AN3182

Calibrating the accelerometer

Doc ID 17289 Rev 1

9/18

2

Calibrating the accelerometer

Section 1 describes the accelerometer parameters and the definition of the pitch and roll tilt

angles. The next step is to calibrate the accelerometer before tilt calculation can take place.

Please note that all accelerometers from ST, including the LIS331DLH, have been factory-

calibrated. For most applications, such as screen portrait/landscape rotation and laptop lid

open/close detection, accelerometer calibration is not necessary. This means that users can

use the zero-g level and sensitivity parameters from the datasheet directly to convert raw

applications that require better than 1° tilt-measurement accuracy, such as automobile alert

systems, tilt-compensated electronic compasses and level monitoring systems,

accelerometer calibration is suggested.

Equation 1

where [A_m] is the 3 x 3 misalignment matrix between the accelerometer sensing axes and

zero-g level (or offset).

The goal of accelerometer calibration is to determine 12 parameters from ACC10 to ACC33,

Equation 2

Calibration can be performed at 6 stationary positions as shown in Table 2. Collect 5 to 10

Ay1 and Az1. Then apply the least square method to obtain the 12 accelerometer calibration

parameters. Refer to Appendix A for additional details.

[]

⎥

⎥

⎥

⎦

⎤

⎢

⎢

⎢

⎣

⎡

+

⎥

⎥

⎥

⎦

⎤

⎢

⎢

⎢

⎣

⎡

⋅

⎥

⎥

⎥

⎦

⎤

⎢

⎢

⎢

⎣

⎡

=

⎥

⎥

⎥

⎦

⎤

⎢

⎢

⎢

⎣

⎡

−

−

−

⋅

⎥

⎥

⎥

⎦

⎤

⎢

⎢

⎢

⎣

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=

⎥

⎥

⎥

⎦

⎤

⎢

⎢

⎢

⎣

⎡

30

20

10

z

y

x

33

32

31

23

22

21

13

12

11

z

z

y

y

x

x

z

y

x

3

x

3

1

z

1

y

1

x

ACC

ACC

ACC

A

A

A

ACC

ACC

ACC

ACC

ACC

ACC

ACC

ACC

ACC

OS

_

A

A

OS

_

A

A

OS

_

A

A

SC

_

A

/

1

0

0

0

SC

_

A

/

1

0

0

0

SC

_

A

/

1

m

_

A

A

A

A

1

A

A

A

A

2

1

z

2

1

y

2

1

x

=

+

+

=