Magnetic deviation

The deviation or deflection ( english deviation, DEV ) is an addition to the magnetic declination be observed deflection of a magnetic compass, which is related to interference fields in the vicinity of the measuring point. It is according to their most important cause also called vehicle magnetism.

Definition

The deviation (Latin for deviation ) corresponds to the angular difference between the direction in which an error-free magnetic needle points, which is only influenced by the magnetic field of the Earth ( MN), and the direction in which rotates a magnetic needle by both the earth's magnetic field as is also affected by the magnetic field of the aircraft or ship.

Causes

The proximity of cobalt -, nickel- and iron-containing (more precisely, ferromagnetic ) objects ( keychain, metal glasses, bicycle, car, steel ship, railway) leads to a change in direction of the magnetic field lines on which aligns the magnetic compass needle. Therefore, subject compasses that are used on vehicles with ferromagnetic materials, which inevitably disturbing influences. If these are not randomly distributed evenly around the compass around, a systematic error in the measurement direction is the result. Even circuits on aircraft and ships generate magnetic fields, especially when DC current flows through the wires.

In addition, there are cyclical, dependent on the rate effects, their influence on the compass changes with the direction in which the vehicle "looks".

A vehicle, except aircraft, vehicle or ship can take many different directions with respect to the earth's magnetic force, thereby changing the direction and strength of the vehicle 's own magnetic field. Therefore, the size and direction of the deviation of the compass, taking on various courses at different levels which repeat themselves mainly with the periods of 360 °, 180 ° and 90 °. They are therefore called whole -, half - and viertelkreisig and can be filtered out of careful, certain measurements.

Discovery of the deviation

The changes in the magnetic field by the deviation based on specific laws that were first discovered by Matthew Flinders. Siméon Denis Poisson presented soon after the deviation in mathematical form dar.

Reduce the deviation

One possible measure against the deviation is to mount a master compass at a location which is better than the bridge or the cockpit suitable. Otherwise or moreover, the deviation can be reduced by additionally attached and generally adjustable, small magnets or iron compositions (magnetic compensation). The remaining deviation is held in a so-called deviation table, from which one can see the necessary correction for each course heading.

Deviation in practice

If a device is installed or dismantled in the cockpit of an aircraft that may have an impact on the deviation of the compass needle. Therefore, the deviation must be redetermined after significant modifications to the airplane. This is done in steps of 30 °. The results of the Deviationsbestimmung are recorded in the deviation table which is suspended for the pilot clearly visible in compass nearby.

Special situation for ships

For vessels made ​​of steel, a special situation is given. The entire (huge ) iron hull is the axis of which is due to the earth's magnetic force to a magnet in the direction of the magnetic meridian. From the ship lying on stack of a portion of this total magnetism is taken permanently by the shock of hammering. Which is known as a permanent magnetism of the vessel. The axis of the permanent magnetic component of the total magnetism remains unchanged even later, when the ship takes a different position relative to the magnetic meridian.

Another part, especially the one in the softer masses of iron magnetism, his induction direction changes constantly with the change in the meridional direction. This part of the overall magnetism is called volatile magnetism. Here the change in direction shall take place not always instantaneous, but only gradually. For Robert Koldewey introduced the concept of a remanent magnetism.

Navigational treatment

The Deviation (DEV ) as the local magnetic variation (VAR ) with OST ( ) or WEST - called (). If Compass North (English compass north, CN, also pointing to the right called North, RWN ) east of miss true north ( magnetic north english, MN ), so it is an eastern Deviation (English east deviation ).

An eastern deviation must always be abused by looking ( tax) rate (MWK, English magnetic heading, MH ) are subtracted to (english compass heading, CH ) to get the compass heading. Exactly the opposite is the case with the western deviation. This must be added to the MH. This then results to be missed, even in the (sea) map true course ( RWK ).

The deviation similar to the mnemonic also applies to the variation:

"West is best ( ! ), East is least ( -! ) "

An eastern deviation is, as already mentioned, positive, as an angle in a clockwise direction is defined as positive. A Western Deviation is correspondingly negative. Above award may also be formulated in mathematical terms. If the deviation to the east so they will be deducted from mißweisenden heading (magnetic heading ).

Is it west they must be added: .

In navigation, the following mnemonic has been naturalized for:

"From the wrong to the right course with the right sign, from the right to the wrong course with the wrong sign! "

Example statement

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