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# Process Instrumentation & Control

Introduction to electrical circuit theory and process instrumentation and control as it applies to the day to day operation in a Chemical plants.

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### Process Instrumentation & Control

1. 1. Welcome to Instrumentation, Process Control and Process Instrumentation & Diagram By: Dr. Zin Eddine Dadach Chemical Engineering department ADMC 1
2. 2.  The first part of this course introduces the students to the basics of electrical circuit theory followed by the latest process instrumentation technology and selection criteria.  This section explains the measurement of common process variables such as temperature, pressure, level and flow and describe their corresponding sensors.  A lab experiment on calibrating a manometer. PART I: Instrumentation 2
3. 3. Define and explain the various circuit components and describe the basic of electronic theory. L.O. #1 3
4. 4.  SENSORS, TRANSMITTERS AND CONVERTERS ARE ELECTRICAL AND ELECTRONIC DEVICES THAT TRANSFORM PHYSICAL PROPERTIES (PRESSURE, PRESSURE DROP, DISPLACEMENT, HEAT..) INTO ELECTRICAL CURRENT  IT IS THEREFORE NECESSARY TO STUDY SOME BASIC THEORIES OF ELECTRICITY 4 THE NEED OF ELECTRONIC IN INSTRUMENTATION
5. 5. CURRENT AMPERE 5
6. 6. WHAT IS CURRENT?  Electrical current is the movement of charged particles in a specific direction  The charged particle could be an electron ,a positive ion or a negative ion  The charged particle is often referred to as a current carrier  In a solid, the current carrier is the electron  The symbol for current is I 6
7. 7.  An ammeter is a measuring instrument used to measure the flow of electric current in a circuit.  Electric currents are measured in amperes, hence the name.  The word "ammeter" is commonly misspelled or mispronounced as "ampmeter" by some. 7 AMMETER?
8. 8.  More modern ammeters are digital, and use an analog to digital converter to measure the voltage across the shunt resistor.  The current is read by a microcomputer that performs the calculations to display the current through the resistor. 8 MODERN AMMETERS
9. 9. Direct current (DC) is the unidirectional flow of electric charge. Direct current is produced by sources such as batteries, thermocouples, solar cells, and electric machines of the dynamo type. DC: Direct Current 9
10. 10.  In alternating current (AC), the movement of electric charge periodically reverses direction. While in direct current (DC), the flow of electric charge is only in one direction. Alternating Current 10
11. 11. 11
12. 12. WHAT IS A VOLTAGE? VOLT 12
13. 13. Voltage is the electric pressure OR POTENTIAL that causes current to flow. Voltage is also known as electromotive force or emf or potential difference. If there is no potential difference (V=0), there will be no current (I=0) 13 VOLTAGE =POTENTIAL
14. 14.  We need a unit to indicate the potential energy between two points such as terminals of a battery.  This unit must specify the energy available ( JOULE is unit for energy) when a charge ( COULOMB is unit for charge) is transported.  The unit of voltage is : Volt= joule/coulomb 14 UNIT OF VOLTAGE?
15. 15.  The moving coil galvanometer is one example of this type of voltmeter. It employs a small coil of fine wire suspended in a strong magnetic field.  When an electrical current is applied, the galvanometer's indicator rotates and compresses a small spring.  The angular rotation is proportional to the current that is flowing through the coil 15 OHMMETER OR GALVANOMETER
16. 16. 16 OHMETER
17. 17.  The opposition a material offers to electrical current is called resistance  All materials offer some resistance to current  Resistance converts electric energy into heat  The symbol for resistance is R  The unit of resistance is the Ohm (Ω) 17 WHAT IS ELECTRICAL RESISTANCE?
18. 18.  Conductance refers to the ability to conduct current.   It is symbolized by letter G  The base unit for conductance is the siemens or S  CONDUCTANCE IS THE EXACT OPPOSITE OF RESISTANCE  R=1/G or G=1/R 18 WHAT IS CONDUCTANCE?
19. 19.  Materials with a big resistance are : INSULATORS or RESISTORS  Examples of insulators : paper, wood, plastics, rubber, glass and mica  Materials with a small resistance are : CONDUCTORS  Examples of conductors : Copper, aluminum, silver 19 CLASSIFICATION OF MATERIALS
20. 20.  OHM’LAW: The relationship between current (I), voltage ( V) and resistance (R) was discovered by the german Georg OHM  I= V/R 20 OHM‘S LAW?
21. 21.  How much current ( I) flows in a circuit where the voltage is 2.8 V and there is a resistance of 1.4 Ω in the circuit? 21 CLASS WORK #1:
22. 22.  How much voltage is required to cause 1.6 amperes in a device that has 30 ohms of resistance?  The current flowing through a 10 kΩ resistor is 35mA. What is the potential energy difference ( voltage) across the resistor?  A lamp has a resistance of 96 ohms . How much current flows through the lamp when it is connected to 120 volts?  A manufacturer specifies that a certain lamp will allow 0.8 ampere of current when 120 volts is applied to it. What is the resistance of the lamp? 22 Home work #1
24. 24.  A great majority of electrical circuits operate more than one load. Circuits which contain two or more loads are called multiple-load circuits.  A multiple-load circuit can be a series circuit, a parallel circuit or a series-parallel circuit 24 INTRODUCTION
25. 25.  A series circuit is the simplest circuit.  The conductors, control and protection devices, loads, and power source are connected with only one path to ground for current flow.  The resistance of each device can be different.  The same amount of current will flow through each.  The voltage across each will be different.  If the path is broken, no current flows and no part of the circuit works 25 A SERIES CIRCUIT
26. 26. 26 SERIES CIRCUIT
27. 27. VT= V1 +V2+V3+…. IT=I1=I2=I3+…… RT= R1 +R2+R3+…. Calculations 27
28. 28. LISTEN..LEARN..THINK..ENJOY YOURSELF 28 EXAMPLE OF CALCULATION
29. 29. LISTEN..LEARN..THINK..ENJOY YOURSELF 29 EXAMPLE OF CALCULATION
30. 30.  A parallel circuit has more than one path for current flow.  The same voltage is applied across each branch.  If the load resistance in each branch is the same, the current in each branch will be the same.  If the load resistance in each branch is different, the current in each branch will be different.  If one branch is broken, current will continue flowing to the other branches 30 PARALLEL CIRCUIT
31. 31. 31 PARALLEL CIRCUIT COMBINATION
32. 32.  VT=V1=V2=V3=…  IT=I1+I2+I3+…  (1/RT)= (1/R1) +(1/R2)+ (1/R3)+… Calculations 32
33. 33. LISTEN..LEARN..THINK..ENJOY YOURSELF 33 EXAMPLE OF CALCULATION
34. 34. 1) THREE RESISTANCES ( 35, 70 AND 45 OHMS) IN SERIES WITH A VOLTAGE SOURCE OF 90V,  CALCULATE : IT,RT,VR1,VR2,VR3 2) WHAT IS THE TOTAL RESISTANCE OF A SERIE OF TWO RESISTORS 20, 30 OHMS IN PARALLEL WITH A SECOND SERIE OF RESISTORS 70, 80 OHMS? LISTEN..LEARN..THINK..ENJOY YOURSELF 34 HOME WORK
35. 35.  Electrical energy is undoubtedly the primary source of energy consumption in any modern household.  Most electrical energy is supplied by commercial power generation plants like Tawillah  The most common power generation plants are fueled by : Fuel gas or fuel oil 35 WHAT IS ELECTRICAL ENERGY?
36. 36.  When a current flows in a circuit with resistance, it does work.  Devices can be made that convert this work into heat (electric heaters), light (light bulbs and neon lamps), or motion (electric motors)  P=W/t  P is the power and the unit is watt,  W is energy in joules and t time in seconds  1 Watt = 1Joule/second. 36 GENERAL DEFINITION OF POWER (P)
37. 37.  Electric power, like mechanical power, is represented by the letter P in electrical equations, and is measured in units called watts (symbol W).  P = I .V  where  P = power in watts  I = current in amperes  V = potential difference in volts37 ELECTRICAL POWER
38. 38.  Joule's law can be combined with Ohm's law to produce two more equations:  P= I2.R  and  P=V2/R  where  R = resistance in ohms.  For example:  (2 amperes)2 × 6 ohms = 24 watts  and  (12 volts)2 / 6 ohms = 24 watts 38 ELECTRICAL POWER: OTHER FORMULAS
39. 39.  What is the power input to an electrical heater that draws 3 amperes from 120 volt outlet?  Find the power used by a resistor of 10 ohms when a voltage of 1.5 v is applied 39 CLASS WORK #2:
40. 40.  How much power is dissipated when 0.2 ampere of current flows through a 100 ohms resistor?  How much energy is taken from the battery by the resistor ( 10 ohms) if the voltage is 1.5 V and the switch is closed for 30 min?  What is the cost of operating a 100 watt lamp for 3 hours if the rate is 6 cents per kWh?  An electrical iron operates from 120 volts outlet and draws 8 amperes of current. At 9 cents per kWh , how much does it cost to operate the iron for 2 hours 40 HOMEWORK #2:
41. 41. Measuring resistances, currents and voltages using multi-meters. LAB #1: Basic electricity 41
42. 42. INSTRUMENTATION FIRST AND THE MOST IMPORTANT STEP OF PROCESS CONTROL 42
43. 43. INSTRUMENTATION USE SENSORS LIKE THERMOCOUPLES, PRESSURE AND FLOW SENSORS TO MEASURE THE DIFFERENT PARAMETERS IN THE PLANT.  INFORMATION IS SENT TO THE CONTROLLER ( IN THE CONTROL ROOM) TO TAKE APPROPRIATE ACTIONS. . 43 DEFINITION OF INSTRUMENTATION
44. 44.  Measurements have got to be one of the most important equipment in any processing plant.  Since successful process control requires appropriate instrumentation, engineers should understand the principles of common instruments. 44 GOOD INFORMATION=GOOD CONTROL
45. 45.  Like human body uses nerves, Sensors are used for process monitoring and for process control.  Sensors are essential elements of safe and profitable plant operation.  This can be achieved only if the proper sensors are selected and installed in the correct locations.  While sensors differ greatly in their physical principles, their selection can be guided by the analysis of a small set of issues . 45 INSTRUMENTATION USE SENSORS
46. 46.  TEMPERATURE  PRESSURE  LEVEL  FLOW 46 THE FOUR MOST IMPORTANT VARIABLES IN ANY INDUSTRIAL PLANT
47. 47. Explain theory and apply the principles of temperature measurement and select the appropriate sensor for the application and discuss their common operating and troubleshooting problems. L.O #2 47
48. 48. TEMPERATURE 48
49. 49.  The temperature is the most important variable in a chemical process. Very often, the temperature should be controlled very precisely like:  In a reactor where the reaction outcome depends on the temperature’  For safety reasons where explosions can occur  Therefore, temperature need to be measured precisely with a very accurate sensor. 49 INTRODUCTION
50. 50.  ITS-90 (International Temperature Scale of 1990- used as a worldwide practical temperature scale in national metrology labs like NIST, NPL et al). 50 INTERNATIONAL STANDARDS FOR TEMPERATURE MEASUREMENTS
51. 51. Fluids and solids are composed of atoms or molecules These atoms or molecules vibrate, rotate and move in general, the atoms have an average energy When is cold, they move slowly and the energy is low when it is hot, they move fast and the energy is high 51 WHAT IS TEMPERATURE?
52. 52.  SCALES ARE INTERNATIONAL STANDARDS USED IN ALMOST ALL THE COUNTRIES  CELSIUS SCALE OR CENTIGRADE SCALE:  FROM 00C ( melting ice) TO 1000C ( boiling water) at 1 atm.  KELVIN SCALE : 0 K = -2730C T (K)= T(0C) + 273 52 SCALES FOR TEMPERATURE
53. 53.  AMERICAN SCALE:  RELATIONSHIP BETWEEN FAHRENHEIT AND CELSIUS SCALES : 320F = 00C 2120F= 1000C  T(0F)= 1.8xT(0C) +32 53 FAHRENHEIT SCALE
54. 54.  RANKINE SCALE : T(0R) = T(0F) + 460 T(0R) = 1.8 x T(K) 54 RANKINE SCALE
55. 55.  Convert 1000C into :  K, 0F,0R  Convert 50 K into:  0C, 0F,0R  Convert -750F into:  0C, K, 0R  Convert 0 0R into:  0C,0F, K 55 HOME WORK
56. 56.  T = temperature  TI = Temperature Indicator ( in plant)  TT= Temperature Transmitter  TC= Temperature Controller  TRC= Temperature Recorder & Controller  TCV= Temperature Control Valve TAG DESCRIPTORS FOR TEMPERATURE 56
57. 57. RTD= RESISTANCE TEMPERATURE DETECTOR THERMISTOR= THERMAL RESISTORS THERMOCOUPLES Radiation pyrometers 57 TEMPERATURE SENSORS USED FOR PROCESS CONTROL SYSTEMS
58. 58. RESISTANCE TEMPERATURE DETECTORS RTD 58
59. 59.  A Resistance Temperature Detector (RTD) is a device with a significant temperature coefficient (that is, its resistance varies with temperature).  It is used as a temperature measurement device, usually by passing a low-level current through it and measuring the voltage drop. 59 DEFINITION OF A RESISTANCE TEMPERATURE DETECTOR
60. 60.  The relationship between the resistance of a RTD and the temperature of the medium is the temperature coefficient α of the RTD .  coefficient α is also the sensitivity of the RTD 60 TEMPERATURE COEFFICIENT α OF A RTD
61. 61.  α IS A LINEAR APPROXIMATION BETWEEN RTD RESISTANCE AND THE TEMPERATURE : R(T)= R(TO) { 1+ α.ΔT}  R(T)= approximation resistance at Temperature T  R(T0)= resistance of RTD at T0  ΔT = T-T0 α depends on R(T0) and α> 0 because Metal resistance increases with temperature61 TEMPERATURE COEFFICIENT α OF A RTD
62. 62. Platinum is very repeatable, quite sensitive and very expensive  For Platinum, coefficient α is around 0.004/0C  Example: for PRTD of 100 Ω, if the temperature increases by 10C, R(T) changes by 0.4 Ω Nickel is not quite as repeatable, more sensitive and less expensive  For Nickel, coefficient α is around 0.005/0C  Example: For RTD of 100 Ω, if the temperature increases by 10C, R(T) changes by 0.5 Ω 62 SENSITIVITY α OF DIFFERENT METALS
63. 63. RTD's are the best choice for repeatability, and are the most stable and accurate. However they have a slow response time and because they require a current source they do have a low amount of self heating. 63 ADVANTAGES & DISATVANTAGES OF RTDs
64. 64.  RTDs work in a relatively small temperature domain, compared to thermocouples, typically from about  -200 °C to a practical maximum of about 650 to 700 °C.  Some makers claim wider ranges and some construction designs are limited to only a small portion of the usual range. 64 RANGE OF TEMPERATURES FOR RTD
65. 65.  A special set of RTD’s are called PRT’s because they use platinum are a material  A special set of PRTs, called SPRTs, are used to perform the interpolation in such labs over the ranges 13.8033 K (Triple point of Equilibrium Hydrogen) to the Freezing point of Silver, 971.78 °C. 65 RANGE OF TEMPERATURE FOR PRT ( PLATINUM RESISTANCE TEMPERATURE)
66. 66. THERMal resisISTORS THERMISTORS 66
67. 67.  Thermistors are temperature sensors that use semiconductor materials not metals like RTD’s  R(T) = R(T0) {1+ α (T-T0)} Semiconductors for temperature sensing have Negative Temperature Coefficient (NTC) OR α< 0  Semiconductor becomes a better conductor of current. Resistance decreases when the temperature increases. 67 DEFINITION OF THERMAL RESISTORS
68. 68.  The characteristics of these devices are very different from those of RTD’s  Thermistors are the most sensitive and fastest temperature measurement devices.  Thermistors can be used for small range of temperatures  Thermistors are non-linear . 68 PROPERTIES OF THERMISTORS
69. 69.  Because the resistance become too high at low temperature, the low limit is -1000C  Because the semiconductor can melt or be deteriorated at high temperatures, the high limit is 3000C  In most cases, the thermistor is encapsulated in plastic , epoxy, Teflon or some other material to protect the thermistor from the environment 69 THERMISTOR’ S LIMITATIONS
70. 70.  Thermistors have a fast output and are relatively inexpensive but are fragile and have a limited range. They also require a current source and do experience more self heating than an RTD and are nonlinear. ADVANTAGES & DISADVANTAGES OF THERMISTORS 70
71. 71. THERMOCOUPLES 71
72. 72.  When a pair of dissimilar metals are joined together for the purpose of measuring temperature, the device formed is called a thermocouple.  Thermocouples for instrumentation use metals of high purity for an accurate temperature/voltage relationship (as linear and as predictable as possible).  Thermocouples cover a range of temperatures from -2620C to 27600C 72 DEFINITION OF THERMOCOUPLES
73. 73. 73 THERMOCOUPLE
74. 74.  Thermocouples suffer from 2 major problems that cause errors when using them 1) Small voltage generated EX: 10C temperature change on a platinum thermocouple results of an output change of 5.8 μV 2) the non-linearity that requires polynomial conversion 74 PROBLEMS OF THERMOCOUPLES
75. 75.  The voltage (emf) produced by a heated junction of two wires is directly proportional to the temperature.  This fairly linear relationship is called SEEBECK EFFECT  Thus, the Seebeck effect provides for us an electric method of temperature measurement  RTD’S AND THERMISTORS USE RESISTANCES FOR MEASUREMENT BUT THERMOCOUPLES USE VOLTAGE 75 SEEBECK EFFECT
76. 76. ε = α. ( T2-T1) WHERE: ε= THE EMF TYPES OF THERMOCOUPLES α = SEEBECK COEFFICIENT T2 ,T1= JUNCTION TEMPERATURE IN K 76 SEEBECK COEFFICIENT
77. 77.  K = Chromel-alumel Temperatures : -190 to 13710C Seebeck Coefficient= 40 μV/0C J = Iron-constantan Temperatures : -190 to 7600C Seebeck Coefficient= 50 μV/0C 77 TYPES OF THERMOCOUPLES
78. 78.  T = Copper-constantan Temperatures: -190 to 7600C Seebeck coefficient : 50 μV/0C E = Chromel-constantan Temperatures : -190 to 14720C Seebeck coefficient: 60 μV/0C 78 TYPES OF THERMOCOUPLES
79. 79.  S= Platinum- 10% Rhodium/Pt Temperatures: 0 to 17600C Seebeck Coefficient: 10 μV/0C R = Platinum-13%Rhodium/Pt Temperatures: 0 to 16700C Seebeck coefficient : 11 μV/0C 79 TYPES OF THERMOCOUPLES
80. 80.  Thermocouples are inexpensive, rugged, and have a fast response time but are less accurate and the least stable and sensitive. Thermocouples also read only relative temperature difference between the tip and the leads while RTD's and thermistors read absolute temperature. ADVANTAGES AND DISDVANTAGES OF THERMOCOUPLES 80
81. 81. Temperature Measurement Comparison Chart Criteria Thermocouple RTD Thermistor Temp Range -267°C to 2316°C -240°C to 649°C -100°C to 500°C Accuracy Good Best Good Linearity Better Best Good Sensitivity Good Better Best Cost Best Good Better COMPARISON BETWEEN THE DIFFERENT TEMPERATURE SENSORS Temperature Measurement Comparison Chart 81
82. 82. Find the seebeck emf (ε) for a thermocouple J with α. = 50 μV/0C if the junction temperatures are 20 and 1000C 82 CLASS WORK
83. 83.  Objective of the lab: I) During the experiment: Reading of the temperature of the water being heated and the corresponding values for the three temperature sensors. II) After the lab, draw the three different calibration curves and find the sensitivity factor α for each sensor using the corresponding formula.  RTD = Resistance vs. Temperature  Thermistors: Resistance vs. temperature  Thermocouples = Voltage vs. Temperature  III) Write a lab report LAB #2 TEMPERATURE SENSORS 83
84. 84. EX: CALIBRATION CURVE OF THERMOCOUPLE 84
85. 85. Explain theory and apply the principles of pressure measurement and select the appropriate sensor for the application and discuss technical issues including calibration. L.O #3 85
86. 86. PRESSURE MEASUREMENT CONTROL & SAFETY 86
87. 87.  Pressure is the second most important measurement in process control  Pressure is controlled for process reason but also for safety reason.  The most familiar device are manometers and gauges but they require a manual operator 87 IMPORTANCE OF PRESSURE
88. 88. DEFINITION OF PRESSURE  PRESSURE IS THE AMOUNT OF FORCE EXERTED ON A UNIT AREA OF A SUBSTANCE: A F P  88
89. 89.  P= Pressure  PI= Pressure Indicator  PT= Pressure Transmitter  PC= Pressure controller  PRC= Pressure Recorder & Controller  PCV= Pressure Control Valve  PSV= Pressure Safety Valve  PRV= Pressure Relief Valve. TAG DESCRIPTORS FOR PRESSURE
90. 90.  SI UNITS: 1Pa = 1N/M2=1KG/S2.M 1ATM (ATMOSPHERIC PRESSURE)= 1.01x105 Pa 1 ATM= 101 kN/M2 1ATM= 760 MM. HG  US UNITS: 1PSIA = 1LBF/IN2 1PSIA = 6894.7 Pa 1ATM= 14.696 PSIA 90 UNITS OF PRESSURE
91. 91.  STATIC PRESSURE IS FOR A FLUID WITH IS NOT IN MOTION EX: FLUID IN A TANK  DYNAMIC PRESSURE IS FOR A FLUID IN MOTION IN PIPES 91 STATIC VS DYNAMIC PRESSURE
92. 92.  P= F/S  F= m.g  P= mg/S = (mgxh)/ (Sxh) =( mgh/V) m/V= ρ  P= ρ.g.h 92 Hydrostatic or Static pressure
93. 93.  THE PRESSURE OF A FLUID IN A PIPE IS MEASURED BY A PRESSURE GAUGE.  FLOW CALCULATED BY BERNOUILLI EQUATION 93 DYNAMIC PRESSURE
94. 94.  IT IS EXTREMILY IMPORTANT TO MAKE THE DIFFERENCE BETWEEN THE ABSOLUTE AND RELATIVE PRESSURE  THE ABSOLUTE PRESSURE IS THE REAL PRESSURE OF THE FLUID WHERE THE RELATIVE PRESSURE IS THE PRESSURE WE READ IN A PRESSURE INDICATOR WITH REFERENCE THE ATMOSPHERIC PRESSURE 94 ABSOLUTE AND GAUGE PRESSURE
95. 95.  PA = PG + 1 ATM  EXAMPLE #1 :EXPRESS A PRESSURE GAUGE OF 155 KPa TO ABSOLUTE PRESSURE WHEN THE ATMOSPHERIC PRESSURE IS 98 Kpa  EXAMPLE #2: WHICH PRESSURE DO YOU READ IN A GAUGE MANOMETER FOR A PRESSURE OF 225 KPa ( ABSOLUTE ) WHEN ATMOSPHERIC PRESSURE IS 101 KPa 95 RELATIONSHIP BETWEEN PA AND PG CLASS WORK
96. 96. In many cases, gauge pressure is more important than the absolute pressure because we read gauge pressure in manometers.  Pg= Pabs- Patm 96 GAUGE PRESSURE
97. 97. PRESSURE INDICATORS 97
98. 98.  PRESSURE IS USUALLY MEASURED FOR INDICATION ONLY BY READING:  GAUGES  U TUBES 98 PRESSURE INDICATORS
99. 99.  A hard metal tube ( bronze or brass) is flattened and one end is closed. Under pressure, the tube is bent into a curve or arc.  The open end is attached to a header by which the pressure can ne introduced inside the tube 99 MANOMETER= GAUGE OR BOURDON TUBE
100. 100. 100 PRESSURE INDICATORS IN PLANTS
101. 101. 101 U-TUBES
102. 102. I) A tank open to atmosphere holds water with a depth of 7 m. Density of water = 1000 kg/m3 a) What is the pressure in a gauge at the bottom of the tank in Pa ? b) Draw the figure showing the manometers readings 102 CLASS WORK
103. 103.  in a closed tank under vacuum, the bottom pressure of an unknown liquid at 1.2 m depth is 12.55 kPa (absolute).  1) Draw a figure showing the manometer readings  2) What is the density of the fluid?  A crude oil, in a tank at 60 kPa top absolute pressure, has a specific gravity of 0.89 and a pressure of the bottom of 345 kPa ( gauge).  1) Draw a figure showing the manometer readings  2) What is the level of the oil in the tank ?  A fluid in a tank has a specific gravity of 0.76 and a absolute pressure at the top 150 kPa and a gauge pressure at the bottom of 140 kPa.  1) Draw a figure showing the manometer readings  2) What is the level of liquid in the tank? HOMEWORK 103
104. 104.  CALIBRATION OF A MANOMETER BY MEASURING THE PRESSURE OF A GIVEN WEIGHT USING A HYDRAULIC OIL  USE DIFFERENT WEIGHTS READ THE PRESSURES IN THE MANOMETER  APPLY THE FORMULA (P=m.g/S) COMPARE the reading with the calculated PRESSURE and calculate the error 104 LAB #3 : calibration of manometers
105. 105. LEVEL MEASUREMENT 105
106. 106. Explain theory and apply the principles of level measurement and select the appropriate sensor for the application instruments and discuss technical problems including calibration. L.O #4 106
107. 107. In any chemical plant, you will find tanks, reservoirs, vessels and drums where liquids are stored. These could be for: The feed of the plant Intermediate between sections The products before selling them Liquid capacities are also found in distillation columns and reactors 107 LIQUID CAPACITIES IN A CHEMICAL PLANT
108. 108. Level of liquid in a vessel should be maintained above the exit pipe because if the vessel empties the exit flow will become zero, a situation that could damage PUMPS. A minimum level of liquid is then necessary to avoid cavitation of the pump This minimum should be known (measured) and respected during the production 108 MINIMUM LEVEL
109. 109.  The level should also have a maximum value to:  not overflow an open vessel (safety for workers)  should not exit through a vapor line of a closed vessel, which could disturb a process designed for vapor ( safety for COMPRESSOR , TURBINES) 109 MAXIMUM LEVEL
110. 110.  L= Level  LI= Level Indicator  LT= Level Transmitter  LC= Level controller  LRC= Level Recorder & Controller  LCV= Level Control Valve  LLA and VLLA: Low level Alarm and Very…  HLA and VHLA: High Level Alarm and Very.. TAG DESCRIPTORS FOR LEVEL 110
111. 111.  Level measurement sensors are divided into two categories:  point level switches for ALARMS  continuous level gauges for CONTROL 111 LEVEL MEASUREMENT SENSORS
112. 112.  Point level is used mostly for SAFETY.  Will operate when the liquid is above or below a certain point.  Switches devices indicate when a vessel is full, empty or at intermediate level  You will have LLA ( low level Alarm) and HLA ( high level Alarm) 112 POINT LEVEL SWITCHES
113. 113. Continuous level gauges provide information about material level at all points in the vessel Continuous level gauges are used for control purpose 113 CONTINUOUS LEVEL GAUGES
114. 114.  Pressure ( hydrostatic)  Float  Nuclear  ultrasonic 114 SENSORS FOR CONTINUOUS LEVEL MEASUREMENT
115. 115.  Float  Capacitance  Conductive level probes  Thermal & light beam 115 SENSORS FOR POINT LEVEL MEASUREMENT
116. 116. 116 ULTRASONIC SENSOR (NO-CONTACT)
117. 117.  The differential pressure is the most commonly used for continuous level measurement of liquids.  a membrane is used where the value  H(Level)= ΔP/ρ.g 117 LEVEL MEASUREMENT BY HYDROSTATIC PRESSURE
118. 118. 118 TANK OPEN TO ATMOSPHERE
119. 119. 119 TANK UNDER PRESSURE OR VACUUM
120. 120.  A tank open to atmosphere holds water. The pressure at the bottom is 200 kPa ( absolute) 1) Draw the figure showing the tank and the differential pressure ’s reading 2) What is the level in the tank ?( density of water = 1000 kg/m3)  In a closed tank under vacuum and containing crude oil ( ρ= 780 kg/m3) , the bottom pressure is 12.55 kPa (absolute). 1) Draw a figure showing the tank and the differential pressure ’s reading. 2) What is the level in the tank?120 Class Work
121. 121.  A crude oil, in a tank at 120 kPa top absolute pressure, has a specific gravity of 0.80 and a gauge pressure of the bottom of 345 kPa . 1) Draw a figure showing the tank and the differential pressure s reading. 2) What is the level in the tank?  A fluid in a tank has a specific gravity of 0.65 and a gauge pressure at the top 150 kPa and a absolute pressure at the bottom of 140 kPa. 1) Draw a figure showing the tank and the differential pressure ’s reading. 2) What is the level of liquid? HOME WORK 121
122. 122. FLOW MEASUREMENT 122
123. 123. Explain theory and apply the principles of flow measurement and select the appropriate sensor for the application and discuss technical problems including calibration. L.O #5 123
124. 124.  Quantity of fluid flowing in a system by unit time.  This quantity can be expressed in three ways:  Volume Flow rate ( Q) :Bring a flask and a stop watch to measure volumetric flow Mass Flow rate ( M)  Weight Flow rate ( W) 124 WHAT IS FLOW?
125. 125. F= Flow FI= Flow Indicator FT= Flow Transmitter FC= Flow controller FRC= Flow Recorder & Controller FCV= Flow Control Valve TAG DESCRIPTORS FOR LEVEL 125
126. 126.  If we know the volume flow rate Q, we can calculate the mass flow rate by : M=ρ.Q  If we know the volume flow rate Q, we can calculate the weight flow by : W=γ.Q 126 RELATIONSHIP BETWEEN FLOWS
127. 127.  The volume flow rate is the volume of fluid flowing past a section per unit time  In a pipe, we can have the relation: Q=A .v (where v is the average velocity of flow)  Units used: SI : EX: v (m /s)  Q (m3/s) US : EX: v (ft /s)  Q(ft3/s) 127 Volume flow rate Q
128. 128.  An average flow rate of water produced by a plant is 11600 m3 /hr. Find the equivalent flow rate in m3/s, mass flow rate in kg/s ( density of water = 1000 kg/m3) and the weight flow rate ( Weight= Mass x gravity) and gravity = 9.8 m/s2 128 CLASS WORK (units)
129. 129.  A) MATERIAL BALANCE OF A PLANT: VERY VERY IMPORTANT  Measure flow of feeds Measure flow of products We should have : IN=OUT in mass ( Otherwise we have leaks in the plant)  B) FLOW IS A IMPORTANT VARIABLE FOR THE SYSTEM ( EX:REACTOR)  WHEN YOU HAVE A RATIO CONTROL SYSTEM 129 WHY WE NEED TO MEASURE FLOWS
130. 130.  In the instrumentation market, we find two types of flow-meters:  Energy-extractive Flow meters Energy additive Flow meters 130 FLOW MEASUREMENT TECHNIQUES
131. 131.  Several sensors rely on the pressure drop or head occurring as a fluid flows by a resistance. 131 THE PRINCIPLE OF FLOW SENSORS
132. 132.  ORIFICE  VENTURI TUBE  FLOW NOZZLE  ELBOW METER  PITOT TUBE  TURBINE 132 MOST IMPORTANT FLOW SENSORS
133. 133. Bernouilli Equation  Old system : use low measurement devices that reduce the energy of the system. The differential pressure is used to measure flow using Bernoulli equation:  Applying Continuity equation: QA=QB ( assuming constant density). Find the relationship between flow ( You want to estimate) and ΔP ( your readings).  this relationship is used in Energy extractive flow meters as a conversion factor 22 2 1 2 1 BB B AA A v g z p v g z p   133
134. 134.  From Bernouilli Equation:  𝑄 = ∆𝑃. 2( 𝐴1. 2 𝐴2 2 ) 𝜌(𝐴1 2 −𝐴2 2) Pressure drop in Pa Area in m2 Density in kg/m3 Q in m3/s Calculating volumetric flow rate Q 134
135. 135.  In a pipe of 0.3 diameter, water is flowing at 600C. We use a venturi tube to measure the flow rate. The venturi tube has a diameter of 0.2 m and we observe a pressure drop of 50 pa  What is the volume flow rate and the conversion factor?  What is the mass flow rate? 135 CLASS WORK
136. 136. PROCESS CONTROL 136
137. 137.  Define the terms used in chemical process control and discuss the role and importance of process control systems in industrial plants.  Define P, PI and PID controllers  Explain feedback control and the dynamic behavior of this controller.  Apply the principles of feed-forward and show how this type of control can be applied.  Describe how the principles of cascade control, ratio, the selective control and split - range control are used in processes control.  Define the principles of computer control and distinguish between direct digital control and supervisory control.  Do experiments and write laboratory reports in a professional manner. PART II: PROCESS CONTROL 137
138. 138. L.O #1 Define the terms used in chemical process control and discuss the role and importance of process control systems in industrial plants. 138
139. 139. 139 THE SEVEN OBJECTIVES OF A CONTROL SYSTEM • 1. Safety • 2. Environmental Protection • 3. Equipment protection • 4. Smooth Operation and production rate • 5. Product Quality • 6. Profit • 7. Monitoring and Diagnosis
140. 140. Example  Heating up the temperature in the tank is a process that has the specific, desired outcome to reach and maintain a design value for the temperature (e.g. 80°C), kept constant over time.  The desired temperature (80°C) is the set point. The controller will manipulate the valve of hot water to maintain the room temperature at 800C. 140
141. 141. 141EXAMPLE OF CONTROL SYSTEM
142. 142. 142WHAT ARE THE DESIGN VALUES?  THE DESIGN ENGINEERS CALCULATE THE VALUES OF SOME VERY IMPORTANT VARIABLES OF THE PROCESS THAT SHOULD BE MAINTAINED CONSTANT IN ORDER TO GIVE MAXIMUM PROFITABILITY BY RESPECTING SAFETY AND ENVIRONMENT ( OPTIMIZATION)  THESE CALCULATED VALUES ARE THEN INTRODUCED AS SET POINTS ( VALUES TO BE RESPECTED) IN THE CONTROLLER ONCE THE PLANT IS BUILT .
143. 143. 143 HOW ARE THE VALUES OF THE IMPORTANT VARIABLES ( SET POINTS) MADE CONSTANT? ACTING ON SOME OTHER LESS IMPORTANT VARIABLES OF THE PROCESS IN ORDER TO SUPPRESS THE EFFECTS OF EXTERNAL DISTURBANCES ON THE IMPORTANT VARIABLES
144. 144. Examples for Process Automation 144
145. 145. Overview of Process Automation The process is “that portion of an automation operation which use energy measurable by some quality such as pressure, temperature, level, flow, (and many others) to produce changes in quality or quantity of some material or energy.” PROCESS Some Quality or Quantity of the Material or Energy Input Energy or Material Desired Result
146. 146. Example of a Temperature Process Heating Element Water Bath Temperature The objective of this process is to maintain a constant water bath temperature.
147. 147. Temperature Process Terminology Heating Element Water Bath Temperature This is a Temperature Process The measuring means is the thermometer. (Temperature Indicator- TI) The process temperature is maintained at a desired point (Set Point – SP) Steam (Control Agent) is used to vary the temperature by opening and closing the control valve (Final Control Element)
148. 148. Level Process Oil Stock Level Indicator Oil Feed to next process The control objective is to maintain a constant liquid level of oil inside the tank (e.g. 100 gallons +/- 20 gallons). The hand valve is opened and closed as required to maintain the desired tank level.
149. 149. Terminology used to describe the process  PROCESS: Level  CONTROLLED VARIABLE: Level by Head pressure at bottom of tank  CONTROL POINT: The level of oil in the tank (Set Point = 100 gallons)  MEASURING MEANS: Level Indicator (Head Pressure)  MANIPULATED AGENT: Volume of oil stock  MANIPULATED VARIABLE: Flow rate of oil (gpm) Oil Stock Level Indicator Oil Feed to next process
150. 150. Basic Model of a Process The process is maintained at the desired point (SP) by changing the FCE based on the value of the PV Manipulated Variable Desired Result Control Agent PROCESS (Temperature, pressure, level, flow) FINAL CONTROL ELELMENT (valve) Measuring Means (transmitter) Process Variable (PV) Controlled Variable Actuating Input pH, conductivity, humidity, density, consistency, etc. Process equilibrium (balance) is when the input energy maintains the output at a constant “desired” point.
151. 151. Basic Model of a Process The measuring means provides the standardized signal that represents the condition of the process, i.e. is the process at the desired point? Manipulated Variable Desired Result Control Agent PROCESS (Temperature, pressure, level, flow) FINAL CONTROL ELELMENT (valve) Measuring Means (transmitter) Process Variable (PV) Controlled Variable Actuating Input pH, conductivity, humidity, density, consistency, etc.
152. 152. Review of Measuring Means Pressure Level Flow Temperature Thermocouples RTDs / Thermistors Filled Systems Bi-metallic Strain gauge Piezo-electric Capacitance Bourdon Tube Head meters (orifice, venturi) Coriolis, velocity, Mass, Mechanical Floats Guided Wave Weight (load cell) Ultrasonic Differential Pressure Transmitters Pressure Transmitter Level Transmitter Differential Pressure Cell Flow Transmitter Temperature Transmitter Pneumatic 3-15 PSI Electrical Current 4 – 20 mA 0 – 20 mA 10 – 50 mA Voltage 0 – 5 V 1 – 5 V 0 – 10 V Digital ON/OFF Field Bus ModBus ProfiBus HART
153. 153. Manual Control Open loop (or manual control) is used when very little change occurs in the Process Variable (PV) Manipulated Variable Desired Result Control Agent PROCESS (Temperature, pressure, level, flow) FINAL CONTROL ELELMENT (valve) Measuring Means (transmitter) Process Variable (PV) Controlled Variable Actuating Input pH, conductivity, humidity, density, consistency, etc. Corrective action is provided by manual feedback
154. 154. THE FOUR BASIC STEPS OF A PROCESS CONTROL SYSTEM HOW DOES IT WORK? 154
155. 155. 155 THE FIRST STEP: TAKING THE INFORMATION  IF WE DO NOT KNOW WHAT IS WRONG, HOW CAN WE CONTROL ? TAKING INFORMATION OF THE IMPORTANT VARIABLES ( Design Values) OF THE PROCESS.
156. 156. 156IN OUR CASE:  Temperature of the tank has to be controlled.  Temperature SHOULD FIRST BE MEASURED. THE EQUIPMENT FOR temperature MEASUREMENT IS : thermocouple
157. 157. 157 THE SECOND STEP OF A PROCESS CONTROL SYSTEM: TRANSMISSION OF THE INFORMATION  LINK BETWEEN THE PLANT AND THE CONTROL ROOM)  THE MEASUREMENT OF THE CONTROLLED VARIABLE IS SENT TO THE CONTROLLER IN THE CONTROL ROOM. THE EQUIPMENT FOR TRANSMISSION IS THE TRANSMITTER Thermocouple is also a transmitter
158. 158. IN OUR CASE: THE ANALOG SIGNAL OF THE VALUE OF FB ( MEASURED VARIABLE) IS TRANSMITTED TO A/D CONVERTER THE RESULTING DIGITAL SIGNAL IS SENT TO THE CONTROLLER (digital or computer software)  WHY A/D CONVERTER? 158
159. 159. 159 THE THIRD STEP :THE CONTROLLER MAKE DECISION THE THIRD STEP IS THE CONTROLLER IN THE CONTROL ROOM  THE CONTROLLER: 1) RECEIVE THE INFORMATION FROM THE PLANT 2) COMPARE IT WITH THE SET POINT 3) CALCULATE THE DIFFERENCE ε BETWEEN THE SET POINT AND THE INFORMATION. 4) MAKE A DECISION FOR ACTION TO BE TAKEN IN THE PLANT.
160. 160. IN OUR CASE: THE CONTROLLER WILL FIRST COMPARE T ( MEASURED VARIABLE) TO ITS SET POINT TSP.  THE CONTROLLER WILL THEN CALCULATE THEIR DIFFERENCE ε =( TSP-T)  THIS DIFFERENCE ε IS MULTIPLIED BY A FACTOR K DEPENDING ON THE TYPE OF CONTROLLER ( P,PI OR PID TO BE STUDIED LATER) 160
161. 161. 161 THE FOURTH STEP: ACTION ON A CONTROL VALVE OR MOTOR IN THE PLANT A SIGNAL FROM THE CONTROLLER, RELATED TO THE DIFFERENCE ε IS SENT TO THE VALVE TO MANIPULATE THE FLOWRATE OF STEAM WHICH IS A LESS IMPORTANT VARIABLE THE VALVE IS THE FOURTH AND LAST EQUIPMENT OF THE PROCESS CONTROL SYSTEM  THE FLOW OF STEAM IS THE MANIPULATED VARIABLE.
162. 162. 162IN OUR CASE  TO ELIMINATE THE EFFECTS OF THE SURRONDINGS ( DISTURBANCES) ON THE IMPORTANT VARIABLE TEMPERATURE WHICH IS MEASURED  TO BRING T AS CLOSE AS POSSIBLE TO ITS SET POINT VALUE TSP THE CONTROLLER ACT ON ANOTHER VARIABLE FA CALLED MANIPULATED VARIABLE
163. 163. 163BLOCK DIAGRAM OF A PROCESS CONTROL SYSTEM
164. 164. CLASS WORK  We want to produce ammonia from nitrogen and hydrogen in a reactor where the temperature should be maintained constant by a coolant in a jacket around the reactor.  Draw the process  Draw the process control system  Show the FOUR steps of the control loop 164
165. 165. THE DIFFERENT CONTROL ACTIONS 165
166. 166. EXAMPLE OF OPEN LOOP SYSTEM : SYSTEM WITH NO CONTROL level LISTEN..LEARN..THINK..ENJOY YOURSELF 166 166
167. 167. LEVEL WITH SET POINT BUT NO CONTROL  LEVEL2 LISTEN..LEARN..THINK..ENJOY YOURSELF 167 167
168. 168. A SYSTEM WITH CONTROL CLOSED LOOP 168
169. 169. 169A) MANUAL CONTROL  DURING START UP AND SHUT DOWN: OPERATOR CONTROL THE PLANT OPERATIONS  LEVEL3
170. 170. 170 AUTOMATIC CONTROL  DURING OPERATING CONDITIONS: THE CONTROLLER TAKES ACTIONS  ON AND OFF CONTROLLER:  CONTROLLER TAKES ACTION ONLY WHEN THE MINIMUM AND THE MAXIMUM OF THE LEVEL ARE REACHED  NOT USED VERY OFTEN ONLY IN SIMPLE SITUATIONS WHEN SAFETY AND PRODUCTIVITY ARE NOT AFFECTED  LEVEL4
171. 171. 171CONTINUOUS AUTOMATIC CONTROL:  THE MOST USED CONTROLLERS: PROPORTIONAL ( P)  PROPORTIONAL- INTEGRAL ( PI)  PROPORTIONAL-INTEGRAL-DERIVATIVE ( PID)
172. 172. 172CONTROL SYSTEM: P,PI,PID  CHANGE THE SET POINT OF THE LEVEL AND OBSERVE THE BEHAVIOR OF THE PROCESS  LEVEL5
173. 173. THE DIFFERENT FUNCTIONS OF A PROCESS CONTROL LOOP Between the measuring device and the final control element, we have different steps and each step has its own function  THE SENSOR : the output ym(t) of the sensor is related to the real value in the controlled variable y (t) by a transfer function  THE TRANSMITTER : The value yt (t) entering the controller is related to ym(t) by a transfer function ( we have delay in the information) LISTEN..LEARN..THINK..ENJOY YOURSELF 173 173
174. 174. DIFFERENT FUNCTIONS  THE CONTROLLER : after comparing to the set point ySP , the input to the controller is then ε (t) = ySP- ym(t). The output c(t) is related to ε (t) by a transfer function of the controller (P,PI,PID) The way c(t) and ε (t) are related depends on the type of controller ( TO BE STUDIED LATER)  THE VALVE: The output signal of the valve is related to c(t) by a transfer function depending on the type of the valve LISTEN..LEARN..THINK..ENJOY YOURSELF 174 174
175. 175. Lab #4:Demonstration lab  Demonstration lab for the pressure controller including:  1) The four steps  2) Converters P/I , I/P for electronic Controllers  3) A/D and D/A converters for digital controllers 175
176. 176. VIDEO FOR BASIC STEPS 176
177. 177. Closed Loop Control Closed loop or feedback control provides a corrective action based on the deviation between the PV and the SP Automatic Controller Output (3-15 psi, 4-20mA etc) CONTROLLING MEANS Manipulated Variable Desired Result Control Agent PROCESS (Temperature, pressure, level, flow) FINAL CONTROL ELELMENT (valve) Measuring Means (transmitter) Controller Input (PV) (3-15psi, 4-20mA etc) Controlled Variable pH, conductivity, humidity, density, consistency, etc. Manual SP
178. 178. Controlling Means Controllers provide the required control action to position the FCE at a point necessary to maintain the PV at the desired SP. PID (single loop feedback controller) DCS (distributed controllers) PLC (programmable logic controllers)
179. 179. Single Loop Feedback Control 1. Measuring Means 2. Controlling Means 3. Final Control Element 4. Temperature Process Temperature Controller and Recorder Sensing Bulb Temperature Transmitter Pneumatic Control Valve Heat Exchanger Steam 2 3 4 1 The TT provides the signal (PV) that represents the condition of the process being controlled. The TIC compares the PV to the SP and opens and closes the FCE to maintain the process at equilibrium.
180. 180. Summary  Process automation makes use of instrumentation to maintain the process at some desired condition.  Common instrumentation used in a process loop are the measuring means (usually transmitters), the controlling means (usually a PID controller), and the Final Control Element (usually some type of valve)  The measuring means provides the feedback signal (PV) used in the process loop. The controlling means operates the FCE based on the difference between the PV and the SP.  Process equilibrium is maintained when the difference between the PV and SP is zero or constant (offset?)
181. 181. NEXT? What are transmitters? What is PID? What are P&ID symbols? What types of FCE are there? What am I doing here? How do I measure? Pressure Level Temperature Flow How do I tune a loop? What is Integral action? What is a? FIC TT LRC PRV Should I use a 3-15 psi or 4- 20 mA valve? Check out
182. 182. TRANSMITTERS, TRANSDUCERS AND CONVERTERS 182
183. 183.  In the context of industrial process control, a "transmitter" is a device that converts sensor measured units into an electrical signal then directs this data (via cabling or wirelessly) to be received by a display or instrumentation control device within the system. 183 Transmitters
184. 184.  Analog transmitters are the most commonly used type in most industrial sectors. The transmitter is connected to the rest of the system via 2 wires which create something know as the 'current loop.'  The two wires can be used for both powering the unit and for transmitting signals typically at a range of 4 mA to 20 mA 184 Analog Transmitter
185. 185.  In an increasing number of industrial situations wireless sensors are an appropriate upgrade to classic industrial transmitters. This is because current of generation sensors offer flexible system solutions which are ideal for temporary installations and in processes with moving parts/objects.  Such wireless sensor networks can be comprised of hundreds or thousands of intelligent sensors. This allows for complex network mapping that can provide advanced solutions to today's processing environments. 185 Wireless transmitters
186. 186.  If the measuring device is pneumatic and the controller is electronic: A P/I transducer is needed to transform a physical movement into electrical current.  The I/P transducer does the opposite direction but not very used because most controllers are now electronic or digital. 186 Transducers: P/I and I/P
187. 187. If the controller is digital and the measuring device is pneumatic, we need:  1) convert pneumatic into electrical by P/I transducer  2) convert electrical to digital using A/D converter. At the exit of the digital controller we need:  1) D/A is the valve is electrical  2) D/A + I/P is the valve is pneumatic 187 Converters: A/D and D/A
188. 188. Define P, PI and PID controllers L.O #2: CONTROLLERS 188
189. 189. CONTROLLERS THE HEART OF PROCESS CONTROL LOOP 189
190. 190.  P CONTROLLER IS PROPORTIONAL CONTROLLER  PI CONTROLLER IS PROPORTIONAL CONTROLLER WITH INTREGRAL ACTION  PID CONTROLLER IS PROPORTIONAL CONTROLLER WITH INTEGRAL ACTION AND DERIVATIVE ACTION. DIFFERENT KINDS OF CONTROLLERS 190
191. 191. PROPORTIONAL CONTROLLER The proportional CONTROLER means that the controller output c(t) is linearly related to the error ε (t) The proportional controller has a gain Kc or Proportional Band (PB) related by the formula (Kc= 100/PB) LISTEN..LEARN..THINK..ENJOY YOURSELF 191 191
192. 192. Chapter 15 - Process Control Methods 192 Proportional Band  Proportional band is defined as the percentage change in the controlled variable that causes the final correcting element to go through 100 percent of its range PB = Controlled Variable % Change FinalCorrecting Element % Change
193. 193. PROPORTIONAL ACTION  The proportional action means that the controller output c(t) is linearly related to the error between set point (SP) and measurement of process output ym (t) : c(t) = Kc .ε(t) = Kc (SP – ym(t) )  The proportional gain Kc of a analog controller can be adjusted by knob in the controller.  Direct or reverse actions ? LISTEN..LEARN..THINK..ENJOY YOURSELF 193
194. 194. SIGN OF THE GAIN KC If he controller is direct acting  the gain K is positive. When the controller is reverse acting  the gain K is negative LISTEN..LEARN..THINK..ENJOY YOURSELF 194
195. 195. PROPORTIONAL BAND  Proportional controllers are defined by their Proportional Band (PB) or the proportional gain (Kc)with PB =100/Kc  For pneumatic valves, we define Kcp which is the output from the controller to the valve. The range of the instrumentation pressure for pneumatic valves is 3 -15 psia.  For electrical valves, we define Kce which is the output from the controller to the valve. The range of the instrumentation current for electrical valves is 4-20 mA. LISTEN..LEARN..THINK..ENJOY YOURSELF 195
196. 196. DIFFERENT SITUATIONS:  A) IF A FULL CHANGE IN THE CONTROLLED VARIABLE IS ALSO A FULL RANGE FOR THE VALVE , WE WILL HAVE: PB= 100%/100%= 1= 100% ,KC=1  IF WE ARE CONTROLLING TEMPERATURE FOR A RANGE OF 60-100, WE WILL HAVE : Kcp = 0.3 PSIA/ DEGRE LISTEN..LEARN..THINK..ENJOY YOURSELF 196
197. 197.  B) IF A 10% CHANGE IN THE CONTROLLED VARIABLE GIVES A FULL RANGE IN THE 100% IN THE VALVE, WE WILL HAVE PB= 10%/100% = 10% IF WE CONTROL TEMPERATURE FOR THE SAME TOTAL RANGE, 10% WILL BECOME 4 DEGRE AND WE WILL HAVE Kcp= 3PSIA/DEGRE THE CONTROLLER IS MORE SENSITIVE LISTEN..LEARN..THINK..ENJOY YOURSELF 197
198. 198.  C) IF A 100% CHANGE IN THE CONTROLLED VARIABLE GIVES A 20% RANGE IN THE VALVE, WE WILL HAVE PB= 100%/20% = 500%, KC=0.2 IF WE CONTROL THE SAME TEMPERATURE , WE WILL HAVE Kcp= 0.06 PSIA/DEGRE THE CONTROLLER IS LESS SENSITIVE LISTEN..LEARN..THINK..ENJOY YOURSELF 198
199. 199. EXAMPLE #1  Let’s consider a control system for a temperature in a process where the output of the controller is a pressure signal to the final element or valve.  The controller is used to control temperature within the range of 600F to 1000F.  The controller is adjusted so that the output signal varies from 3 psi (valve fully open) to 15 psi (valve fully closed) as the controlled temperature (measured) varies from 710F to 750F. Fpsi FF psipsip Kcp 0 00 /3 )7175( )315(         %10100. )60100( )7175( 00 00     FF FF PB LISTEN..LEARN..THINK..ENJOY YOURSELF 199
200. 200. EXAMPLE #2  Now, if we consider a PB of 75% for the same range of 600F to 1000F, what will be the Gain Kc?  From the PB formula, we find ΔT ( the change of the measured variable)  From the Gain formula: FFrangePBT 00 30)40.(75.0.  Fpsi F psipsi Kcp 0 0 /4.0 30 )315(    LISTEN..LEARN..THINK..ENJOY YOURSELF 200
201. 201. OFFSET OF PROPORTIONAL CONTROLLER  An important characteristic of a proportional controller is the OFFSET  In a proportional controller, there is always a residual error of the controlled variable.  It can be minimized by a large Kc which also reduce the PB  See figure 9-10 page 198 LISTEN..LEARN..THINK..ENJOY YOURSELF 201
202. 202. EXAMPLES OF USES OF A PROPORTIONAL CONTROLLER  Proportional controllers are mostly used for level control where variations of the controlled variables carry no economical and where others control modes can easily destabilize the loop  It is actually recommended for controlling the level of a surge tank when manipulating the flow of the feed to a critical downstream process. LISTEN..LEARN..THINK..ENJOY YOURSELF 202
203. 203. CHARACTERISTICS OF PROPORTIONAL CONTROLLER  Relationship between the output c(t) and error ε (t) is:  c(t) = Kc .ε(t) = Kc .ε(t)  Proportional Controller gives always an Off-Set, which is a difference between the controlled variable and set point.  A proportional controller will have the effect of reducing the rise time but never eliminate THE OFF SET  Increasing the gain or decreasing the PB will eliminate decrease off set but gives fluctuations 203
204. 204.  We can reduce the off set by increasing the gain BUT if the gain is too high, the controller become too sensitive and we will experience fluctuations and instability. GAIN AND OFF SET 204
205. 205. Selecting the Right Proportional band or PB That bit was the “hard part” to understand... But it is not so difficult to understand if we take a look at what it does in the actual application... 205
206. 206. PB too small C° (t) SV PB correct C° (t) SV PB too large C° (t) SV A Proportional Band that is too narrow causes hunting! The TC will than behave like an ON/OFF controller! A correctly sized P-Band results in an Overshoot, followed by an Undershoot and than Stabilization, with a small offset near the Set Point. With a (far) too large P-band the Setpoint temperature will never be reached! (As the heater capacity will be reduced too much). This will create a large offset from the Set Point! P-Action.The right setting of PB is very important ! 206
207. 207. Lets have a look now what will happen if we add the PI controller That explains the P-Action so far... The “Integral Action” 207
208. 208. Chapter 15 - Process Control Methods 208 The need of an Integral Action  Because of the introduction of offset in a control process, proportional control alone is often used in conjunction with Integral control.  Offset is the difference between set point and the measured value after corrective action has taken place
209. 209. Chapter 15 - Process Control Methods 209 Integral or Reset Action  Integral control is also referred to as reset control as the set point is continuously reset as long as an error is present  Integral adjustments that affect the output are labeled 3 ways:  Gain - expressed as a whole number  Reset - Expressed in repeats per minute  Integral Time - Expressed in minutes per reset
210. 210.  PI controller is a Proportional controller in which integral action is added. It has then two constants: A) PB B) Integral time An integral control will have the effect of eliminating the OFF SET , but it may make the response more oscillatory and needs longer to settle. PI OR PROPORTIONAL INTEGRAL CONTROLLER 210
211. 211.  The output of the controller is related to the error ε (t) by the relationship:  c(t) = Kc { 1+ (1/τi.s) }. ε(t); τi is the integral time.  Integral action eliminates the off set but the response becomes more oscillatory and needs longer to settle down. CHARACTERISTICS OF PI 211
212. 212.  As explained: The I-Action eliminates the Offset, but influences the whole process from the start ( fluctuations).  Making the Integral time shorter will give you more intense control with a quicker response to eliminate the offset. But a too short Integral time would result in “oscillation” (=hunting) !  Making the Integral time too long will reduce the possibility of hunting but will slow down your overall Process response. So the RIGHT setting is very important. The right Integral Time 212
213. 213. The setting of the right I-Time is very important ! 0 20 40 60 80 100 120 140 °C SP PV @ I=80s PV @ I=38s PV @ I=20s SV: 100o C The best way is to explain with a real control graph : A too long I-Time slows down the whole Process The RIGHT I-Time will enable the TC to reach the Setpoint quickly and to eliminate the Offset correctly. Making the I-Time too short creates a (large) overshoot. Also takes a long time to correct: Example of behaviour after a disturbance 213
214. 214. Lets have a look now at the PID controller Well.. That explains the “P+I Action”... The “Differential Action” 214
215. 215. Chapter 15 - Process Control Methods 215 Derivative Action  For rapid load changes, the derivative mode is typically used to prevent oscillation in a process system  The derivative mode responds to the rate of change of the error signal rather than its amplitude  Derivative mode is never used by itself, but in combination with other modes  Derivative action cannot remove offset
216. 216. PID or Proportional Integral Derivative Controller  PID controller is a PI controller in which the derivative action is added. It has then three constants:  A) PB  B) Integral time : τi  C) Derivative : τd  A derivative action will have the effect of increasing the stability of the system, reducing the overshoot, and improving the transient response. 216
217. 217.  The relationship between the output of the controler and the error ε(t) is c(t) = Kc { 1+ (1/τi.s) + τd.s }. ε(t); τi is the integral time and τd is the derivative time  All design specifications can be reached. CHARACTERISTICS OF PID 217
218. 218. A too long D-Time leads to “excessive” response! Than we will Over- and Undershoot the setpoint. (Far too long D-time will create oscillation, like ON/OFF Controller) A correctly sized D-Time results in a fast return to the Set Point. Could be followed by a small overshoot and than return rapidly to the Setpoint. With a too short D-time the Process will behave like a PI (only) controller, so will have a (too) slow response to disturbances. Note: With a setting of D-Time of 0 sec, we will have a PI Controller! The right setting of the D-Action is also very important ! o C o C o C The value of the D-Time is usually around ¼ of the I- Time. (For example: if the I-Time is 180sec., than the D- Time will be 45sec.) 218
219. 219. CONCLUSION: These 3 actions combined: * The “P-Action” * The “I-Action” * The “D-Action” = PID controller. That was a “tough part” to combine these 3 actions.... 219
220. 220. CL RESPONSE RISE TIME- First Time to reach set point OVERSHOOT- Highest value/set point value SETTLING TIME- Time to be inside 5% of set point OFF SET Kp Decrease Increase Small Change Decrease τi Decrease Increase Increase Eliminate τd Small Change Decrease Decrease Small Change EFFECTS OF PB, INTEGRAL TIME AND DERIVATIVE TIME ON THE PROCESS 220
221. 221. Chapter 15 - Process Control Methods 221 Control Mode Summary
222. 222. The following additional explanation can also help to understand the actions of the PID-controller: • The “P-Action” deals with the “present” Depending on the deviation from the Setpoint: more or less Output capacity will be given. • The “I-Action” deals with the “past” If we have been below setpoint: the Output will be increased. If we have been above setpoint: the Output will be decreased. • The “D-Action” deals with the “future” If the controlled variable is going down: the Output will be increased. If the controlled variable is going up: the Output will be decreased. This “combination”, of “Present + Past + Future”, makes it possible to control the application very well. 222
223. 223. TUNING THE CONTROLLER The task of controller tuning is usually left to an instrument technician with experience in the cause and effect of process reaction and controller adjustments. 223
224. 224. 224 Usefulness of PID Controls  Most useful when a mathematical model of the plant is not available  Many different PID tuning rules available  Sources  K. Ogata, Modern Control Engineering, Fourth Edition, Prentice Hall, 2002, Chapter 10  IEEE Control Systems Magazine, Feb. 2006, Special issue on PID control Proportional-integral-derivative (PID) control framework is a method to control uncertain systems 
225. 225. 225 Type A PID Control  Transfer function of PID controller  The three term control signal              sT sT K sE sU sG d i pPID 1 1        ssEKsE s KsEKsU dip  1
226. 226. 226 PID-Controlled System PID controller in forward path
227. 227. Chapter 15 - Process Control Methods 227 Control Mode Summary
228. 228. Chapter 15 - Process Control Methods 228 Tuning the Controller  Fine-tuning is the process to optimize the controller operation by adjusting the following settings:  Gain setting (proportional mode)  Reset rate (integral mode)  Rate (derivative mode)  Three steps are taken when tuning a systems  Study the control loop  Obtain clearance for tuning procedures  Confirm the correction operation of the system components
229. 229. 229 PID Tuning  Controller tuning---the process of selecting the controller parameters to meet given performance specifications  PID tuning rules---selecting controller parameter values based on experimental step responses of the controlled plant  The first PID tuning rules proposed by Ziegler and Nichols in 1942  Other resource: K. Ogata, Modern Control Engineering, Prentice Hall, Fourth Edition, 2002, Chapter 10
230. 230. Chapter 15 - Process Control Methods 230 Trial-and-Error Tuning  Does not use mathematical methods, instead a chart recorder is used and several bump tests are made in the proportional and integral modes  Trial-and-error tuning is very time consuming and requires considerable experience on the part of the technician or operator
231. 231. 231 Ziegler-Nichols Tuning Methods Two formal procedures for tuning control loops: Step response of plant Continuous cycling method
232. 232. 232 PID Tuning---First Method Start with obtaining the step response
233. 233. 233 The S-shaped Step Response Parameters of the S-shaped step response
234. 234. 234 The S-Shaped Step Response  The S-shaped curve may be characterized by two parameters: delay time L and time constant T  The transfer function of such a plant may be approximated by a first-order system with a transport delay     1   Ts Ke sU sC Ls
235. 235. 235 PID Tuning---First Method
236. 236. 236 Transfer Function of PID Controller Tuned Using the First Method
237. 237. 237 Ziegler-Nichols PID Tuning---Second Method Use the proportional controller to force sustained oscillations
238. 238. Chapter 15 - Process Control Methods 238 Continuous Cycling Method  The continuous cycling method analyzes the process by forcing the controlled variable to oscillate in even, continuous cycles  The time duration of one cycle is called an ultimate period. The proportional setting that causes the cycling is called the ultimate proportional value  These two values are then used in mathematical formulas to calculate the controller settings
239. 239.  For a set point change : set the proportional band to high value and reduce this value to the point where the system becomes unstable  The proportional band that required causing continuous oscillation is the ultimate value PBu.  The ultimate periodic time is Pu.  From these two values the optimum setting can be calculated. 239 ULTIMATE PROPORTIONAL BAND
240. 240. Chapter 15 - Process Control Methods 240 Continuous Cycle Calculations  Proportional only controller  Proportional Gain  Kc = Gu x 0.5 KC = proportional gain, Gu= ultimate gain  Proportional Band  PB = Pbu x 2 PB = proportional band PBu = ultimate proportional band
241. 241. The frequency of continuous oscillation is the cross over frequency ωco Pu= 2Π/ωco 241 Pu = Ultimate period of sustained cycle
242. 242. 242 Graphic method to Find Pu or Pcr Measure the period of sustained oscillation
243. 243. 243 PID Tuning
244. 244. 244 Transfer Function of PID Controller Tuned Using the Second Method
245. 245. Chapter 15 - Process Control Methods 245 Ziegler-Nichols Reaction Curve Tuning Method  This method avoids the forced oscillations that are found in the continuous cycle tuning method  Cycling should be avoided if the process is hazardous or critical  This method uses step changes and the rate at which the process reacts is recorded  The graph produces three different values used in mathematical calculations to determine the proper controller settings
246. 246. Chapter 15 - Process Control Methods 246 Reaction Curve Tuning Formulas
247. 247. CONTROL VALVES FINAL CONTROL ELEMENT 247
248. 248. Final Control Elements These are some devices the controller operates:  Pneumatic valves,  solenoid valves,  rotary valves,  motors,  switches,  relays,  variable frequency drives.
249. 249.  Control valves are valves used to control conditions such as flow, pressure, temperature, and liquid level by fully or partially opening or closing in response to signals received from controllers that compare a "set-point" to a "process control variable" whose value is provided by sensors that monitor changes in such conditions 249 Definition
250. 250.  The opening or closing of control valves is usually done automatically by electrical, hydraulic or pneumatic actuators.  Positioners are used to control the opening or closing of the actuator based on electric, or pneumatic signals.  These control signals, traditionally based on 3-15psi (Pneumatic Valves), more common now are 4-20mA ( Electrical Valves) for industry, 0-10V for HVAC systems.  The introduction of "Smart" systems, HART, Fieldbus Foundation, and Profibus being the more common protocols. 250 Types of Control Valves
251. 251. 251 Actuator & positioner of a control valve
252. 252.  Control valves are used by automated systems to adjust flow rates.  The adjustments are dependent on the controlling system's setup. They can be automated based on sensor data and presets or manually controlled by an operator at a remote workstation.  For pneumatic valves, an actuator changes the current from the controller into pressure.  The relationship of current and pressure is calculated based on the process specifications and the equipment used.  This system will be designed by control vendors or in-house engineers in most cases. 252 ELECTRICAL OR PNEUMATIC CONTROL VALVES?
253. 253.  When an issue develops in a manufacturing process, the control valve will be designed to move into an open or closed position.  The safer option is dictated based on the process and the process stream involved. For this reason, valves that require energy to be open, are called:  Air or electricity to open  Fail-close  Reverse Acting The valves that require energy to be closed, are called:  Air or electricity to close  Fail-open  Direct Acting 253 Fail-Open and Fail-Close Valves
254. 254. Control valves Reverse acting: Fail-close or Air to Open Direct Acting: Fail-Open or Air to close 254
255. 255. Fail-open valves will open and continue to allow flow when the control valve loses energy in a failure situation.  For example, a valve might fail open to avoid allowing pressure of non-harmful gas to build up.  Cooling system control valves will usually fail open, since in most cases overcooling a system will not harm the equipment. When a failure causes energy to be lost, fail-close valves will close to keep streams contained until they can be checked and fixed.  Toxic streams will almost always fail closed to prevent contamination.  Reactor heating streams usually fail closed in order to avoid feeding energy to runaway reactions. 255 Examples for Fail –open & Fail-close Valves
256. 256. 256 Flow Characteristics of the Control Valve  The relationship between control valve capacity and valve stem travel is known as the Flow Characteristic of the Control Valve.  Trim design of the valve affects how the control valve capacity changes as the valve moves through its complete travel.  Because of the variation in trim design, many valves are not linear in nature. Valve trims are instead designed, or characterized, in order to meet the large variety of control application needs.  Many control loops have inherent non linearity's, which may be possible to compensate selecting the control valve trim.
257. 257.  The most common characteristics are shown in the next figure.  The percent of flow through the valve is plotted against valve stem position. The curves shown are typical of those available from valve manufacturers.  These curves are based on constant pressure drop across the valve and are called inherent flow characteristics. 257 Flow Characteristics
258. 258. 258 Inherent Flow characteristics Curves
259. 259.  When valves are installed with pumps, piping and fittings, and other process equipment, the pressure drop across the valve will vary as the plug moves through its travel.  When the actual flow in a system is plotted against valve opening, the curve is called the Installed Flow Characteristic. 259 Installed Flow Characteristics
260. 260. In most applications, when the valve opens, and the resistance due to fluids flow decreases the pressure drop across the valve. This moves the inherent characteristic:  •A linear inherent curve will in general resemble a quick opening characteristic  •An equal percentage curve will in general resemble a linear curve 260 Installed flow Characteristics
261. 261. VALVES 261
262. 262. Valve Types Ball Valve Butterfly Valve Gate Valve Globe Valve Check Valve 262
263. 263. Ball Valve Sphere with a port in a housing, rotate to expose channel.  Applications: Flow control, pressure control, shutoff, corrosive fluids, liquids, gases, high temp.  Advantages – low pressure drop, low leakage, small, rapid opening  Disadvantages – seat can wear if used for throttling, quick open may cause hammer263
264. 264. Ball Valve 264
265. 265. Gate Valve Sliding disk, perpendicular to flow Applications: Stop valves, (not throttling), high pressure and temp, not for slurries, viscous fluids Advantages – low pressure drop when fully open, tight seal when closed, free of contamination buildup Disadvantages – vibration when partially open, slow response and large actuating force 265
266. 266. Gate Valve 266
267. 267. Butterfly Valve rotating disk on a shaft, in a housing Low pressure, large diameter lines where leakage is unimportant Advantages – low pressure drop, small and light weight Disadvantages – high leakage, high actuation forces so limited to low pressures 267
268. 268. Butterfly Valve 268
269. 269. Check Valves allows flow in only one direction Swing valve similar to butterfly except hinged along one edge rather than rotate about the diameter, used primarily for check valves. 269
270. 270. Check valve 270
271. 271. Rupture Disk (not a valve – ruptures at a set pressure) 271
272. 272. PROCESS CONTROL SYSTEMS 272
273. 273. Servo & Regulator Problems  Two major problems could happen in any plant:  1) REGULATOR: The most common situation is when a disturbance appears in the plant. The controller will make correction to bring the controlled variable to set point.  2) SERVO: Very often, operators in the control room will have to change the set point of some controlled variable. How the controller will bring the controlled variable to the new set point.  Both situations will be investigated in the labs 5 & 6. 273
274. 274. LABS #5 & 6 Controlling pressure in a tank using digital P, PI and PID digital controllers  Tuning of a P, PI and PID controller to maintain the pressure in a water tank constant during servo or regulator situations:  Lab #5: The main objective of the lab is to analyze and compare the graphs of the P,PI and PID controllers.  Lab #6: Study constants of controllers to avoid instability in the plant. 274
275. 275. L.O #3 Explain feedback control and the dynamic behavior of this controller. 275
276. 276. 276 Driving your car Sense Vehicle Speed Compute Control “Law” Actuate Gas Pedal  Goals  Stability: system maintains desired operating point (hold steady speed)  Performance: system responds rapidly to changes (accelerate to 65 mph)  Robustness: system tolerates perturbations in dynamics (mass, drag, etc)
277. 277. Basic Feed back Control House is too cold Furnace Thermostat Controller recognized the house is too cold sends signal to the furnace to turn on and heat the house furnace turns on heats the housenatural gas house temperature measured is temperature below setpoint? Set-point = 200C Controlled variable: temperature (desired output) Input variable: temperature (measured by thermometer in thermostat) Set-point: user-defined desired setting (temperature) Manipulated variable: natural gas valve to furnace (subject to control) 277
278. 278.  Output of the system y(t) is fed back to the set-pint r(t) through measurement of a sensor  Controller senses the difference between the set point and the output and determines the error ε(t)  Controller changes the manipulated variable u to Process to eliminate the error. Feedback Control is a Single Loop 278
279. 279. Example #2 for Feedback Control Examples:  Room temperature control  Automatic cruise control  Steering an automobile  Supply and demand of chemical engineers Controller Transmitter Set point stream Temp sensor Heat loss condensate
280. 280. Feedback Control-block diagram Terminology:  Set point  Manipulated variable (MV)  Controlled variable (CV)  Disturbance or load (DV)  Process  controller Σ Controller process Sensor + transmitter + -Set point Measured value error Manipulated variable Controlled variable disturbance
281. 281. 281 THE ELEMENTS OF A FFEDBACK PROCESS CONTROL SYSTEM  LEVEL6:
282. 282. 282 A modern Feedback Control System
283. 283.  Feedback control is not predictive: Controlled variable has to be affected before controller takes action  Requires management or operators to change set points to optimize system: - Changes can bring instability into system - Optimization of many input and output variables almost impossible Limitations of Feedback Control 283
284. 284. Apply the principles of feed-forward and show how this type of control can be applied. L.O #4 284
285. 285. 285 FEED-FORWARD CONTROL  The feedback control can never achieve perfect control of a chemical process  Why?  Because the feedback control reacts only when it has detected a deviation of the CONTROLLED VARIABLE from the desired set point.  However, the feed-forward control measures the disturbance directly and takes control action to eliminate its impact on the CONTROLLED VARIABLE  Therefore  Feed-forward controllers have the theoretical potential to achieve perfect control
286. 286. Feedforward Control Window is open Furnace Feedforward Recognize window is open and house will get cold in the future: Someone reacts and changes controller setpoint to turn on the furnace preemptively. furnace turns on heats the housenatural gas house temperature is currently OK turn on furnace Decrease setpoint to turn furnace on Pre-emptive move to prevent house from getting cold 286
287. 287.  Feed-forward control avoids slowness of feedback control  Disturbances are measured and accounted for before they have time to affect the system  In the house example, a feed-forward system measured the fact that the window is opened  As a result, automatically turn on the heater before the house can get too cold  Difficulty with feed-forward control: effects of disturbances must be perfectly predicted  There must not be any surprise effects of disturbances Feed-forward is a single loop 287
288. 288. 288 THE FEEDBACK AND FEED FORWARD CONTROL Both control involve a single loop with : One measurement  One manipulated variable. However:  In a feedback control, we measure the controlled variable  In a feed-forward control, we measure the disturbance
289. 289. L.O #5 Describe how the principles of cascade control, ratio, the selective control and split - range control are used in processes control. 289
290. 290. MULTI LOOPS PROCESS CONTROL SYSTEM 290
291. 291. 291 CONTROL SYSTEMS WITH MULTIPLE LOOPS  Other simples configurations which may use: * More than one measurable variable and one manipulated variable * One measurable variable and more than one manipulated variable
292. 292. CASCADE CONTROL In this configuration, we have :  More than one measurement  One manipulated variable 292
293. 293. 293 CASCADE CONTROL LOOPS  Cascade control is two control loops using two different measurements :  1) One measurement for the controlled variable  2) One measurement for the disturbance  3) One manipulated variable  The loop that measures the controlled variable is the dominant or primary or master control loop  The loop that measures the disturbance is the secondary or slave loop
294. 294. CASCADE FOR HEAT EXCHANGER 294
295. 295. Cascade for jacketed CSTR TRC FC Tc T, Ca W Set Point Wc 2A  B
296. 296. Ratio Control is a special type of feed- forward control  Two disturbances are measured and held in a constant ratio  It is mostly used to control the ratio of flow-rates of two streams RATIO CONTROL : 296
297. 297. EX: RATIO CONTROLLER IN A BURNER 297
298. 298. RATIO CONTROL LOOP 298
299. 299. We measure both flow-rates and take their ratio  The ratio is compared to the desired ratio  The error is sent to the ratio controller Strategy of ratio control: 299
300. 300. 300 SELECTIVE CONTROL  In this kind of control, we  One manipulated variable  Several controlled output  Since with one manipulated variable, we can control only one output, The selective control systems transfer control action from one controlled output to another according to need  we will discuss * Override Control * Auctioneering control
301. 301. 301 SAFETY OF EQUIPMENTS: OVERRIDE CONTROL  During the normal operation of a plant or during its startup or shutdown , it is possible that a dangerous situation may arise and may lead to destruction of equipment.  In such cases, it is necessary to change from production control to safety control in order to prevent a process variable from exceeding an allowable upper or lower limit  This can be achieved by the use of switches: The switch is used to select between the production controller and the safety controller.  The HSS ( high selector switch) is used whenever a variable should not exceed an upper limit  The LSS ( low selector switch) is used whenever a variable should not exceed a lower limit.
302. 302. EXAMPLE OF OVERRIDE The steam header must be maintained above a minimum pressure (PC FOR SAFETY). Steam from the header is used to heat water in a heat exchanger. The temperature of the hot water is controlled by TIC-101 (PRODUCTION CONTROLLER) SAFETY FIRST: t is more important that the header pressure be above its minimum than that the water temperature be at its set-point. 302
303. 303. 303
304. 304. 304 SAFETY OF EQUIPMENTS: AUCTIONEERING CONTROL In this control system, among several similar measurements, the one with the highest value will feed the controller  This is a selective control between several measured variables.
305. 305. EX: TUBULAR REACTOR 305
306. 306.  The split range control has  One measurement only ( Controlled variable)  More than one manipulated variable ( control valve)  If the valves are pneumatic: The instrumentation pressure range ( 3-15 psia) is divided.  If the valves are electrical: The instrumentation current ( 4-20 mA) is divided.  Ex: If we have two pneumatic valves:  Valve #1 will operate between 3- 9 psia and Valve #2 will operate between 9 - 15 psia. SPLIT RANGE CONTROL 306
307. 307. Split Range Flow Control  In certain applications, a single flow control loop cannot provide accurate flow metering over the full range of operation.  Split range flow control uses two flow controllers (one with a small control valve and one with a large control valve) in parallel.  At low flow rates, the large valve is closed and the small valve provides accurate flow control.  At large flow rates, both valve are open. 307
308. 308. EX: Split Range Temperature Control TT Cooling Water Steam Split-Range Temperature Controller TT TC RSP 308
309. 309. L.O #6: DIGITAL CONTROL SYSTEM THE CONTROLLER IS A SOFTWARE IN COMPUTER 309
310. 310. DIGITAL CONTROLLER  Digital control is a branch of control theory that uses digital computers to act as system controllers.  Depending on the requirements, a digital control system can take the form of a microcontroller to an ASIC to a standard desktop computer.  Since a digital computer is a discrete system, the Laplace 310
311. 311. PLC: Programmable Logic Controller CPU System User Ladder Diagram Working memory registers Input Flag Output Input Module Output Module 311
312. 312. DIGITAL CONTROLLER Typically, a digital controller requires:  A/D conversion to convert analog inputs to machine readable (digital) format  D/A conversion to convert digital outputs to a form that can be input to a plant (analog)  A program that relates the outputs to the inputs 312
313. 313. 313 Block diagram of a digital control system control: difference equations D/A and hold sensor 1 r(t) u(kT) u(t)e(kT) + - r(kT) plant G(s) y(t) clock A/D T T y(kT) digital controller voltage → bit bit → voltage
314. 314. An Large Size PLC  The main module measures 19” x 20” x 14.5”.  have upto 10,000 I/O points  supports all functions  expansion slots to accommodate PC and other communication devices. Allen-Bradley PLC-3 314
315. 315. A Small Size PLC  Measures 4.72”x 3.15” x 1.57”.  32 I/O points  Standard RS 232 serial communication port Allen-Bradley MicroLogix 1000 315
316. 316. PLC ARCHITECTURE Programmable controllers replace most of the relay panel wiring by software programming. Processor I/O Modules Memory Power Supply Program Loader Printer Cassette Loader EPROM Loader Switches Machines Peripherals External Devices PC A typical PLC316
317. 317. PLC COMPONENTS 1. Processor Microprocessor based, may allow arithmetic operations, logic operators, block memory moves, computer interface, local area network, functions, etc. 2. Memory Measured in words. ROM (Read Only Memory), RAM (Random Access Memory), PROM (Programmable Read Only Memory), EEPROM (Electric Erasable Programmable ROM), EPROM (Erasable Programmable Read Only Memory), EAPROM (Electronically Alterable Programmable Read Only Memory), and Bubble Memory. 317
318. 318. PLC COMPONENTS3. I/O Modular plug-in periphery AC voltage input and output, DC voltage input and output, Low level analog input, High level analog input and output, Special purpose modules, e.g., high speed timers, Stepping motor controllers, etc. PID, Motion 4. Power supply AC power 5. Peripheral hand-held programmer (HHP) CRT programmer operator console printer simulator EPROM loader graphics processor network communication interface modular PC 318
319. 319. Distributed Control Systems 319
320. 320. Distributed Control Systems  Collection of hardware and instrumentation necessary for implementing control systems  Provide the infrastructure (platform) for implementing advanced control algorithms
321. 321. History of Control Hardware  Pneumatic Implementation:  Transmission: the signals transmitted pneumatically are slow responding and susceptible to interference.  Calculation: Mechanical computation devices must be relatively simple and tend to wear out quickly.
322. 322. History (cont.)  Electron analog implementation:  Transmission: analog signals are susceptible to noise, and signal quality degrades over long transmission line.  Calculation: the type of computations possible with electronic analog devices is still limited.
323. 323. History (cont.)  Digital Implementation:  Transmission: Digital signals are far less sensitive to noise.  Calculation: The computational devices are digital computers.
324. 324. Advantages of Digital System  Digital computers are more flexible because they are programmable and no limitation to the complexity of the computations it can carry out.  Digital systems are more precise.  Digital system cost less to install and maintain  Digital data in electronic files can be printed out, displayed on color terminals, stored in highly compressed form.
325. 325. Computer Control Networks 1. PC Control:  Good for small processes such as laboratory prototype or pilot plants, where the number of control loops is relatively small PROCESS Final control element Data acquisition Main Computer Display
326. 326. Computer Control Networks 2. Programmable Logic Controllers:  specialized for non-continuous systems such as batch processes.  It can be used when interlocks are required; e.g., a flow control loop cannot be actuated unless a pump has been turned on.  During startup or shutdown of continuous processes.
327. 327. DCS: Computer Control Networks Operator Control Panel Main Control Computer Operator Control Panel Archival Data Storage Supervisory (host) Computer PROCESS Local Computer Local Computer Local Computer Local Display Local Display Data highway To other Processes To other Processes Local data acquisition and control computers 3. DCS •Most comprehensive
328. 328. DCS Elements-1  Local Control Unit: This unit can handle 8 to 16 individual PID loops.  Data Acquisition Unit: Digital (discrete) and analog I/O can be handle.  Batch Sequencing Unit: This unit controls a timing counters, arbitrary function generators, and internal logic.  Local Display: This device provides analog display stations, and video display for readout.  Bulk Memory Unit: This unit is used to store and recall process data.
329. 329. DCS Elements-2  General Purpose Computer : This unit is programmed by a customer or third party to perform optimization, advance control, expert system, etc  Central Operator Display: This unit typically contain several consoles for operator communication with the system, and multiple video color graphics display units  Data Highway : A serial digital data transmission link connecting all other components in the system. It allow for redundant data highway to reduce the risk of data loss  Local area Network (LAN)
330. 330. Advantages of DCS  Access a large amount of current information from the data highway.  Monitoring trends of past process conditions.  Readily install new on-line measurements together with local computers.  Alternate quickly among standard control strategies and readjust controller parameters in software.  A sight full engineer can use the flexibility of the framework to implement his latest controller design ideas on the host computer.
331. 331. Modes of Computer control signals from digital computer Local PID controller Supervisory Control mode Direct digital Control mode valve setting from computer Flow measurement to computer 1.Manual 2.Automatic • PID with local set point 3.Supervisory • PID with remote set point (supervisory) 4.Advanced
332. 332. Additional Advantage Digital DCS systems are more flexible. Control algorithms can be changed and control configuration can be modified without having rewiring the system.
333. 333. Categories of process information ExampleType Relay, Switch Solenoid valve Motor drive 1. Digital Alphanumerical displays2. Generalized digital Turbine flow meter Stepping motor 3. Pulse Thermocouple or strain gauge (mill volt) Process instrumentation (4-20 am) Other sensors (0-5 Volt) 4. Analog
334. 334. A/D and D/A converters or transducers are the Interface between digital computer and analog instruments (A/D) Transducers convert analog signals to digital signals. (Sensor Computer) (D/A) Transducers convert digital signals to analog signals. (Computer Valve)
335. 335. Data resolution due to digitization  Accuracy depends on resolution.  Resolution depends on number of bits: Resolution = signal range × 1/(2m -1) m = number of bits used by the digitizer (A/D) to represent the analog data
336. 336. Data Resolution  Signal = 0 - 1 Volt, 3 bit digitizer: Analog range covered Analog equivalent Digital Equivalent Binary representation 0 to 1/14 1/14 to 3/14 3/14 to 5/14 5/14 to 7/14 7/14 to 9/14 9/14 to 11/14 11/14 to 13/14 13/14 to 14/14 0 1/7 2/7 3/7 4/7 5/7 6/7 1 0 1 2 3 4 5 6 7 0 0 0 0 0 1 0 1 0 0 1 1 1 0 0 1 0 1 1 1 0 1 1 1
337. 337. Data Resolution 0 1/7 2/7 3/7 4/7 5/7 6/7 1 0 1 2 3 4 5 6 7 Analog data Digitaldata
338. 338. Utilization of DCS  DCS vendor job:  installation  Control Engineer Job:  Configuration  Built-in PID control:  How to Tune the PID control?
339. 339. Utilization of DCS  Implementation of advanced control:  Developed software for control algorithms, DMC, Aspen, etc.  Control-oriented programming language supplied by the DCS vendors.  Self-developed programs using high-level programming languages (Fortran, C++)
341. 341. DCS Vendors  Honeywell  Fisher-Rosemont  Baily  Foxboro  Yokogawa  Siemen
342. 342. PI&D AND PFD 342
343. 343.  Process flow diagrams (PFDs) are used in chemical and process engineering. These diagrams show the flow of chemicals and the equipment involved in the process.  Generally, a Process Flow Diagram shows only the major equipment and doesn't show details. PFDs are used for visitor information and new employee training. DEFINITION OF PFD 343
344. 344.  A Process and Instrument Drawing (P&ID) includes more details than a PFD. It includes major and minor flows, control loops and instrumentation.  P&ID is sometimes referred to as a Piping and Instrumentation Drawing. These diagrams are also called flow-sheets.  P&IDs are used by process technicians and instrument and electrical, mechanical, safety, and engineering personnel. DEFINITION OF PI&D 344
345. 345. PFD & PI&D In both diagrams arrows show the flow of material and symbols show tanks, valves, and other equipment. The symbols used vary somewhat from organization to organization. So you may see several different symbols that all represent a motor. 345
346. 346. EXAMPLE OF PFD 346
347. 347. EQUIVALENT PI&D 347
348. 348. P& ID SYMBOLS ISA Symbols and Loop Diagrams 348
349. 349.  Piping and Instrumentation Diagrams or simply P&IDs are the “schematics” used in the field of instrumentation and control (Automation)  The P&ID is used to by field techs, engineers, and operators to better understand the process and how the instrumentation is inter connected. INTRODUCTION 349
350. 350.  Most industries have standardized the symbols according to the ISA Standard S5.1 Instrumentation Symbol Specification. Piping & Instrumentation Drawing (original) Process & Instrumentation Diagram (also used) Process Flow Diagram – PFD (simplified version of the P&ID) ISA Standard S5.1 Instrumentation Symbol Specification 350
351. 351. Building the P&ID using examples like pressure or temperature control. L.O #1 351
352. 352. 352
353. 353. 353
354. 354. From the typical example, define Tag Numbers and Tag Descriptors. L.O #2 354
355. 355. 355
356. 356. 356
357. 357. Learn the ISA S5.1 Identification Letters like (TI, PC, LR, TRC, …) L.O #3 357
358. 358. 358
359. 359. Class work: identify the following 359
360. 360. Determine the instrumentation location L.O #4 360
361. 361. 361
362. 362. Learn about Shared Displays/Shared Control and draw a summary of instrument type & location L.O #5 362
363. 363. 363
364. 364. 364
365. 365. PIPING & CONNECTIONS SYMBOLS L.O #6 : Identify Piping, Connection and valves Symbols 365
366. 366. 366
367. 367. VALVE SYMBOLS 367
368. 368. 368
369. 369. Different industrial examples will be studied. L.O #7 369
370. 370. 370
371. 371. CLASS WORK 371
372. 372. SOLUTION 372
373. 373. PFD: PROCESS FLOW DIAGRAM 373
374. 374. 374
375. 375. PFD Drawing Symbols 375
376. 376. Other Symbols for PFD Table 1.2 : Conventions Used for Identifying Process Equipment Process Equipment General Format XX-YZZ A/B XX are the identification letters for the equipment classification C - Compressor or Turbine E - Heat Exchanger H - Fired Heater P - Pump R - Reactor T - Tower TK - Storage Tank V - Vessel Y designates an area within the plant ZZ are the number designation for each item in an equipment class A/B identifies parallel units or backup units not shown on a PFD Supplemental Information Additional description of equipment given on top of PFD 376
377. 377. Equipment Numbering  XX-YZZ A/B/…  XX represents a 1- or 2-letter designation for the equipment (P = pump)  Y is the 1 or 2 digit unit number (1-99)  ZZ designates the equipment number for the unit (1-99)  A/B/… represents the presence of spare equipment377
378. 378. Examples T-905 is the 5th tower in unit nine hundred P-301 A/B is the 1st Pump in unit three hundred plus a spare 378
379. 379. Equipment Information  Equipment are identified by number and a label (name) positioned above the equipment on the PFD  Basic data such as size and key data are included in a separate table (Equipment Summary Table). 379
380. 380. Streams identification 380
381. 381. Process and Utility Streams 381
382. 382. Number of streams and information Stream Number 1 2 3 4 5 6 7 8 9 10 Temperature (°C) 25 59 25 225 41 600 41 38 654 90 Pressure (bar) 1.90 25.8 25.5 25.2 25.5 25.0 25.5 23.9 24.0 2.6 Vapor Fraction 0.0 0.0 1.00 1.0 1.0 1.0 1.0 1.0 1.0 0.0 Mass Flow (tonne/h) 10.0 13.3 0.82 20.5 6.41 20.5 0.36 9.2 20.9 11.6 Mole Flow (kmol/h) 108.7 144.2 301.0 1204.4 758.8 1204.4 42.6 1100.8 1247.0 142.2 Component Mole Flow (kmol/h) Hydrogen 0.0 0.0 286.0 735.4 449.4 735.4 25.2 651.9 652.6 0.02 Methane 0.0 0.0 15.0 317.3 302.2 317.3 16.95 438.3 442.3 0.88 Benzene 0.0 1.0 0.0 7.6 6.6 7.6 0.37 9.55 116.0 106.3 Toluene 108.7 143.2 0.0 144.0 0.7 144.0 0.04 1.05 36.0 35.0 A Portion of Table 1.5 382
383. 383. Class work: identify all the information 383
384. 384. CASE STUDY FOR THE COURSE 384