Inertial Measurement Unit


Initial data sets were captured via a commerical 9-axis IMU from an external supplier (this is NOT a Freescale unit). The unit is capable of capturing data for linear acceleration, angular velocity and magnetic field. It is USB-based, and is teathered to a PC via a USB cable. This may have slight effect on some measurements such as free fall. Measurements are typically gathered via a custom .NET Visual C++ program operating on a Netbook. Data is captured into Matlab-compatible text files, and then processed via Matlab. Data files measurements are all in LSBs. Scaling to actual units shown in figures is done in Matlab.

The magnetic sensors are Magneto-Inductive sensors, specified at +/-200uT, but I have confirmed with the manufacturer that they have a MUCH broader range. Sample rate is 125Hz for all sensors.

Gyro measurements show a large "at rest" offset (this is not unusual for gyros). Both accelerometer and magnetometer give values close to expected values for gravity and earth magnetic field respectively. I have not performed the integrations necessary to confirm accuracy of gyro measurements.

The magnetic sensors are Magneto-Inductive sensors, specified at +/-200uT, but I have confirmed with the manufacturer that they have a MUCH broader range. Sample rate is 125Hz for all sensors.

Sensor Resolution Range Comments
Accelerometer 2.93 mg/LSB +/-6g
Magnetometer 0.0488 uT/LSB specified to +/- 200uT, but actually MUCH wider
Gyro 0.98 degrees/second/LSB +/-2000 degrees/second Verification Pending
Allan Variance measurements were taken for this IMU in spring, 2010.

Charts are shown below for acceleration, gyro and magnetics.


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