What are The Errors Of The Gyro Compass

The Angle at which the principal axis of a gyro compass deviates from the geographical true north direction in azimuth is called the gyro compass error. The gyro compass error is also the difference between the ship's true course and the gyro compass course or the difference between the true north and the gyro compass north. The error of gyro compass includes latitude error, velocity error, shock error, swing error and baseline error.

Latitude error or damping error

Cause: It is caused by the vertical damping method.

Elimination method:

(1) External compensation method-calculate the size and sign of the latitude error according to the latitude error formula, and deduct it from the reading of the gyro compass;By turning the baseline or the compass dial, the Angle of the baseline and the rotation is equal to the error value, or the compass dial makes the Angle of its rotation reverse the equivalent of the latitude error, and the course read from the compass dial is the true course without the error. It should be emphasized that the external compensation method only deducts the error value from the compass dial and does not change the stable position of the main shaft of the compass.

(2) Internal compensation method—calculate and output the signal transformed according to the law of latitude error, and apply the compensation torque to the gyro compass.The main shaft can be stabilized in the meridian plane, and the error is fundamentally eliminated.

Speed error

Cause: The movement of the base changes the implicated movement of the main axis of the gyro compass, resulting in pointing errors.

Elimination method:

(1) Speed error correction table;

(2) External compensation method-use mechanical simulation method to calculate the error value according to the expression of speed error and deduct it from the heading reading;

(3) Internal compensation method-calculate and output the regular speed error compensation torque to compensate the gyro compass.

Other errors：

1) Impact error

When a ship is maneuvering, under the action of inertial force, the main axis of the gyro compass changes from the stable position at the beginning of the maneuver to the stable position at the end of the maneuver within the duration of the maneuver.The error caused by the influence of the inertial force on the compass is called the impact error. The impact error caused by the inertial force acting on the gyro compass gravity control equipment is called ballistic deflection error. The impact error caused by the inertial force acting on the damping equipment is called ballistic damping error.

2) Baseline error

The main and sub-compass of the gyro compass have reference lines for reading the course, called lubber linc. When installing or using the compass, the error occurs when the compass baseline does not coincide with or parallel to the bow and stern lines.The size and sign of the baseline error do not change with time, which is a fixed error. When the baseline is deflected to the starboard,the azimuth reading of the compass is greater than the true azimuth, and this is the west error, represented by W; When the baseline is deflected to the larboard, the compass bearing reading is less than the true bearing, then the baseline error is the east error, represented by E.

3) Swing error

The error produced by the gyro compass when the ship is swaying.Ships swing in the wind and waves is periodic, when the swing will have a periodic inertia force, this inertia force acts on the compass, so that the error generated by the fiber is called the swing error. The swaying error of gyro compass refers to the pointing error caused by the inertial force which changes periodically when the ship is swaying as the gravity control equipment used for gyro compass. The rocking error of the compass is related to the structural parameters of the compass, the installation position of the compass, the swaying attitude of the ship, the latitude of the ship and the swaying direction of the ship. Especially when the ship is sailing along the corner course and rolling, the swing error is the largest.

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