ISM303DAC datasheet(21/80 Pages) STMICROELECTRONICS

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ISM303DAC

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 ratio of the output digital data expressed in LSB units and the

applied magnetic field expressed in mG (milligauss). It can be measured, for example, by

applying a known magnetic field along one axis and measuring the digital output of the

device.

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 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 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.

3.4

Magnetic dynamic range

The magnetic dynamic range of the sensor can be fully exploited when the applied magnetic

field is entirely aligned with one of the sensitive axes of the sensor.

In presence of a stray field in the cross-axis direction, the exploitable magnetic dynamic

range (maximum module) can decrease.

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