Principle and characteristics of magnetic compass

Magnetic compass is a kind of pointing instrument made by the principle that magnetic needle can point to the magnetic north (south) pole of the earth under the action of geomagnetic force. As an important navigation instrument, the magnetic compass has been installed and used on marine ships for a long time. At present, although modern ships have been equipped with advanced nautical instruments such as gyroscopes (Gyro), satellite navigation (GPS), etc., because modern magnetic compasses have the characteristics of simple structure, reliable performance and no dependence on external conditions, they are still necessary. Navigation instruments are installed and used by marine vessels. The International Maritime Organization (IMO), classification societies, and ship inspection agencies of all countries clearly stipulate that marine ships should be equipped with magnetic compasses, and should correct their self-differences and have self-difference tables.

1. Magnetic compass classification

　　A. According to whether there is liquid in the magnetic compass, there are two types of liquid compass and dry compass. The compass of the liquid compass is suspended in a compass filled with liquid. Due to the damping effect of the liquid, the stability of the compass is better when the ship is swaying. In addition, due to the buoyancy of the liquid, the friction force between the compass support shaft needle and the bearing can be reduced, thus improving the sensitivity of the compass. The company's products are liquid compasses.

　　B. According to the purpose of magnetic compass, there are standard compass and steering compass. The standard compass is generally vertical and installed on the top deck (compass deck) of the cab. Because of its high position, unobstructed, and little influence of ship's magnetism, it is used to observe the course and determine the direction of the target and correct the steering compass, so it is called the standard compass.

　　 Steering compass is generally a desktop, installed in the cab, used to observe the course and steering. The company produces various types of standard compasses and steering compasses.

　　C. According to the diameter of the compass surface, commonly used are 190mm, 165mm, 130mm, 100mm.

2. Magnetic compass deviation and correction

　　The magnetization of the steel ship by the geomagnetic field will generate the ship's magnetism, which will affect the pointing accuracy of the magnetic compass, so-called "self-difference". This self-difference can be corrected by the compass master. The magnetic compass produced by our company is equipped with a high-efficiency self-difference correction device.

3. Installation of magnetic compass

　　A. The magnetic compass should be installed on the longitudinal centerline of the ship as much as possible. The first line of the compass cabinet should be coincident (or parallel) with the longitudinal centerline of the ship.

　　B. The minimum distance between the standard magnetic compass and any ferromagnetic substance is 1 meter.

4. Daily maintenance of magnetic compass

　　A. Normally, the magnetic compass should be covered with a compass cap (the standard compass should be covered with a compass cover).

　　B. Keep the colorless and transparent liquid in the basin to eliminate air bubbles.

　　C. Keep the Luopin shaft, the normally flat ring shaft lubricated, and rotate flexibly.

　　D. Periodically check the half cycle of the compass, sensitivity, and refill the compass basin if necessary.

　　E. No magnetic objects should be placed near the compass, and the compass should not be exposed to high temperature and vibration for a long time.

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