LSM303CTR datasheet(17/53 Pages) STMICROELECTRONICS

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LSM303C

Terminology

3.1

Sensitivity

3.1.1

Linear acceleration sensor sensitivity

Sensitivity describes the gain of the 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 time. The sensitivity tolerance describes the

range of sensitivities of a large population of sensors.

3.1.2

Magnetic sensor sensitivity

Sensitivity describes the gain of the sensor and can be determined, for example, by

applying a magnetic field of 1 gauss to it.

3.2

Zero-g level

The zero-g level offset (LA_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 will measure 0 g for the X-axis and 0 g for the Y-axis whereas the Z-axis

will measure 1 g. The output is ideally in the middle of the dynamic range of the sensor

(content of OUT registers 00h, data expressed as two’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 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 with temperature, see Table 3 “Zero-g level change vs. temperature”

(LA_TCOff). The zero-g level tolerance (TyOff) describes the standard deviation of the

range of zero-g levels of a population of sensors.

3.3

Zero-gauss level

Zero-gauss level offset (M_TyOff) describes the deviation of an actual output signal from the

ideal output if no magnetic field is present.

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