1. © Copyright 2016Operator Generic Fundamentals Operator Generic Fundamentals Components - Controllers and Positioners

2. © Copyright 2016Operator Generic Fundamentals Terminal Learning Objective At the completion of this training session, the trainee will demonstrate mastery of this topic by passing a written exam with a grade of ≥ 80% on the following area: 1.Describe the arrangement and operation of typical controllers and positioners within process control systems. 2 TLO’s

3. © Copyright 2016Operator Generic Fundamentals TLO 1 1.1Describe the characteristics of a control system, including process controllers and position controllers. 1.2Describe the operation of bistable alarm and control circuits. 1.3Define the following process control related terms: proportional band, gain, closed loop system, offset, feedback, deviation, deadband, direct acting, and reverse acting. 1.4Describe the operation of an automatic controller, including proportional control system, proportional-integral (PI) control, proportional-derivative (PD) control, and proportional-integral- derivative (PID) control. 1.5Describe the operation of a controller in the automatic and manual modes. 3 TLO 1 – Describe the arrangement and operation of typical controllers and positioners within process control systems. TLO 1

4. © Copyright 2016Operator Generic Fundamentals Enabling Learning Objectives for TLO 1 1.6Describe the operation of temperature controllers and pressure controllers. 1.7Describe the operation of mechanical and electronic speed-control devices. 1.8Interpret logic diagrams and determine controller outputs. 1.9Describe the design and operation of the following types of valve actuators: pneumatic, hydraulic, solenoid, and electric motor. 4 ELOs

5. © Copyright 2016Operator Generic Fundamentals Characteristics of Controllers and Positioners Control Systems Designed to maintain a system –Temperature –Pressure, etc. Use several control elements working together Capability for remote and local operation Actuator provides precise positioning 5 ELO 1.1 – Describe the characteristics of a control system including process controllers and position controllers. ELO 1.1

6. © Copyright 2016Operator Generic Fundamentals Process Controllers Sensor Detect actual value of controlled parameter –Temperature –Pressure –Flow Measured parameter must be converted into usable signal for control system Transducer/Transmitter Converts sensor signal into pneumatic or electrical signal Transmits pneumatic or electrical signal to controller 6 ELO 1.1

7. © Copyright 2016Operator Generic Fundamentals Process Controllers Controller Compares value of measured parameter to desired value or setpoint Develops error signal Sends error signal to final control element Final Control Element Takes controller output signal and manipulates component in response to error signal –Open and/or close a valve –Turn ON or OFF alarm –Throttle open or closed air-operated valve –Turn ON or OFF heaters –Etc. 7 ELO 1.1

8. © Copyright 2016Operator Generic Fundamentals Operation of a Simple Controller 8 ELO 1.1 Figure: Process Control System Operation

9. © Copyright 2016Operator Generic Fundamentals Bistable Operation Bistables are two position switches –They are either on or off, depending on the input variable When input reaches setpoint, they are “on” When input returns to below setpoint, they are “off” May have a reset band above or below the “on” setpoint –prevent excessive cycling 9 ELO 1.2 – Describe the operation of bistable alarm and control circuits. ELO 1.2

10. © Copyright 2016Operator Generic Fundamentals Two-Position Controller Simplest type of controller Device that has two operating conditions: –Completely ON –Completely OFF Uses Bistable symbol to show how parameter controlled –Turns ON on an increasing signal –Turns ON on a decreasing signal –Turns OFF at same value as ON value –Turns OFF at different value than ON value 10 ELO 1.2

11. © Copyright 2016Operator Generic Fundamentals Two-Position Controller Example 1 11 ELO 1.2 Figure: Input/Output Relationship for a Two-Position Controller

12. © Copyright 2016Operator Generic Fundamentals Two-Position Controller Example 2 12 ELO 1.2 Figure: Two-Position Control System

13. © Copyright 2016Operator Generic Fundamentals Bistable Symbols Which of the four bistable symbols is used for the previous slide example?(opens valve on low level, closes valve on high level) 13 ELO 1.2 Figure: Bistable Symbols

14. © Copyright 2016Operator Generic Fundamentals Bistable Example - Explained Consider a set of axes for each bistable being examined –ON and OFF – for bistable setting –Low and High - for parameter value that is being controlled This symbol used since: –Valve opens on low level –Valve closes on different high level Another example of this: –PZR Backup heaters o Energize on decreasing RCS pressure o Deenergize on different higher RCS pressure 14 Parameter Value Bistable Setting Low High OFF ON Setpoint Reset point Level decreases to Setpoint Bistable turns ON to open makeup valve Level increases to Reset point Bistable turns OFF to close makeup valve ELO 1.2

15. © Copyright 2016Operator Generic Fundamentals Bistable Operation Knowledge Check Which of the following bistables energize on an increasing signal and deenergize on a different signal decreasing? A. B. C. D. Correct answer is C. 15 ELO 1.2

16. © Copyright 2016Operator Generic Fundamentals Bistable Operation Knowledge Check – NRC Bank Refer to the drawing of four bistable symbols (see figure below). A temperature controller uses a bistable that turns on to actuate a warning light when the controlled temperature reaches a high setpoint. The bistable turns off to extinguish the warning light when the temperature decreases to 5°F below the high setpoint. Which one of the following bistable symbols indicates the characteristics of the bistable? A. 1. B. 2. C. 3. D. 4. 16 Correct answer is D. ELO 1.2

17. © Copyright 2016Operator Generic Fundamentals Process Control Terms Proportional Band (PB) Change in value of controlled variable that results in full travel of the final control element –Input/Output Gain Ratio of amount of change in final control element to amount of change in the controlled variable –Output/Input Factor by which magnitude of error signal will be increased Gain is reciprocal to proportional band 17 ELO 1.3 – Define the following process control related terms: proportional band, gain, closed loop system, offset, feedback, deviation, deadband, direct acting, and reverse acting. ELO 1.3

18. © Copyright 2016Operator Generic Fundamentals Process Control Terms Closed-Loop System System in which the parameter being controlled feeds into the controller –Temperature out of letdown heat exchanger, for example –Most controller loops are “closed-loop” types Offset Deviation that remains after a process has stabilized Difference between setpoint and steady-state value of the controlled parameter 18 ELO 1.3

19. © Copyright 2016Operator Generic Fundamentals Process Control Terms Feedback Information on controlled variable sent back to the controller for finer control –For example, Turbine governor control valve position might feed back to EHC Deviation Difference between setpoint and the actual value Also called “error” Deadband Range of values around setpoint of measured variable where no action occurs –Recall the tank level bistable example Prevents oscillation or hunting in proportional control systems 19 ELO 1.3

20. © Copyright 2016Operator Generic Fundamentals Process Control Terms Direct Acting vs Reverse Acting Controller Relationship of controller input to controller output Must also consider –Normal operation of system and fail position of valve Direct Acting Controller input increases, controller output increases –Input goes from 4 to 20 milliamps –Output to air-operated valve goes from 3 to 15 psi Reverse Acting Controller input increases, controller output decreases –Input goes from 4 to 20 milliamps –Output to air-operated valve goes from 15 to 3 psi 20 ELO 1.3

21. © Copyright 2016Operator Generic Fundamentals Process Control Terms - Application Consider the following controller face images to apply these definitions: Image 1Image 2 21 ELO 1.3 Output 0 %100 %50 % Input 70°F 120 ° F 95 o F ControllerFace Output 0 %100 %50 % 120 ° F70 ° F 95 o F ControllerFace What is the GAIN?2 Gain =Output/Input 100%/(120 ° F-70 ° F) 100/50 = 2 Direct or Reverse Acting? Direct As temperature increases from 70-120 Output goes from 0-100% What is the GAIN?Still 2 Gain =Output/Input 100%/(120 ° F-70 ° F) 100/50 = 2 Direct or Reverse Acting? Reverse As temperature decreases from 120-70 Output goes from 0-100%

22. © Copyright 2016Operator Generic Fundamentals Process Control Terms Knowledge Check – NRC Bank The difference between the setpoint in an automatic controller and the steady-state value of the controlled parameter is called ________. A.offset B.gain C.deadband D.feedback Correct answer is A. 22 ELO 1.3

23. © Copyright 2016Operator Generic Fundamentals Process Control Terms Knowledge Check – NRC Bank An automatic flow controller is being used to position a valve in a cooling water system. A signal that is proportional to valve position is received by the controller. This signal is referred to as... A.gain B.bias C.feedback D.error Correct answer is C. 23 ELO 1.3

24. © Copyright 2016Operator Generic Fundamentals Operation of an Automatic Controller Mode of Control – manner in which control system makes corrections relative to deviation Mode of control depends on characteristics of process being controlled –Some processes can be operated over wide band –Others must be maintained very close to setpoint –Some processes change slowly, while others change almost immediately 24 ELO 1.4 – Describe the operation of an automatic controller, including proportional control, proportional-integral (PI) control, proportional- derivative (PD) control, and proportional-integral-derivative control (PID). ELO 1.4

25. © Copyright 2016Operator Generic Fundamentals Modes of Automatic Control Four modes of automatic control commonly used: –Proportional –Proportional-integral (or proportional-plus-reset) [PI] –Proportional-derivative (or proportional-plus-rate) [PD] –Proportional-integral-derivative (or proportional-plus-reset-plus- rate) [PID] 25 ELO 1.4

26. © Copyright 2016Operator Generic Fundamentals Proportional Controller Proportional Mode Referred to as throttling control Controller only matches supply to demand –Parameter stabilizes at new “Control Point” –Does not bring parameter back to setpoint Proportional Control Output Proportional controller provides linear stepless output that –positions valve at intermediate positions, –as well as "full open" or "full shut” 26 ELO 1.4

27. © Copyright 2016Operator Generic Fundamentals Proportional Level Controller Example Flow of supply water into tank controlled to maintain tank level within narrow band Components –Fulcrum and lever assembly used as proportional controller –Float chamber is level measuring element –4 inch stroke valve is final control element 27 Figure: Proportional System Controller ELO 1.4

28. © Copyright 2016Operator Generic Fundamentals Proportional Level Controller Example 28 ELO 1.4

29. © Copyright 2016Operator Generic Fundamentals Proportional Level Controller Example If fulcrum setting changed: –2 inches, or 50% of input, causes full 4 inch stroke, or 100% of output o Proportional band would become 50% o Gain is 2 –Recall, the “smaller” the band, the “larger” the gain 29 ELO 1.4 Figure: Proportional System Controller

30. © Copyright 2016Operator Generic Fundamentals Integral (Reset) Control Integral Control - controller in which magnitude of output is dependent on magnitude of input –Smaller amplitude input causes slower magnitude of output –Approximates mathematical function of integration –Also known as reset control Major advantage –controlled variable returns to setpoint following a disturbance Two disadvantages are: –Slow response to error signal –Initially allows a large deviation, can lead to system instability and cyclic operation 30 ELO 1.4

31. © Copyright 2016Operator Generic Fundamentals Definition of Integral Control Device that performs mathematical function of integration is called integrator Mathematical result of integration is called integral Not a function of “how far from setpoint”, but “how long from setpoint” 31 ELO 1.4

32. © Copyright 2016Operator Generic Fundamentals Integral Output Example Integrator acts to transform step change of input to 10% into gradually changing signal Constant of integrator causes output to change 0.2% per second for each 1% of input Input amplitude is repeated in output every 5 seconds As long as input remains constant at 10%, output will continue to ramp up every 5 seconds until integrator saturates 32 Figure: Integral Controller Output for a Fixed Input ELO 1.4

33. © Copyright 2016Operator Generic Fundamentals Integral Flow Control System Example 33 ELO 1.4

34. © Copyright 2016Operator Generic Fundamentals Integral Flow Control System Example – Controller Operation Integral controller maintains constant flow rate System setpoint maintains flow demand of 50 gpm –Corresponds to control valve opening of 50% When actual flow is 50 gpm, zero error signal sent to input of integral controller Controller output is initially set for 50%, or 9 psi, to position 6- in control valve to position of 3- in open 34 ELO 1.4 Figure: Integral Flow-Rate Controller

35. © Copyright 2016Operator Generic Fundamentals Integral Flow Control System Example – Controller Operation Measured variable decreases from 50 gpm to 45 gpm ⇒ positive error of 10% applied to input of controller –Controller has a constant of 0.1 seconds -1; controller output magnitude is 1% per second –Controller output increases from initial point of 50% at 1% per second –Causes control valve to open further at rate of 1% per second ⇒ increasing flow 35 ELO 1.4 Figure: Integral Controller Response

36. © Copyright 2016Operator Generic Fundamentals Integral Flow Control System Example – Controller Operation Controller acts to return process to setpoint –Repositions control valve –Measured variable moves closer to setpoint –New error signal is produced –Cycle repeats until no error exists 36 ELO 1.4 Figure: Integral Controller Response

37. © Copyright 2016Operator Generic Fundamentals Integral Flow Control System Example – Controller Operation Controller responds to amplitude and duration of error signal –Can cause final control element to reach "fully open/shut" position before error reaches zero –Final control element could remain at extreme position –Error must be reduced by other means 37 ELO 1.4 Figure: Integral Controller Response

38. © Copyright 2016Operator Generic Fundamentals Proportional Integral Control Combination of proportional and integral modes of control Combining two modes results in gaining advantages and compensating for disadvantages of two individual modes 38 ELO 1.4

39. © Copyright 2016Operator Generic Fundamentals Proportional-Integral Control Advantage of proportional control –Output produced as soon as an error signal exists –Quickly repositions final control element –Compensates for disadvantage of integral mode, that an integral controller does not immediately respond to new error signal 39 ELO 1.4 Figure: Response of PI Control

40. © Copyright 2016Operator Generic Fundamentals Proportional-Integral Control Advantage of integral control mode –Output repositions final control element until error reaches zero –Eliminates residual offset –Compensates for disadvantage of proportional control that causes a residual offset error to exist for most system conditions 40 ELO 1.4 Figure: Response of PI Control

41. © Copyright 2016Operator Generic Fundamentals Proportional-Integral Control Example Heat exchanger system - equipped with proportional-integral controller 41 ELO 1.4 Figure: Heat Exchanger Process with PI Control

42. © Copyright 2016Operator Generic Fundamentals Proportional-Integral Control Example Response curves illustrate –Heat demand (cold water flow) –Measured variable – hot water outlet temperature Process undergoes demand disturbance –Reduces flow of hot water out of heat exchanger –Temperature and flow rate of steam into heat exchanger remain constant –Temperature of hot water out begins to rise 42 ELO 1.4 Figure: Effects of Disturbance on a PI Controller

43. © Copyright 2016Operator Generic Fundamentals Proportional-Integral Control Example Proportional action response –Control valve returns hot water outlet temp to new control point –Residual error remains (offset) Adding integral response –Produces larger output for given error signal –Greater adjustment of control valve –Quickly returns to setpoint –Eliminates offset error 43 ELO 1.4 Figure: Effects of Disturbance on a PI Controller

44. © Copyright 2016Operator Generic Fundamentals Reset Windup PI controllers that receive a large error signal can undergo reset windup –Large sustained error signal causes controller to drive to its limit to try and restore system control –System experiences large oscillations as controller restores controlled variable to setpoint –Can be caused by large demand deviation or when initially starting up system PI control mode not well-suited for processes that are frequently shut down and started up due to this effect 44 ELO 1.4

45. © Copyright 2016Operator Generic Fundamentals Proportional-Derivative Control Systems Control mode in which derivative section is added to proportional controller Derivative section responds to rate of change of error signal, not amplitude of error –Causes controller output to be initially larger in direct relation with error signal rate of change o Higher error signal rate of change ⇒ sooner final control element is positioned to desired value Added derivative action reduces initial overshoot of measured variable 45 ELO 1.4

46. © Copyright 2016Operator Generic Fundamentals Definition of Derivative Control Differentiator – device that produces derivative signal Provides output directly related to: –Rate of change of input –Derivative constant Derivative constant defines differential controller output –Expressed in units of seconds 46 ELO 1.4 Figure: Derivative Output for a Constant Rate of Change

47. © Copyright 2016Operator Generic Fundamentals Definition of Derivative Control Differentiator transforms changing signal to constant magnitude signal Derivative control cannot be used alone as control mode –Steady-state input produces zero output in differentiator Derivative action typically combined with proportional action such that proportional section output serves as derivative section input 47 ELO 1.4 Figure: Derivative-Control Output

48. © Copyright 2016Operator Generic Fundamentals Advantage of Derivative Control Proportional action provides an output proportional to error –If error is changing slowly (not step change) proportional action is slow Added rate action provides quick response to error 48 ELO 1.4 Figure: Response of PD Control

49. © Copyright 2016Operator Generic Fundamentals Proportional-Derivative Control Example Same heat exchanger system as previously analyzed Temperature controller now uses PD controller 49 ELO 1.4 Figure: Heat Exchanger Process with PD Control

50. © Copyright 2016Operator Generic Fundamentals Proportional-Derivative Control Example Proportional only control mode responds to decrease in demand –Residual offset error remains Adding derivative action –Only one small overshoot –Rapid stabilization to new control point –Does not eliminate offset error 50 ELO 1.4 Figure: Effect of Disturbance on a PD Controller

51. © Copyright 2016Operator Generic Fundamentals Proportional-Derivative Applications Leading action of controller output compensates for processes with lagging characteristics –Large capacity –Slow-responding –For example, temperature control Disadvantage is that derivative action responds to any rate of change in error signal, including noise –Not typically used fast responding processes such as flow control or noisy processes PD controllers are useful with processes which are frequently started up and shut down because they are not susceptible to reset windup 51 ELO 1.4

52. © Copyright 2016Operator Generic Fundamentals Proportional-Integral-Derivative Proportional-integral-derivative (PID) controllers combine all three control actions Gain benefit from all three modes of control –Proportional – good stability –Integral – eliminate offset error –Derivative – good stability Used for processes that cannot tolerate continuous cycling or offset error, and require good stability 52 ELO 1.4

53. © Copyright 2016Operator Generic Fundamentals Proportional-Integral-Derivative Controller Response For example, error is due to slowly increasing measured variable –Proportional action produces output proportional to error signal –Integral action produces output, changing due to increasing error –Derivative action produces output whose magnitude is determined by rate of change 53 ELO 1.4 Figure: PID Control Responses

54. © Copyright 2016Operator Generic Fundamentals Proportional-Integral-Derivative Controller Response Response curves are drawn assuming no corrective action is taken by control system As soon as output of controller begins to reposition final control element, magnitude of error should begin to decrease Controller will bring error to zero and controlled variable back to setpoint 54 ELO 1.4 Figure: PID Control Responses

55. © Copyright 2016Operator Generic Fundamentals PID Controller Response to Demand Disturbance Now assume action is taken in response to disturbance –Proportional action of controller stabilizes process –Reset action combined with proportional action causes measured variable to return to setpoint –Rate action combined with proportional action reduces initial overshoot and cyclic period 55 ELO 1.4 Figure: PID Controller Response Curves

56. © Copyright 2016Operator Generic Fundamentals Operation of an Automatic Controller Knowledge Check The water level in a tank is being controlled by an automatic level controller and is initially at the controller setpoint. A drain valve is then opened, causing tank level to decrease. The decreasing level causes the controller to begin to open a makeup water supply valve. After a few minutes, a new steady-state tank level below the original level is established, with the supply rate equal to the drain rate. The controller in this system uses __________ control. A.proportional, integral, and derivative B.proportional and integral C.proportional only D.bistable Correct answer is C. 56 ELO 1.4

57. © Copyright 2016Operator Generic Fundamentals Operation of an Automatic Controller Knowledge Check – NRC Bank Refer to the drawing of a lube oil temperature control system (see figure below). If the temperature transmitter fails high (high temperature output signal), the temperature controller will position the temperature control valve more __________, causing the actual heat exchanger lube oil outlet temperature to __________. A.open; decrease B.open; increase C.closed; decrease D.closed; increase Correct answer is A. 57 ELO 1.4

58. © Copyright 2016Operator Generic Fundamentals Operation of an Automatic Controller Knowledge Check – NRC Bank Which one of the following describes the response of a direct acting proportional-integral controller, operating in automatic mode, to an increase in the controlled parameter above the controller set point? A.The controller will develop an output signal that continues to increase until the controlled parameter equals the controller set point, at which time the output signal stops increasing. B.The controller will develop an output signal that will remain directly proportional to the difference between the controlled parameter and the controller set point. C.The controller will develop an output signal that continues to increase until the controlled parameter equals the controller set point, at which time the output signal becomes zero. D.The controller will develop an output signal that will remain directly proportional to the rate of change of the controlled parameter. Correct answer is A. 58 ELO 1.4

59. © Copyright 2016Operator Generic Fundamentals Automatic and Manual Controller Operation Typical controller –Many popular controller types found in industrial applications o Extremely versatile –Can be adapted to control various types of industrial equipment and processes o Pressure, temperature, valve position, etc. 59 ELO 1.5– Describe the operation of a controller in automatic and manual modes. ELO 1.5

60. © Copyright 2016Operator Generic Fundamentals Controller Operation Operated in either automatic or manual mode Mode depends on: –complexity of process being controlled –specific operational requirements 60 ELO 1.5 Figure: Typical Digital Controller

61. © Copyright 2016Operator Generic Fundamentals Controller Operation Pulser knob Display pushbutton Alphanumeric display Auto/manual pushbutton 61 ELO 1.5 Figure: Typical Digital Controller

62. © Copyright 2016Operator Generic Fundamentals Automatic Operation Controller reacts to control a particular process parameter based on setpoint –Automatically responds to any deviation from setpoint –Adjusts output in order to adjust control element and return controlled parameter to setpoint Adjustment can be made to setpoint –Operator adjusts setpoint using pulser knob –Will continue to respond automatically to new setpoint 62 ELO 1.5

63. © Copyright 2016Operator Generic Fundamentals Manual Operation Controller does not attempt to maintain its programmed setpoint –Maintains constant output to its control element regardless of changes in controlled parameter –Proportional, Integral, and/or Derivative features ALL removed Pulser knob must be adjusted by operator in order to change output of controller –Requires constant attention by operator 63 ELO 1.5

64. © Copyright 2016Operator Generic Fundamentals Controller Transfer Operation When transferring control from automatic to manual: –Normally manual tracks automatic o Usually no perturbation shifting to Manual –During instrument failures o Manual removes failed instrument o Control of parameter is regained with pulser knob When transferring control from Manual to Automatic –Ensure alternate instrument working correctly –Ensure parameter back at normal value –Place controller in Automatic –Verify no abnormal system perturbation (bumpless transfer) 64 ELO 1.5

65. © Copyright 2016Operator Generic Fundamentals System Response to Controller Inputs A decreasing SG water level will: Increase SG level control signal Raise control air pressure Causing feed control valve to open further 65 ELO 1.5 Figure: Pneumatic Control System - PWR

66. © Copyright 2016Operator Generic Fundamentals System Response Practice Question Knowledge Check If personnel manually decrease the level control signal, how will the pneumatic control system affect SG level A.Level will decrease because the valve positioner will close more, reducing control air pressure, which causes the feed control valve to close more. B.Level will decrease because the valve positioner will open more, increasing control air pressure, which causes the feed control valve to close more. C.Level will increase because the valve positioner will close more, reducing control air pressure, which causes the feed control valve to open more. D.Level will increase because the valve positioner will open more, increasing control air pressure, which causes the feed control valve to open more. Correct answer is A. 66 ELO 1.5

67. © Copyright 2016Operator Generic Fundamentals Automatic and Manual Controller Operation Knowledge Check – NRC Bank A flow controller has proportional, integral, and derivative control features. Which one of the following lists the effect on the control features when the controller is switched from the automatic mode to the manual mode? A.Only the derivative feature will be lost. B.Only the integral and derivative features will be lost. C.All proportional, integral, and derivative features will be lost. D.All control features will continue to influence the controller output. Correct answer is C. 67 ELO 1.5

68. © Copyright 2016Operator Generic Fundamentals Temperature and Pressure Controller Operation Both types function in the same manner: –Takes the parameter variable from the sensor –Compares it to a setpoint –Develops an error signal –Sends error signal to final control element o Only part that might differ is what gets operated as a result –Might compare feedback from final control element to sensor input o To adjust error signal 68 ELO 1.6 – Describe the operation of temperature controllers and pressure controllers. ELO 1.6

69. © Copyright 2016Operator Generic Fundamentals Proportional Temperature Control 69 ELO 1.6 Figure: Proportional Temperature-Control System

70. © Copyright 2016Operator Generic Fundamentals Controller Response to Demand Changes Purpose of system is to provide hot water at setpoint of 75ºF System must handle demand disturbances that affect outlet temperature Controller set up to function as shown in figure 70 Figure: Proportional-Controller Characteristics ELO 1.6

71. © Copyright 2016Operator Generic Fundamentals Controller Response to Demand Changes If measured variable drops below setpoint –Positive error is developed –Control valve opens further 71 Figure: Proportional-Controller Characteristics ELO 1.6

72. © Copyright 2016Operator Generic Fundamentals Controller Response to Demand Changes If measured variable goes above setpoint –Negative error developed –Control valve throttles down (opening is reduced) 72 Figure: Proportional-Controller Characteristics ELO 1.6

73. © Copyright 2016Operator Generic Fundamentals Controller Response to Demand Changes 50% proportional band causes full stroke of valve between a +25ºF error and a -25ºF error 73 Figure: Proportional-Controller Characteristics ELO 1.6

74. © Copyright 2016Operator Generic Fundamentals Controller Response to Demand Changes When error is zero, controller provides 50% (9 psi) signal to control valve As error changes, controller produces an output proportional to magnitude of error Control valve compensates for demand disturbances that cause process to deviate from setpoint in either direction 74 Figure: Proportional-Controller Characteristics ELO 1.6

75. © Copyright 2016Operator Generic Fundamentals Temperature and Pressure Controller Operation Knowledge Check Refer to the drawing of a lube oil temperature control system (see figure below). The temperature control valve is currently 50 percent open. If the cooling water inlet temperature decreases, the temperature controller will position the temperature control valve more __________, causing cooling water differential temperature through the heat exchanger to __________. A.closed; increase B.closed; decrease C.open; increase D.open; decrease Correct answer is A. 75 ELO 1.6

76. © Copyright 2016Operator Generic Fundamentals Operation of a Speed Controller Senses speed of component and governs speed Speed could be controlled by a throttle such as in a diesel governor Servomotor may be used to operate throttles Speed can be sensed mechanically, electrically, or a combination of both 76 ELO 1.7 – Describe the operation of mechanical and electronic speed control devices. ELO 1.7

77. © Copyright 2016Operator Generic Fundamentals Speed Controllers/Governors Mechanical Speed Senses speed on rotating element such as diesel or turbine shaft –Attach flyweights to the shaft –As shaft rotates, rotational force causes the weights to extend radially outward –Force is proportional to the square of rotational speed Provides trouble free speed sensing 77 ELO 1.7

78. © Copyright 2016Operator Generic Fundamentals Speed Controllers/Governors Force balanced by compression of the spring Ballhead rotates with the shaft Flyweights move out radially away from the shaft due to the rotation Flyweight arms in contact with a non-rotating speeder rod Speeder rod is free to move axially along the shaft Transmits radial movement of flyweights into axial movement of speeder rod 78 Figure: Mechanical Speed Sensor ELO 1.7

79. © Copyright 2016Operator Generic Fundamentals Speed Controllers/Governors Governors can be used to directly sense speed and adjust the supplied fuel –In a diesel generator the speed controls the generator output frequency Speed used to generate an electronic signal to a hydraulic actuator Hydraulic actuator generates a corresponding hydraulic signal to move the fuel racks –Hydraulics are generally shaft driven by the engine Movement of speeder rod can be used to control a fuel mechanism Governors can be extremely complex with several modes of control 79 ELO 1.7

80. © Copyright 2016Operator Generic Fundamentals Simple Mechanical Governor For example, load on a diesel engine is increased Speed decreases Flyweights move inward Speeder rod lowers Directs more fuel to the engine 80 Figure: Mechanical Governor ELO 1.7

81. © Copyright 2016Operator Generic Fundamentals Speed Controllers/Governors Electronic Speed Teeth attached to rotating shaft rotate through a magnetic field of a permanent magnet –Electrical pulse is induced in a pickup coil –Electrical signal compared to desired speed –Throttles adjust supplied steam accordingly Used to control speed of steam turbine –Turbine may have an additional wheel with 60 teeth on the turbine shaft Overspeed trip mechanism may be similar to the speed sensor –Mechanical arrangement provides a reliable method to protect equipment 81 ELO 1.7

82. © Copyright 2016Operator Generic Fundamentals Speed Controllers/Governors Example: Electrical signal from a steam turbine governor failed low Speed control governor continues to open Turbine throttles to raise speed –As the turbine speed increases, Electronic signal feeds the new speed back to the governor and throttle position adjusts as necessary Electric speed indication is low no matter what the actual turbine speed is so the governor will keep trying to open the throttles Turbine speed would increase until mechanical overspeed trip point is reached shutting the throttles 82 ELO 1.7

83. © Copyright 2016Operator Generic Fundamentals Droop Mode vs Isochronous Mode The type of speed control utilized by the diesel generator (D/G) varies –Droop Mode o Used when D/G is started and paralleled to bus for testing –If in Droop Mode on an isolated bus, load changes would effect speed o Maintains D/G speed at speed changer setting –backed up by mechanical governor o % Speed Droop = No Load - Full Load Speed / No Load –Isochronous Mode (Emergency Mode) o Used when D/G is ONLY source to AC Vital Bus o Controller returns D/G to speed setpoint for 60 Hz for any change in load –Loads sequenced on to minimize impact on D/G 83 ELO 1.7

84. © Copyright 2016Operator Generic Fundamentals Operation of a Speed Controller Knowledge Check – NRC Bank An emergency diesel generator (D/G) is operating as the only power source connected to an emergency bus. The governor of the D/G is directly sensing D/G __________ and will directly adjust D/G __________ flow to maintain a relatively constant D/G frequency. A.speed; air B.speed; fuel C.load; air D.load; fuel Correct answer is B. 84 ELO 1.7

85. © Copyright 2016Operator Generic Fundamentals Operation of a Speed Controller Knowledge Check – NRC Bank In a flyball-weight mechanical speed governor, the purpose of the spring on the flyball mechanism is to ____________ centrifugal force by driving the flyballs ___________. A.counteract; apart B.aid; together C.counteract; together D.aid; apart Correct answer is C. 85 ELO 1.7

86. © Copyright 2016Operator Generic Fundamentals Operation of a Speed Controller Knowledge Check – NRC Bank A diesel generator (DG) is supplying an isolated electrical bus with the DG governor operating in the speed droop mode. Assuming the DG does not trip, if a large electrical bus load trips, bus frequency will initially... A.increase, then decrease and stabilize below the initial value. B.increase, then decrease and stabilize above the initial value. C.decrease, then increase and stabilize below the initial value. D.decrease, then increase and stabilize above the initial value. Correct answer is B. 86 ELO 1.7

87. © Copyright 2016Operator Generic Fundamentals Interpret Logic Diagrams Logic symbols allow user to determine the operation of a component or system as the input signals change Reader must understand each of the specialized symbols Commonly see logic symbols on equipment diagrams Three basic types of logic gates: –AND –OR –NOT Each gate is a very simple device that only has two states, on and off. 87 ELO 1.8 – Interpret logic diagrams and determine controller outputs. ELO 1.8

88. © Copyright 2016Operator Generic Fundamentals Logic Symbols 88 ELO 1.8

89. © Copyright 2016Operator Generic Fundamentals Logic Diagram Example Refer to the valve controller logic diagram in the figure. Which one of the following combinations of inputs will result in the valve receiving an open signal? Answer Discussion – Place “1” or “0” working backwards to the inputs. The only combination where it is not met is in D because 1 is off and 3 is off. 89 ELO 1.8 1 10 0 0 One or both of Inputs 2 and 3 must be 0. Inputs 1.2.3. A.OnOff B.OffOn C.OnOffOn D.OffOnOff

90. © Copyright 2016Operator Generic Fundamentals Logic Diagrams Knowledge Check Refer to the valve controller logic diagram (see figure below). Which one of the following combinations of inputs will result in the valve receiving a CLOSE signal? INPUTS 1.2.3.4. A.OnOnOffOff B.OffOffOnOff C.OnOffOffOn D.OnOnOnOff Correct answer is B. 90 ELO 1.8

91. © Copyright 2016Operator Generic Fundamentals Types of Valve Actuators Valves can require remote operation when they –Are large in size –Require quick operation –Located in hazardous areas Four types of actuators used for remote operation are: –Pneumatic –Hydraulic –Solenoid –Electric motor 91 ELO 1.9 – Describe the design and operation of the following types of valve actuators: pneumatic, hydraulic, solenoid, and electric motor. ELO 1.9

92. © Copyright 2016Operator Generic Fundamentals Pneumatic Valve Actuator 92 ELO 1.9 Figure: Pneumatic-Actuated Control Valve

93. © Copyright 2016Operator Generic Fundamentals Pneumatic Valve Actuator Initially, with no supply air, –Spring forces diaphragm upward –Holds valve fully open Supply air pressure increases –Air pressure forces diaphragm downward –Closes control valve Supply air pressure decreases –Force of spring forces diaphragm upwards –Opens control valve Valve can be held at intermediate position 93 Figure: Pneumatic-Actuated Control Valve ELO 1.9

94. © Copyright 2016Operator Generic Fundamentals Actuator Failure Position 94 Figure: Pneumatic Actuator with Controller and Positioner ELO 1.9

95. © Copyright 2016Operator Generic Fundamentals Valve Positioner Purpose –Converts the 3-15 psi control air pressure to a higher supply air pressure to move the valve actuator o Supply air is usually from Service Air or Instrument Air Valve Positioner for AOV usually consists of three (3) gages –Control air pressure (from I/P) o 3-15 psi –Supply air pressure available o Usually > 100 psi –Supply air pressure to actuator o Varies 95 Figure: Pneumatic Actuator with Controller and Positioner ELO 1.9

96. © Copyright 2016Operator Generic Fundamentals Valve Positioner System Example Previous SG Water Level Control drawing –Control air signal (3-15 psi) operates a pilot valve –Regulates more or less Supply Air to valve actuator to FRV 96 ELO 1.9 Figure: SGWLC Valve Positioner Example

97. © Copyright 2016Operator Generic Fundamentals Valve Positioner Knowledge Check – NRC Bank The purpose of the valve positioner is to convert... A.a small control air pressure into a proportionally larger air pressure to adjust valve position. B.a large control air pressure into a proportionally smaller air pressure to adjust valve position. C.pneumatic force into mechanical force to adjust valve position. D.mechanical force into pneumatic force to adjust valve position. Correct answer is A. 97 ELO 1.9

98. © Copyright 2016Operator Generic Fundamentals Hydraulic Actuators Operation of hydraulic actuator like pneumatic actuator Each uses motive force to overcome spring force to move valve Normally used if: –Large amount of force is required to operate a valve o for example, large steam system valves Piston type most common Can also be designed to fail-open or fail-closed to provide a fail-safe feature 98 ELO 1.9

99. © Copyright 2016Operator Generic Fundamentals Hydraulic Actuator Design Typical piston-type hydraulic actuator consists of: –Cylinder –Piston: slides vertically inside separates cylinder into two chambers –Spring: contained in upper chamber of cylinder –Hydraulic fluid, supply and return line: contained in lower chamber –Stem: transmits motion from piston to valve 99 Figure: Piston-Type Hydraulic Actuated Control Valve ELO 1.9

100. © Copyright 2016Operator Generic Fundamentals Hydraulic Actuator Design Initially, with no supply air, –Spring forces piston upward –Holds valve fully open Hydraulic fluid pressure increases –Fluid pressure forces piston downward –Closes control valve Hydraulic fluid pressure decreases –Force of spring forces piston upwards –Opens control valve Valve can be held at intermediate position 100 Figure: Piston-Type Hydraulic Actuator ELO 1.9

101. © Copyright 2016Operator Generic Fundamentals Electric Solenoid Actuators A typical electric solenoid actuator consists of: –Coil: Provides upward force –Armature: Transmits force from coil to vertical motion –Spring: Applies downward force –Stem: Transmits force motion from armature to valve 101 Figure: Electric Solenoid Actuator ELO 1.9

102. © Copyright 2016Operator Generic Fundamentals Solenoid Actuator Advantages & Disadvantages Advantages Quick operation Easier to install than pneumatic or hydraulic actuators Disadvantages Only two positions: fully open and fully closed Don’t produce much force ⇒ usually only operate relatively small valves 102 ELO 1.9

103. © Copyright 2016Operator Generic Fundamentals Electric Motor Actuators Some motor actuators are designed to operate in only two positions –fully open or fully closed Other electric motor actuators can be positioned in intermediate positions 103 Figure: Motor Actuator ELO 1.9

104. © Copyright 2016Operator Generic Fundamentals Electric Motor Actuator Design & Operation Motor moves stem through gear assembly Motor reverses its rotation to either open or close valve Clutch and clutch lever disconnects electric motor from gear assembly –allows valve to be operated manually with handwheel 104 ELO 1.9 Figure: Motor Actuator

105. © Copyright 2016Operator Generic Fundamentals Electric Motor Actuator Design & Operation Most are equipped with limit switches and/or torque limiters –Usually limit switch stops motor when opening –Usually torque limiter stops motor when closing 105 ELO 1.9 Figure: Motor Actuator

106. © Copyright 2016Operator Generic Fundamentals Types of Valve Actuators Knowledge Check An air-operated isolation valve requires 2,400 pounds-force applied to the top of the actuator diaphragm to open. The actuator diaphragm has a diameter of 12 inches. If control air pressure to the valve actuator begins to increase from 0 psig, which one of the following is the approximate air pressure at which the valve will begin to open? A.21 psig B.34 psig C.43 psig D.64 psig Correct answer is A. 106 ELO 1.9

107. © Copyright 2016Operator Generic Fundamentals NRC KA to ELO Tie KA #KA StatementROSROELO K1.01Function and operation of flow controller in manual and automatic modes3.13.21.4 K1.02Function and operation of a speed controller2.62.71.7 K1.03Operation of valves controllers in manual and automatic mode3.1 1.5 K1.04 Function and operation of pressure and temperature controllers, including pressure and temperature control valves2.83.01.6 K1.05Function and characteristics of valve positioners2.52.81.1, 1.9 K1.06Function and characteristics of governors and other mechanical controllers2.32.61.7 K1.07Safety precautions with respect to the operation of controllers and positioners2.32.61.5 K1.08Theory of operation of the following types of controllers: electronic, electrical, and pneumatic2.12.61.8, 1.9 K1.09 Effects on operation of controllers due to proportional, integral (reset), derivative (rate), as well as their combinations2.42.51.4 K1.10Function and characteristics of air-operated valves, including failure modes2.42.81.9 K1.11Cautions for placing a valve controller in manual mode2.82.91.5