LSM303DLHC datasheet(14/42 Pages) STMICROELECTRONICS

14 / 42 page

Module specifications

LSM303DLHC

14/42

Doc ID 018771 Rev 1

2.6

Terminology

2.6.1

Linear acceleration sensitivity

Linear acceleration sensitivity describes the gain of the accelerometer sensor and can be

determined by applying 1

g acceleration to it. As the sensor can measure DC accelerations,

this can be done easily by pointing the axis of interest towards the center of the Earth,

noting the output value, rotating the sensor by 180 degrees (pointing to the sky) and noting

the output value again. By doing so, ±1

g acceleration is applied to the sensor. Subtracting

the larger output value from the smaller one, and dividing the result by 2, leads to the actual

sensitivity of the sensor. This value changes very little over temperature and also very little

over time. The sensitivity tolerance describes the range of sensitivities of a large population

of sensors.

2.6.2

Zero-g level

Zero-

g level offset (TyOff) describes the deviation of an actual output signal from the ideal

output signal if no acceleration is present. A sensor in a steady-state on a horizontal surface

measures 0

g in the X axis and 0 g in the Y axis whereas the Z axis measures 1 g. The

output is ideally in the middle of the dynamic range of the sensor (content of OUT registers

00h, data expressed as 2’s complement number). A deviation from the ideal value in this

case is called Zero-

g offset. Offset is, to some extent, a result of stress to the MEMS sensor

and therefore the offset can slightly change after mounting the sensor onto a printed circuit

board or exposing it to extensive mechanical stress. Offset changes little over temperature,

see “Zero-

g level change vs. temperature”. The Zero-g level tolerance (TyOff) describes the

standard deviation of the range of Zero-

g levels of a population of sensors.

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