mupgamage

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Marine Control Systems and Automation- 1

• By Malaka Udayanga

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Subject Overview

• 1. General introduction of Marine Control systems
  and Automation
• 2. Measurement of Temperature
• 3. Measurement of Pressure
• 4. Measurement of Level
• 5. Measurement of Flow
• 6. Other Measurements
• 7. Transmission of Signals
• 8. Final Controlling Elements
• 9. Control Theory
• 10. Principals of Pneumatic Control

11. Controllers 12. Control Circuits 13. Remote
Control Diesel Propulsion 14. Air Supply 15.
Monitoring Systems 16. Governors 17. Programmable
Logic Controllers 18. Digital Technology 19.
Analysis and Application 20. Essential
Requirements for the Automatic Operation of
Marine Machinery
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Instrumentation Control?
Instruments are used to sense and display the
condition of a process.
Controllers determine what happens within a
process.
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What is Process?

• A system, having defined boundaries, which uses
  energy flow into and out of the process in order
  to produce some form of result.

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Examples of marine processes and energy flows

• Main engine jacket cooling water temperature.
• Energy in Fuel combustion. Energy out
  Cooling water
• The pressure in an air bottle.
• Energy in Air compressor Energy out
  Usage of air
• The speed of a generator.
• Energy in Fuel combustion Energy out
  Electrical power

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Types of process
Limits of self-regulation

• Self-regulating
• Non-self-regulating

If the inflow is increased sufficiently, the
water level will eventually reach the top of the
tank and overflow. The reverse will happen if the
inflow is decreased - the tank will eventually
empty. If a process has no ability to absorb and
release energy, then it will have no means of
self-regulation.
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Steady-state condition

• All processes can achieve a steady-state
  condition in which there is no change in the
  energy transfer into or out of the process.
• e.g. a room in which the inside temperature
  exactly equals the outside temperature and where
  there is no heat energy lost or gained by the
  room. A process in this state will not need
  controlling because nothing will alter.

Energy flow out of room balances energy flow
into room
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Automatic Control System

• An automatic control system can maintain
  stabilized condition without the intervention of
  human operator.
• It compares the actual condition with the command
  and operates to reduce the deviation.
• As the automatic controller has replaced the
  human. The device contains a sensor to represent
  eye, comparator controller to represent brain,
  and an actuator to represent muscle to depict the
  functioning of the human operator

• The three basic elements of a control system

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Control and Instrumentation Terminology

• Specialized technical language and specialized
  terminology utilizes in Automation industry. Some
  general terms are

No Terminology Description
1 Desired Value, The value operator desires to obtain.
2 Set point / Reference value Command signal to the controller to obtain desired value
3 Process Variable - PV Any varying operational and physical conditions, such as temperature, pressure, flow rate, density, or chemical composition.
4 Measured variable the condition of the process fluid that must be kept at the designated set point.
6 Error Error is the difference between the measured value and the set point and can be either positive or negative.
6 Duration Duration refers to the length of time that an error condition has existed.
7 Off set Offset is a sustained deviation of the process variable from the desired value.
8 Final Controlling Element device that physically changes a process in response to a change in control system set point, relevant to actuators include valves, dampers, fluid couplings, gates, etc
9 Dead time the delay from when a controller output (CO) signal is issued until when the measured process variable (PV) first begins to respond.
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Control and Instrumentation Terminology
No Terminology Description
11 Overshoot Amount by which a changing process variable exceeds the desired value following a change in the system.
12 Gain Change in output divided by the change in input.
13 Hunting The phenomenon of continuous fluctuation of measured variable above and below the desired value due over sensitiveness.
14 Droop Percentage of reduction in speed/Frequency/voltage when the load increases from 0 to 100.
15 Dead Band A range of value over which a signal may vary without initiating any response.
16 Stability Stability is the ability to maintain desired value without fluctuating. Instability results in hunting or oscillation due to over correction.
17 Feedback Transmission of a signal from a late stage to an earlier stage in a control system.
18 Transducer A transducer is a device that translates a one form of signal into a different form of signal.
19 Telemetering Signal transmission over a considerable distance.
20 Disturbances Disturbance is some factor which disturb the system
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History of Automation and Control

• Centrifugal flyball governor used for regulating
  the speed of steam engines by James Watt in 1788.
  

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Compare pneumatic, hydraulic and
electronic-electrical control systems

• Mechanical
• Pneumatic
• Hydraulic
• Electrical
• Electronic

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Pneumatic Control Systems

• Advantages

• Disadvantages

• Simple
• Wide range of environments
• Intrinsically safe
• Lightweight
• Require minimal maintenance
• Durable components

• Pressure loss
• Specific range of use not interchangeable
• Easily contaminated
• Costly to maintain

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Hydraulic Control System

• Disadvantages

• Advantages

• Robust strong healthy
• Holds forces
• Maintains power - Hydraulic actuators can have
  their pumps and motors located a considerable
  distance away with minimal loss of power.

• Leakages occur
• Multiple components - including a fluid
  reservoir, motor, pump, release valves, and heat
  exchangers, along with noise reduction equipment.

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Electrical / Electronic control systems

• Advantages

• Disadvantages

• Very precise
• Low noise level
• Highest precision control setting
• Zero leakage

• Cannot be used in hazardous environments
• Can overheat

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• Analogue Vs Digital

• Electrical Vs Electronic

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Control systems

• A control system can be defined as an arrangement
  of interconnected elements that interact, in some
  predetermined manner, in order to maintain, or
  change the condition of a process
• A process can be either manually by human
  intervention or automatically. The same
  principles apply to both
• Control system can be defined as
• Open Loop system
• Closed Loop system

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Open loop system
Also called a non-feedback controller, is a type
of controller that computes its input into a
system using only the current state and its model
of the system. A characteristic of the open-loop
controller is that it does not use feedback to
determine if its output has achieved the desired
goal of the input. This means that the system
does not observe the output of the processes that
it is controlling. Examples of open loop
control- A washing machine cycle control. A
bread toaster. A microwave cooker. Fuel tank
heating (without temperature indication.)
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Close loop system
There is feedback between the output and the
input. A sensing or measuring element is situated
inside of the process. The measuring element
detects what is happening within the process and
produces a feedback signal to a comparator. The
comparator compares the actual condition or value
of the process with the desired condition or set
value of the process and, if the two are not the
same, produces an error signal. The error signal
is then used by the control element to change,
via the correcting element, the energy flow into
or out of the process. Thus, a control sequence
can be established that continuously attempts to
eliminate any deviation of the actual value from
the desired value of the process.