Issues with barometer

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sam g
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Joined: Tue Jan 20, 2015 9:58 am

Issues with barometer

Post by sam g » Tue Jan 20, 2015 10:04 am

Hi all, I'm new to Arduino and am loving it. I am having issues with the barometer module. I am using un modified source code from Gift Hub (following link from freetronics site). The temp is reading around 8 degrees C lower than it should, and barometric pressure around 15 hPa lower than it should. Is anybody else having issues - I just want to use it as a real time weather monitor. Thanks

Freetronics Staff
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Location: Melbourne, Australia

Re: Issues with barometer

Post by angusgr » Tue Jan 20, 2015 10:09 pm

Hi Sam,

This seems like it's out of spec. If you trust the other measurements you're calibrating against then the sensor should be accurate to +/-1C and +/-4mbar (hPa).

If you think it's faulty then you can return it to the retailer you bought it from, or please email and we'll arrange a direct replacement.

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Joined: Fri Apr 03, 2015 10:57 am

Re: Issues with barometer

Post by BobTindo » Fri Apr 03, 2015 12:27 pm

Hi forum,

I recently acquired a Barometric Pressure Sensor Module as an addition to an existing instrument that uses a Sensirion SHT75 Temp/Humidity sensor, an Arduino Nano, LCD Display and a AD5754 DAC.
Integration was very easy because the I2C lines were unused and results from the sensor were immediately displayable.

Problem is the results from the Baro sensor looked to be totally wrong!
I.E. The Baro Temperature readings is 21.8 - 22.1C (too low) and Pressure is 958,7 to 958.82 (again too low). I'm working in an air conditioned room with the thermostat set to 26 deg and the Sensirion sensor displays 26.6 - 26.65 C (69-70% RH).
I don't have a barometer to cross check the pressure but the local weather station reports 1006.1mB.
I'm inclined to believe the SHT sensor temp (can't be positive about pressure) but not the Baro sensor.

Did a Google search on the Baro sensor accuracy and noticed an update to the Freetronics/Barosensor library posted by Angus two days ago, so downloaded it and gave it a try;
Results now are Baro Temperature readings is 36.7 - 37.0 (now too high), pressure is 999.4 - 999.5mB (better). Room temperature and WX pressure basically unchanged.

Tried the old library again, and is back to the old results!
(Note: also used the Github library supplied "SimpleBaro" example and got the same readings from the Baro sensor).

This does not give me a very warm feeling about the accuracy provided by the library where an update causes 15 degrees change in temp and 41 milliBar change in pressure, and the're still not what I would regard as the correct values.

Anyone else having perceived accuracy issues with this sensor ?
Do I have a bad sensor ? (but why such a big change when updating the library?)

Thanks for listening...

Freetronics Staff
Freetronics Staff
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Joined: Tue Apr 09, 2013 11:19 pm
Location: Melbourne, Australia

Re: Issues with barometer

Post by angusgr » Wed Apr 08, 2015 12:08 am

Hi Bob,

Thanks for taking the time to report the problem, sorry to hear about the issues you're having.

The changes last week were in response to someone reporting integer overflow issues causing bad readings in some ranges. It seems this caused a regression breaking some other readings. I've just committed another set of changes which will hopefully fix things in both cases.

I also added a new test sketch called "CalibrationDebug", if you install the library then you can find it in the Arduino IDE under File -> Examples -> BaroLibrary -> CalibrationDebug. If the values still seem wrong, can you please run this sketch and send me the output? Thanks.

The underlying issue here is that all of the sensors ship with different factory-installed calibration constants, and it seems like different combinations of constants and sensor readings were tripping different overflow or integer conversion errors.


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Joined: Sun Apr 09, 2017 7:38 am

Re: Issues with barometer

Post by ConspicuousSam » Sun Apr 09, 2017 7:59 am

I've been having a similar issue with the temp 3-4 degrees higher and the pressure about 6mbar lower than reported by my local weather station. I ran the debug code and here's what came back.

Code: Select all

Initialising sensor...
Outputting debug values:
C1 = 0xAA3C
C2 = 0xAC33
C3 = 0x6598
C4 = 0x6729
C5 = 0x6E61
C6 = 0x6836
d1 first = 0x6623294
d2 first = 0x7350730
d1 second = 0x6622796
d2 second = 0x7353612
d1 third = 0x6622360
d2 third = 0x7355805
result (fourth) = OK
Temp (fourth) = 23.85
Pressure (fourth) = 997.34
Error (fourth) = 0

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