1. Instrumentation I - Session 5 Session 5 - Agenda ActivityEst. Time 1. Agenda 2. Introduction to Primary Sensors, Transmitters and Transducers (Chapter 9) 3. Component Purpose and Operation, Transmitter Signals and Scaling Transducers and Signals, Pneumatic and Electrical Signals (Chapter 9) BREAK 4. Introduction to Controllers/Terms (Chapter 10) 5. Controller Switching, Types of Controllers, Final Control Element Overview (Chapter 10) 6. Control loops: Control valves and regulators (Chapter 11) LUNCH BREAK 7. Review Test #3 8. Next session plan (Review for the final exam, chapters 1-12), Group Activity ( lab- movie )

2. Instrumentation I - Session 5 Learning Objectives 1. Describe the relationship between the measuring instruments (pressure, temperature, level, and flow) and their role in the overall control loop process. 2. Describe the purpose and operation of the transmitter (D/P Cell) in a control loop. 3. Discuss differential pressure in relation to the process input to the transmitter. 4. Compare and contrast the transmitter input and output signals. 5. Describe the function of a current to pneumatic transducer (signal converter). 6. Describe the relationship between a 3 psig to 15 psig air signal and a 4 ma to 20 ma electric signal. 7. Given a process control scheme, explain how a control loop functions.

3. Instrumentation I - Session 5 Sensors  Sensors can be mechanical or electronic. A thermocouple is an example of an electronic sensor that can be directly connected to a controller.  Thermocouples and RTDs are examples of discrete temperature sensors that are usually installed in a thermowell extending into the process.

4. Instrumentation I - Session 5 Primary Sensors, Transmitters and Transducers  The transmitter produces an output signal that carries the measurement information to the next instrument in the loop.  The sensor detects the process variable and the transducer converts one energy form into another.

5. Instrumentation I - Session 5 Transmitters  After being sensed and measured, the process variable measurement is transduced (converted) by the transmitter circuit into a standard instrument signal.  The standard instrument signals are 4-20 mA (electronic), 3-15 psig (pneumatic), or digital.

6. Instrumentation I - Session 5 Differential Pressure and the Transmitter  The differential pressure transmitter is a commonly used transmitter in the processing industry.  Differential pressure transmitters can measure pressure and differential pressure as well as infer level, flow rate, and even density.

7. Instrumentation I - Session 5 Transmitter Signals The output of the transmitter is typically converted into one of the common standard instrument signals. In an analog electronic control loop, a thermocouple with a millivolt input to the transmitter has a 4-20 mA output. Pressure inputs, as well as analytical measurements applied to transmitters, also have a corresponding 4- 20 mA output signal.

8. Instrumentation I - Session 5 Scaling n Scaling is the act of equating the numerical value of one scale to its mathematically proportional value on another scale. n For example, the measurement applied to a standard analog electronic pressure transmitter is represented on an appropriate pressure scale while the output signal is represented on a milliampere scale. (pages 143,144) n To better understand the relationship between the input of a transmitter and its output, calculating the input of a transmitter by observing its output is useful. (table 9-1)

9. Instrumentation I - Session 9 Scaling Terms n Upper Range Value (URV) – The number at the top of the scale. Expressed as one number. n Lower Range Value (LRV) – The number at the bottom of the scale. Expressed as one number. n Range – Range defines the set of values that exist between the LRV of a scale and the URV of a scale. It is expressed as two numbers. (Example 50 psig to 150 psig) n Span – Span is the algebraic difference between the upper range value of a scale minus the lower range value value of a scale expressed as one number. (Example: If URV=150 psig and LRV=50 psig, then Span=100psig)

10. Instrumentation I - Session 5 Calculating the Output of a Transmitter Page 144

11. Instrumentation I - Session 5 Transducers Transducer is a device that converts one energy form to another. Transducers can convert quantities such as temperature and pressure Into an electronic form.

12. Instrumentation I - Session 5 Transducer Signals A common instrument signal transducer converts an analog electronic signal (4-20 mA) into a pneumatic signal (3-15 psig). This device is called an I/P(current to pneumatic) transducer.

13. Instrumentation I - Session 5 Chapter 10 – Objectives (Page 1) 1. Define terms associated with controllers: n auto/manual switch n local/remote switch n setpoint n tuning n direct acting n reverse acting n proportional band/gain n integral/reset n derivative/rate 2. Define “bumpless” transfer of auto to manual/manual to auto control. 3. Describe the process for switching from auto control to manual control on a local controller.

14. Instrumentation I - Session 5 Chapter 10 – Objectives (Page 2) 4. Describe the process for switching from manual control to automatic control on a local pneumatic controller without bumping the process. 5. Demonstrate various control skills, such as: n make setpoint adjustments on a local controller n operate a local controller in manual mode n make setpoint adjustments on a remote pneumatic controller n switch from manual to automatic control on a remote pneumatic controller without bumping the process. 6. Given a drawing or actual local pneumatic controller, read the chart and state the high and low range values. 7. Given a simulator or actual device, identify if a control loop is in control or out of control and identify the information used to make the decision.

15. Instrumentation I - Session 5 Chapter 10 – Objectives (Page 3) 8. Given a drawing or actual device, identify and describe the operation of the following: n local controller n remote controller n split range controller n cascade/remote setpoint (RSP) controller n ratio controller 9. Provide an application requiring the following devices: n local controller n remote controller n split range controller n cascade/remote setpoint (RSP) controller n ratio controller 10. Describe the role of the final control element as it relates to the process and the control loop.

16. Instrumentation I - Session 5 Chapter 10 – Objectives (Page 4) 11. Describe three types of final control elements and provide an application for each type: n control valve – manipulates a process flow (liquid/gas) in response to a control signal n damper/louver – manipulates an air flow to control draft setting or temperature setting n motor – starts or stops in response to a control signal. 12. Given a drawing or actual instrument, identify and describe the operation of the following: n louver/damper final control element n variable speed motor used as a final control element n instrument air regulator

17. Instrumentation I - Session 5 Controllers  The controller is a device in a control loop that operates automatically to regulate a process variable.  In a simple feedback control loop, the controller first compares the value of the measurement signal to a setpoint value. The result of this comparison produces another value called the error.  The error signal is then acted upon by one or more separate action components (control algorithms) to generate an appropriate output signal.

18. Instrumentation I - Session 5 Controller Front Panel  Auto/manual switch  Output adjustment in manual (thumb wheel)  Remote/local switch (RSP) is received from an external source(usually another controller)  Set point knob  Process value  Set pointer  Scale  Figure 10-2 (Page 152)

19. Instrumentation I - Session 5 Controller Side Panel  Direct/Reverse acting Direct acting: increasing input process variable goes to increasing output power, increasing temperature turns on the heater on controller Indirect acting: increasing input (measured variable) goes to decreasing output power, increasing temperature turns off the heater  Proportional band (Gain) (A proportional band of 100 percent means that it takes a full range or 100 percent change in input to drive the output of the controller through its full range. PB=(1/Gain)*100%

20. Instrumentation I - Session 5 Controller Side Panel  Gain is a proportioning factor describing how the magnitude of the input relates to the magnitude of the output.  Gain of 1 means the controller will respond to an input change of 10 percent by producing an output change of 10 percent. (Page 154)  Integral action (Reset) is designed in a controller to eliminate the offset (error) in feedback control loops.  Derivative action (Rate) Rate of a controller responds to the rate of change of the controlled variable. The faster the rate of change in the error signal, the greater the derivative response.

21. Instrumentation I - Session 5 Local Controller Physically mounted in the processing area near the other instruments in the loop.

22. Instrumentation I - Session 5 Remote Controller  It is not located in the processing area.  They are found mostly in panels located in control rooms.  Figure shows a pressure loop with the transmitter and control valve located in the processing area.  JB-100 and JB-200 are bundle tubes for connecting and distributing points.

23. Instrumentation I - Session 5 Split Range Controller  The output of a controller may be divided between two final control elements.  Modern digital controllers can have more than one output. So, they can be split range controllers.  For example, the signal from output 1 could be 4-11.4 mA (3-8.5 psig) to valve A, while output 2 could be 12.6-20 mA (9.5-15 psig) to valve B Both valves receive the full range output of the controller. (Page 156)

24. Instrumentation I - Session 5 Cascade/Remote Set Point (RSP) Controller  RSP controller is characterized by the output of one controller becoming the remote setpoint of another  The primary controller is responding to the temperature of the product while the secondary controller is operating to control steam flow.(page 157)

25. Instrumentation I - Session 5 Ratio Controller  Ratio control loops are designed to ratio the rates of flow between two separate flows entering a mixing point.

26. Instrumentation I - Session 5 Final Control Elements  A final control element is the last active device in the instrument control loop.  They manipulate operation on the process that brings about a change in the controlled variable.  The most common are control valves, louvers, and variable speed drives.

27. Instrumentation I - Session 5 Control valves  They manipulate the flow rate of some component in a process that will in some way affect the measured value of the controlled variable.  An actuating device is mounted to the control valve. The actuator changes an instrument signal into a linear or rotary motion.

28. Instrumentation I - Session 5 Manipulated Stream=Controlled Stream n A simple feedback control loop controlling flow rate where the controlled variable is the same stream as the manipulated variable. n In this example, the controller adjusts the signal to the control valve, which manipulates the flow rate of the material moving through the process.

29. Instrumentation I - Session 5 Manipulated Stream=Controlled Stream n The transmitter then measures the resulting flow rate and feeds the new measurement value back to the controller where the control cycle continues.

30. Instrumentation I - Session 5 Manipulated Stream=Controlled Stream n A heat exchanger where the temperature transmitter (product side) is located on the outlet of the tube side and control valve is located on the inlet to the shell side. n In this example, the manipulated stream is not the same as the controlled stream.

31. Instrumentation I - Session 5 Louver/Damper n Louvers and dampers are devices similar in design to shutters or miniblinds used to control airflow. n They can be opened (positioned parallel to one another when fully opened) n Each louver in an industrial airflow system usually pivots on a shaft that runs parallel across its midsection.

32. Instrumentation I - Session 5 Electric Motors n If an electric motor is automatically turned on and off by a controller responding to a process variable, then the motor can be considered as a final control element or an actuator of the final control element. n Variable speed motors are used to control fluid pumping rates, conveyor belt speeds, and other final controlling devices.

33. Chapter 11 Control Valves and Regulators Instrumentation I - Session 05

34. Instrumentation I - Session 11 Chapter 11 – Objectives (Page 1) 1. Given a drawing or actual device, identify the main components of a control valve: n body n bonnet n disc n actuator n stem n seat n spring n valve positioner n handwheel n I/P transducer 2. Given a drawing or actual device, identify and describe the following: n current to pneumatic transducer n indications of a sticking control valve.

35. Instrumentation I - Session 11 Chapter 11 – Objectives (Page 2) 3. Define terms associated with valves and other final control elements: n “air to close” (fail open) n “air to open” (fail closed) n fail last/in place/as is 4. Describe operating scenarios in which fail open, fail closed, and fail last positions are desirable. 5. Discuss the purpose of diaphragm valve actuators and piston valve actuators. 6. Compare and contrast a spring and diaphragm actuator to a cylinder actuator. 7. Explain why the action of a valve actuator may not correspond with the action of the valve.

36. Instrumentation I - Session 11 Chapter 11 – Objectives (Page 3) 8. Describe a valve positioner and explain three of its uses. 9. Explain the function of each of the three gauges located on a pneumatic valve positioner. 10. Given a pressure indication for each of the three gauges on a valve positioner, predict what the control valve movement will be. 11. Describe two ways a controller’s output signal can be reversed at the valve so the valve’s action is opposite of the controller output signal. 12. Describe a control scheme that utilizes reversing a controller’s output signal at the valve. 13. Explain how reversing a controller’s output signal at the valve affects the valve’s fail safe position upon loss of air.

37. Instrumentation I - Session 11 Chapter 11 – Objectives (Page 4) 14. Explain the purpose and operation of the following: n globe valves n three-way valve n butterfly valves 15. Given a drawing, picture, or actual device, identify and describe pressure regulators. 16. Define the following terms associated with regulators: n back pressure regulator (self-actuated) n pressure reducing regulator 17. Given a Process Flow Diagram and/or P&ID, locate and identify pressure regulators used in process control. 18. Given an instrument air pressure regulator, perform the following tasks: n blow down regulator to check for condensate or oil n set specific pressure for operating final control element.

38. Instrumentation I - Session 05 Control Valve Key Components n Control valves operate the process by producing a differential pressure drop across the valve. n A control valve has an actuating device or actuator. The actuator changes an instrument into a linear or rotary motion. n This motion drives the flow controlling mechanism (e.g., plug or disc)

39. Instrumentation I - Session 05 Control Valve Key Components  The body is the housing component.  The valve bonnet is the top portion of the valve body and connects the valve body to the actuator.  The valve plug assembly that includes the valve stem moves to open or close the flow path through the valve.  The actuator is the device that provides motion to the valve using a spring diaphragm, spring piston, or double acting piston.  The stem is the pushing and pulling rod that transfers the motion of the actuator to the valve plug.(page 170)

40. Instrumentation I - Session 05 Control Valve Key Components  The seat in a valve is the stationary part of the valve trim connected to the body that comes in contact with the valve plug. When the plug is fully seated, the flow the valve stops.  The spring provides the energy to move the valve in the opposite direction of the diaphragm loading motion to its fail-safe condition.  The diaphragm is the flexible member that creates a force to move the stem.

41. Instrumentation I - Session 05 Control Valve Key Components  A valve positioner is actually a proportional – only controller.  The position of the valve stem is sensed by a mechanical link that is directly connected to the positioner.  A handwheel is an actuator accessory that is used to manually override the actuator or to limit its motion.  An I/P or current to pneumatic transducer is a device that converts a milliampere signal into a pneumatic pressure.  The most common use for an I/P transducer is to provide the source of energy needed to drive a diaphragm or piston actuator.  A current to pneumatic transducer typically receives a 4-20 mA current signal and converts it to a 3-15 psig pneumatic signal.

42. Instrumentation I - Session 05 Fail Conditions n Control valve are responsible for regulating the movement of fluids in a process. n If there is a power or air failure, they should move to a safe position. n If there is an I/P transducer before the valve, loop (current) failure should also be considered when determining valve fail position.

43. Instrumentation I - Session 05 Fail Conditions n If a plant loses power or air supply, the design engineers must recognize the required fail safe conditions during the design phase of a plant and choose each control valve response accordingly. n When an air to open control valve loses its instrument air signal or supply, the valve fails closed because a return spring provides more opposing force than the decreasing instrument air applied to the diaphragm. n Preventing overflowing a tank is a good example for this case.

44. Instrumentation I - Session 05 Fail Conditions n If a plant loses power or air supply, the valve fails open because the return spring provides more opposing force than the diminishing instrument air applied to the diaphragm and the force applied by the process. n Failing a pressure relief valve on a reactor in these conditions should be fail in the open position preventing a pressure buildup that may rupture the vessel.

45. Instrumentation I - Session 05 Fail Conditions n Actuators without a spring or other return mechanism usually fail in their last position just prior to loss of power unless the process pressure is high enough to change the valve position

46. Instrumentation I - Session 05 Actuator Operation Figure 11-5 Actuator Operation

47. Instrumentation I - Session 05 Spring and Diaphragm Actuator n Very common n Low cost n High mechanical advantage

48. Instrumentation I - Session 05 Piston Type Actuator n Can accept much higher input pressures n Single acting: - spring opposed the piston is opposed by a spring - the air cushion type has a pressure trapped under the piston and the air compresses as the piston is pushed down. Then, as the instrument signal is reduced, the trapped compressed air pushes the piston back up

49. Instrumentation I - Session 05 Piston Type Actuator n Double acting: - the instrument air pressure is routed to both sides of the piston

50. Instrumentation I - Session 05 Valve Positioners – Position the Valve n The function of a positioner is to make the valve position match the controller output signal. n The valve positioner positions the moving parts of a valve in accordance to a predetermined relationship with the instrument signal received from the loop controller.

51. Instrumentation I - Session 05 Valve Positioners – Mimic the Valve Trim Type

52. Instrumentation I - Session 05 Valve Positoner Operation

53. Instrumentation I - Session 05 Output Signals

54. Instrumentation I - Session 05 Globe Control Valve

55. Instrumentation I - Session 05 Three-Way Control Valve

56. Instrumentation I - Session 05 Butterfly Control Valve

57. Instrumentation I - Session 05 Regulators

58. Instrumentation I - Session 05 Backpressure Regulators

59. Instrumentation I - Session 05 Pressure Reducing Regulators

60. Instrumentation I - Session 05 Symbols for Back Pressure Regulator

61. Instrumentation I - Session 05 Symbols for Pressure Reducing Regulator