"AN5286精密加速度计校准1.0：传感器融合库函数数学原理详解"

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AN5286 Precision Accelerometer Calibration Rev. 1.0 is an application note provided by NXP Semiconductors that outlines the mathematics behind the functions found in the Sensor Fusion Library and precisionAccelerometer.c file. This document serves as a guide for calibrating accelerometer devices in order to ensure accurate and reliable performance. The calibration process detailed in AN5286 involves various mathematical calculations and adjustments to correct for any errors or inaccuracies in the accelerometer readings. By following the step-by-step instructions provided in the application note, users can improve the overall precision and sensitivity of their accelerometer sensors. It is important to note that all information presented in AN5286 is subject to legal disclaimers, and users are advised to carefully follow the guidelines outlined in the document. Additionally, NXP Semiconductors retains all rights to the content provided in this application note. In conclusion, AN5286 Precision Accelerometer Calibration Rev. 1.0 is a valuable resource for individuals and organizations looking to optimize the performance of their accelerometer devices. By implementing the calibration techniques described in this document, users can enhance the accuracy and reliability of their sensor data for a wide range of applications.

NXP Semiconductors

AN5286

Precision Accelerometer Calibration

AN5286

All information provided in this document is subject to legal disclaimers.

Application note

Rev. 1.0 — 21 June 2016

4 of 20

1.3 Software Functions

Table 1. Sensor Fusion software functions

Functions

Description

Reference

void fComputeAccelCalibration4(struct

AccelBuffer *pthisAccelBuffer, struct

AccelCalibration *pthisAccelCal,

struct AccelSensor* pthisAccel)

Determines the

coefficients of the 4

parameter accelerometer

calibration model.

void fComputeAccelCalibration7(struct

AccelBuffer *pthisAccelBuffer, struct

AccelCalibration *pthisAccelCal,

struct AccelSensor* pthisAccel)

Determines the

coefficients of the 7

parameter accelerometer

calibration model.

void fComputeAccelCalibration10(struct

AccelBuffer *pthisAccelBuffer, struct

AccelCalibration *pthisAccelCal,

struct AccelSensor* pthisAccel)

Determines the

coefficients of the 10

parameter accelerometer

calibration model.

2. Differences From Magnetic Calibration

The four-, seven- and ten-element accelerometer calibration models described in this

document have two minor differences from the equivalent four-, seven- and ten-element

magnetic calibration models described in AN5019 “Magnetic Calibration Algorithms”.

The first difference is that the geomagnetic field strength  varies between 27 µT and

65 µT (more than 240 %) over the earth's surface whereas the gravitational field strength

 varies by just 0.7 %. The magnetic calibration algorithms therefore solve for  on the

assumption that the soft iron gain matrix has unit determinant implying no shielding or

amplification of the geomagnetic field. The accelerometer calibration models, in contrast,

fit the local gravitational field to have magnitude exactly 1 gravity by scaling the gain

matrix determinant appropriately.

The second difference is that the geomagnetic inclination angle  varies from –90

at the

south geomagnetic pole to +90

at the north geomagnetic pole and is unknown without

knowledge of one's location. The gravity vector in the global frame 





always points

exactly downwards at all locations and defines the local zero tilt plane. It is therefore

straightforward in the accelerometer calibrations algorithms to define one measurement

as representing flat and computing the rotation correction matrix that will force zero tilt

angle irrespective of the mounting angle of the accelerometer in the final product. This is

documented in Section 7.

The application of the algorithms also differs between the magnetic and accelerometer

calibration cases. The magnetometer measurements are unaffected by acceleration and

can therefore be taken while the product is moving and rotating. Typically several

hundred magnetometer measurements are used to compute the magnetic calibration.

The accelerometer, in contrast, is sensitive to acceleration as well as the applied

gravitational field and so its calibration measurements must be taken when the

accelerometer is stationary, isolated from vibration and the measurements then averaged

to minimize measurement noise. Typically, 12 high-quality measurements are used to

compute the precision accelerometer offset, gain and cross-axis calibration corrections.

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