NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Fluxgate compass /benefits of 3 axis
From: George Huxtable
Date: 2002 Feb 1, 09:54 +0000
From: George Huxtable
Date: 2002 Feb 1, 09:54 +0000
Jared Sherman said- >George- > < Trouble is, you need a FAST > response to the tilting of the deck > > >There are now solid-state accelerometers, literally you can buy a single >IC chip off the shelf that is a solid-state accelerometer capable of >generating data "instantly" for all three axes of motion. Among other >things they are used to track for inertial navigation systems. I don't >think they've replaced anything on the Polaris submarines, but they should >be more than adequate for generating correction data on a fluxgate >compass. ======================== George Huxtable responds- We are discussing trying to make a fluxgate system immune from the effects of sea-state. Doesn't matter how small, cheap, compact, fast, an accelerometer is. Any device that measures acceleration due to gravity will find it inextricably confused with the other transient accelerations that rough weather creates. Some sort of sensor of the vertical is certainly required, to establish the averaged attitude of the vessel (e.g. any long-term heeling). A 3-axis accelerometer could do that part of the job perfectly well, but a fast response in that sensor is not needed. Quite the reverse, in fact: fast changes should be filtered out, to remove the contribution from short-term accelerations caused by the sea-state. What's needed is a fast sensor for ROTATION, to measure changes of deck-tilt about the two relevant axes, roll and pitch, independent of gravity and acceleration, to correct the output of the fluxmeter. A strap-down inertial navigator for an aircraft (or, presumably, a sub.) requires such rotation-sensors, to determine the orientation of its 3-axis accelerometer. The ultimate instrument for doing that job on an aircraft is the ring-laser "gyro". George Huxtable. ------------------------------ george@huxtable.u-net.com George Huxtable, 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK. Tel. 01865 820222 or (int.) +44 1865 820222. ------------------------------