The Magic of a Fluxgate compass Part One By Michael Pignéguy It is highly unlikely that the English physicist and chemist Michael Faraday (1791-1867) set about to discover how, by moving a pair of magnets encased in copper wire through the earth's magnetic field, it would be the basis of something that would make life a whole lot easier in keeping boats and ships on track by not requiring an actual helmsman. With just basic schooling, he joined the workforce at the age of 14 as an apprentice to a book binder and book dealer. But unlike the other apprentices, Faraday took the opportunity to read the books brought in for bookbinding, one of which was the 3rd Edition of the Encyclopaedia of Britannica in which there was an article on electricity which fascinated him. After creating a crude electrostatic generator and performing simple experiments in electrochemistry, he was invited to attend chemical lectures by Sir Humphry Davy. In 1812 Faraday became a laboratory assistant to Sir Humphry and by 1820 had achieved a reputation as an analytical chemist. It was in the early 1820s that Faraday was able to prove that a magnetic pole could be isolated and moved in a circle around a current-carrying wire. This device, which transformed electrical energy into mechanical energy, was the first electric motor. It was on August 20, 1831 that Faraday conducted his most famous experiment and one that would eventually lead on to the manufacture of today's autopilot. He wound an insulated wire that was connected to a battery around one side of a thick iron ring. On the opposite side he wound a secondary circuit consisting of similar wire connected to a galvanometer. When the primary circuit was closed he saw the result on the galvanometer in the secondary circuit, proving that current from the primary circuit had been induced into the secondary circuit due to the influence of the magnetic fields of the iron ring. But what took him by surprise was when he 'opened' (switched it off) the circuit he saw the galvanometer jump in the opposite direction! Turning off the current had also somehow induced another current that was equal but opposite to the original current, and it was in the secondary circuit. Hopefully you are still with me here as we are still on the trail of the autopilot! Faraday then went on experimenting as he wanted to determine just how an induced current was produced, and he discovered that when a permanent magnet was moved in and out of a coil of wire, a current was induced into the wire. He knew that magnets were surrounded by lines of magnetic force, and from his early experiments he went on to create the first dynamo by rotating a copper disc between the poles of a powerful magnet. At that time he seemed to be unaware, at least it's not mentioned, of the influence that the earth's magnetic field would have on permeable material that was encased in copper wire. Faraday went on to discover amazing properties of magnetism and electricity in Electrochemistry, and Queen Victoria granted him the use of a house at Hampton Court ( with all expenses paid) also offering him a knighthood, which he turned down. As with many great scientists of the day, Faraday's discoveries were all achieved by his curiosity, drive, reading, experimentation, and original thought. Mr Google was not even in the same universe at that time! The Fluxgate Compass development It arguably is one of the most useful, but largely unseen, navigational tools that is available to the marine industry today. Today's fluxgate compass is using the same principles as discovered by Faraday in 1831, but in ways that he probably could not have imagined at the time. The fluxgate compass is really the electronic version of a traditional magnetic compass, but because it creates an electrical output, it has more applications than the former. It does have the disadvantage of requiring a constant electrical input and the possible failing of electrical components, none of which I have experienced in a fairly long maritime career. A big advantage is that it can be placed just about anywhere on board, although a place devoid of very local magnetic deviations should be avoided. Having said that, the vessel that I am currently managing and skippering, a 20m nine year old 'go fast' launch, has its fluxgate compass mounted under the stainless steel work bench in the engine room, very close to tool boxes and only a metre away from one of the main engines! It's possibly the worst location for a fluxgate compass, but so far I have yet to experience any problems with it. But it is a relatively simple device with no moving parts and consists of a wire coil wound around a permeable core which again is surrounded by a second coil. This core is magnetically surrounded by a current cycle in opposing directions which is called 'excitation'. Now this is where the magic starts to happen as the excitation results into a plus and minus saturation of the core, and with no external magnetic field present, the flux in one half cancels out the flux in the other half. It's rather like the unit is in neutral. The 'external' influence referred to (ignoring the boat's own deviation influences which can be automatically corrected), is the earth's own magnetic field. When the fluxgate unit is now turned in any amount through the earth's magnetic field, this creates an induced current in the secondary coil which results in a signal that is dependent on polarity and the earth's magnetic field. This particular signal (now outgoing micro electrical current) is enhanced and can be used for feedback and recovery. Using this signal as an input means that the direction, or course, of any vessel can be altered and it can, for example, control an autopilot, or give a stabilised display to a chart plotter and radar, and wind direction instruments. Part Two continues in the next Newsletter
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'BoatSmart' is a new maintenance service for boat owners in Gulf Harbour. The local franchise owner is member Gavin Auld. For more information see 
