Basic Marine Automation Handout PDF

I. Introduction to Marine Automation A. Terminologies 1. Instrumentation – A collection of devices or instrument or their application for the purpose of observation, measurement or control. 2. Control system - It is a system used to regulate a process, monitor a pro...

I. Introduction to Marine Automation A. Terminologies 1. Instrumentation – A collection of devices or instrument or their application for the purpose of observation, measurement or control. 2. Control system - It is a system used to regulate a process, monitor a process, or indicate when a process has reached a desired result. 3. Automation – the technique of automatically controlling a system by using instruments in order to balance the supply and demand of a process 4. Mechanization- It is the process of providing human operators with machinery that assists them with the muscular requirements work. 4. Open Loop System – A control loop without feedback which makes it simple 5. Close Loop System – A control loop with continuous feedback of the current status of the system which makes it more accurate in terms of control. This control, however, is more complicated. 6. Controlled Variable – The variable in the system you want to control. This is also the variable wherein you assign a set point. 7. Set Point – A value of a process variable you want to maintain. 8. Manipulated Variable – the variable in the system you change in order to correct the process. 9. Disturbance Variable – any variable that can disturb the process. Example: ambient temperature 10. Primary Element – the device that measures variables in a system 11. Secondary Element – the device that processes the signal coming from the primary element and gives a corrective signal to the final control element. 12. Final Control Element – the device that changes the manipulated variable to correct the process. Usually these are the control valves. B. Types of Control System 1. Open Loop System 2. Close Loop System C. Process Variables D. Components of a Typical Control System E. Function of the Components of a Typical Control System II. Principles of Process Measurements A. Pressure Measurements 1. Primary Elements a) Bourdon Tube – C-type bourdon tubes are usually used in ordinary pressure gauge. Helical and Spiral type are used for high pressure applications. b) Diaphragm – a device usually made of rubber which creates a partition between two areas. It usually moves and reacts due to pressure applied on it. c) Bellows – a device that expands or retract due to pressure.  d) Strain gauge – a device which changes resistance proportional to the pressure applied on it. An increase in pressure results in an increase in resistance. e) Piezoelectric Transducer – a device which is composed of a quartz crystal that when subjected to pressure creates a very small electrical signal proportional to the amount of force exerted to it. = f) Variable Capacitance Transducer – a device consist of two plates wherein the capacitance is varied by the change in the distance of the plates. The distance between the two plates is proportional to amount of pressure that acts on the area of the plates. 2. Units of pressure – There are lots of different pressure units being used on- board a ship. For SI units the basic unit is Pascal which is very small. The  most widely used unit of pressure is BAR. In English system, PSI is most widely used. A conversion table is shown below. 3. Local Reference – A pressure gauge serves as a local indication for pressure measurement. For differential pressure, a U-tube manometer is often used. If ever a pressure alarm is indicated in the control system, we checked if it is true by using these instruments as reference. 4. Remote Control – Pressure switch and pressure transmitters are used to measure pressure in the system and gives a corresponding signal to the controller. Sometimes, switches are used to give alarm signals or as an  emergency switch to cut-off electrical signals. Pressure transmitter gives a standard output of 4 to 20 mA or 0.2 to 1.0 Bar. B. Level Measurements 1. Units of level – Level may be measured in terms of innage or ullage. For SI units, we use millimeter, centimeter, meter or percentage. In English system, inches, feet and percentage are the usual units used. 2. Local Reference – A sight glass serves as a local indication for level measurement. Sounding tape is also used to verify the actual level of the process. If ever a level alarm is indicated in the control system, we checked if it is true by using these instruments as reference or by visually checking the actual level. 3. Remote Control – Level switch and level transmitters are used to measure level in the system and gives a corresponding signal to the controller. Sometimes, switches are used to give alarm signals or as an emergency switch to cut-off electrical signals. Level transmitter gives a standard output of 4 to 20 mA or 0.2 to 1.0 Bar. C. Temperature Measurements 1. Units of temperature – Temperature is measured using the SI units of Celsius or Centigrade, oC. In ANSI system, Fahrenheit, oF, is used. There are also other units of temperature measurement, Kelvin and Rankine. Kelvin = Celsius + 273 Rankine = Fahrenheit + 460 Celsius = 5/9 (Fahrenheit – 32) 2. Local Reference – A bimetallic device or a fluid expansion device serves as a local indication for temperature measurement. Some also used an infrared radiation type of device for special purpose. Others use change-of-state devices to indicate temperature ranges. 3. Remote Control – Temperature switch and temperature transmitters are used to measure temperature in the system and give a corresponding signal to the controller. Temperature switches are used to cut-off electrical signals that exceed a predefined limit. The most common sensors connected to transmitters are the thermocouples and the RTDs (metallic). Thermocouples  give an output signal of millivolts and the RTD such as Pt100 gives an output measured in ohms. These signals are then converted into standard instrumentation signals. Thermocouple – consist of two different metals that are joined at one end. This junction is use to measure a process. The junction is said to create current flow due to the Seebeck Effect. The output is in millivolts and the device has a polarity. RTD – consist of pure metal that changes resistance as temperature changes. Example: Pt100 = Platinum, with 100 ohms at 0oC Pt1000 = Platinum, with 1000 ohms at 0oC D. Flow Measurements 1. Units of flow – Flow can be measured using volumetric flow rate or mass flow rate. Volumetric flow (Q) is defined as the volume of fluid that passes a given point in a pipe per unit of time. Q=vXA Mass flow rate (W) is defined as the mass or weight flowing per unit time. Typical units are pounds per hour.  W=XQ multiply by Convert to Convert from US gpd US gpm cfm IMP gpd IMP gpm m3/s 22800000 15852 2119 19000000 13200 m3/min 380000 264.2 35.32 316667 220 m3/h 6333.3 4.403 0.589 5277.8 3.67 liter/sec 22800 15.852 2.119 19000 13.20 liter/min 380 0.2642 0.0353 316.7 0.22 liter/h 6.33 0.0044 0.00059 5.28 0.0037 US gpd 1 0.000695 0.000093 0.833 0.000579 US gpm 1438.3 1 0.1337 1198.6 0.833 cfm 10760.3 7.48 1 8966.9 6.23 Imp gpd 1.2 0.00083 0.00011 1 0.00069 Imp gpm 1727.3 1.2 0.161 1439.4 1 multiply by Convert to Convert from 3 3 3 m /s m /min m /h liter/sec liter/min liter/h 3 m /s 1 60 3600 1000 60000 3600000 3 m /min 0.0167 1 60 16.67 1000 60000 3 m /h 0.000278 0.0167 1 0.278 16.67 1000  multiply by Convert to Convert from 3 3 3 m /s m /min m /h liter/sec liter/min liter/h liter/sec 0.001 0.06 3.6 1 60 3600 liter/min 0.0000167 0.001 0.06 0.0167 1 60 -7 liter/h 2.7 10 0.000017 0.001 0.00028 0.0167 1 -8 US gpd 4.39 10 0.0000026 0.000158 0.000044 0.0026 0.158 US gpm 0.000063 0.00379 0.227 0.0630 3.785 227.1 cfm 0.00047 0.028 1.699 0.472 28.32 1698.99 -8 Imp gpd 5.26 10 0.0000032 0.000189 0.0000526 0.00316 0.1895 Imp gpm 0.000076 0.0046 0.272 0.076 4.55 272.7 2. Local Reference – Rotameters are used to indicate the actual flow rate. Some are using totalizer to measure the average flow rate for a certain period of time. 3. Remote Control – There are several methods on how to measure flow rate. Head Method or Differential Pressure Flowmeters - measure flow by inferring the flow rate from the drop in differential pressure (dP) across an obstruction in the process pipe. Some of the common dP flowmeters are orifice plates, venturi tubes, flow nozzles, wedge flow meters, pitot tubes, and annubars.  Velocity Flowmeters - With velocity devices, the flow rate is determined by measuring the velocity of the flow and multiplying the result by the area through which the fluid flows. Typical examples of velocity devices include turbine, vortex shedding, magnetic, and Doppler ultrasonic flowmeters Displacement Method or Volumetric Flowmeter - flowmeters measure flow by measuring volume directly. Positive-displacement flowmeters use high-tolerance machined parts to physically trap precisely known quantities of fluid as they rotate. Common devices include rotary-vane, oval-gear, and nutating-disk flowmeters III. Instrument Calibration A. Terminologies 1. Calibration – The process of determining the uncertainty (or accuracy of an instrument by comparing the measurement or output with that of a known standard, in order to determine and correct the error. 2. Calibrator – The instrument which serves as the standard of comparison in calibration. 3. Accuracy – The degree of conformity of an indicated value to a recognized, accepted value, or ideal value. 4. Accuracy rating – A number that defines a limit that errors will not exceed , when the device is used under specified operating conditions. Example: +/- 5% A +/- sign precedes the number. If the sign is not shown it is understood to be present. Accuracy rating is expressed in several forms, each one having a reference. 4.1 In terms of % of FS – FS means full scale or the upper range value (URV) 4.2 In terms of % of Span – Span means URV –LRV 4.3 In terms of % of Reading – Reading means the process variable at the ideal point at the center of the range. 4.4 In terms of actual error of the variable – the value is in engineering units of the variable 5. Precision – the measure of whether several readings by the same instrument conforms 6. Rangeability – the ability of a transmitter to change its range. 7. Traceability – the property of the result of a measurement whereby it can be related to appropriate standard, generally international or national standards, through an unbroken chain of comparisons. 8. Sensitivity – the smallest change of measured quantity to which the instrument responds