Moog Crossbow GNAV540 - Manual (Page 40)

Page 40
GNAV540 User Manual
7430‐0808‐01 Rev. B
in the horizontal plane. Using NAV‐V iron effects IEW 2.2, the hard and soft can be viewed by selecting the
ation Menu Misalignment option on the Configur e magnetic ci
For calibration instructions, refer to
, and viewing th rcle during the calibration.
Aligning the Magnetometer on page 57.
Magnetometer Alignment Using Code
The unit provides a command interface for initiating the hard iron/soft iron calibration without using NAV‐VIEW
2.2. To do so, send a
command to initiate the calibration, and then rotate the user system 360 degrees. The C
WC W
d has two options: auto‐termination and manual termination.
• With auto‐termination, the unit tracks the yaw movement and after 380 degrees of rotation returns the
calibration complete response,
comman
CC
. The auto‐termination sequence can falsely terminate if the 360 degree
s o rotation is not completed within two (2) minute f the WC command initiation.
• Manual termination requires sending a second WC command with the termination code in the payload.
Manual termination is a good option when the user system moves very slowly (e.g., large marine vessel) and
te completing the 360 degree rotation may require more than two minu s.
The status of the magnetometer calibration is indicated by the softwareErrorÆdataErrorÆmagAlignOutOfBounds
error flag available in the T0 packet. You can access the hardIronScaleRatio and softIronScaleRatio calibration data
as configuration fields in NAV‐VIEW 2.2, or by using the communication protocol. Also, the softwareError bit of the
ftw
masterFail byte within the BIT word is transmitted in every measurement packet. When the unit has not been
properly calibrated, this so areError bit will be set to fail (high).
The calibration complete (CC) command response message contains the X and Y hard iron bias, as well as the soft
iron ratio. This information can be interpreted to give an indication of the quality of the calibration. For more
information on the hard iron bias and soft iron ratio effects refer to Compensation for Magnetic Fields on page 39.
Refer to Chapter 9. Communicated with the GNAV540 Unit for details of WC and CC commands.
Installation Guidelines—External Magnetometer
Field Installation
• For a proper calibration and alignment, the GNAV540 unit must be installed in its operating environment,
which it will be used. such as the land vehicle or aircraft in
• If using an external magnetometer:
o
The magnetometer must be mounted at least 24” away from large ferrous objects and fluctuating
magnetic fields. Failure to locate the magnetometer in a clean magnetic environment will affect the
attitude solution.
o
Configuring the pitch and level offsets of the magnetometer must be performed before calibrating
the GNAV540 unit.
EMI Protection and Grounding
• Ensure the magnetometer is not exposed to large magnetic fields. This could permanently magnetize
internal components and degrade magnetic heading accuracy.
• For EMI protection, the magnetometer must be connected with a shielded cable that is connected to the I/O
connector shell.
o
connector shell. Ensure the case of the magnetometer is electrically connected to the I/O
o
The shell should be electrically connected to the user’s cable shield.