LSM303AH Datasheet, PDF (20/82 Pages) –

Terminology
3
Terminology
LSM303AH
3.1
3.1.1
3.1.2
3.2
3.3
Sensitivity
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.
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.
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.
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 is defined as the magnetic field driven along one sensitive
axis, giving the maximum digital output value.
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