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The ideal state for a magnetic encoder is when the center of the rotating shaft, permanent magnet, and Hall element are aligned on the same straight line. This configuration is called Shaft-End (shaft end configuration). However, even with Shaft-End configuration, there will still be slight installation errors due to “shaft eccentricity.”
Once shaft eccentricity occurs, the magnetic field strength detected by the Hall element will change, leading to errors in the angle detection accuracy. It is very difficult to completely eliminate shaft eccentricity. In the Shaft-End configuration, if the Hall element is installed in an area with a uniform transverse magnetic field, then even if shaft eccentricity exists, the input magnetic field strength will not change significantly.
Therefore, compared with Hall elements that detect the strength of the longitudinal magnetic field, Hall elements that detect the strength of the transverse magnetic field can reduce the impact of shaft eccentricity on angular error.
Radially magnetized magnets paired with Hall elements that detect transverse magnetic field strength
Sometimes, axially magnetized permanent magnets are chosen to weaken the magnetic field leakage on the sides, thereby reducing the adverse effects of magnetic field leakage on surrounding equipment. However, compared with radially magnetized magnets, axially magnetized magnets have a smaller magnetic field area, and the angular error caused by axial eccentricity is relatively greater.
Axially magnetized magnets paired with Hall elements that detect transverse magnetic field strength
As mentioned above, the advantage of the Shaft-End configuration is that by combining radially magnetized magnets with Hall elements that detect transverse magnetic field strength, it is easy to achieve an encoder that is resistant to shaft eccentricity. In fact, in addition to the Shaft-End method, Hall elements also have an Off-Axis installation method, which will be detailed in subsequent chapters.
Introduction to previous Hall magnets;
Which side of the magnet should be induced by the Hall sensor?