FXOS8700CQ datasheet(8/86 Pages) FREESCALE

8 / 86 page

Sensors

Freescale Semiconductor, Inc.

3Terminology

3.1

Sensitivity

Sensitivity is represented in mg/LSB for the accelerometer and

μT/LSB for the magnetometer. The magnetometer sensitivity is

fixed at 0.1

μT/LSB. The accelerometer sensitivity changes with the full-scale range selected by the user. Accelerometer

sensitivity is 0.244 mg/LSB in 2g mode, 0.488 mg/LSB in 4g mode, and 0.976 mg/LSB in 8g mode.

3.2

Zero-g and Zero-Flux offset

For the accelerometer, zero-g offset (TyOff) describes the deviation of the output values from the ideal values when the sensor

is stationary.

With an accelerometer stationary on a level horizontal surface, the ideal output is 0g for the X and Y axes, and 1g

for the Z-axis. The deviation of each axes output from the ideal value is called zero-g offset. Offset is to some extent a result of

stress on the 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. For the magnetometer, zero-flux offset describes the deviation of the output signal

from zero when the device is shielded from external magnetic field sources (i.e. inside a zero-gauss chamber).

3.3

Self-Test

Self-Test can be used to verify the accelerometer and magnetometer transducer functionality without the need for an external

acceleration or magnetic field stimulus. When the accelerometer self-test is activated, an electrostatic actuation force is applied

to the sensor, simulating a small acceleration. In this case the sensor X, Y, Z outputs will exhibit a change in DC levels related to

the selected full-scale range (sensitivity). When self-test is activated, the device output level is given by the algebraic sum of the

signals produced by the acceleration acting on the sensor and by the electrostatic self-test force. When self-test is activated for

the magnetometer, an internal magnetic field is generated along the X, Y and Z axes. The sensor response will be the sum of

the ambient magnetic field and the self-test induced field.

FXOS8700CQ датащи(PDF) 8 Page - Freescale Semiconductor, Inc