About Hard and Soft Iron Distortions .
Magnetic measurements will be subjected to distortion. These distortions are considered to fall in one of two categories; hard or soft iron. Hard iron distortions are created by objects that produce a magnetic field. A speaker or piece of magnetized iron for example will cause a hard iron distortion. If the piece of magnetic material is physically attached to the same reference frame as the sensor, then this type of hard iron distortion will cause a permanent bias in the sensor output. Soft iron distortions are considered deflections or alterations in the existing magnetic field. These distortions will stretch or distort the magnetic field depending upon which direction the field acts relative to the sensor. This type of distortion is commonly caused by metals such as nickel and iron. In most cases hard iron distortions will have a much larger contribution to the total uncorrected error than soft iron.
Learn more about them :
- https://www.sensorsmag.com/components/compensating-for-tilt-hard-iron-and-soft-iron-effects
- https://www.nxp.com/docs/en/application-note/AN4246.pdf
Using Artificial Intelligence for magnetometer calibration on ESPrtk .
ESPrtk’s calibration quality is very high.
ESPrtk version 3.9.8 uses artificial intelligence (AI) to solve noise removal and automatically find the calibration matrix very accurately.
It has been tested many times with different data inputs (a lot of noise, missing spherical data) and both solved them perfectly.
Using AI solves problems that old algorithms cannot solve such as determining eccentricity and distortion with noisy input data samples (or simply being unable to determine where ‘standard shape’ of the input data).
The result was astonishing, with 99.99% eliminated noise. The algorithm works very well, even when only 1/4 surface points data exist in input data. Distortion and eccentricity due to hard-iron and soft-iron are completely removed.
Testing results.
During the development of AI calibration algorithm for ESPrtk. We wrote a program to create different data samples with real-world effects such as deformation of hard iron and soft iron, noise, roughness, duplicate pattern, etc.
You can also download it here: Link Download
For more using magnetometer calibration tool on ESPrtk, go to this page .
Below are some capture images of the calibration results.
Exam 1.
| Configure | Value | Configure | Value |
|---|---|---|---|
| Samples | 1000 | Offset X | -244 |
| Sphere radius | 50 | Offset Y | 200 |
| Rough Noise | 9 % | Offset Z | -155 |
| Random Noise | 20 % | Scale X | 100 % |
| Remove_Y_axis | 0% | Scale Y | 152 % |
| Download | Link | Scale Z | 40 % |
Exam 4.
| Configure | Value | Configure | Value |
|---|---|---|---|
| Samples | 1000 | Offset X | -220 |
| Sphere radius | 50 | Offset Y | 150 |
| Rough Noise | 11 % | Offset Z | -223 |
| Random Noise | 80 % | Scale X | 151 % |
| Remove_Y_axis | 0 % | Scale Y | 53 % |
| Download | Link | Scale Z | 200 % |
Exam 6.
| Configure | Value | Configure | Value |
|---|---|---|---|
| Samples | 1000 (removed 1/2 sphere surface X-axis ) | Offset X | 160 |
| Sphere radius | 50 | Offset Y | 152 |
| Rough Noise | 8 % | Offset Z | 206 |
| Random Noise | 28 % | Scale X | 65 % |
| Remove_Y_axis | 50 % | Scale Y | 135 % |
| Download | Link | Scale Z | 61 % |
Exam 7.
| Configure | Value | Configure | Value |
|---|---|---|---|
| Samples | 1000 (removed 1/2 sphere surface Y -axis ) | Offset X | 132 |
| Sphere radius | 49 | Offset Y | -158 |
| Rough Noise | 2 % | Offset Z | 146 |
| Random Noise | 20 % | Scale X | 100 % |
| Remove_Y_axis | 50 % | Scale Y | 200 % |
| Download | Link | Scale Z | 100 % |
Exam 8.
| Configure | Value | Configure | Value |
|---|---|---|---|
| Samples | 1167 (removed 3/4 sphere surface Y -axis ) | Offset X | -112 |
| Sphere radius | 50 | Offset Y | 152 |
| Rough Noise | 0 % | Offset Z | -137 |
| Random Noise | 5 % | Scale X | 100 % |
| Remove_Y_axis | 75 % | Scale Y | 200 % |
| Download | Link | Scale Z | 100 % |
ESPrtk Homepage 
