LSM330 Datasheet, PDF (19/75 Pages) STMicroelectronics – Power-down and sleep modes

LSM330
3
Terminology
Terminology
3.1
Sensitivity
Linear acceleration sensitivity can be determined by applying 1 g acceleration to the device.
Because the sensor can measure DC accelerations, this can be done easily by pointing the
selected axis towards the ground, noting the output value, rotating the sensor 180 degrees
(pointing towards 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 over time. The sensitivity tolerance describes the range of
sensitivities of a large number of sensors.
Angular rate sensitivity describes the angular rate gain of the sensor and can be determined
by applying a defined angular velocity to the device. This value changes very little over
temperature and also very little overtime.
3.2
Zero-g and zero rate level
Linear acceleration 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 will measure 0 g on both the X-axis and Y-axis, whereas the Z-axis will
measure 1 g. Ideally, the output is 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 over temperature, see “Linear
acceleration zero-g level change vs. temperature” in Table 3. The zero-g level tolerance
(TyOff) describes the standard deviation of the range of zero-g levels of a group of sensors.
Angular rate zero-rate level describes the actual output value if there is no angular rate
present. The zero-rate level of precise MEMS sensors is, to some extent, a result of stress
to the sensor and therefore the zero-rate level can slightly change after mounting the sensor
onto a printed circuit board or after exposing it to extensive mechanical stress. This value
changes very little over temperature and over time.
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