Compass safe distance
The traditional compass is still an important device in modern navigation on all ships, in case all other systems fail.
It responds sensitively to magnetic fields and large quantities of metal, which may deflect the earth's magnetic field. For this reason, devices in the bridge area of ships or even in the cockpit of aircraft must prove that they do not unduly interfere with emergency navigation systems. For this purpose, the impact of the device on the earth's magnetic field in its surroundings is determined.
The standards and procedures in this area include the following:
- IEC 60945 Sec 11 – Compass safe distance
This test determines the distances above which a device does not cause undue deviations of the standard compass and steering compass on ships. The actual deviation varies with the strength of the earth's magnetic field at various points on earth. Near the equator, it is in the range of 0.1° for the standard compass and 0.3° for the steering compass; in high latitudes, it increases up to 1° and 3° respectively. Each part of the test object must be tested in the location and position relative to the compass or magnetometer in which the maximum error on the compass occurs. Each test object is tested in 3 states:
a) In the magnetic state in which it is supplied, switched off
b) After normalization, switched off
c) Switched on
Normalization describes a process by which the greatest possible homogeneity of the magnetic flux in the test object is achieved by placing it in Helmholtz coils.
Carsten Möller Carsten Möller
Head of EMC Laboratory
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