Compass, an instrument for measuring horizontal directions in the field. Used to determine the direction in which the moving ship, aircraft, ground vehicles, the direction in which there is a pedestrian, the direction to an object or landmark. Compasses are divided into two main classes: the magnetic compass type of switches used by surveyors and tourists, and non-magnetic, such as the radio compass and gyro.


Compass card. To determine the directions in a compass compass rose (Fig. 1) - dial with 360 divisions (corresponding to one degree every corner), tagged so that the reading is zero clockwise. Toward the north (north, N, or C) usually corresponds to 0 , to the east (Ost, O, E, or B) - 90 , to the south (south, S, N or S) - 180 , to the west (West , W, E or W) - 270 . This is the main compass rumba (the compass). Between them there are "the quarter" Rumba: north-east, or E (45 ), south-east or NE (135 ), south-west or SW (225 ) and north-west or W (315 ). Between the main and quarter are 16 "major" points of the compass, such as the north-north-east and north-northwest (once it was another 16 points of the compass, such as the "shadow-north-west", simply called rumba).


Principle. The device indicating the direction should be some reference direction, from this point to all the others. In such a magnetic compass direction is the line connecting the North and South Pole. In this direction, he set a bar magnet, if it hung so that it can rotate freely in the horizontal plane. The fact that the Earth's magnetic field acts on the magnetic rod turning couple, setting it in the direction of the magnetic field. A magnetic compass is part of the core is magnetized needle that measurement itself is installed in parallel to the magnetic field of the Earth.

Compass dial. This is the most common form of the magnetic compass. It is often used in a handheld version. In the slip compass (Figure 2) there is a thin magnetic needle, set free in the middle point on the vertical axis, which allows it to rotate in a horizontal plane. The northern end of the arrow marked, and coaxially mounted compass rose with it. When measuring the compass must be held in the hand, or set on a tripod so that the plane of rotation of the arrow was strictly horizontal. Then the northern end of the arrow points to the north magnetic pole of the Earth. Compass, adapted for surveyors, a DF unit, ie instrument for measuring the azimuth. It is usually equipped with a telescope that is rotated to align with the desired object, then to consider the azimuth compass rose on the subject.

Liquid Compass. Liquid Compass, a compass or a floating compass card - is the most accurate and stable of all magnetic compasses. It is often used on ships and is therefore called the ship. The design of such diverse compass, in an exemplary embodiment, it is a fluid-filled "pot", in which the vertical axis is fixed aluminum compass rose. On opposite sides of the axis to the bottom compass card attached pair or two pairs of magnets. In the center of a compass card hollow hemispherical protrusion - float that reduces pressure on the bearing axis (when the pot is filled with a liquid compass). Compass card axis passed through the center of the float rests on a stone toe, usually manufactured from synthetic sapphire. Saddle mounted on a fixed disk "feature of the course." At the bottom of the pot, there are two openings through which the liquid can be poured into the expansion chamber to compensate for changes in pressure and temperature.

Compass rose compass floats on liquid. Liquid also soothes compass card fluctuations caused by pitching. The water is not suitable for the marine compass, as it freezes. A mixture of 45% ethyl alcohol and 55% distilled water, the mixture of glycerine and distilled water or high purity petroleum distillate.

Bowler compass cast in bronze and is equipped with a glass cover with a seal, which eliminates the possibility of leakage. At the top of the pot is fixed azimuth, or DF, ring. It allows you to determine the direction of different objects relative to the course of the ship. Bowler compass mounted in a suspension on the inner ring of the universal (cardan) joint, where it is free to rotate, keeping the horizontal position in pitching.

Bowler compass fixed so that the shooter or his special mark, called ESP, or black line, called ESP feature points to the ship's bow. If you change the course of the ship compass card is held in place by magnets, consistently maintains its direction north - south. At offset coursework marks or features regarding compass card can be controlled exchange rate.


Error of magnetic compass

Amendment compass called the dismissal of his testimony from true north (north). Reason - the deviation of the needle and the magnetic declination.

Deviation. Compass points to the so-called compass, not magnetic north (magnetic north), and the corresponding lines of the angular difference is called deviation. It is caused by the presence of local magnetic fields superimposed on the magnetic field of the Earth. Local magnetic field can create the hull, cargo, large masses of iron ore, located near the compass, and other objects. The correct direction is obtained by considering a compass readings corrected for deviation.

Ship's magnetism. Local magnetic fields created by the hull and the vessel covered by the concept of magnetism, are divided into variable and fixed. Variable ship magnetism induced in the steel hull Earth's magnetic field. Voltage alternating marine magnetism varies depending on the course of the vessel and the latitude. Permanent ship magnetism induced in the process of construction of the ship when under the influence of vibration caused by, for example, operations, riveting, steel casing is a permanent magnet. Voltage and polarity (direction) of the permanent magnetism of the ship depends on the location (latitude) and the orientation of the hull during its assembly. Permanent magnetism is partially lost after launching boat in the water and after the visit it in rough seas. In addition, it is somewhat different in the "aging" of the case, but it changes significantly reduced after the ship's operation during the year.

Ship's magnetism can be decomposed into three mutually perpendicular components: longitudinal (relative to the ship), the transverse horizontal and transverse vertical. The deviation of the needle caused by the ship's magnetism, correct by placing permanent magnets near the compass, parallel to these components.

Binnacle. Ship's compass is usually installed in the universal joint on a special stand called a binnacle. Binnacle rigidly and securely attached to the deck of the vessel, usually in the middle line of the latter. Binnacle mounted on also magnets to compensate the effect of ship magnetism, and secured protective cap for the compass compass card with an internal illuminator. Previously carried out in a binnacle carved figures out of wood, but modern ships is simply a cylindrical stand.

Magnetic declination. Magnetic variation - is the angular difference between magnetic and true north, due to the fact that the Earth's magnetic north pole shifted by 2100 km of the true, geographical.

Variation chart. Magnetic variation changes over time and from place to place on the earth's surface. The measurements of the magnetic field of the Earth to get the card decline, which give the magnetic declination and its rate of change in different regions. Contours of zero declination these cards coming out of the north magnetic pole, called agony, and the contours of equal magnetic declination - isogony.