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SeaTRAX User Manual Page 13

Other Considerations

The SeaTRAX measures the total magnetic field within its vicinity, which is a

combination of Earth’s magnetic field and local magnetic sources and distortions.

While the SeaTRAX’s calibration algorithm can compensate for local static magnetic

sources, it is not possible to compensate for dynamic changes in the magnetic field.

Consequently, it is recommended to keep the SeaTRAX away from dynamic

magnetic fields. If this is not possible, then take measurements only when the state of

the magnetic field is known. For example, if an electric motor is nearby take

measurements only when the motor is off. Alternatively, different sets of magnetic

calibration coefficients can be generated in advance for various states and then called

when appropriate. Using the prior example, generate and use one set of coefficients

for when the motor is off and another set for when the motor is on.

The main objective of a magnetic user calibration is to compensate for hard-iron and soft-

iron distortions to the magnetic field caused by components within the user’s host system.

To that end, the SeaTRAX needs to be mounted within the host system and the entire host

system needs to be moved as a single unit during a user calibration. The SeaTRAX allows

the user to perform a calibration only in a 2D plane or with limited tilt, but provides the

greatest accuracy if the user can rotate through 360° of heading and at least ±45°of tilt.

The following subsections provide instructions for performing a magnetic calibration of a

SeaTRAX system. Several calibration mode options exist, as summarized in Table 5-1. To

meet the accuracy specification, the number of samples should be the “Minimum

Recommended” value, or greater. Calibration may be performed using Studio or using the

PNI binary protocol, and up to 8 sets of magnetic calibration coefficients may be saved. The

recommended calibration patterns described in the following subsections provide a good

distribution of sample points. Also, PNI recommends the location of the SeaTRAX remain

fairly constant while only the orientation is changed.

Table 5-1: Magnetic Calibration Mode Summary

Calibration

Mode

Static Accuracy

Tilt Range

during Cal

Minimum

Recommended

# of Samples

Allowable #

of Samples

Full-Range

0.3° rms

>±45°

10 – 32

2D Calibration

<2°

<±5°

10 – 32

Limited-Tilt

<2° over 2x tilt

range

±5° to ±45°

10 – 32

Hard-Iron-Only

Restores prior

accuracy

>±3°

4 - 32

1 2 ... 13 14 15 16 17 18 19 20 21 22 23 ... 76 77

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Pni SeaTRAX Manuel d'utilisateur Page 18

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