SYSTEM OPERATION – Rudder Speed
Page 51 of 80
and deceleration can be used under open loop NFU control when you
would like the rudder to stop moving immediately upon releasing the NFU
input device.
Proportional directional valves are controlled by the DSC through a PID
loop which constantly adjusts rudder speed giving the best rudder
performance through smooth, quite and precise positioning of the steering
gear. Toggling between slow and fast rudder speeds allows the DSC to
change the directional valve current profile and alter the flow rate of the
hydraulic system.
3.5 DUAL INDEPENDENT SYSTEMS
Vessels with twin independent rudder systems will have two independent
DSC / MCP systems installed. At each steering control station one MCP
may be used that contains independent circuit board for the port and
starboard systems. Each steering control device will have independent
input sensors (i.e. potentiometers or encoders) operated by a common
handle or wheel. Analog FFU input devices with two potentiometers will
naturally be synchronized because they are absolute devices coupled to
the same shaft. Digital FFU input devices use incremental encoders
which are not naturally synchronized. Upon initialization of a digital FFU
input the port and starboard rudders may be at different angles, therefore
the two rudders must follow a synchronization procedure upon selection of
the DIGITAL FFU mode.
Twin independent systems using a digital FFU input device must include a
communication line between the port and starboard DSC’s (see 1.2.2
).
Upon selection of the DIGITAL FFU mode the port and starboard DSC’s
will pass information between them as to the actual position of each
rudder. Now each system will know the position of both rudders. The two
systems will calculate the average of the two rudder positions and that
average will be used in each system as the initial digital FFU rudder
position. This process will ensure that when a synchronized DIGITAL FFU
mode is selected both rudders will start at the same position. Each time
the DIGITAL FFU mode is selected the two systems will go through the
initialization process, even if DIGITAL FFU mode is already selected.
Using the average of the two rudder angle will provide the most stability
when switching from an independent mode to the synchronized DIGITAL
FFU mode. If both rudders were already at the same angle then the
average will be that angle and the rudders will not move. If both rudders
were at opposite hard over angles then upon selecting DIGITAL FFU
mode the two rudders will move to the midship position.
Doc No.: MAN01504, 20-02-06 DSC 100 & MCP 100 Manual
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