Compensating for a magnet in a device with a magnetometer

Question

I'm working on a device that relies on data from a magnetometer. Unfortunately, the device also needs to have a fairly powerful magnet on it. Given that the design is fairly flexible, and within manufacturing tolerance I can know precisely where the magnet is and the layout of the magnetic field it should produce, is there a way to compensate for having a magnet in the device?

Is there some mathematical means of cancelling out the contribution of the inbuilt magnet, or perhaps shielding the magnet from the remainder of the device somehow, as the magnet is only needed for mounting the device to metal surfaces and nothing else?

William Hird · Answer

Some fluxgate magnetometers have their sensor mounted inside Helmholtz coils and the coils can be used to compensate for errors in the sensor caused by external (or in your case, internal) magnetic fields or ferrous materials which disturb the natural flux lines of the earth's magnetic field. So yes, you can compensate for the effect of the magnet using Helmholtz coils but you may find that you have to run a lot of DC current through them to cancel the magnetic field of the magnet.

Answered by William Hird on November 5, 2020

niels nielsen · Answer

Magnetic compasses for serious work will contain two small permanent magnets with their N/S axies perpendicular to each other built into the compass housing; these are carefully rotated one way or the other to null out the influence of other magnetic materials nearby on the compass readings. I do not know if this technique would be effective in your case, where the magnet nearby is large and powerful.

You are better off devising another attachment method that does not rely on magnets!

Compensating for a magnet in a device with a magnetometer

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