LSM303D Datasheet, PDF (16/52 Pages) STMicroelectronics – Embedded temperature sensor

Terminology
3
Terminology
LSM303D
3.1
Set/reset pulse
The set/reset pulse is an automatic operation performed before each magnetic acquisition
cycle to recover the initial magnetization state of the sensor and therefore the linearity of the
sensor itself.
3.2
3.2.1
3.2.2
3.3
3.4
Sensitivity
Linear acceleration sensor sensitivity
Sensitivity describes the gain of the sensor and can be determined, for example, 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 gain of the sensor and can be determined, for example, by
applying a magnetic field of 1 gauss to it.
Zero-g level
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
measures 0 g on the X-axis and 0 g on the Y-axis, whereas the Z-axis measures 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). 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 “Zero-g level change vs. temperature”. 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 describes the deviation of an actual output signal from the ideal
output if no magnetic field is present. Thanks to the set/reset pulse and to the magnetic
sensor read-out chain, the offset is dynamically cancelled. The Zero-gauss level does not
show any dependencies on temperature and power supply.
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