Terminology

AN3182

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Doc ID 17289 Rev 1

very stable versus temperature change. So temperature compensation for the zero-g

level can be ignored.

●

An - Acceleration noise density: This parameter defines the standard resolution the

user can obtain from the accelerometer (once the desired BW is selected).

1

σ resolution =

. The higher BW leads to lower resolution.

●

NL - Non linearity: This parameter defines the maximum error between the outputs and

the best fit straight line. For example, at ±2.0 g full-scale range, the non linearity of

0.5% of FS means the largest error is 0.5% * 4000 mg = 2 mg, which corresponds to

0.1°. When the application requires measurements of around the 0 g condition (as with

tilt measurement), the non-linearity effect is negligible and can be ignored.

●

CrossAx - Cross-axis sensitivity: The cross-axis effect arises due to natural

misalignment of die positioning on the package substrate. Even if negligible in most

applications, for very accurate tilt measurement the cross-axis sensitivity effect can be

easily compensated for by following the procedure in Section 2: Calibrating the

accelerometer. Moreover, when the device is placed on the final application board, the

accelerometer calibration compensates both the device cross-axis sensitivity, and the

misalignment between the accelerometer sensing axes and the board axes.

1.3

Definitions

Assume that the LIS331DLH accelerometer is installed in a handheld device, such as a cell

phone, a PDA or simply on a PCB board as shown in Figure 1.

Figure 1.

Accelerometer inside a handheld device

same direction as the device body axes.

Pitch and roll angles are referenced to the local horizontal plane, which is perpendicular to

the Earth's gravity.

●

Pitch (

α) is defined as the angle between the X

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

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

A

⁄

()

BW Hz

()

⋅