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RMS noise of accelerometers and gyroscopes

The noise density of the accelerometer and gyroscope data is irrespective of the output frequency. The values are specified in the data sheets of the various products. However, if it is desired to have a lower RMS noise, the MTi 10/100-series offer the possibility to automatically decrease the noise and bandwidth of the measurements by lowering the output rate of the data. The onboard algorithms will integrate the data over a longer period of time. This has two effects: the RMS noise lowers but on the other hand, it lowers the bandwidth which means that movements with a bandwidth higher than 50% of the output data rate cannot be detected (but they are integrated in the data). 

To show this, an MTi lying still for 10 seconds was configured to output acceleration data at 400 Hz, 100 Hz, 10 Hz and 1 Hz. The difference in the noise is clear. The standard deviations that correspond to these four output data rates are:

400 Hz: 0.0137 m/s²

100 Hz: 0.0068 m/s²

10 Hz: 0.0022 m/s²

1 Hz: 0.0007 m/s²

 

 

In order to demonstrate the reduced bandwidth, an MTi-300 was held motionless on a table and configured to output acceleration data at 400 Hz, 100 Hz, 10 Hz and 1 Hz. The casing of the MTi was then tapped by hand, several times. The resulting z-axis acceleration plots are shown below. In the 400 Hz signal, the resulting damped vibrations can clearly be seen. The 100 Hz signal already shows a significant reduction of their intensity. In the plots for 10 Hz and 1 Hz, the vibrations were completely filtered out by the strapdown integration algorithm.

 

AutomaticBandwidthReduction.png

Note: these four experiments were carried out individually, but at the same tapping frequency and intensity.

 

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