Rolls-Royce Helicon X3 P&T Control System

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. 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. 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.

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. 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

automatically switch to and engage the Backup Control. Lever order signals and feedback are monitored and verified against adjustable 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.

Backup Control Operation If a failure occurs on important parts of the Normal control for the Pitch/Azimuth/RPM control function, the control will automatically be switched over to the backup control system. A system failure audible and visible alarm will be activated on each of the control panels. The thruster control will continue to follow the lever in command, and command transfer is done by using the common in command buttons. The command can be transferred between all bridge position and the bridge control levers will continue to work as in Normal Control. A failure that occurs on important parts of the Backup control for the Pitch/Azimuth/ RPM control function, will not affect the Normal control system. If a system failure occurs on the Backup Control an audible and visible alarm will be activated on each of the control panels

Backup Control Limitations The backup control system has only interface to the control levers. The backup control system does not have interface to external control systems like Dynpos, Joystick or Autopilot.

Local Control Local control is used if both the normal control and the backup control fail to operate the thruster azimuth. The thruster azimuth can be operated locally on the actuator unit. The Control System must first be disconnected from the actuator unit. This can be done by means of the Local Control switch mounted in front of the Actuator Interface Unit, or by disconnecting the plug from the actuator unit. If frequency converter used, operate service switch inside converter cabinet. The Thruster Instruction Manual will give more details for Local Control operation. Azimuth Indication The azimuth indication system independent of the normal control system by means of separate transmitters and electronic circuits. The Azimuth indicators are connected in series, and are driven from the Backup Control system.

RPM Control The RPM Control function system controls the speed signal to the frequency converter for electrical drives or the engine governor for diesel or gas engines. RPM Control Electric Drive Motor The RPM Control system includes selection of different operational modes: 

 • Separate Mode 

 • Combined Mode Selection between modes is possible by means of push buttons. RPM Control can be managed from engine control room only or from additional control panels. External RPM Control External RPM order signals from system as DP/Joystick/Auxiliary systems can be connected to the rpm controller. The external rpm signal are checked against adjustable preset limits. Any error conditions on the rpm input signal will initiate a warning to the alarm plant and an error message will be displayed on the control panel. RPM Order Output The output signal from the controller is scaled to meet the actuator signal range from idle to full rpm, and then fed to external governor, IP converter or frequency converter. The output will follow a linear curve between idle and full rpm order. The RPM output rate of change is adjustable and can be adapted to the engine/frequency converter reversing speed from idle to full rpm (increasing order) and vice versa (decreasing order). Propeller/Shaft RPM Indication The propeller/shaft RPM indicators are connected in series and are driven from the Backup Control system. Command Transfer The term Command transfer is used to describe the procedure performed when the control is transferred between manoeuvre stations without acceptance on either of the stations. This is normally the procedure between wheelhouse (bridge) stations.