AIS2IH datasheet(12/63 Pages) STMICROELECTRONICS

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Terminology and functionality

3.1

Terminology

3.1.1

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

Zero-g level offset

Zero-g level offset 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 on the X-axis and 0 g on 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 ideal value in this

case is called zero-g level 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 offset change vs. temperature”.

AIS2IH

Terminology and functionality

DS12421 - Rev 4

page 12/63

AIS2IH Datasheet(PDF) 12 Page - STMicroelectronics