Conversion of g (acceleration due to gravity) to m/s²

Aaronia GPS and Data-Logger (also logging/including: Gyro, Tilt, Air Pressure, Height, Speed, Digital Compass)

Conversion of g (acceleration due to gravity) to m/s²

Postby stm » Wednesday 5. August 2015, 15:43

Formular for GPS Logger Tilt sensor (raw data):

1g = 9,80665 m/s²

x (m/s²) = (tilt.x/8192) * 9,80665
y (m/s²) = (tilt.y/8192) * 9,80665
z (m/s²) = (tilt.z/8192) * 9,80665

That's it!
stm
 
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Re: Conversion of g (acceleration due to gravity) to m/s²

Postby Rabman » Friday 7. August 2015, 16:53

Should I interpret that the raw data in on the micro SD card for acceleration is in g's * 8192?

What is the meaning of the 8192 constant?

For example data out of the GPS Logger is:

$PAAG,DATA,T,202514.0,385,-8191,65,A*31

Do I interpret the data as follows?

X-axis: 385/8192 = 0.04699 g or 0.461 m/s^2
Y-Axis: -8191/8192 = -0.9999 g or -9.804 m/s^2
Z-Axis: 65/8192 = 0.008 g or 0.078 m/s^2

Thanks
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Re: Conversion of g (acceleration due to gravity) to m/s²

Postby Moderator » Saturday 8. August 2015, 10:30

No that is wrong.
Take your sample data

$PAAG,DATA,T,202514.0,385,-8191,65,A*31


The calculation for m/s² is:

x (m/s²) = (tilt.x/8192) * 9,80665
y (m/s²) = (tilt.y/8192) * 9,80665
z (m/s²) = (tilt.z/8192) * 9,80665

(1g = 9,80665 m/s²)


So you need to calculate for m/s²:

X-axis: (385/8192)*9,80665 = 4,52086565 m/s²
Y-Axis: (-8191/8192)*9,80665 = -96,1443966 m/s²
Z-Axis: (65/8192)*9,80665 = 0,7649187 m/s²

The output of our 3D 14-bit accelerometer is operating in the ±2g range. This will change by 8192 counts as the accelerometer is rotated 180° with an axis, giving an average sensitivity of one count per 0.022° change in tilt.
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Re: Conversion of g (acceleration due to gravity) to m/s²

Postby JonC » Monday 28. September 2015, 19:38

Unfortunately I think your calculations are wrong and Rabman was correct. You have both used the same formula, but your answers are incorrect.

Applying the calculations to my data I am reading maximum values at +4G, but you say it is currently set to +2G as a maximum. Have I somehow managed to change the range? If so, how to I change it to +/-8G?

Thanks,

Jon.
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Re: Conversion of g (acceleration due to gravity) to m/s²

Postby Moderator » Tuesday 29. September 2015, 08:27

At the moment the default for sure is 2G not 4G. At the moment it is not possible to change that value.
We are currently working on a new firmware which will offer more flexibility (can set to 2G, 4G, 8G or even 16G maximum).
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