Compasses Flashcards
What is a direct indicating compass
It’s a magnet pointing to magnetic north
Indicating compass
It uses a magnetic detector unit to provide an electrical signal relating to magnetic north and it is cross referenced with a directional gyro
Process for true north?
Compass north + deviation —> magnetic north + variation = true north
Why do we use true north?
It never moves, it’s the basis for all maps, constant output from INS
3 soft iron effects
DC Current, Weapons/Cargo, Variation
Hard iron effects
Lightning strike, vibration, same place too long, certain equipment fitted
What is horizontality?
Prevents magnetic dip, it raises the pivot above the CofG
What is sensitivity?
Detecting small changes, using stronger magnets and lubricating the pivot
What is aperiodicity?
Prevents oscillations, add in damping wires
What are the 2 components of a gyro magnetic compass?
Magnetic detector unit, directional gyroscope
What is the role of the MDU in the GMC?
It detects earths magnetic field and gives a long term magnetic heading.
What is the role of the DG in the GMC?
Short term heading device. Read- gyro manufacturing imperfections, apparent- caused by earths rotation
What does it mean if annunciation indicates XO
MDU and DG are synchronised
What does it mean if X or O is displayed on annunciator
MDU and DG are no longer synchronised
