another app Barometer HD which allows you to calibrate the barometer to give a correct pressure reading and consequently a correct altitude. It is free in the Play Store.
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Old July 9th, 2012, 08:34 AM   #5 (permalink)
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in case you get the pressure from the airports metar (ie. 1016 qnh) its the airports actual qnh level. this is the virtual pressure calculated down to sea level, not its pressure at the airport level. which means that the qnh pressure should be the pressure at sea level at the moment where the airport is located. a pilot knows the height level of an airport (for example 1800 feet). the rough formula is about 1 hpa per 30 feet in midrange temperatures. a pilots altimeter (when he got the qnh from a nearby airport on radio transmission or airport atis) should show 1800 feet when adjusted to 1016 hpa qhn in the moment he lands his plane.

so if you get a 1004 pressure from an airport metar report, this means that the pressure of 1004 hpa is the actual one at sea level, not at the actual airports level. if your sgs3 reads 994 hpa in this moment i would guess that your phone is about 300 feet above sea level then ((1004-994)*30), because every hpa means about 30 feet. but still it depends on the current temperature and humidity. my sgs3 works perfectly when i do all the math. the baros are pretty well calibrated in the manufacturing process and as far as i know it can show a altitude difference of only 13 centimeters, which is quite good!

to see your current altitude above sealevel with automatic metar updates for your smartphone i would suggest the app "sensitve barometer" from the play market (its a perfect app, easy to use, free and without any ads in it!). so you dont have to do all the math for yourself and can clearly read your current altitude. you only have to type in the nearest airports icao-code for the app. please keep in mind that metar reports are generated every 2 hours, where the actual pressure could be a different one within the range of a few feet. (which does'nt really bother me since my landings are the worst you've ever seen )

hope this helps a bit. cheers
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Old July 9th, 2012, 12:34 PM   #6 (permalink)
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this could be some interesting read for you.
we tested the sgs3 in flight with a glider as we use it for
navigation. there are also some links within the article about
the pressure sensor of the sgs3.

google translation (not perfect though!):

videomatrix.net

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