Magnetic sensor calibration in general
In order to accurately measure azimuth, it is important to calibrate the magnetic field sensor output.
Calibration means obtaining the correct magnetic field value from the sensor's output.
Because the sensor's output is proportional to the ambient magnetic field, once the sensitivity and 0 point are known, the correct magnetic field value can be found from the sensor output .
Calibration is not necessarily required every time before compass use, but it must also not be neglected for a long time.
The reason that calibrating at the time of shipping isn’t sufficient is that the sensor's characteristics depend on the temperature and magnetization condition of nearby parts.
For MI type compass, we know from experience that the sensitivity changes are relatively little.
Rather, it is important to calibrate the origin, since the origin may shift considerably.
If an azimuth calculation is made with the origin shifted, the situation displayed below may result and the azimuth calculation results will be incorrect.
For a detailed explanation of the calibration method, please refer to the "Principles of Calibration" page.
- Manual calibration and Automatic calibration -
To know the origin, it is most critical that the sensor output be seen under a magnetic shield. Still, there must be a method that the end user can use that does not require such shielding.
That method is to spatially turn the sensor through one complete revolution in the earth's magnetic field and look for the max-min points in the output peak.
For example, for the X-Y sensor axis, turn the sensor one complete revolution while level and record the output. When the output is recorded, there will be a circle at the X-Y output axis level.
This center is the origin.