DocID026445 Rev 1

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AN4509

Calculating tilt angles

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A single axis of the accelerometer with 360° rotation is shown in Figure 2 and 3.

Figure 2. 360° rotation of a single axis of the accelerometer

Figure 3. Plot of 360° rotation of a single axis of the accelerometer

1.2

Tilt sensing

1.2.1

Single-axis tilt sensing

From Figure 2 and 3, 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 sine 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 1 shows the sensitivity at different tilt angles. In other

words, the sine function has good linearity at [0° 45°], [135° 225°] and [315° 360°] as shown

in Figure 3.