Specifications

BMA180

Preliminary data sheet

Bosch Sensortec

Rev. 1.0 Page 66 / - proprietary information - 06 March 2009

as copying and passing on to third parties. BOSCH and the symbol are registered trademarks of Robert Bosch GmbH, Germany.

Specifications within this document are preliminary and subject to change without notice. Document is not intended for publication.

9.4.1.1 Standard earth field calibration method

1. Orientate the device at well-defined angles to the gravitational field (see following figure

for the definition of the polar coordinates θ and ϕ. θ is the angle between the z-axis of

the sensor and the g-force, ϕ the angle between the z-g-plane and the x-axis component

which lies in the z-x-plane and which is perpendicular to the g-force).

2. Choose range (e. g. 2 g)

3. Read stored offset trimming values OffsetX, OffsetY, OffsetZ.

4. Measure output signals A

, A

in LSB.

5. Calculate new correction values (for 2g-mode sensivitiy = 4096 LSB/g)

Since the offset trimming steps slightly vary, highest precision can be reached by using a

successive approximation procedure, e. g. repeating the procedure above several times by

starting from step 4. Highest accuracy could be reached by choosing 1 g-mode (e. g. first

calibration in 2 g-mode, second in 1 g-mode).

9.4.1.2 Offset calibration by use of offset fine-tuning feature

Using this method, the device has to be placed in an appropriate way to the g-vectors (e. g.

perpendicular or in parallel). Placement under a certain angle (e. g. non-perpendicular or non-

parallel) with respect to the g-vector means: the offset is regulated with respect to this “new” g-

vector, thus an error is made. The regulation accuracy could be very high, but the device

manufacturer has to take care about proper placement of the devices during calibration.