Off topic but interesting?? Magnetics

Eric Smith <eric(a)brouhaha.com> wrote: Hi Flux-gate compasses are completely different than laser rotational accelerometers. The laser devices only detect rotation by integrating the amount of Doppler shift caused by rotating the ring. This is subject to drift because it is integrating. Still, because of the short wavelength of light and the fact that they pass the light several times in a loop, these can run for days with almost no drift. Flux-gate compasses depend on magnetic fields. They can be fooled by magnets just like a regular compass. The way that they work is to have two perpendicular windings over ( but not through ) a toroidal core. There is also a winding in the normal manner through the core. The way it works it that one builds a field in the inner winding until the core saturates. Since the field is even around the core, there is no coupling to the two coils that are perpendicular over the core. When the coil saturates, it is as though the core is no longer magnetic. The earths field lines that were distorted and pulled into the core are now released. The problem is that this happened slowly so the two coils didn't see much of this change in field. The current in the inner coil is cut off quickly ( usually the spike is dumped in to a zener diode of a high voltage ). The earths magnetic field suddenly see a magnetic material. It snaps into the core but in order to do so, the field lines must cross the windings of the two perpendicular sense coils. The orientation of north is related to the vector sum of the pulses generated in these two sense windings. Still, when space craft fly, they keep track of direction using mechanical gyroscopes. So, what do you know? Dwight