SBAA539 March 2022 TMAG5170 , TMAG5170-Q1 , TMAG5173-Q1 , TMAG5273
Beyond the material properties of the magnet that will influence the strength of the field, mechanical misalignments and tolerances may result with non-linearity in angle calculations.
At a high level, the end error results that will be observed fall into four main categories. These each have a direct impact on the linearity of the measurement and need to be managed appropriately to minimize final angle error. These are:
Amplitude mismatch is the dominant factor which will influence accuracy. When plotting the separate inputs against each other, it is possible to compare against the ideal unit circle.
Notice that at the axis crossings, the error will be zero. At points in between, the error may become quite significant. This is typically managed by applying a normalization factor to either of the two input sources. Either the amplitude of the larger input may be attenuated, or the amplitude of the smaller input may require an increase in gain. This function is integrated into both TMAG5170 and TMAG5273 to assist with system calibration.
Input referred offset results with inputs not centered about zero. This imbalance results with the unit circle not being properly centered.
Phase error between the two inputs used for arctangent calculations results from the inputs being out of phase by more or less than 90 degrees. Combined together, the resulting plot of these inputs appears similar to the amplitude mismatch case, but is not skewed along either axis.
Distortion is the result of the magnetic inputs being sensed not being purely sinusoidal. This may result from various factors such as inconsistent range to the magnet or irregularities in magnet shape. For instance, rotating a non-circular magnet or varying the distance to the sensor may produce inputs with a more complex non-linearity.