Align the center of the target board to the center of the coil board, with acceptable tolerances, for accurate angle measurement. Follow these steps to calibrate the encoder for best accuracy:

• Set the reference angle based on the magnet alignment to the sensor. This error can be saved in the microcontroller for runtime absolute position calculation. This error is also known as Angle offset in a system.
• Electrical offset calibration - See the Calibration of AMR Angle Sensors application report for the offset calibration procedure. If the sensor cannot be rotated across the full range, then the electrical offsets cannot be calibrated.
• Amplitude mismatch calibration - See the Calibration of AMR Angle Sensors application report for the amplitude mismatch calibration procedure. If the sensor cannot be rotated across the full range, then the amplitude mismatch cannot be calibrated.

Further error sources include nonlinearity of the sensor signal chain such as the 3^rd harmonics, and a mechanical error through coupling a reference angle encoder to the shaft of the absolute inductive encoder. The following figures outline the error source and the impact to the angular error to understand and compensate these types of errors.

Figure 3-11 Shaft Adapter Mechanical Displacement

Figure 3-13 Target Board and Coil Board Displacement

Figure 3-12 Mechanical Angle Error Due to Shaft Adapter Displacement

Figure 3-14 Electrical Angle Error due to Target Board and Coil Board Displacement

Figure 3-15 to Figure 3-17 show examples of the electrical offset, gain-mismatch and nonlinearity (3^rd harmonics) of the sensor signal chain impact the angle error.

Figure 3-15 Electrical Angle Error due to Sine Signal and Cosine Signal Chain Offset (0.1%)

Figure 3-17 Electrical Angle Error due to Sine Signal and Cosine Signal Chain Nonlinearity (0.1%)

Figure 3-16 Electrical Angle Error due to Sine Signal and Cosine Signal Gain Mismatch (0.1%)

Because the outer coils have 16 periods, multiply the electrical angle error order by 16 to get the mechanical angle error order. Table 3-3 summarizes the impact on the angular error pattern.

For more information on angle position calculation algorithms, see also the Achieving Highest System Angle Sensing Accuracy application report.