MARINE AUTOMATION AND CONTROL

The actuating power may also be any one of these three and not necessarily the same as the control medium. Electrical control signals are usually of small voltage or current values which are unable to effect actuator movement. Pneumatic or hydraulic power would then be used for actuator operation. A separate pneumatic power supply may be used even when the control signal is pneumatic, as described in the previous section. Hydraulic actuator power is used where large or out of balance forces occur or when the correcting unit is of large dimensions itself. Hydraulic control with separate hydraulic actuation is a feature of some types of steering gear.

Control Systems Onboard Ships - Boiler Water Level Control System.

Water Level Control for LP Boilers STEAM FLOW BOILER CONTROLLER SET POINT LEVEL TRANSMITTER FEED CONTROL VALVE

Steam Temperature Control System

Boiler Combustion Control System

Cooling Water Temperature Control System.

Cooling Water Temperature Control System.

Fuel Oil Viscosity Control System CONTROLLER SET POINT CORRECTING UNIT FUEL OIL STORAGE TANK F.O. HEATER TO ENGINE STEAM OUT MEASURING UNIT

Automatic Steering System

Automatic Load Control of Alternators.

Assignment 2, Q1 How do you make this system automatic? How do you incorporate alarms for low oil level and dirty filters? How do you make the standby pump start automatically when the oil pressure is low? S.W. IN S.W.OUT MAIN COOLER ENGINE DUPLEX FILTER 3-WAY CONTROL VALVE L.O. SUMP L.O.PUMP TANK M.E. LO Temperature Control System

Assignment 2, Q2  Sketch an electrically operated control valve of any design.  What are the factors that need to be considered for selecting trim materials?.  Identify the materials commonly used for control valve trim.

Assignment 2, Q3  Sketch an oily water separator system showing how the oil content in the discharge water is controlled and kept within allowable limits.

Adjusting valves: Do you believe in automation? Central control room • Overview of entire process • Make immediate adjustment anywhere • Safe location • History of past operation Process pictures courtesy of Petro-Canada Products

Centralised Control  The automatic control concept, correctly developed, results in the centralising of control and supervisory functions. All ships have some degree of automation and instrumentation which is centred around a console.  Modern installations have machinery control rooms where the monitoring of control functions takes place. The use of a separate room in the machinery space enables careful climate control of the space for the dual benefit of the instruments and the engineer.

Centralised Control

 Control consoles are usually arranged with the more important controls and instrumentation located centrally and within easy reach.



 The display panels often make use of mimic diagrams. These are line diagrams of pipe systems or items of equipment which include miniature alarm lights or operating buttons for the relevant point or item in the system. A high- temperature alarm at, for instance, a particular cylinder exhaust would display at the appropriate place on the mimic diagram of the engine. Valves shown on mimic diagrams would be provided with an indication of their open or closed position, pumps would have a running light lit if operating, etc.

Mimic Diagram / Panels

 The grouping of the controllers and instrumentation for the various systems previously described enables them to become part of the complete control system for the ship.  The ultimate goal in the centralised control room concept will be to perform and monitor every possible operation remotely from this location. This will inevitably result in a vast amount of information reaching the control room, more than the engineer supervisor might reasonably be expected to continuously observe. It is therefore usual to incorporate data recording and alarm systems in control rooms.

Data Logging and Alarm Monitoring System

 The alarm system enables the monitoring of certain measured variables over a set period and the readings obtained are compared with some reference or desired value. Where a fault condition is located, i.e. a measured value different from the desired value, audible and visual alarms are given and a print-out of the fault and the time of occurrence is produced.  Data recording or data logging is the production of measured variable information either automatically at set intervals or on demand.



Unattened Machinery Spaces The sophistication of modern control systems and the reliability of the equipment used have resulted in machinery spaces remaining unattended for long periods. In order to ensure the safety of the ship and its equipment during UMS operation certain essential requirements must be met: 1. Bridge control. A control system to operate the main machinery must be provided on the bridge. Instrumentation providing certain basic information must be provided. 2. Machinery control room. A centralised control room must be provided with the equipment to operate all main and auxiliary machinery easily accessible.

3. Alarm and fire protection. An alarm system is required which must be comprehensive in coverage of the equipment and able to provide warnings in the control room, the machinery space, the accommodation and on the bridge. A fire detection and alarm system which operates rapidly must also be provided throughout the machinery space, and a fire control point must be provided outside the machinery space with facilities for control of emergency equipment. 4. Emergency power. Automatic provision of electrical power to meet the varying load requirements. A means of providing emergency electrical power and essential lighting must be provided. This is usually met by the automatic start up of a standby generator.

Maintenance of Control Systems

Comparison of Pneumatic, Electric and Hydraulic Control Media  Pneumatic systems use compressors to store air under high pressure. When released, this pressurized air pushes on machine parts, making them move.  Electric systems use electric generators to supply machine parts with power, which electric motors use to make parts move.  Pneumatic machines can be made without using flammable parts or materials.  Electricity is always a potential fire hazard.  Pneumatic systems can operate even when the electricity goes out.

Advantages of Pneumatic Control Systems  The low cost of the components  The ease of design and implementation  The huge range of available components  The use of air limits the force/torque that can be generated providing a safety feature  Pneumatic systems can operate even when the electricity goes out. Disadvantages of pneumatic systems  compared with electrical and hydraulic actuators is that the motive fluid (air) is compressible and hence accurate speed control and position control is difficult and often requires ancillary systems.  need air compressors and other support equipment.

Advantages of Hydraulic Systems  Compared to pneumatic and electric systems is that high forces and torques can be developed with comparatively compact motors without the need for gearboxes.  Very accurate motion controls are possible using sophisticated servo valves. Disadvantages of Hydraulic Systems  relatively high cost of components  the need to condition and contain the hydraulic fluid.

Care & Maintenance of Control Systems  For satisfactory continuous operation any controller or control system should receive periodic inspection and careful intelligent maintenance.  Dirt, corrosion and wear are the enemies of control.  Clean conditions must be effected in the ship before the equipment is installed.

 The main machinery as well as the control system requires adequate maintenance.  Many cases of unsatisfactory performance can be traced to faults in the main machinery.  Many operators are prone to overlook this point and spend much time investigating the control system rather than the machinery itself.

 Pneumatic and hydraulic components require very little maintenance.  The various pivots and links in the system should be free of friction and in good working order.  Oil must never be applied to a pneumatic system except for by specific instruction from the manufacturer.  Connections in pneumatic and hydraulic systems should be tight and should always be checked for leakage.

 Non-ferrous materials such as copper or brass should be used for air-supply lines. Steel pipe will ultimately rust and small solid particles will cause future difficulty.  The greatest problem with pneumatic systems is the maintenance of clean, dry air at constant pressure.  Moisture is usually adequately removed with a storage tank of proper size and a compressor after cooler.

 The air compressor should never be overloaded since it will pump more oil when running at high loads.  Effective removal of moisture also helps in the problem of frozen air lines.  Air lines should be located to avoid low- temperature areas such as the upper deck.  The importance of maintaining a very high degree of cleanliness when working on control systems cannot be over-emphasized.

 Because of fine clearances involved in pneumatic and hydraulic components it is imperative that the system remain free of contamination.  The same need of cleanliness applies to electrical systems since dirt generates electrical noise.  To prevent dirt entering a system the following precautions should be taken before any work is commenced:

1. Thoroughly clean the outside of fittings, pipes, components and surrounding structure before disconnecting any pipes. 2. When pipelines are disconnected fit dust caps to pipes and unions, mask any exposed surfaces immediately and make certain that it is not possible for foreign matter to enter the system. 3. When drying pipes or components use only clean, dry compressed air, i.e. from a bottle and not from a compressor. 4. When flushing pipes use clean carbon tetrachloride from a clean container. 5. Maintain clean hands and tools.

 With instruments only minor servicing, e.g. zero adjustment and functional checking, should be done in situ.  When repairs or re-calibration are needed the instrument should be removed and replaced by another so that maintenance can be carried out in a workshop.  A generous allowance of space (more than is normal for a fitting or machine shop) is amply justified by the consequent ease and tidiness of operation. The shop itself should dry, warm and clean.

 If an efficient record system is used then information will be collected to show the amount of servicing required.  The provision of block diagrams of control systems and the identification of components is vitally important.  Such block diagram should be inside panel doors or other convenient location.  Control valves can be mounted the wrong way round and without an external indication of flow it is a long tedious process to discover the fault and carry out rectification.

Electrical Hazards  The resistance of the human body is quite high only when the skin is dry. The danger of electric shock is therefore much greater for persons working in a hot, humid atmosphere since this leads to wetness from body perspiration. Fatal shocks have occurred at as low as 60V and all circuits must be considered dangerous.

 All electrical equipment should be isolated before any work is done on it. The circuit should then be tested to ensure that it is dead. Working near to live equipment should be avoided if at all possible. Tools with insulated handles should be used to minimise risks.  The treatment of anyone suffering from severe electric shock must be rapid if it is to be effective. First they must be removed from contact with the circuit by isolating it or using a non-conducting material to drag them away. Electric shock results in a stopping of the heart and every effort must be made to get it going again. Apply any accepted means of artificial respiration to bring about revival.

Maintenance of Electrical Equipments  With all types of electrical equipment cleanliness is essential for good operation. Electrical connections must be sound and any signs of sparking should be investigated. Parts subject to wear must be examined and replaced when necessary. The danger from a.c. equipment in terms of electric shocks is far greater than for similar d.c. voltages. Also a.c, equipment often operates at very high voltages. Care must therefore be taken to ensure isolation of equipment before any inspections or maintenance is undertaken.

 The accumulation of dirt on electrical equipment will result in insulation breakdown and leakage currents, possibly even an earth fault.  Moisture or oil deposits will likewise affect insulation resistance. Regular insulation resistance measurement and the compiling of records will indicate the equipment requiring attention. Ventilation passages or ducts may become blocked, with resultant lack of cooling and overheating.  Oil deposits from a direct-coupled diesel engine driving an open generator (usually d.c.) can damage windings and should therefore be removed if found.  Totally enclosed machines should be periodically opened for inspection and cleaning since carbon dust will remain inside the machine and deposit on the surfaces.

 Brushgear should be inspected to ensure adequate brush pressure and the springs adjusted if necessary. New brushes should be 'bedded in‘ to the commutator or slipring shape with fine glass paper. Sparking at the commutator will indicate poor commutation. This may require polishing of a roughened commutator surface. The mica insulation between commutator segments may require undercutting if it protrudes, or simply cleaning if deposits have built up.

 Control equipment, such as starters, will require attention to contacts which may be worn or pitted as a result of arcing. Contactors usually have a moving or wiping action as they come together. This helps clean the surfaces to provide good electrical contact, and also the arc produced during closing and opening is not at the finally closed position. The contactor contact surfaces of frequently used equipment should therefore be subject to regular inspections.

Emergency Generator Supply In the event of a main generating system failure an emergency supply of electricity is required for essential services. This can be supplied by batteries, but most merchant ships have an emergency generator. The unit is diesel driven and located outside of the machinery space.  The emergency generator must be rated to provide power for the driving motors of the emergency bilge pump, fire pumps, steering gear, watertight doors and possibly fire fighting equipment. Emergency lighting for occupied areas, navigation lights, communications systems and alarm systems must also be supplied. Where electrical control devices are used in the operation of main machinery, these too may require a supply from the emergency generator.

 A switchboard in the emergency generator room supplies these various loads. It is not usual for an emergency generator to require paralleling, so no equipment is provided for this purpose. Automatic start up of the emergency generator at a low voltage value is usual on modern installations.