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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?

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  • $\begingroup$ Is there a particular reason why the device needs to be attached with a magnet? Why not adhesives, screws, or a suction cup? $\endgroup$
    – Wasabi ♦
    Sep 26, 2018 at 1:31
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    $\begingroup$ It needs to be removable mounting to a porous-coat metal surface. Adhesives would wear out, and suction cups wouldn’t work on a porous surface. If you can think of an alternative, I’m all ears $\endgroup$
    – TheEnvironmentalist
    Sep 26, 2018 at 15:24
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    $\begingroup$ Ok, so it needs to be removable. But after removal, will it (usually) be placed back onto the same equipment or is it a once-and-done deal? If it has to be removable but will (almost) always return to the same place, can't you bolt (or something) a semi-permanent "base" to whatever it is you're measuring, and then just have the device "slot" onto the base? The device is therefore easily removable, while the base takes a bit more work to place and remove, but that's work that'll only happen once throughout the "experiment". $\endgroup$
    – Wasabi ♦
    Sep 26, 2018 at 17:07
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    $\begingroup$ @Wasabi As it happens, no consistent location. More like you stick the thing wherever you happen to be at the moment, and any permanent means of attaching anything to the mount surface would be problematic. Adhesives could work if the longevity was such that they could continue to adhere for thousands of stick/unstick cycles over at least a few years. $\endgroup$
    – TheEnvironmentalist
    Sep 26, 2018 at 19:03
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    $\begingroup$ @Wasabi Fairly anything you could expect to find in a machine shop. Versatility and rapid attachment/detachment is key, and falling off could mean falling into a saw blade/oven/etc. Also the machine shops are time rented, so no modifying someone else’s machine shop. $\endgroup$
    – TheEnvironmentalist
    Sep 26, 2018 at 23:29

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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.

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  • $\begingroup$ ^And you may find that this is less cost-effective/sensible that simply finding another way to attach the device to metal surfaces, as alluded to by Wasabi... $\endgroup$
    – Jonathan R Swift
    Sep 26, 2018 at 10:12
  • $\begingroup$ @JonathanRSwift; I know that, but the OP wanted a possible way to do it anyway. $\endgroup$
    – William Hird
    Sep 26, 2018 at 14:54
  • $\begingroup$ @jonathan See above in the question comments for reasons for the magnet. If you can think of an alternative way of attaching a repeatedly-remountable device to a porous-coat metal surface, I’d be endlessly grateful $\endgroup$
    – TheEnvironmentalist
    Sep 26, 2018 at 15:26
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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!

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