Where to get the G acceleration values?  

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JonC
 JonC
(@jonc)
Eminent Member
Joined: 5 years ago
Posts: 23
18/03/2015 1:03 pm  

Hello,

I have recently bought a GPS data logger to use in an aircraft for flight analysis. One of the selling points for me was that in your brochure you state is has... "3D/Triaxial Accelerometer with up to 4mg resolution (+/- 2g, +/- 4g or +/- 8g range / 10.000 g shock tolerant)" which is very important for what I need to analyse.

Can you please tell me how to read the G accelerations from it, as I cannot find an option for this at all on the software?

Also, looking at the data my barometer is reading 1014 hPa when the pressure reading given to me by Air Traffic Control was 1024 hPa. Is this pressure different for a reson, is it always 10hPa lower? Does the calibration affect the barometer?

Thanks,

Jon.


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mm_dev
(@mm_dev)
Member Admin
Joined: 9 years ago
Posts: 287
18/03/2015 3:51 pm  

Hello,

The GPS software only displays processed data, for the acceleration sensor that means that data is translated into degree to get the orientation of the device.
To get the actual g values you first need to record the raw sensor values in the software or on the SD card. The format of that data as well as the control protocol in case you want to access the device directly is described in http://spectran-developer.net/ftp/doc/G ... 140718.pdf
The g values would be variables x, y and z in the code listing of the "Accelerometer values" section (For every record the x,y,z speed is stored in m/s together with a time stamp. With help of the time stamp you can easilly calculate the acceleration in m/s² from the speed data). Acceleration = [DELTA speed]/[time]
E.G.:
You set the recording rate to 1 so you get a speed reading every second.
Lets pretend the first reading is 50m/s and the 2nd reading is 40m/s. In that case your DELTA speed will be 10m/s (50m/s-40m/s). Timeduration is 2 seconds.
Acceleration = [DELTA speed]/[time] = 10/2 = 5m/s²

As for the barometer, it simply depends on the weather conditions since it measures the air pressure, so you need to add an offset (depening on weather). You might get that offset by checking the height information from the installed GPS sensor.


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