IIS2DLPCTR datasheet(19/69 Pages) STMICROELECTRONICS

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DocID031788 Rev 4

19/69

IIS2DLPC

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”.

IIS2DLPCTR 数据表(PDF) 19 Page - STMicroelectronics