It is evident that the sensor inputs at this range are appropriate for
, but there is significant amplitude
mismatch between the X and Y axes. If these inputs were used directly, the resulting angle calculation would
effectively map an elliptical input. The arctangent is a circular function, and so this contributes significant
measurement error if not corrected. Mapping the X and Y magnitudes into a coordinate plane reveals this
relationship.
Bx (mT)
B
y (mT)
-100 -80
-60
-40
-20
0
20
40
60
80
100
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
10
20
30
40
50
60
70
80
90
100
Natural By
Corrected By
Figure 2-9. Benefit of Amplitude Matching in Angle Calculations
The effective angle error is significant. To counter this effect, attenuate the (X-axis) results or the (Y-axis) result
requires a gain increase. Either transformation results in normalization of the inputs for the angle calculation and
resolves this error to the expected circular format.
5.9-mm Airgap Magnetic Field Inputs
shows that the in-plane alignment is not ideal for
in the SOT-23
package option due to the directionality of the magnetic field vector. When perfectly coplanar to the center of the
rotating magnet, there is no vertical component. If using the SOT-23 package option for this device, the sensor
detects the Z-component of the field vector which in this alignment is 0 mT for all angles. Instead, it is more ideal
to use the LPG through-hole package in this location. TIDA-060040 includes an optional component footprint
for this package variant adjacent to the target location for the SOT-23 package. Make sure the sensors have
the same vertical spacing from the PCB to ensure each observes an equivalent input from the rotating magnet,
and that the sensor is installed orthogonal to the surface of the PCB. If using the
solution, remove the
unused package option to allow for a more ideal PCB layout.
System Overview
Absolute Angle Encoder Reference Design With Hall-Effect Sensors for
Precise Motor Position Control
9
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