Calibrating The Compass; Entering The Known Magnetic Deviation - Edgetech 4125 SIDE SCAN User Manual

5 5 .3

Calibrating the Compass

The compass in the tow vehicle is factory calibrated to magnetic north. To provide a more accurate target
location, however, it is necessary to enter the known magnetic deviation for the survey location into the
compass to obtain true north.
5.3.1

Entering the Known Magnetic Deviation

To enter the known magnetic deviation:
1. Activate the system and connect to the tow vehicle through the remote desktop connection with
IP address 192.9.0.101.
2. Close the Sonar.exe window on the desktop.
3. Using the remote desktop program Choose
Start/Programs/Accessories/Communications/HyperTerminal.
4. In the Connect To dialog box, select COM3 from the Connect Using drop-down list box, and then
click OK.
5. In the Port Settings dialog box, click Restore Defaults.
6. Select 19200 from the Bits per second drop-down list box, and then click OK.
The COM3 window opens.
7. Confirm that there are compass data being received in the COM3 window as shown in
on page 5-8.
8. Press <Esc>, and then uppercase "Q."
9. Enter the declination angle to correct for deviation. The value is in 10x degrees and ranges from -
1800 to 1800. For example, enter -150 for -15.0 degrees and 92 for 9.2 degrees.
10. Close HyperTerminal and start sonar.exe.
If it is suspected that the heading information is not accurate, the compass should be re calibrated.
Calibrating the compass requires a flat, easily-rotated, continuously-level platform on which to lay the tow
vehicle. Mark the four cardinal points (0, 90, 180, and 270 degrees) on the platform using a hand-held
compass.
There are two compass calibration procedures: "hard iron" and "soft iron." Hard iron calibration cancels
out the effects of magnetized ferrous materials near the compass for all three magnetic sensing elements:
X, Y, and Z. Soft iron cancels out the effects of non-magnetized ferrous materials. The hard iron calibration
should be performed first, followed immediately by the soft iron calibration.
5-5
Figure 5-6