Calculating tilt angles

AN4509

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DocID026445 Rev 1

1.2.2

Dual-axis tilt sensing

When a dual-axis tilt sensing approach is used, the user should be aware of two different

situations in which this approach could limit overall accuracy or even inhibit tilt calculation.



Figure 4, Example A: Rotate the accelerometer counter-clockwise around the dotted

arrow with

 angle. When  is less than 45°, the X-axis has higher sensitivity, while the

Y-axis has lower sensitivity. And when

 is greater than 45°, the X-axis has lower

sensitivity while the Y-axis has higher sensitivity. Therefore, when the two-axis

approach is used, it is always recommended to calculate the angle based on the

orthogonal axis to a ±1 g condition.



Figure 4, Example B: At this position, both the X and Y axes have high sensitivity.

However, without the help of a third axis (for example the Z-axis), it is impossible to

distinguish a tilt angle of 30° from one of 150° because the X-axis has the same

outputs at these two tilt angles.

Figure 4. Tilt sensitivity of a dual-axis accelerometer

Table 1. Tilt sensitivity of single axis accelerometer

Tilt [°]

Acceleration [g]

0

0.000

17.452

15

0.259

16.818

30

0.500

15.038

45

0.707

12.233

60

0.866

8.594

75

0.966

4.37

90

1.000

0.152