SYSTEM OPERATION – Rudder Speed
Page 50 of 80
directional valve is used, either an on-off valve with a high speed solenoid
or a proportional directional valve.
On-Off Directional Valves
For systems using an on-off directional valve with a high speed solenoid,
the rudder speeds are determined by the fast and slow flow settings on
the hydraulic power unit. When the rudder speed setting is toggled to the
slow setting the high speed solenoid will always be off and the rudder will
always move at the slow speed. When the rudder speed setting is toggled
to the fast rudder setting the high speed solenoid will be controlled by the
DSC.
Under NFU control, the high speed solenoid will turn on a short time after
the directional valve is turned on. This will allow the rudder to step up to
the fast speed if the NFU device is activated long enough. Upon releasing
the NFU device the system will immediately turn off the high speed
solenoid while holding the directional valve on for a short time longer.
This will provide a short step down of the rudder speed when the NFU
device is released. The amount of step up and step down time under NFU
control is adjustable through the DSC setup program.
Under any FFU mode, the steering control system will turn on the high
speed solenoid whenever the difference between the commanded rudder
position and the actual rudder position is greater than a programmed
angle for a specific length of time. The high speed solenoid will turn off
when the difference between the commanded rudder position and the
actual rudder position is less than the programmed angle. The angle and
time at which the high speed solenoid will be switched is adjustable
through the DSC setup program. This arrangement allows the system to
step the rudder speed up and down depending on the magnitude of the
commanded rudder movement.
Autopilot systems interfaced with directional solenoid command signals
will operate as described for NFU modes and those interfacing with analog
rudder command signals will operate as described for FFU modes.
Proportional Directional Valves
For systems using proportional directional valves, the rudder speeds are
determined by fast rudder and slow rudder profiles configured through the
DSC setup program. Fast rudder speed is input as the number of
seconds desired to move the rudder from one hard over to the other. This
number should not exceed about 90% of the hydraulic system’s maximum
output flow. The slow rudder speed is input as a percentage of the fast
rudder speed. Values are also programmed, in seconds, for acceleration
and deceleration of the rudder in FFU and NFU modes. Separate values
are input for FFU and NFU modes. This is so that shorter acceleration
Doc No.: MAN01504, 20-02-06 DSC 100 & MCP 100 Manual
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