AS5040 10-BIT PROGRAMMABLE MAGNETIC ROTARY ENCODER
15 Angular Output Tolerances
15.1 Accuracy
Accuracy is defined as the error between measured
angle and actual angle. It is influenced by several
factors:
the non-linearity of the analog-digital converters,
internal gain and mismatch errors,
non-linearity due to misalignment of the magnet
As a sum of all these errors, the accuracy with centered
magnet = (Errmax – Errmin)/2 is specified as better than
±0.5 degrees @ 25°C (see igure 24).
Misalignment of the magnet further reduces the
accuracy. Figure 23 shows an example of a 3D-graph
displaying non-linearity over XY-misalignment. The
center of the square XY-area corresponds to a centered
magnet (see dot in the center of the graph). The X- and
Y- axis extends to a misalignment of ±1mm in both
directions. The total misalignment area of the graph
covers a square of 2x2 mm (79x79mil) with a step size of
100µm.
For each misalignment step, the measurement as shown
in igure 24 is repeated and the accuracy
(Errmax – Errmin)/2 (e.g. 0.25° in igure 24) is entered as
the Z-axis in the 3D-graph.
Linearity Error over XY-misalignment [°]
6
5
4
°3
2
1
0
y
1000
800
600
400
200
0
-200 x
-400
-600
-800
-1000
Figure 23: Example of linearity error over XY misalignment
The maximum non-linearity error on this example is
better than ±1 degree (inner circle) over a misalignment
radius of ~0.7mm. For volume production, the placement
tolerance of the IC within the package (±0.235mm) must
also be taken into account.
The total nonlinearity error over process tolerances,
temperature and a misalignment circle radius of 0.25mm
is specified better than ±1.4 degrees.
The magnet used for this measurement was a cylindrical
NdFeB (Bomatec® BMN-35H) magnet with 6mm diameter
and 2.5mm in height.
linearity error with centered magnet [degrees]
0.5
0.4
0.3
0.2
0.1
0
1
-0.1
-0.2
-0.3
-0.4
-0.5
Errmax
transition noise
55 109 163 217 271 325 379 433 487 541 595 649 703 757 811 865 919 973
Errmin
igure 24: Example of linearity error over 360°
Revision 1.6, 03-Oct-06
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