4 Mechanical Error Sources

The various non-linearities are typical byproducts of system level mechanical errors. These typically are caused by assembly tolerances and produce various combinations of the previously discussed patterns.

These errors may be the results of any of the following conditions:

• Magnet tilt and wobble
• Magnet eccentricity
• Sensor alignment
• Sensor placement offset

What will be evident, is that for any configuration, it will be beneficial to limit manufacturing variances in order to achieve consistent performance across all systems.

These errors will be individually simulated using a magnet which has a diameter of 6 mm and a thickness of 3 mm. Sensor position will be 4 mm from the nearest magnet face for either in-plane or on-axis alignment. For off-axis alignment, the sensor will be placed immediately 4 mm below the outer diameter of the magnet. The magnet grade will be N52.

Magnet Eccentricity

If the magnet is not centered about the rotation axis of the shaft, then a different sort of wobble will emerge.

Figure 4-8 On Axis Alignment with Eccentricity

FIGURE of Eccentricity

In this case, the magnet will oscillate within its own plane. The result is an angle dependent magnet location. This error may cause significant angle errors. An offset from center of 0.1 mm produces the following errors. In each case, the displayed angle error resulting from amplitude mismatch or offset have already been corrected, and the residual error is the result of either non ideal phase or input distortion.

Figure 4-9 On Axis: Magnetic Field Inputs with Eccentricity

Figure 4-11 Off Axis: Magnetic Field Inputs with Eccentricity

Figure 4-13 In Plane: Magnetic Field Inputs with Eccentricity

Figure 4-10 On Axis: Angle Error with Eccentricity

Figure 4-12 Off Axis: Angle Error with Eccentricity

Figure 4-14 In Plane: Angle Error with Eccentricity

Sensor Alignment

Proper system alignment typically requires the sensor to be placed orthogonal to the rotating magnet.

Figure 4-15 On Axis Alignment with Sensor Tilt

This alignment may be impacted by tilt of the rotating shaft, or by tilt of the actual sensor. During solder reflow, many surface mount devices self-align to the PCB footprint and some variability may exist as the solder cures. Rotation by just a few degrees about each axis produces the following errors. In each case, the displayed angle error resulting from amplitude mismatch or offset have already been corrected, and the residual error is the result of either non ideal phase or input distortion.

Figure 4-16 On Axis: Magnetic Field Inputs with Sensor Tilt

Figure 4-18 Off Axis: Magnetic Field Inputs with Sensor Tilt

Figure 4-20 In Plane: Magnetic Field Inputs with Sensor Tilt

Figure 4-17 On Axis: Angle Error with Sensor Tilt

Figure 4-19 Off Axis: Angle Error with Sensor Tilt

Figure 4-21 In Plane: Angle Error with Sensor Tilt

Sensor Placement Offset

Sensor placement offset is the result of the final sensor location not matching the intended design.

Figure 4-22 On Axis Alignment with Position Offset

This may be the result of assembly challenges from the position the device aligns to during solder reflow to tolerances of system component locations within the larger system. An offset of 0.5 mm in both X and Y directions will produce the following errors. In each case, the displayed angle error resulting from amplitude mismatch or offset have already been corrected, and the residual error is the result of either non ideal phase or input distortion.

Figure 4-23 On Axis: Magnetic Field Inputs with Position Offset

Figure 4-25 Off Axis: Magnetic Field Inputs with Position Offset

Figure 4-27 In Plane: Magnetic Field Inputs with Position Offset

Figure 4-24 On Axis: Angle Error with Position Offset

Figure 4-26 Off Axis: Angle Error with Position Offset

Figure 4-28 In Plane: Angle Error with Position Offset