Are there any places on the globe where magnetometers won't work?
For example, if you took a Honeywell HMC5843 to the North or South magnetic pole, would they fail to function properly?
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asked Jan 19 '11 at 6:40
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1\$\begingroup\$ Perhaps in an enclosed chamber made of iron or mu-metal? \$\endgroup\$ – vicatcu Jan 19 '11 at 13:58
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\$\begingroup\$ @vicatcu, it should still work perfectly there. I'd think it might not do so well in a volcanic region though. \$\endgroup\$ – Nick T Jan 20 '11 at 22:36
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You wouldn't be able to use it as a compass exactly at the magnetic pole, as the magnetic field would be vertical.
You probably already know about the need to correct for magnetic declination, which is the angle between magnetic north and true north. It varies irregularly over the earth and over time. Take a look at a declination map (such as this one), and notice that there is no unique value for declination at the magnetic poles.
So the magnetometer works everywhere since it gives you the correct magnetic field X/Y/Z components; you just can't always use it as compass.
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\$\begingroup\$ So it seems it will work for applications like helicopter "heading hold", since those applications only care about relative changes and not absolute compass-like directions. We will be able to hover our magnetometer-controlled UAV's right over either magnetic pole! \$\endgroup\$ – Mark Harrison Jan 20 '11 at 22:27
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\$\begingroup\$ @Mark Harrison - Maybe close to the magnetic pole, but not "right over", since even the relative changes would start to be huge (in the horizontal plane, at least). What would you expect to happen if you told it to head straight north as it approached the north magnetic pole? But for all practical purposes, it should be fine (would it really work in the weather of the north pole anyway?). \$\endgroup\$ – Reinstate Monica Jan 21 '11 at 13:45
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Surely they would not fail, they will show you the magnetic field just like anywhere else, it will just be quite wierd.
You still will be able to use it as a compass there if you would get approximate GPS fix to correct for magnetic pole location (but math would be way harder in comparison to usual "dumb" compass).
answered Jan 19 '11 at 12:24
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Justin's answer is spot on -- the magnetometer will work anywhere, but the readings may not be useful to you at the magnetic poles.
Regarding magnetic declination & inclination, there's software for a World Magnetic Model published by the US NGA & UK DGC that returns the expected magnetic fields strength & direction for a given location/date. http://www.ngdc.noaa.gov/geomag/WMM/DoDWMM.shtml
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A magnetometer will 'work' anywhere there is a magnetic field that is large enough to be detected by that particular sensor. This is determined by the noise floor of the sensor, i.e. the magnitude at which the S/N ratio is large enough that the signal information can be recognized over the system noise level.
And direction matters. Even for vector sensors.
I don't think that there is anywhere on Earth, or in the Solar System inside of the orbit of Venus, where, say, a squid (or a SERF) couldn't detect a magnetic field. I think there are many fluxgates that could detect a magnetic field anywhere on Earth (which, off the top of my head, is around 0.5 Gauss - a very large value).
The important thing to recall is that there are around a dozen major classes of magnetic sensors and they all have different specs, the main one being the resolution (i.e. the smallest signal they can detect, - the noise floor).
Why do you want to find a place they don't work?
