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AN3182 数据表(PDF) 9 Page - STMicroelectronics |
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AN3182 数据表(HTML) 9 Page - STMicroelectronics |
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9 / 18 page  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 measurements Ax, Ay and Az to normalized measurements Ax1, Ay1 and Az1. For 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. The relationship between the normalized Ax1, Ay1 and Az1 and the accelerometer raw measurements Ax, Ay and Az can be expressed as, Equation 1 where [A_m] is the 3 x 3 misalignment matrix between the accelerometer sensing axes and the device body axes, A_SCi (i = x, y, z) is the sensitivity (or scale factor) and A_OSi is the zero-g level (or offset). The goal of accelerometer calibration is to determine 12 parameters from ACC10 to ACC33, so that with any given raw measurements at arbitrary positions, the normalized values Ax1, Ay1 and Az1 can be obtained, resulting in: Equation 2 Calibration can be performed at 6 stationary positions as shown in Table 2. Collect 5 to 10 seconds of accelerometer raw data with ODR = 100 Hz at each position with known Ax1, Ay1 and Az1. Then apply the least square method to obtain the 12 accelerometer calibration parameters. Refer to Appendix A for additional details. [] ⎥ ⎥ ⎥ ⎦ ⎤ ⎢ ⎢ ⎢ ⎣ ⎡ + ⎥ ⎥ ⎥ ⎦ ⎤ ⎢ ⎢ ⎢ ⎣ ⎡ ⋅ ⎥ ⎥ ⎥ ⎦ ⎤ ⎢ ⎢ ⎢ ⎣ ⎡ = ⎥ ⎥ ⎥ ⎦ ⎤ ⎢ ⎢ ⎢ ⎣ ⎡ − − − ⋅ ⎥ ⎥ ⎥ ⎦ ⎤ ⎢ ⎢ ⎢ ⎣ ⎡ = ⎥ ⎥ ⎥ ⎦ ⎤ ⎢ ⎢ ⎢ ⎣ ⎡ 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 = + + = |
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