Showing posts with label control systems. Show all posts
Showing posts with label control systems. Show all posts


Main Engine Control System for Internal Combustion Marine Diesel Engines

Main engine control system is used for automatic remote control and protection of main ship's diesels. It permits to change direction and speed rotation of propeller directly from the bridge by navigators. The system consists of the equipment installed on the bridge, engine control room (ECR) locally mounted near the engine.

Main Engine Control System for Internal Combustion Marine Diesel Engines

The set of Engine Remote Control equipment in ECR essentially consists of a panel fitted up with the various signalling, alarm and control facilities, in addition to the electronic modules (both logic and analog).

Electronic Control Modules Rack comprises:
a) Engine starting and reversal logic module, with LED display (direction of rotation indicator) of logic status and starting set-point adjust potentiometer status;
b) Digital/analog engine RPM converter with cut-in thresholds and LED display of the status of the thresholds and thresholds adjusting potentiometers.
c) Engine control programmer with LED display of stand-by, RPM reduction, emergency, etc. and acceleration gradient adjusting potentiometer.
d) RPM controller with potentiometers for variables and operating limits adjustment.
e) Torque lirniter, with limit indicator.

Locally Mounted Equipment comprises electro-hydraulic type actuator, for remote control of the fuel linkages; the said actuator is continuously linked mechanically to the lever and is therefore driven by the manual handwheel when it is deenergized.

The equipment also comprises induction type pick-ups to monitor the number of RPM's and rotating direction, as well as a five-position servo-motor, complete with four devices to position the engine local control lever for reversing gears and starting air distributors for engine stop, running ahead, starting ahead, running astern, starting astern. Equipment on Bridge comprises:

1. Engine telegraph.
2. Automatic control panel. It has the following items mounted on panel front:
a) Manual power limiter.
b) Engine speed fine adjustment potentiometer.
c) Illuminated push-button for bridge control demand.
d) "Control transfer inhibited" signal display.
e) "Control on the bridge/ECR" signal display.
f) Direction of engine rotation indicator (LED).
g) Engine RPM indicator.
h) Fuel oil lever actuator position indicator.
3. Shield push-button for emergency stop and emergency manoeuvring.

Digital Computer Integrated Automation Systems

Digital Computer Applications

There are such applications of minicomputers as: Supervision of plant operating data with alarm recording, data logging and process monitoring of the process.

Automation and control systems can be conveniently integrated with minicomputer digital processors. Interface units apt to handle all inputs and outputs problems from the process to the computer (Fig. 1) are available, depending on the type of solution contemplated.

Fig. 1. Process of the computer

On demand digital display of plant variables. Event recording: print out of the various plant variables on occurrence of an event, with the chronological history of groups of events in their exact sequence.

Recording of the value of the various plant variables in the time intervals preceeding the occurrence of a fault condition.

Trend recording: recording of the tendency of a variable to exceed set-point value over a short and medium term.

Recording of the maximum off-normal drift of a variable from threshold value.

Sequence control: for groups of variables.

Optimization of complex automation systems with set-point value correction by the computer.

Plant efficiency and performance calculations.

Operator guide: processing of the data collected by comparison with the optimum memorized operating program in order to furnish guidance to the operator.

Information storage: collection of data relating to plant operation. Formulation of consents and locks based on complex programs including non-linear functions of plant parameters.

Data communication: local processing of the variables by the peripheral microcomputers with data transmission to the central microcomputer. Microcomputer. The microcomputer is a control unit with extremely flexible program; modern electronic technology has made this facility available for application in the solution of control problems which heretofore had to be handled by wired logic or relay logic.

Easily expandable high speed programs include complex arithmetic and logic operations.

The microcomputer itself comes as a conventional electronic unit mounted on standard racks apt to contain several plug-in type modules. The following modules are fitted in the standard rack:
  1. Central Processor Unit (CPU). CPU performs arithmetical and logical calculations at high speed with 8 bit words: it performs all the processing functions and is capable of addressing itself up to 64 memory bits.
  2. Electronic type programmable memory (PROM) or fixed memory (ROM).
  3. Memory module for electronic type data.
  4. Input module connecting the CPU with the process.
  5. Output module, to dispatch the microcomputer information toward the process.
  6. Interface module, to adapt the input signals and input/output card capacity to the multiplexing and demultiplexing units and for A/D to D/A conversion.
Computer Hardware

The heart of the system is the Central Processing Unit (CPU), which holds both program and data, an Arithmetic-Logic Unit (ALU), which contains processing circuitry such as an adder, shifter, and a few fast registers for holding the operands, and the instruction currently being processed (Fig. 2). The program counter would also be included in the ALU.

One part of the CPU is a set of routing circuits which provide path between storage and the ALU and input/output controllers or channels. Many storage or input devices may be wired to one channel; but only one device per channel can be transmitting information from or to main storage at any one time.

Fig. 2. General organization of a computer system

In general, large computers may be thought of as having four distinct parts: a high-speed calculating unit, a memory unit, an input device and an output device.

Unmanned Machinery Spaces (UMS) Ships — Control and Alarm Requirements

The number of UMS ships has increased rapidly over the past few years. Control systems are much more reliable now than they were when first applied to ships. Educating the crew to understand control functions is now undertaken by most shipowners. More ships will, in future, be fitted with remote-control systems as a means of reducing crews.

Unmanned Machinery Spaces (UMS) Ships — Control and Alarm Requirements

Nowadays, however, far more UMS ships are in operation. Crews have grown familiar with the systems and training is more prolific. In the immediate future more owners will adopt UMS, not only as a means of cutting crew to a minimum and thus cut operational costs, but also for reasons of safety.

Remote-control systems. As a number of remote-control stations may be installed, operation must only be possible for one station at a time. There should be no misunderstanding as to which station has control at any time one time, thus there should be continuous indication at all the main control stations showing which one has control. When control is transferred from one station to another, a warning must be given. Only one station which has taken control must acknowledge the fact.

There must be means by which the propulsion machinery can be stopped from the bridge, regardless of whether another station is being operated. Any orders activated from the bridge are to be indicated in the control rooms.

Indicators of the speed and direction or rotation of reversible engines, or the propeller pitch and speed of rotation must be fitted on the bridge. Additionally, an independently-operated stand-by control should be provided in the engine room. It must be able to override the remote control system.

For diesel plant with fixed-pitch propellers the fuel supply and direction of engine rotation should be effected by a single control lever. The controls must operate the machinery in a time sequence acceptable for the engines, and able to shut-off the fuel supply if the desired and actual direction of rotation of the engine and the cam-shaft position does not match.

In addition to alarm indication for the lubricating oil system, the system must be able to shut down the engine if lubricating (lube) oil is lost. The circuit and sensors for this function must be additional to the alarm circuit required.

On the bridge, both audible and visual alarms are to operate and indication given when the speed of the main engines is to be reduced due to the following fault condition: high scavenge air temperature, oil mist detected in crankcase, low piston coolant outlet flow, low piston coolant pressure, also for low cylinder coolant pressure if on a separate circuit.

Where the lube oil cooling water and oil fuel booster pumps are not driven by the main engine, the standby pump is to start automatically if the discharge pressure from the working pump falls below a predetermined value.

Automatic Control System of Electrical Power Plants

Shutting Down

In order to avoid running the sets at excessively low loads, the set which is next in sequence will be shut down when the load has fallen to a value below a predetermined level.

The shutting down instruction can be initiated by the stop push button being depressed, by a critical or non-critical alarm being initiated, or for diesels by excessive alternator capacity being available. The ordinary shutting down program implies that the set is first unloaded.

When the load has fallen below about 10%, the circuit breaker is tripped and the engine is allowed to run for one minute for the temperature to equalize before the stop solenoid is energized for the period normally necessary for the engine to run down. Starting and stopping instructions interrupt each other, except when the stop instruction is caused by an alarm, the stop instruction then having priority.

Automatic Control System for Ships Electrical Power Plants

The automatic control system is designed for controlling turbo- and diesel-driven electric generating plant, predominently onboard ships.

The purpose of the automatic control equipment is to ensure that the power demand of a ship is generated in an economical manner and also to ensure that any faults occurring will not cause damage to the machinery.

During fully automatic operation the equipment carries out starting, synchronizing and load sharing on one or several diesel alternators as the power demand increases, as well as disconnecting and stopping the diesel alternator in the event of excessive power being available.

The starting of turbo alternator is usually done manually although synchronizing and load sharing is performed automatically. In the event of a fault on one set, a diesel alternator will automatically be started and connected to the main busbars. In the event of a serious fault, the set will immediately be disconnected and stopped, this involving the danger of black-out. At black-out a programmed number of sets will be started and the set which is first to reach frequency will be connected to the busbars. The other diesels are then synchronized in the usual manner. A special unit in the automatic is available for program-blocking of connection of large loads, thus allowing the automatic equipment to ensure that there is always sufficient power available before the load is connected.

The system is designed for unmanned engine rooms (UER). The only manual operations needed are: starting up the turbos, selection of the sequence of diesel alternators, blocking of a set whenever this may be required, resetting of start blocking caused by an alarm, choice of a program with a minimum number of units in operation.

The automatic control equipment is designed to meet the requirements made by classification societies on equipment in unmanned engine rooms. This implies that some of the functions of the automatic control equipments are monitored so that an alarm will be initiated if the system is not entirely in functional condition.

The automatic control equipment can be connected to the general alarm system on board, provided that this system is designed for breaking contact functions during alarm conditions.

Main Functions

The system is designed for the following functions:
  1. Prelubrication of stationary diesel alternator sets for adjustable periods and at adjustable intervals.
  2. Starting, synchronizing and load distribution among the sets when a starting order is received, in accordance with a predetermined program.
  3. Unloading, tripping of the circuit breaker and shutting down of a set on receipt of a stop instruction, in accordance with a predetermined program.
  4. Maintaining the frequency of the distribution network constant within ±0.1 Hz regardless of the load.
  5. Issuing starting instructions to diesel sets in accordance with a variable sequence, when the load on the sets which are then in service exceeds the predetermined level for an adjustable period of time.
  6. Issuing shutting-down instructions to diesel sets in accordance with a variable sequence, when the load on the sets then in service falls below a predetermined level for an adjustable period of time. The sequence of starting and stepping of sets may be selected by means of a switch in the control panel.
  7. Replacing a set on which a non-critical alarm is operative, by another unit.
  8. Stopping a device set when a critical alarm is initiated.
  9. Blocking the starting procedure for a set on which an alarm is operative, until the resetting push button or the alarm has been depressed.
  10. Starting and connecting to the distribution network a predetermined number of diesel alternator sets in the event of a black-out.
  11. Ensuring that sufficient alternator capacity is available before programmed loads are connected.
  12. Transmitting information concerning alarms to the general alarm system.

As soon as the lower frequency alarm limit has been passed, the synchronizing unit will be switched in and will sense the difference in phase relationship and frequency between the alternator and busbars.

On the basis of these parameters, a control signal will be generated and will actuate the speed governor so that the generator will be rapidly brought into synchronism with the busbars. The voltage difference between the alternator and the busbars is detected by a breaker closing unit which will initiate closure of the circuit breaker as soon as the voltage difference tends towards zero at a sufficiently slow rate. If the difference in amplitude is excessively large, closure of the breaker is blocked.

The synchronizing process is supervised so that if it lasts for more than a predetermined period, a synchronizing alarm will be initiated causing the set to be stopped and further starting attempts to be blocked.

Starting Program for Diesel and Turbo Alternators

If the load on the sets in service should exceed a certain percentage of the rated output, a new set must be connected in. That level is normally 80 percent. However, in some systems the levels for starting a new set are detected on the basis of the sum. of all the sets then in service, e. g. the total power available.

This arrangement allows for better utilization of the sets. In order to avoid starting a new set as a result of the appropriate level being temporarily, e. g. when starting a new consumer with a large starting current demand, the starting instruction is delayed by an adjustable period.

On receipt of automatic starting order, the prelubrication pump will first be started and when its pressure switch delivers a signal to indicate that the oil system is pressurerized, the solenoid of the starting air valve will be energized. The supply of starting air is maintained until the ignition speed has been exceeded or for a predetermined maximum period, normally 5 s.

If the engine fails to start, the attempt is repeated, normally twice, at an interval of about 5 s. If all starting attempts have failed, the "starting failure" alarm will be initiated. This alarm will also be initiated if the engine has failed to attain normal speed after a predetermined period, normally 30 s.

When the ignition speed has been exceeded preexcitation is initiated by a contact function which persists until the voltage is acknowledged or an alarm is initiated. At this speed a time delay is also initiated for activating certain alarms, e. g. alarms for low voltage, low frequency and low lubricating oil pressure.

The turbo is always started manually since it is never used as a stand-by set and the taking into operation of a turbo is based on the fact that you know that the steam power supply will be sufficient for some time.

Furthermore, there are often certain visual checks to be done when starting up a turbo.


Each set is protected against damage which could occur in the event of deviation from normal values. Such deviations are sensed by means of transmitters in the automatic equipment or on the set. If a fault is detected, an alarm will be initiated but this can be delayed for up to 60 s.

An alarm may initiate tripping, stopping and blocking of the starting procedure on the set concerned. Alarm indications are provided in the control panel, where resetting of the alarm can also take place. The alarms can be either non-critical (NCR) or critical (CR). A critical alarm will stop the engine automatically immediately, since the set is considered to be in danger of sustaining damage. Non-critical alarms cause shutting down in accordance with the ordinary shutting-down program and the starting procedure is blocked.

Black-out Program

In the event of a black-out, the automatic equipment will start a certain number of diesel alternators. The set which is the first to acknowledge the frequency receives the instruction to switch onto the busbars. If the first set does not succeed in switching onto the busbars, it will be blocked and the next is allowed to make the attempt, etc.

The reason for starting more than one diesel is primarily to prevent a fault on one set from delaying the clearing of the black-out condition, and in addition, the load often increases rapidly when the black-out condition has been cleared, and it is then advantageous to have at least one additional alternator about to be synchronized onto the busbars.

The black-out condition is sensed by the automatic equipment by the fact that there is no voltage on the busbars and that all breakers are tripped. Both of these conditions must thus be satisfied.

Programming of Large Loads

If a relatively large load is switched onto the network, a load surge will occur and this may cause overloading and in the worst case, tripping of the circuit breakers due to overcurrent. The risk of not taking this faet into account is illustrated by the starting current of a directly starting induction motor being 5—10 times the rated current.

For preventing such damages automatic control system is provided with unit, designed to control switching in such large loads.

The request for switching in a certain load is made in the form of a closing contact function. The load to be switched in is exceeded, switching in of the load is blocked until conditions render this possible, i.e. until a new diesel has been synchronized onto the busbars.

If the power limit is not exceeded, clearance is given for immediate switching in of the load. When the load is switched in, the simulation is switched off, since the load will be metered by the ordinary equipment.

Control Systems. General Requirements

Automated machinery provided with automatic or remote control system, as well as, to the necessary extent, with monitoring systems, is in addition to be provided with means of local control.

In each case of failure in automatic or remote control systems, the possibility of local control is to be maintained.

Where machinery or installation is remotely controlled, it should be possible for the operator to check, with sufficient reliance, from his control station whether his command has been carried out by remote control system.

Each automatic or remote control system is to prevent the automatic restart of controlled machinery after its stopping by the safety or by emergency manual stop. Restart should be possible after manual reset.

Where machinery space of the ship is to be continuously attended by one person, the extent of the necessary remote or automatic control will be specially in view of the location of the control station and manning routine of machinery, as well as their service requirements.