It's a very generic question.
Any idea what effect a really strong magnet would do long-term to a co-located magnetometer (e.g. MAG3110 or any magnetometer in general)?
Just interested to hear if anyone may have observed problems with any potential magnetometer pre-configuration if used for a long period in strong fields.
Freescale uses a magnetic sensor technology called "TMR" (Tunnelling Magneto Resistive). The native sensors for this technology are "in-plane". These handle X and Y portions of the 3D vector naturally. In order to get "Z", we utilize a flux-guide which redirects Z axis field such that it can be sensed with an in-plane sensor. If the magnetic field exceeds specifications (10 mT), that flux-guide will retain some residual magnetism (your offset) when you take the original source away. This is known as "perming". If you reapply the opposite side of the same magnet, you will probably see the offset shift a similar amount the other side of the baseline. There is no internal mechanism to reverse flux guide perming.
There is a second physical mechanism that can apply to all axes, as it affects the free layer of the MJT. The maximum field here is the maximum range of the sensor (1 mT for the MAG3110). There is a software reset bit (AUTO_MRST_EN) which is recommended before every read cycle that can reset the MJT.
On a related note, where does the 100,000µT maximum (100mT) come from in the datasheet?
What will happen if a magnetic field is applied greater than this value? Does this effect the X, Y and Z axis the same way?
Will powering down the device prevent perming or is it a material property of the flux guide.
I've witness the perming you mentioned above in the Z direction on some MAG3110 sensors and it does seems to be permanent until the polarity of the interrogator magnet changes. Is perming in the X and Y direction as impactful as the Z direction?
I'll take a stab at your questions, as I discussed these topics some time ago with our local magnetics expert. But before that, please understand, NXP does NOT guarantee operation beyond maximums in our datasheets. Discussion of the background beyond those specifications in these forums is FYI only, and does not constitute NXP relaxing those specs for a given application. Now that I've got that out of the way:
There are THREE different mechanisms in play on these sensors:
All of the above apply whether the part is powered or not.
I hope that helps.