This document summarizes an interactive seminar on split range control challenges and solutions. It introduces the presenters and their expertise in process control. Several signs of an excellent operator training system are listed humorously. The seminar then demonstrates issues that can arise from standard split range control through virtual process simulations, such as limit cycles. Recommendations are provided to address these issues, including using a smart split range point, cascade control, valve position control, and advanced PID techniques. Attendees are invited to future seminars and encouraged to provide feedback.

1. Interactive Opportunity Assessment Demo and Seminar (Deminar) Series for Web Labs – Split Range Control March 9, 2011 Sponsored by Emerson, Experitec, Monsanto, & Mynah Created by Greg McMillan and Jack Ahlers www.processcontrollab.com Website - Charlie Schliesser (csdesignco.com)

2. Welcome Gregory K. McMillan Greg is a retired Senior Fellow from Solutia/Monsanto and an ISA Fellow. Presently, Greg contracts as a consultant in DeltaV R&D via CDI Process & Industrial. Greg received the ISA “Kermit Fischer Environmental” Award for pH control in 1991, the Control Magazine “Engineer of the Year” Award for the Process Industry in 1994, was inducted into the Control “Process Automation Hall of Fame” in 2001, was honored by InTech Magazine in 2003 as one of the most influential innovators in automation, and received the ISA “Life Achievement Award” in 2010. Greg is the author of numerous books on process control, his most recent being Essentials of Modern Measurements and Final Elements for the Process Industry. Greg has been the monthly “Control Talk” columnist for Control magazine since 2002. Greg’s expertise is available on the web site: http://www.modelingandcontrol.com/

3. ISA Automation Week - Oct 17-20 Call for Papers Deadline is March 28 !

4. Legends Cutler and Liptak Give Keynotes

5. Top Ten Signs of an Excellent Operator Training System (OTS) (10) Plant production rate is higher than model (9) Online yield metrics are off-scale high (8) Operators postpone vacations to get more time on OTS (7) Operators do an opportunity assessment of process control improvements (6) Operators are more interested in the process than doughnuts (5) Operators invite automation engineers on fishing trips to discuss control strategies (4) Calendars in break room feature control strategy of the month (3) Operators take the ISA exam to be a Certified Automation Professional (CAP) (2) Executives hang out in the control room to learn about process control And the Number 1 sign: Source: “Operators Unleashed”, Control Talk, Control, Feb 2011 http://www.controlglobal.com/articles/2011/AutomationOperators1102.html

6. Top Ten Signs of an Excellent Operator Training System (OTS) (1) Executives ask operators to autograph screen prints of online process metrics

7. PID Output is split between multiple final control elements, such as dampers, valves, and VFDs New Split Range Lab04

8. Splitter Detail Load to set valves operating point Valve 1 Valve 2 Zone near seat where stiction is increased S’v = Sv * (1+ Zone-Stroke)

9. Split Range Applications High rangeability flow Small and large valves in parallel Different final control elements Damper and variable frequency drive for flow and pressure control Opposing effects Coolant and steam valves for reactor temperature control Acid and base reagent valves for neutralizer pH control Carbon dioxide and sodium bicarbonate for bioreactor pH control Vent and nitrogen valves for vessel pressure control Significantly different costs Waste fuel and purchased fuel for boiler control Waste reagent and purchased reagent for pH control Recycle versus purchased reactant for composition control Low and high cost chemicals for KAPPA number control for paper brightness

10. Split Range Problems Nonlinear installed characteristic Flattening at high end and minimum flow at low end of stroke range both increase as the ratio of valve/system drop decreases Low cost flow is often slower and/or erratic making tight control difficult Bark and lime are slow and waste and recycle streams have unpredictable compositions Larger limit cycle for larger valve or damper Since stick slip is a % of stroke (flow capacity), flow limit cycle is larger for larger valve High seal and seat friction near closed position Stick-slip can be an order of magnitude greater (worse for tight shutoff rotary valves) Wire drawing of internal element and seating surfaces near closed position High velocities cause streamline cracks and erosion of surfaces Flashing Vena contractor pressure below vapor pressure causes choking and vibration High breakaway and unbalance forces near closed position Overshoot can be 15% or more (worse for tight shutoff rotary valves) Manipulated flows have different process dynamics Process gain, deadtime, and time constant vary with type of manipulated flow Steam shock Steam pressure wave and water droplets cause erratic temperature measurement

11. The Essential Problem Nearly all split range loops oscillate across the split range point wearing out valves, wasting resources, and increasing process variability

12. Installed Valve Characteristic for Equal Percentage Trim Valve pressure drop ratio (DPR) for installed characteristic: Characteristic 1: DPR= 0.5 Characteristic 2: DPR= 0.25 Characteristic 3: DPR= 0.125 Characteristic 4: DPR= 0.0625

13. Limit Cycles from Stick-Slip and Backlash Stiction Backlash

15. http://www.modelingandcontrol.com/2009/03/application_notes.htmlEnhanced PID (PIDPlus) with wireless trigger level and noise band for patience at split range point and feedforward timing errors and to reduce limit cycles Velocity limit and dynamic reset limit to slow down transition into split range Precise valves (sliding stem with diaphragm actuators & digital positioners) Splitter sets flow controllers instead of valves to isolate installed characteristic Split range point chosen to compensate for differences in valve and process gain Adaptive tuning and control to schedule tuning as function of PID output

16. AC 1-1 Smart Split Range Point Reagent Smart in terms of valve gain compensation but not smart in terms of valve sensitivity ! Small (Fine) Large (Coarse) Splitter Split Range Block For large valve 4x small valve flow: PID Small Large OutValveValve 0% 0% 0% 20% 100% 0% 20% 100% 0% 100% 100% 100% Neutralizer PID Controller AT 1-1

17. Smart Split Range Point

18. AC 1-1a AC 1-1b PID Valve Sensitivity and Rangeability Solution 1 Reagent Large (Coarse) Small (Fine) Neutralizer PID Controller or PIDPlus with sensitivity limit AT 1-1 Proportional only Controller or PIDPlus with sensitivity limit

19. AC 1-1 ZC 1-1 PID Valve Sensitivity and Rangeability Solution 2 Reagent Small (Fine) Large (Coarse) Integral only Controller or PIDPlus with sensitivity limit Neutralizer PID Controller or PIDPlus with sensitivity limit AT 1-1

20. Nomenclature Ao = amplitude of limit cycle (%) Bv = valve backlash (deadband) (%) G = split range gap (%) Kc = PID gain (dimensionless) Kv1 = valve 1 gain (Flow e.u. / CO %) Kv2 = valve 2 gain (Flow e.u. / CO %) Kp1 = process gain for valve 1(PV e.u. / Flow e.u.) Kp2 = process gain for valve 2(PV e.u. / Flow e.u.) Km = measurement gain (CV % / PV e.u.) S1 = 1st split ranged span (PV e.u.) S2 = 2nd split ranged span (PV e.u.) Sm = span of measurement scale (PV e.u.) Sv = valve stiction (resolution) (%) Ti = PID integral time (sec/repeat) To = period of limit cycle (sec)

21. Split Range Demo 1 Objective –Show effect of the standard split range point Activities: In Lab04 Splitter verify traditional split range array = 0 50 50 100 Click on Trend icon next to faceplate icon and look at Lab04 chart In Lab04Splitter detail vary low load between 5% and 15% and check response In Lab04Splitter detail varyhigh load between 35% and 45% and check response

22. Split Range Demo 2 Objective– Show effect of the smart split range point Activities: In Lab04 Splitter detailset smart split range array = 0 20 20 100 In Lab04Splitter detail varylow load between 5% and 15% and check response In Lab04Splitter detail vary high load between 35% and 45% and check response

23. Split Range Demo 3 Objective– Show effect of standard PID for stiction at split range point Activities: In Lab04 Splitter detail use smart split range array = 0 20 20 100 In Lab04 Splitter detail set increased stiction zone = 20% In Lab04 Valve1 and Valve2 detail set stiction resolution step = 0.5% In Lab04Splitter detail setload 25% and check response

24. 100% 90% x o 80% o 70% Valve Signal x x o 60% o Valve Signal and Actual Stroke 50% x o x o 40% Actual Valve Stroke x x o 30% o 20% x o x 10% o x o x 0% 0 3 4 6 1 2 5 7 9 8 10 Digital Updates Sensitivity (Threshold Effect)

25. 100% 90% x o 80% o x 70% Valve Signal o x 60% o Valve Signal and Actual Strokes x 50% o x o x 40% Actual Valve Stroke o x 30% o x 20% o x 10% o x x o 0% 0 3 4 6 1 2 5 7 9 8 10 Digital Updates Resolution (Quantization Effect)

26. Split Range Demo 4 Objective– Show effect of standard PID for stiction at split range point Activities: In Lab04 Splitter detail use smart split range array = 0 20 20 100 In Lab04 Splitter detail set increased stick-slip zone = 20% In Lab04 Valve1 and Valve2 detail set stiction resolution step = 0.5% In Lab04 Measurements detail set Refresh = 1000 sec and Sensitivity = 1% In Lab04 PID detail enablePIDPlus

28. compensates for gross differences in manipulated flows

29. Use cascade control where splitter output is flow controller setpoint

30. isolates valve nonlinearity from process PID

31. Use valve position control to increase sensitivity and rangeability

32. Use smart proportioned load and setpoint feedforward

33. Use precise control valves with valve drop > 25% system drop and 2x actuator size

34. Use PIDPlus (sensitivity set to ignore insignificant measurement & valve changes)

35. eliminates limit cycles

36. reduces transitions across split range point

37. reduces valve position control interactions

38. Use smart directional velocity limit and dynamic reset limit to slow down transition into split range point to avoid unnecessary excursions to opposing flow

39. reduces reagent use and energy use and avoids vent system overload

40. Use smart directional velocity limit and dynamic reset limit to slow down valve position control to avoid unnecessary corrections and reduce interaction

41. Mount jacket temperature sensor sufficiently downstream to reduce steam shock

43. Not an emulation but a DCS (SimulatePro)

44. Independent Interactive Study

45. Structural Changes “On the Fly”

46. Advanced PID Options and Tuning Tools

47. Enough variety of valve, measurement, and process dynamics to study 90% of the process industry’s control applications

48. Learn in 10 minutes rather than 10 years

49. Online Performance Metrics

50. Standard Operator Graphics & Historian

51. Control Room Type Environment

52. No Modeling Expertise Needed

53. No Configuration Expertise Needed

54. Rapid Risk-Free Plant Experimentation

55. Deeper Understanding of Concepts

56. Process Control Improvement Demos

57. Sample Lessons (Recorded Deminars)A new easy fast free method of access is now available that eliminates IT security issues and remote access response delays

58. Help Us Improve These Deminars! WouldYouRecommend.Us/105679s21/

59. Join Us June 8, Wednesday 10:00 am CDT PID Control for Sustainable Manufacturing (How PID features can increase process efficiency and capacity and provide environmental and property protection) Look for a recording of Deminar 12 at: www.ModelingAndControl.com www.EmersonProcessXperts.com

60. QUESTIONS? Thank you for attending – book drawing! Now Available for purchase at amazon.com and the isa bookstore