MARINE AUTOMATION AND CONTROL

Marine Automation and Control Lesson 1 - Introduction

What is Automatic Control System? Defined as a system in which the value of a controlled condition is compared with a desired value and corrective action is taken dependent on the deviation, without the inclusion of a human element. An automatic control system thus includes: a) the plant, b) the detecting or sensing element, c) the measuring or indicating element, d) the controller

Manual vs Automatic Control  Manual – Open Loop Control - (Local or Remote) - Corrective action left to the human operator.  Automatic Control – Close Loop Control - Automatic process - Controller provides the necessary corrective action.

A BASIC CONTROL SYSTEM (OPEN LOOP) DISTURBANCES INPUT PROCESS OUTPUT CORRECTING MEASURING UNIT UNIT A BLOCK DIAGRAM

A BASIC CONTROL SYSTEM (CLOSE LOOP) DISTURBANCES INPUT PROCESS OUTPUT CORRECTING MEASURING UNIT UNIT CONTROLLER SET POINT







Advantages of Automation  Improved conditions for seagoing staff by transferring much of “donkey work” from manual operation to automatic operation, paricularly the more unpleasant tasks such as soot blowing, cleaning of oil purifiers  Savings due to more efficient use of seagoing staff by transfer from watchkeeping to day work; routine maintenance can be carried out more efficiently by a day worker.  Possible increase in the availability of the ship due to improved degree of operation and maintenance.  Saving in maintenance costs due to improvement in efficiency of the machinery  Possible fuel cost saving due to improvement in efficiency of operation of the machinery.  Increased safety due to greater reliability of automated equipment and systems

Controller Classification Controller Characteristic Sub- Categories 1. Is it Automatic? a) Automatic b) Semi-Auto c) Manual 2. Where are the Components? a) Local b) Remote c) Centralized d) Distributed 3. What is Controlled? a) Position b) Speed c) Process

4. How it functions? a) Open Loop b) Close loop 5. What mode is used? c) Feedforward 6. What media is used? d) Feedback e) Analog f) Digital a) Proportional b) Rate c) Reset d) Multimode a) Pneumatic b) Hydraulic c) Electric d) Mechanical e) Electronic f) Multimedia

Control System Requirements 3 MAIN REQUIREMENTS:  Good Stability  Allowable Deviation  Suitable Speed of Response OTHER REQUIREMENTS:  Reasonable costs  Compatible with other interacting system  Easy to maintain and repair  Withstand its operating environment

JACKET COOLING WATER TEMPERATURE CONTROL SYSTEM Signal HEADER TANK SET POINT CONTROLLER S.W. IN S.W.OUT M.U. COOLER MAIN 3-WAY ENGINE CONTROL VALVE J.W.PUMP A TYPICAL PROCESS CONTROL SYSTEM ONBOARD SHIP.

Important Definitions Elements: Physical Devices 1. Final Control Element: The component which receives a signal from the controller and directly changes the manipulated variable. 2. Process: The system under control excluding the controller itself. 3. Measuring Element: The component which senses the value of and converts information about the controlled variable into a form of information. 4. Controller: The component which evaluates the difference between the controlled variable from its set point and creates a correction signal to drive the final control element.

Important Definitions Signals: Quantities or Qualities 1. Manipulated Variable: The process variable which is altered by the controller to change the value of the controlled variable. Sometimes called the Input 2. Controlled Variable: The process variable which is measured and controlled. Sometimes called the Output. 3. Set Point: An independent input parameter which is the instruction given to the controller which determines the stabilized value of the controlled variable. 4. Deviation: The difference between the value of the controlled variable and the set point as created by (the comparing element of) the controller. 5. Actuating Signal: The signal sent from the controller to the final control element. 6. Disturbances: Uncontrolled process variables which affect the value of the controlled variable.

Marine Automation and Control Lesson 2 - Measuring Instruments

Learning Objectives  Comprehend the measurement of pressure, temperature, level and flow.  Comprehend the units of measurement  Comprehend various measurement devices

What Do We Measure?  LENGTH (in, ft, yd, mm, cm)  AREA (sqin, sqft, sqm, )  VOLUME (cuft, cum)  MASS (lb, kg)  FLOW (gal/h, l/s, m3/hr)  TIME (s, min, h)  PRESSURE (psi, cm of Hg, bar, kg/cm2, )  TEMPERATURE (F, C)  SPEED (Knots, rpm, km/h, m/s)

TEMPERATURE  A measure of a substance’s internal kinetic energy  [Simply stated] The degree of hotness or coldness of a substance, as measured on a thermometer

Temperature Measurement  Scales  Conversions  Fahrenheit (F)  F = 1.8*C + 32  Rankine (R)  R = F + 459.67  Celsius (C)  C = (F-32) / 1.8  Kelvin (K)  K = C + 273.15 Fahrenheit and Celsius based on boiling and freezing points of water Rankine and Kelvin based on absolute zero - more precise thermodynamic study.

Temperature Measuring Devices  Expansion Thermometers  Liquid in Glass  Bimetallic  Filled System / Distant Reading  Pyrometers  Thermocouple  Resistance  Radiation and Optical Pyrometers

Liquid in Glass Thermometer

Bimetallic Expansion Thermometer

Distant Reading Thermometer

Thermocouple

Resistance Temperature Device

Radiation Pyrometer

Thermometers

PRESSURE  Force exerted on a unit area  Measured in psi (other units include atm, in Hg, mm Hg, bar, kg/cm2)  Atmospheric pressure at sea level is 14.7 psia, 0 psig, 1 atm, 29.92 in Hg, 760.0 mm Hg  absolute pressure (psia) = gage pressure (psig) + 14.696

Pressure Relationships  Pressure Relationships Pa = Patm + Pg Patm = 14.7 psi or 29.92 in. Hg or 1 bar.  Barometric Pressure - A measure of air pressure that correlates with weather and altitude.

Pressure Measuring Devices  Manometer  Bourdon tube  Bellows gage

Manometer

Bourdon Tube

Bellows Gauge

Pressure Gauges

Level Gauges

Flowmeters  Mechanical flowmeters measure flow using an arrangement of moving parts, either by passing isolated, known volumes of a fluid through a series of gears or chambers (positive displacement) or by means of a spinning turbine or rotor.  All positive displacement flowmeters operate by isolating and counting known volumes of a fluid (gas or liquid) while feeding it through the meter. By counting the number of passed isolated volumes, a flow measurement is obtained.

Flowmeters

Measuring Instruments cont’d. A bimetallic strip is made up of two different metals firmly bonded together. When a temperature change occurs different amounts of expansion occur in the two metals, causing a bending or twisting of the strip. A helical coil of bimetallic material with one end fixed is used in one form of thermometer (Figure 15.7). The coiling or uncoiling of the helix with temperature change will cause movement of a pointer fitted to the free end of the bimetallic strip. The choice of metals for the strip will determine the range, which can be from - 30°C to +550°C.

The thermocouple is a type of electrical thermometer. When two different metals are joined to form a closed circuit and exposed to different temperatures at their junction a current will flow which can be used to measure temperature. The arrangement used is shown in Figure 15.8, where extra wires or compensating leads are introduced to complete the circuit and include the indicator. As long as the two ends A and B are at the same temperature the thermoelectric effect is not influenced. The appropriate choice of metals will enable temperature ranges from ~200°C to +1400°C.



Radiation Pyrometers A pyrometer is generally considered to be a high-temperature measuring thermometer. In the optical, or disappearing filament, type shown in Figure above, radiation from the heat source is directed into the unit. The current through a heated filament lamp is adjusted until, when viewed through the telescope, it seems to disappear. The radiation from the lamp and from the heat source are therefore the same. The current through the lamp is a measure of the temperature of the heat source, and the ammeter is calibrated in units of temperature.

Various pick-up devices can be used in conjunction with a digital counter to give a direct reading of speed. An inductive pick-up tachometer is shown in Figure 15.17(a). As the individual teeth pass the coil they induce an e.m.f. pulse which is appropriately modified and then fed to a digital counter. A capacitive pick-up tachometer is shown in Figure 15.17{b). As the rotating vane passes between the plates a capacitance change occurs in the form of a pulse. This is modified and then fed to the digital counter.

Viscosity measurement Viscosity control of fuels is essential if correct atomisation and combustion is to take place. Increasing the temperature of a fuel will reduce its viscosity, and vice- versa. As a result of the varying properties of marine fuels, often within one tank, actual viscosity must be continuously measured and then corrected by temperature adjustment. The sensing device is shown in Figure 15.20. A small constant speed gear pump forces a fixed quantity of oil through a capillary (narrow bore) tube. The liquid flow in the capillary is such that the difference in pressure readings taken before the capillary and after it is related to the oil viscosity. A differential pressure gauge is calibrated to read viscosity and the pressure values are used to operate the heater control to maintain some set viscosity value.

Oil-in-water monitor Current regulations with respect to the discharge of oily water set limits of concentration between 15 and 100 parts per million. A monitor is required in order to measure these values and provide both continuous records and an alarm where the permitted level is exceeded. The principle used is that of ultra- violet fluorescence. This is the emission of light by a molecule that has absorbed light. During the short interval between absorption and emission, energy is lost and light of a longer wavelength is emitted. Oil fluoresces more readily than water and this provides the means for its detection. A sample is drawn off from the overboard discharge and passes through a sample cell (Figure 15.23). An ultra-violet light is directed at the sample and the fluorescence is monitored by a photoelectric cell. The measured value is compared with the maximum desired value in the controller/recorder. Where an excessive level of contamination is detected an alarm is sounded and diverting valves are operated. The discharging liquid is then passed to a slop tank.

Control Signals  A controller is composed of elements, each of which accepts an input and creates an output.  These inputs and outputs are called signals and are the information being transferred into or away from the components or elements.  The signals are being transmitted from one element to the next.  The components are the system; the pieces of information passing between the components are the signals.

 The various physical forms of media in which these signals are transmitted in marine applications are:  Mechanical  Pneumatic  Hydraulic  Electrical  Electronic  Sometimes the signal is also given (send) to a component which is not part of the automatic control system. They are front panel indicators, repeaters, alarm systems, automatic data gathering and recording systems and remote monitoring systems.

 Signals which are transferred from one element to another must have a means of getting there. They are achieved by using one of the following forms of physical connection:  Linkages  Shafts and gears  Pipes  Electrical wires  Wireropes and cables

Common Terms  Receiver – any device which receives a signal in any medium.  Any device that creates a signal is called a transmitter, converter, sensor or transducer depending on how its being used in the system.  Transducer, most commonly used – a device that receives information from one system and changes the medium or the form of the signal and provides and output that is representative of the input information.  Transmitter – is a transducer that responds to a measured variable and creates a standard transmission signal which is a function only of the measure variable.  Converters – are also transducers, however, they are distinguished by the fact that they received standard signals, change the signal’s form and retransmits it into the rest of the system.

Control Signals – Standard Ranges Most modern equipment works on the following standard signal ranges. · Electric 4 to 20 mA · Pneumatic 0.2 to 1.0 bar · Digital standards Older electrical equipment use 0 to 10 V. The advantage of having a standard range is that all equipment is sold ready calibrated. This means that the minimum signal (Temperature, speed, force, pressure and so on) is represented by 4 mA or 0.2 bar and the maximum signal is represented by 20 mA or 1.0 bar. So the purpose of processing and conditioning is usually to convert the output into the standard range.