Calibrate IMUs
- Gisela Roberts
- Former user (Deleted)
In Capture and Visualize modes, if you plan to collect global angles, you must calibrate each of the IMU sensors to ensure that the data is stable and to minimize drift.
Important
With Firmware 10 and later, sensor calibration is retained between trials when you collect global angles.
Calibration is continuous when global angles are either being streamed or captured onboard the sensor.
The calibration is retained, even if you close the app, relaunch Capture.U and capture another trial with global angles, provided the new trial takes place within a two-hour period.
However, you must re-calibrate for the next global angles trial if:
- The subsequent trial does not collect global angles, for example, if you collect global angles and then collect a raw data trial.
- The sensors are inactive for longer than two hours.
To calibrate the sensors:
Start streaming global angles. (If you're not sure how to do this, see Start Capture.U and choose a collection mode and select the instructions for your chosen collection mode.)
Tip: If you want to use real-time feedback to verify the calibration, you can calibrate in Real-Time Insight mode and then after calibration, capture global angles in To Sensor mode.In all modes, when you start collecting data, a warning message is displayed if a sensor calibration is required.
When you're capturing or streaming global angles in To Sensor or To Device modes, IMU sensors that require calibration display a 'Require Calibration' icon
at the top right of the sensor on the sensor selection screen. (In Real-Time Insight and AR Visualization modes, the sensor calibration indicator is only displayed when you select the sensors.) Wave the sensor in a figure-of-eight for at least 10 seconds, ensuring that it rotates through all three axes during the motion.
Put the sensor on a flat surface and spin it through two full rotations around the z axis.
Tip: To avoid any unwanted influence on the sensor, avoid placing it in proximity to anything metallic.- Wait at least five seconds until the data has stabilized.
In Real-Time Insight and AR Visualization modes, you can observe that x angle is 0 and the y angle is 0 (the figure-of-eight provides enough information for the sensor to self-calibrate). However, the z angle may have a non-zero value, depending on how it is rotated relative to the magnetic north. - Rotate the sensor on the flat surface for at least five seconds until z is also 0.
In To Device and To Sensor modes, to let you know that a sensor is calibrated, after 60 seconds, a C (Calibrated) icon
is displayed at the top right of the sensor.
In Real-Time Insight and AR Visualization modes, check that the graphs for all three axes are now at zero. After you have calibrated each sensor, you can attach the sensors to your subject and collect data in the required collection mode.
Tips for calibration:
- As calibration is a continuous process, we recommend that after calibration you collect a trial in which the subject is wearing the sensors and in the same environment that they will be performing the movement to be collected.
- If you plan to collect global angles, after the sensors are attached to a subject, allow a few seconds for onboard calibration to initiate before starting the movement that is to be collected.
