LSM6DB0 Datasheet, PDF (20/66 Pages) STMicroelectronics – 3D accelerometer, 3D gyroscope and signal processor

Terminology
5
Terminology
LSM6DB0
5.1
Sensitivity
Linear acceleration sensitivity can be determined, for example, 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.
An angular rate gyroscope is device that produces a positive-going digital output for
counterclockwise rotation around the axis considered. Sensitivity describes the gain of the
sensor and can be determined by applying a defined angular velocity to it. This value
changes very little over temperature and time.
5.2
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.
Zero-rate level describes the actual output signal 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 time.
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