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After you run through the calibration process, you will see the correction values
generated by the process. At this point, the soft iron calibration is completed. You
should go back and check the cardinal points with your system. You should see your
system more inline with the cardinal points.
If the compass is still not reporting accurate information compared to the known good
reference compass you should run through the calibration process again and carefully
check each step. In some cases, the magnetic field may be too disturbed for accurate
calibration and distance from soft iron is the best solution.
Compass Settings Relating to Filtering Measurements (Not Required for
Most Applications)
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Since the OS5000 family of digital compasses use a fast 3-axis accelerometer to
sense the gravity (1G) static vector to determine its Roll and Pitch angle you may
need to filter out other dynamic acceleration introduced by your platform. These
accelerations will decrease the accuracy of the Roll and Pitch estimation using
Euler angles. Introducing filtering will improve the accuracy if the platform
acceleration is dynamic and can be filtered out.
Note: The future OS5000-USG compass will introduce rate Gyros and Kalman
filters which can remove most short-term dynamic acceleration effects. This
product is in development and should be released in the future.
1) Analog to Digital Converter Decimation Filter
The analog to digital converter is an AD7799 24 bit Sigma delta converter. It has
an internal decimation filter that sets the filter period and the sampling update
rate.
The lower the setting the faster the update rate can be. If your using a
40hz output rate you should set this value from 3 to 2.
<esc>D (1-9) enter ! to change the update rate
1: 470 Hz, 4ms settling time
2: 242 Hz, 8ms settling time
3: 123 Hz, 15 ms settling time (factory default)
4: 62 Hz, 32 ms settling time
5: 50 Hz, 40 ms settling time
6: 39 Hz, 48 ms settling time
7: 33.2 Hz, 60 ms settling time
8: 19.6 Hz, 101 ms settling time, 90 dB rejection of 60Hz noise
9: 16.7 Hz, 120 ms settling time, 90 dB rejection of 50Hz noise
Use the higher values if you have large electrical or vibration noise you need to
filter out, at a much lower update rate.
