AN3182 datasheet(7/18 Pages) STMICROELECTRONICS

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AN3182

Terminology

Doc ID 17289 Rev 1

7/18

keeps moving from a vertical position (-90°) back to a flat level again. For example, in

Figure 2, Yb is fixed, Xb is rotating from Pitch = 0° to +30°, +90°, +150° and +179.9° for

a positive direction.

●

Roll (

β) is defined as the angle between the Y

b axis and the horizontal plane. Assume

that the roll angle resolution is 0.1°, then it goes from 0° to +179.9° when rotating

around the Xb axis with the Yb axis moving downwards from a flat level, and then keeps

moving from a vertical position (+90°) back to a flat level again. The roll angle goes

from 0° to -180° when the Yb axis is moving upwards from a flat level, and then keeps

moving from a vertical position (-90°) back to a flat level again. For example, in

Figure 3, Xb is fixed, Yb is rotating from roll = 0° to +30°, +90°, +150° and +179.9° for a

positive direction.

Figure 2.

Pitch definition

Figure 3.

Roll definition

Assume Ax, Ay, Az is the accelerometer raw measurement in the format of LSBs. Table 2

shows the sign definition of the raw sensor data at 6 stationary positions with respect to the

known Earth gravity vector. For example, in Figure 1, Xb and Yb are level and Zb is pointing

down. Therefore, Ax = Ay = 0, Az = +1 g.

AN3182 Datasheet(PDF) 7 Page - STMicroelectronics