LSM303D datasheet(16/52 Pages) STMICROELECTRONICS

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Terminology

LSM303D

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DocID023312 Rev 2

Terminology

3.1

Set/reset pulse

The set/reset pulse is an automatic operation performed before each magnetic acquisition

cycle to recover the initial magnetization state of the sensor and therefore the linearity of the

sensor itself.

3.2

Sensitivity

3.2.1

Linear acceleration sensor sensitivity

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

3.2.2

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.

3.3

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 on the X-axis and 0 g on 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 two’s complement). 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 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.

3.4

Zero-gauss level

Zero-gauss level offset describes the deviation of an actual output signal from the ideal

output if no magnetic field is present. Thanks to the set/reset pulse and to the magnetic

sensor read-out chain, the offset is dynamically cancelled. The Zero-gauss level does not

show any dependencies on temperature and power supply.

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