Magnet Selection Guideline for Shaft-End configuration

Application Note of Angle Sensors

The AKM angle sensor (AK74xx) enables the measurement of magnetic fields (Bx, By) parallel to the chip surface and can detect the absolute angle of the magnetic field over the full range of 0 to 360 degrees.

A non-contact rotary angle sensor can be easily built with only a magnet and a sensor. However, for those who have never used a magnetic-based sensor until now or are considering AKM's rotation angle sensor for the first time, it is not easy to select the optimal magnet and determine the sensor arrangement. This document is a guideline for magnet selection when constructing a magnetic encoder system in the Shaft-End Configuration

The Shaft-End Configuration is where the magnet center and sensor center are aligned on the axis of rotation as shown in Figure 1. Figure 2 shows the magnetic fields (Bx, By) with respect to the rotation angle for the Shaft-End Configuration.

Figure 1: Shaft-End Configuration
Figure 2: Magnetic Field (Bx, By) vs. angle

*Bz=0 if there is no misalignment in the Shaft-End

Examples 1 and 2 are taken from the example data in this document. It is published that the data such as the installable range of the sensor and the angle error due to the misalignment when using our recommended magnet. The verification data is caliculated by the magnetic field simulation. 

In addition to the characteristics when using the recommended magnet, the following verification results are also available:

  • Installable range of the sensor and the angle error when the magnet size varies slightly from the recommended magnet.
  • Installable range of the sensor and the angle error when changing magnet shape and material from the recommended magnet.
Example 1: Range for Gap Between Sensor and Magnet (Recommended Magnet)
Example 2: Misalignment vs. Angle Error (Recommended Magnet)