Upgraded IMU Calibration for Each Mission or Each Time Power is Applied

Each time the upgraded IMU is powered up, it takes a few minutes for it to find north. Each time you power up, before deploying, point the ROV (or the bow direction on the DVL head) north and make sure the heading output goes to zero degrees. If it does not, you may need to let the system sit for a few minutes, then rotate the ROV around the Z axis a few times until it does.

Compared to the Baseline IMU, the upgraded IMU is much better at keeping track of its own calibration status in its own internal non-volatile memory and figuring out when it is moved to a new magnetic environment. It does take some time when it is newly mounted to adjust itself, so it is a good idea to run the ROV around for five minutes or so, making as many maneuvers as possible, to let the IMU self-calibrate.

While not strictly necessary, you can sometimes speed up the Upgraded IMU’s acquisition of north. When you power up, wait at least 60 seconds, then tip the ROV onto its front, side or stern, and let it sit that way for 30 seconds. This lets the IMU estimate the bias on the gyro that is aligned with gravity when the ROV is in the normal orientation. Again, not necessary but maybe a little helpful.

The upgraded IMU sends the following status messages: "OK" and "WAIT". For the most part, you can ignore these. However, if the status is stuck in WAIT for more than 5 or 10 seconds then something may be amiss. Cycling the power is the only known fix for this.