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Why Does The Magnetic Compass Installed On The Ship Need To Be Calibrated?

The article mainly focuses on the pointing principle of the magnetic compass, the change of the magnetic properties of the ship and its influence on the magnetic compass, the inseparable relationship between the ship navigation and the magnetic compass. On the one hand, the basic principle of the magnetic compass is introduced, and on the other hand, the magnetic compass is explained. The important role played in ensuring the safe navigation of the ship.


1. The principle of pointing the magnetic compass


As early as more than 2,600 years ago, our ancestors discovered that "the magnets call for iron, or lead them," and "ci" is now "magnetic". Later, he invented the "Sinan", "Sinan" can guide the North, in order to create a compass. This is the great contribution of the Chinese nation to world civilization.


The earth is a large magnet with a magnetic field on its surface, its two magnetic poles, close to the two poles of the earth, but not coincident, and it moves very slowly. We call the magnetic pole close to the north pole of the earth called the magnetic north pole, and the magnetic pole close to the south pole of the earth is called the magnetic south pole.


A magnetic needle with a fulcrum in the middle, when there is no ferromagnetic material around it, one end of the magnetic needle points to the magnetic north pole and the other end points to the magnetic south pole.


Every day we use the magnetic compass, its core pointing part is the floating chamber. In order to get enough finger force. Usually two or four magnetic bars are installed in the floating chamber. Under the action of the earth's magnetic field, the magnetic rod points to the "north" (ie, the magnetic north pole) and the other end to the "south" (ie, the magnetic south pole). Then fix a dial around the floating chamber and make a baseline on the compass basin. Then we will see the direction. However, the "North" referred to by the Luo Jing is called the magnetic north is not the true north of the Earth's true meridian. The error between magnetic north and true north is called magnetic difference.


2. Changes in the magnetic properties of ships and their effects on magnetic compasses


General ships are made of steel. Under the action of the Earth's magnetic field, steel is magnetized and magnetic.


Ships are usually equipped with generators, wires and a large number of electrical equipment. These electrical devices also generate magnetic fields during use. This magnetic field also has an effect on the ship itself - the hull is magnetized.


Ships docked at the same terminal for more than a month. Due to the magnetization of the Earth's magnetic field, the original magnetic properties of the ship will also change.


When the ship is subjected to severe vibrations, the magnetic field of the ship itself also changes.


The ship was hit by heavy winds and waves at sea, and the ship was hit by other ships. Or accidentally collided with the dock when leaving the dock. Both can change the magnetic properties of the ship itself.


When the ship is repaired, such as replacing steel on board or adding equipment, especially near the magnetic compass, even small steel parts can affect the magnetic properties of the ship.


When a ship accidentally loses fire, even if it is a partial fire, it will have a greater impact on the magnetic properties of the ship. It also affects the magnetic compass.


When the ship is loaded with steel (including magnetite). Because these steels are magnetic. Therefore, the magnetic properties of the hull have changed.


It is particularly noteworthy that when the ship is loaded and unloaded by a strong magnetic crane, the hull will be severely magnetized, at which point the ship's magnetic compass will be severely deviated. And the magnetic compass on the ship is unstable for a long time! The change is big!


The magnetic compass is installed on the ship. In addition to being affected by the Earth's magnetic field, it is also affected by the hull's magnetic field. The magnetic sizes of various ships are different. The effect on the magnetic compass installed on this ship is also different. More than 170 ° ~ 180 °, ranging from 10 ° ~ 20 °. Only after measurement can you know.


3, the ship needs magnetic compass


Although modern technology gives the ship a precise positioning of the satellite locator. But every ship must have an "old" magnetic compass. It is an indispensable pointing instrument in the navigation of ships. It is also a reliable guarantee for the safe navigation of ships.


The magnetic compass installed on the ship is not accurate due to the magnetic properties of the hull. It is impossible to use it for navigation because of inaccurate pointing. Therefore, the magnetic compass must be corrected. Finally, the error in each of the main headings is measured and made into a self-difference table. This magnetic compass can be used for navigation to ensure the safety of the ship.