Underwater Navigation System for AUVSI Sub

SENSOR CALIBATIONS

(magnetometer)

The MAG3110 magnetometer on the Sensortag must be calibrated for hard and soft iron biases. Hard iron biases are permenent magnetic offsets present at the current location, and soft iron biases are non-permenent biases created from nearby electronic and magnetic fields. These soft-iron biases skew the magnetometer data to become elliptical and tilted from the major and minor axes. Plots were generated by rotating the Sensortag in as many positions as possible to gather many data points and traced out a 'full' ellipsoid. The data of uncompensated magnetometer data is shown below. Notice the offset from the origin.

The first compensation that is to be accomplished is the hard iron compensation. The results are shown below (notice the shift to the origin).

hard iron compensated (shifted to origin)

After the hard iron bias is compensated for, the soft iron bias must be compensated for. This compensation will take the traced ellipsoid and fit it into a sphere. The soft iron bias compensation results are shown below.

compensated magnetometer is sphere centered at origin

(accelerometer)

Static data was collected from the accelerometer to determine the accelerometer offset from 1g down. The results are shown below. Notice the -0.1 g bias in the x direction. This offset from the tilt on the PCB will need to be compensated for, but is not a huge issue at this point in the navigation design.