Anisotropic Magnetoresistance (AMR)
Anisotropic magnetoresistance or AMR
The AMR sensor chip works as a "strong field" sensor; sensor magnetization follows the cogwheel's stronger magnetic field. Since sensor signals are dependent only on the resulting angle between the direction of magnetic field and current, the amount of magnetization is not critical. The sensor chip, therefore, measures a mere 0.5 × 1.8 mm². The strong field principle also produces a signal that is widely independent of mechanical tolerances.
To create a fixed 90-degree phase relationship between channels A and B, the AMR sensor chip comprises two sets of four ferromagnetic metal strips. A Wheatstone's Bridge arrangement shifts one against the other by a quarter of the cogwheel's pole pitch. Each magnetic pole, consequently, gives a complete and practically harmonic-free sinusoidal signal that is suitable for multiplying signals using interpolation. The index signal is produced digitally, prompted by the signal of an additional AMR sensor in the magnetic disc's index pole.
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