Rolls-Royce Helicon X3, User Manual

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System Description
Page 12 of 16 Doc. No.: 13S000411
Revision: A
Copyright © 2010 Rolls-Royce plc
operate the propeller pitch locally from the pitch control valve.
4.1.6 Pitch Indication
The Pitch Indication system is independent of the Normal Pitch Control system by
means of separate transmitters and electronic circuits. The pitch indicators are connected
in series and are driven from the Backup Control system.
4.1.7 Pitch Order Scaling
The system may need to reduce the pitch order for different reasons. The pitch reduction
can either be activated from a digital or anlogue input signal.
To reserve engine power to heavy consumers as alternators, fire pumps, etc., it may be
necessary to reduce the available propeller output power. This is normally done by
means of a fixed propeller pitch reduction.
If the drive motor is a diesel engine the system is prepared to handle a fuel limiter
contact, from the RPM governor (i.e. high scavange air pressure). If the contact is closed
the pitch order will stop increasing to a higher value, only decrease of pitch order against
zero is possible.
For azimuth thrusters, a pitch reduction will be activated if the azimuth order is changed
faster then the thruster azimuth servo can follow.
4.2 Thruster Azimuth Control
The azimuth control function is to obtain the correct thruster azimuth position in
accordance to the control lever order. Valve controlled hydraulic motors or frequency
controlled electro motors perform the positioning of the thruster azimuth.
Detailed information regarding the hydraulic system or motor data is available in the
Thruster Instruction manual.
Note: Test point angle signals are /- 100%, repres/- 180 degrees.
Some test points are named with degrees, displaying the angle in degrees
(+/- 180 degrees).
4.2.1 Normal Control
The azimuth controller computes the thruster position and order on the basis of signals
from the thruster feedback and control levers. A two-wiper linear potentiometer
provides two outputs with 90 degrees of phase shift named cosine and sine phase
respectively.
The lever order signals and feedback signals are monitored and verified against alarm
limits. If the signals exceed the limits this will release an alarm to the alarm plant with
a visual and audible system failure alarm on the manoeuvre stations.
4.2.2 Backup Control
The Backup Control system consists of closed loop control identical to the normal
control system. The Backup Control is a separate system, and is independent of the
Normal Control system. A system failure in the Normal Control system will