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Re: Automatic deviation calculation by electronic compasses
From: George Huxtable
Date: 2009 Nov 23, 23:41 -0000
From: George Huxtable
Date: 2009 Nov 23, 23:41 -0000
Joe Schultz reminded me-"George, "flux-gate compass" is a mature technology." Yes, I am aware of that. In fact, flux-gates, which employ staurating magnetic cores, have been used for measuring magnetic fields for far longer than the 25 years that Joe tells us they have been used in US Navy compasses. And indeed, they are not the only form of magnetic sensor that can be used for such purposes. More recent devices, such as those that Frank Reed has described, use the magnetoresistive effect, which allows them to be even more compact. But we were not discussing the magnetic sensor mechanism itself, but the way such a magnetic sensor can be arranged to self-correct for local magnetic perturbation. I wonder: were those "first gas-turbined frigates" that Joe refers to, built of steel? If so, I'm interested in what, if anything, was in place as a first-order correction for deviation, if these were, as Joe's words "self-correcting" compasses. Did they have the familiar correction magnets, and the hollow soft-iron spheres placed to port and starboard of the compass housing? I would be surprised if any electronic correction algorithm, such as we have been discussing, was capable of tackling the enormous deviations that a steel vessel gives rise to, without some such first-order corrections. George. contact George Huxtable, at george@hux.me.uk or at +44 1865 820222 (from UK, 01865 820222) or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK. ----- Original Message ----- From:To: Sent: Monday, November 23, 2009 7:50 PM Subject: [NavList 10801] Automatic deviation calculation by electronic compasses First tried at the fleet level in the first gas-turbined frigates (US Navy) at least 25 years ago. The objective was to get a self-correcting magnetic compass as backup to the gyro-compass, and explore the possibility of removing the then "large footprint" gyro-compass altogether. Taken over by GPS/inertial with a gyro-compass backup. Today's minature electronics means you can buy a relatively inexpensive flux-gate compass and wear it like a wrist-watch. Timex is one brand. Fun is jogging a box (or ellipse) over a steel pipeline. All machines have their limitations. Joe -- NavList message boards: www.fer3.com/arc Or post by email to: NavList@fer3.com To , email NavList+@fer3.com -- NavList message boards: www.fer3.com/arc Or post by email to: NavList@fer3.com To , email NavList+@fer3.com