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3.3.2 Automatic Power-Up Deviation Calibration
Automatic power-up deviation calibration is accomplished by turning the vessel through four
complete circles within 10 minutes of power-up. The procedure is as follows:
1. Ensure that the compass has been properly installed per Section 2.
2. Warm up the compass by operating it for approximately 10 minutes.
3. Turn the vessel (either direction) such that you complete a full 360° turn in 2½ minutes or
less (try not to go below 1 minute for a complete circle).
4. While continuing to turn the vessel as indicated in step 3, remove the power from the
compass and reapply power (this initiates deviation calibration).
5. Continue turning the vessel through four complete circles in less than 10 minutes from
the time power was applied.
6. Successful deviation is indicated when the SSC300 outputs the following sequence:
a) 0 Degrees for two seconds followed by
b) 90 degrees for two seconds followed by
c) 180 degrees for two seconds followed by
d) 270 degrees for two seconds followed by the actual heading
While turning the vessel, try to maintain a circle by holding the rudder at a constant angle. In
addition, try to minimize the vessel’s pitch and roll by calibrating on calm, flat water.
3.4 Installation-Offset Correction (Second Time)
After installation and successful magnetic deviation calibration, it is important to repeat
installation-offset correction so that the displayed compass heading, pitch, and roll match the
actual vessel heading, pitch, and roll. Please refer to Section 3.2 for details on how to perform
the procedure.
4 Variation
Variation is the angular difference between the true meridian (great circle connecting the
geographic poles) and the magnetic meridian (direction of the lines of magnetic flux). Variation
has different values at different locations on the earth with most areas undergoing change to the
variation over time.
Normally, heading information is displayed as either a “true” heading (a direction relative to the
geographic poles) or it is displayed as a “magnetic” heading (a direction relative to the lines of
magnetic flux). North-seeking gyrocompasses are capable of measuring direction relative to the
geographic poles (“true”) whereas magnetic compasses measure direction relative to the earth’s
local magnetic flux (“magnetic”).
The SSC300 is a magnetic compass; therefore, it requires an external source for variation if you
want to view your heading in “true” format. The SSC300 is capable of receiving variation in one
of three ways; 1) via the NMEA 0183 interface, 2) via the NMEA 2000
®
interface, or 3) through
manual variation entry.
