AN3182

Calculating tilt angles

Doc ID 17289 Rev 1

11/18

Figure 5.

360° rotation of a single axis of the accelerometer

Figure 6.

Plot of 360° rotation of a single axis of the accelerometer

3.2

Tilt sensing

3.2.1

Single-axis tilt sensing

From Figure 5 and 6, it can be observed that the sensor is most responsive to changes in tilt

angle when the sensing axis is perpendicular to the force of gravity. In this case, the

sensitivity is approximately 17.45 mg/° [= sin(1°) - sin(0°)]. Due to the derivate function of

the sin function, the sensor has lower sensitivity (less responsive to tilt angle changes) when

the sensing axis is close to its +1 g or -1 g position. In this case, sensitivity is only 0.15 mg/°

[= sin(90°) - sin(89°)]. Table 3 shows the sensitivity at different tilt angles. In other words, the

sin function has good linearity at [0° 45°], [135° 225°] and [315° 36°] as shown in Figure 6.

Table 3.

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