Setting Reference North Heading; Set-Up Suggestions - Red Line Instruments FG1 User Manual

shifting the centre from the origin and induced magnets ('soft') modify the circle into
an ellipse. The results of our investigation show that there is always a residual
error due to the fact that real magnetic objects do not behave exactly according to
the model outlined. Technician is aware that the need for a constant angular velocity
is onerous but the benefit is that it provides a very low residual error – less than
0.5°.
Note that the calibration is different if the unit is mounted upside-down.
Calibration must always be done with the unit in its final mounted position. The essential
point of the calibration is remove the influence of external magnetic components in
the vicinity – the nearby pieces of iron and steel –so it is essential that these remain
unchanged after calibration. If any significant iron component is altered – such as
the installation of new equipment or replacement of equipment such as winches or
engines – then the calibration must be re-done.
4 .3 Terminating a bad calibration
If the process is faulty in any way – such as would happen if the manoeuvre cannot be
completed, the process can be terminated by the NMEA command listed and the
original factory default (linear) table is restored. Alternatively this can be done by
pressing both Switches together for at least 1 second.
NOTE that there should be a delay of at least 5 seconds after termination before a new
calibration process is initiated.

4 .4 Setting reference NORTH heading

Switch 2 (and also a NMEA command) is provided to set 'zero'. The FG1 should
a. first be auto-calibrated
b. then be aligned to North

4 .5 Set-up suggestions

When the FG1 is fixed in place and connected it can be calibrated as described
above. Choose a calm day and a region of water where there are no currents. Set
the boat turning to left or right at a slow rate and fix the wheel or tiller. Then, when
the turning is steadily under way, press the auto-calibrate button and watch the
LED.
When calibration is completed the boat can be on its way and the next task is to set
North. This is best done by identifying transits on a chart and heading the boat on
the transit. Again this should be done in the same conditions so that the heading
can be lined up on the transit and maintained while the set-zero button is pressed.
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