Math help: calibrating adxl375

[Vindhyachal.takniki]

I have read the two calibration app note as I have attached. I am using adxl375.

1. I have been able to do 6 point calibration correctly as in AN4399.

2. Now I want to do 12 point calibration as in DM00119044 or AN4399.
Page 8 of DM00119044 shows the matrix for calculation.

This matrix will yield to 18 equations right? As below. Now I have 18 equations & 12 variables.
Is there any software which can solve these for me:

Code: [Select]

/* 18 equations */

/* +z axis */
a11*30 + a12*50 + a13*2548 + o1 = 0
a21*30 + a22*50 + a23*2548 + o2 = 0
a31*30 + a32*50 + a33*2548 + o3 = 1

/* -z axis */
a11*20 + a12*10 + a13*980+ o1 = 0
a21*20 + a22*10 + a23*980 + o2 = 0
a31*20 + a32*10 + a33*980 + o3 = -1

/* +y axis */
a11*30 + a12*1911 + a13*50 + o1 = 0
a21*30 + a22*1911 + a23*50 + o2 = 1
a31*30 + a32*1911 + a33*50 + o3 = 0

/* -y axis */
a11*20 + a12*49 + a13*10+ o1 = 0
a21*20 + a22*49 + a23*10 + o2 = -1
a31*20 + a32*49 + a33*10 + o3 = 0

/* +x axis */
a11*2303 + a12*30 + a13*50 + o1 = 1
a21*2303 + a22*30 + a23*50 + o2 = 0
a3/* +z axis */1*2303 + a32*30 + a33*50 + o3 = 0

/* -x axis */
a11*392 + a12*20 + a13*10+ o1 = -1
a21*392 + a22*20 + a23*10 + o2 = 0
a31*392 + a32*20 + a33*10 + o3 = 0

3. Now for 15 point calibration as in AN4399. page 33. They had added a cubic nonlinearity.
What is its purpose?
Why to add cubic factor here?

[electr_peter]

2. Now I want to do 12 point calibration as in DM00119044 or AN4399.
Page 8 of DM00119044 shows the matrix for calculation.
...

All is explained in the app note.

3. Now for 15 point calibration as in AN4399. page 33. They had added a cubic nonlinearity.
What is its purpose?
Why to add cubic factor here?

Have you read a note?
Nonlinear elements in calibration model allows to compensate for sensor nonlinearity.

[Vindhyachal.takniki]

1. From Page 8 of DM00119044 matrix, I have made 12 equations. now how to solve that. i didn't understand the way it is done in DM00119044?

2. Sorry I didn't frame my qyery right. The 15 point calibration in AN4399 is for freescale accelerator or I can apply in adxl375 also?

[electr_peter]

1. From Page 8 of DM00119044 matrix, I have made 12 equations. now how to solve that. i didn't understand the way it is done in DM00119044?

DM00119044 suggests to use LS method, it is pretty straightforward. See appendix.

2. Sorry I didn't frame my qyery right. The 15 point calibration in AN4399 is for freescale accelerator or I can apply in adxl375 also?

You can use same calibration method for both devices, it is independent of accelerometer used. Note that 15 point method will be valid only if you can assure that your calibration points are exact.