Baseline IMU Status-Assisted Initial Calibration Procedure

This procedure applies only to the baseline IMU and should be followed if you can see the calibration state.

The extended data message has a field to show the calibration state of the individual IMU components (see message definition). To take advantage of this information, your IMU dance changes to go like this (for initial mounting calibrations only; this should not be needed for each start-up):

• Set up where you can watch the calibration status as you move the ROV (or whatever the DVL is mounted to).

• Wait for the gyroscope status to reach “3” (second digit of IMU status). This can usually be done by just leaving the unit sit still. If on a rocking boat or other moving platform and the gyro status does not reach “3” within 60 seconds, go on to the next steps.

• Imagine the DVL head is enclosed in a cube (or maybe it is really mounted in a cube-like structure like a Blue ROV). Lay each face of the cube containing the head down on a stable platform for about 5 seconds per face (i.e., you are laying on six orthogonal faces). Move smoothly between each position, and don’t “thunk” the system when you set it on any face. Watch the accelerometer status (third digit of IMU status) and repeat this a couple of times until the status reaches “3”. If you’ve done three sets of faces without achieving a “3” status, go to the next step.

• Imagine the DVL head is enclosed in a cube (or maybe it is really mounted in a cube-like structure like a Blue ROV). Lay each face of the cube containing the head down on a stable platform for about 5 seconds per face (i.e., you are laying on six orthogonal faces). Move smoothly between each position, and don’t “thunk” the system when you set it on any face. Watch the accelerometer status (third digit of IMU status) and repeat this a couple of times until the status reaches “3”. If you’ve done three sets of faces without achieving a “3” status, go to the next step.

• Rotate the system about its vertical axis a few times, back and forth, being sure to rotate at least 500 degrees each direction. Flip the system upside down and make the same kind of rotations. Try to move smoothly and not too slow or fast (about 2 to 4 seconds for a 360-degree rotation is good). Watch the magnetometer (fourth digit of IMU status) until the status reaches “3”. If you’ve done three sets of right-side-up and upside-down rotations without achieving a “3” status, go to the next step.

• Wave the system around randomly until the system status (all digits) reaches “3333”. If it does not reach three within about twenty seconds, go back to the beginning and repeat the steps.

• Note that it is normal for the system status to drop below “3333” during operation. This is usually nothing to worry about. The key is to achieve the “3333” status at least once.