CIMU Accelerometer Calibration

The accelerometers are subject to slight aging effects, and to temperature effects. Generally, you really only need to calibrate these every three to six months.

Since gravity is uniform everywhere (at least within the measurement capability of the sensors), you can run the calibration anywhere there is a solid, stable surface. Generally a boat will not be stable enough unless the wind is dead calm. To begin, click the "Calc Accel Cal" button as seen in the figure below.

Three plus/minus axis representations will appear on the display. The axes show signal levels on the three principal exes of the CIMU. Note the X and Y axes of the CIMU are close to the device axes, and you can use the cap mounting screws as a reference to the X and Y axes. The goal is to align the axes with gravity to get a maximum signal on each axis, both plus and minus, and keep them stable long enough to collect data (nominally one second).

The figure below shows the display just after stating the cal. By chance, the device was stable and sitting vertically on its nose, and the +Z axis was acquired almost immediately. The red lines show signal levels, and you can see the +Z is at full signal level, and the X and Y axes are near zero. For the X and Y axes, lay the device on its side and raise and lower the nose slightly, while rotating around the long axis in order to both maximize the signal of the desired axis and minimize the signal of the other axis.

A gray background on the axis indicates the axis still needs to be collected. A green background indicates collection is complete on the axis. An axis background will turn orange when gravity is aligned closely enough to take data, but the device has not been stable long enough to collect the data.

Move the device to collect the other axes. The figure below shows the process a little more than halfway completed.

When all six axis directions are collected, you will have the opportunity to commit them to the device. If you like what you have collected, you can click the "Commit Accel" button and the parameters will be sent to the device to overwrite the previous parameters. If you're finished, click the "Exit" button.

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