| The compass display has at its heart a 3-dimensional compass using flux detection for its results. This is interfaced to a small dual core microprocessor which drives a screen. This is all powered by a battery bottle containing a NiMH battery that will run the complete unit for 50 hours.
The subsea bottles are rated to a depth of 100M. The screen has a frame update of 30 FPS, which is much faster than the update rate from the compass unit which is running at 9600 BPS. The compass uses a hard and soft algorithm that works with magnetic flux detection. Its field detection can be disturbed by anything that contains iron, or outputs electromagnet radiation. It has a calibration function that must be performed if its installation is to be close to such things that cause it to become unstable. The calibration will take into account the disturbance as it is rotated through 360 degrees, and it will compensate out the flux changes. Internal to the compass is a 3 axis accelerometer, which is used to calculate heading compensations at different pitch and roll angles. |
The compass unit has an RS232 port that is used to see the data directly from the compass unit, and perform the calibration using a simple RS232 terminal program. The calibration cannot be done whilst running on battery power, as the same connection is used. To do a calibration the unit has to be run via the deck test cable and PSU.
