Split Range Control - Greg McMillan Deminar

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Presented March 9, 2011 by Greg McMillan as on-line demo/seminar. Video recording available at: http://www.screencast.com/users/JimCahill/folders/Public

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Split Range Control - Greg McMillan Deminar

  1. 1. Interactive Opportunity Assessment<br />Demo and Seminar (Deminar) Series <br />for Web Labs –<br />Split Range Control <br />March 9, 2011<br />Sponsored by Emerson, Experitec, Monsanto, & Mynah<br />Created by<br />Greg McMillan and Jack Ahlers<br />www.processcontrollab.com Website - Charlie Schliesser (csdesignco.com)<br />
  2. 2. Welcome<br />Gregory K. McMillan <br />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/<br />
  3. 3. ISA Automation Week - Oct 17-20<br />Call for Papers<br />Deadline is <br />March 28 !<br />
  4. 4. Legends Cutler and Liptak Give Keynotes<br />
  5. 5.  Top Ten Signs of an Excellent Operator Training System (OTS)<br />(10) Plant production rate is higher than model<br />(9) Online yield metrics are off-scale high<br />(8) Operators postpone vacations to get more time on OTS<br />(7) Operators do an opportunity assessment of process control improvements<br />(6) Operators are more interested in the process than doughnuts<br />(5) Operators invite automation engineers on fishing trips to discuss control strategies<br />(4) Calendars in break room feature control strategy of the month<br />(3) Operators take the ISA exam to be a Certified Automation Professional (CAP)<br />(2) Executives hang out in the control room to learn about process control<br />And the Number 1 sign:<br />Source: “Operators Unleashed”, Control Talk, Control, Feb 2011<br />http://www.controlglobal.com/articles/2011/AutomationOperators1102.html<br />
  6. 6.  Top Ten Signs of an Excellent Operator Training System (OTS)<br />(1) Executives ask operators to autograph screen prints of online process metrics<br />
  7. 7. PID Output is split between multiple final control <br />elements, such as dampers, valves, and VFDs<br />New Split Range Lab04<br />
  8. 8. Splitter Detail<br />Load to set valves operating point<br />Valve 1<br />Valve 2<br />Zone near seat <br />where stiction is increased<br />S’v = Sv * (1+ Zone-Stroke) <br />
  9. 9. Split Range Applications<br />High rangeability flow<br />Small and large valves in parallel<br />Different final control elements <br />Damper and variable frequency drive for flow and pressure control<br />Opposing effects<br />Coolant and steam valves for reactor temperature control<br />Acid and base reagent valves for neutralizer pH control<br />Carbon dioxide and sodium bicarbonate for bioreactor pH control<br />Vent and nitrogen valves for vessel pressure control<br />Significantly different costs<br />Waste fuel and purchased fuel for boiler control<br />Waste reagent and purchased reagent for pH control<br />Recycle versus purchased reactant for composition control<br />Low and high cost chemicals for KAPPA number control for paper brightness<br />
  10. 10. Split Range Problems<br />Nonlinear installed characteristic<br />Flattening at high end and minimum flow at low end of stroke range both increase as the ratio of valve/system drop decreases<br />Low cost flow is often slower and/or erratic making tight control difficult <br />Bark and lime are slow and waste and recycle streams have unpredictable compositions<br />Larger limit cycle for larger valve or damper<br />Since stick slip is a % of stroke (flow capacity), flow limit cycle is larger for larger valve<br />High seal and seat friction near closed position<br />Stick-slip can be an order of magnitude greater (worse for tight shutoff rotary valves)<br />Wire drawing of internal element and seating surfaces near closed position<br />High velocities cause streamline cracks and erosion of surfaces <br />Flashing <br />Vena contractor pressure below vapor pressure causes choking and vibration<br />High breakaway and unbalance forces near closed position<br />Overshoot can be 15% or more (worse for tight shutoff rotary valves)<br />Manipulated flows have different process dynamics<br />Process gain, deadtime, and time constant vary with type of manipulated flow<br />Steam shock<br />Steam pressure wave and water droplets cause erratic temperature measurement<br />
  11. 11. The Essential Problem<br />Nearly all split range loops oscillate<br />across the split range point<br />wearing out valves, <br />wasting resources, <br />and increasing <br />process variability <br />
  12. 12. Installed Valve Characteristic for <br />Equal Percentage Trim<br />Valve pressure drop ratio (DPR)<br />for installed characteristic:<br />Characteristic 1: DPR= 0.5 <br />Characteristic 2: DPR= 0.25<br />Characteristic 3: DPR= 0.125<br />Characteristic 4: DPR= 0.0625 <br />
  13. 13. Limit Cycles from <br />Stick-Slip and Backlash<br />Stiction<br />Backlash<br />
  14. 14. Split Range Solutions<br />Eliminate split range for rangeability and different costs by P-only control of small valve or high cost flow and PID control of large valve or low cost flow<br />Eliminate split range for rangeability by valve position controller that positions large valve or low cost flow to keep small valve or high cost flow manipulated by process PID in best throttle range (minimum throttle position for high cost flow)<br />Smart proportioned feedforward control to help solutions 1 and 2 <br />Model Predictive Control for rangeability and different costs - see article “Model Predictive Control can Solve Valve Problem” and Application Notes 1 and 2<br /><ul><li>http://www.controlglobal.com/articles/2005/533.html
  15. 15. http://www.modelingandcontrol.com/2009/03/application_notes.html</li></ul>Enhanced PID (PIDPlus) with wireless trigger level and noise band for patience at split range point and feedforward timing errors and to reduce limit cycles<br />Velocity limit and dynamic reset limit to slow down transition into split range<br />Precise valves (sliding stem with diaphragm actuators & digital positioners)<br />Splitter sets flow controllers instead of valves to isolate installed characteristic<br />Split range point chosen to compensate for differences in valve and process gain<br />Adaptive tuning and control to schedule tuning as function of PID output<br />
  16. 16. AC <br />1-1<br /> Smart Split Range Point<br />Reagent<br />Smart in terms of valve gain<br />compensation but not smart<br />in terms of valve sensitivity !<br />Small<br />(Fine)<br />Large<br />(Coarse)<br />Splitter<br />Split Range<br />Block<br />For large valve 4x small valve flow:<br />PID Small Large<br />OutValveValve<br />0% 0% 0%<br />20% 100% 0%<br />20% 100% 0%<br />100% 100% 100%<br />Neutralizer<br />PID Controller<br /> AT <br />1-1<br />
  17. 17. Smart Split Range Point<br />
  18. 18. AC <br />1-1a<br /> AC <br />1-1b<br /> PID Valve Sensitivity and Rangeability Solution 1 <br />Reagent<br />Large<br />(Coarse)<br />Small<br />(Fine)<br />Neutralizer<br />PID Controller<br />or PIDPlus with<br />sensitivity limit<br /> AT <br />1-1<br />Proportional only Controller<br />or PIDPlus with<br />sensitivity limit<br />
  19. 19. AC <br />1-1<br /> ZC <br />1-1<br /> PID Valve Sensitivity and Rangeability Solution 2 <br />Reagent<br />Small<br />(Fine)<br />Large<br />(Coarse)<br />Integral only Controller<br />or PIDPlus with<br />sensitivity limit<br />Neutralizer<br />PID Controller<br />or PIDPlus with<br />sensitivity limit<br /> AT <br />1-1<br />
  20. 20. Nomenclature<br />Ao = amplitude of limit cycle (%)<br />Bv = valve backlash (deadband) (%)<br />G = split range gap (%)<br />Kc = PID gain (dimensionless)<br />Kv1 = valve 1 gain (Flow e.u. / CO %)<br />Kv2 = valve 2 gain (Flow e.u. / CO %)<br />Kp1 = process gain for valve 1(PV e.u. / Flow e.u.)<br />Kp2 = process gain for valve 2(PV e.u. / Flow e.u.)<br />Km = measurement gain (CV % / PV e.u.)<br />S1 = 1st split ranged span (PV e.u.)<br />S2 = 2nd split ranged span (PV e.u.)<br />Sm = span of measurement scale (PV e.u.)<br />Sv = valve stiction (resolution) (%)<br />Ti = PID integral time (sec/repeat)<br />To = period of limit cycle (sec)<br />
  21. 21. Split Range Demo 1<br />Objective –Show effect of the standard split range point<br />Activities:<br />In Lab04 Splitter verify traditional split range array = 0 50 50 100<br />Click on Trend icon next to faceplate icon and look at Lab04 chart <br />In Lab04Splitter detail vary low load between 5% and 15% and check response<br />In Lab04Splitter detail varyhigh load between 35% and 45% and check response<br />
  22. 22. Split Range Demo 2<br />Objective– Show effect of the smart split range point<br />Activities:<br />In Lab04 Splitter detailset smart split range array = 0 20 20 100<br />In Lab04Splitter detail varylow load between 5% and 15% and check response<br />In Lab04Splitter detail vary high load between 35% and 45% and check response<br />
  23. 23. Split Range Demo 3<br />Objective– Show effect of standard PID for stiction at split range point<br />Activities:<br />In Lab04 Splitter detail use smart split range array = 0 20 20 100<br />In Lab04 Splitter detail set increased stiction zone = 20%<br />In Lab04 Valve1 and Valve2 detail set stiction resolution step = 0.5%<br />In Lab04Splitter detail setload 25% and check response<br />
  24. 24. 100%<br />90%<br />x<br />o<br />80%<br />o<br />70%<br />Valve<br />Signal<br />x<br />x<br />o<br />60%<br />o<br />Valve Signal<br />and Actual Stroke<br />50%<br />x<br />o<br />x<br />o<br />40%<br />Actual<br />Valve <br />Stroke<br />x<br />x<br />o<br />30%<br />o<br />20%<br />x<br />o<br />x<br />10%<br />o<br />x<br />o<br />x<br />0%<br />0<br />3<br />4<br />6<br />1<br />2<br />5<br />7<br />9<br />8<br />10<br />Digital Updates<br />Sensitivity (Threshold Effect)<br />
  25. 25. 100%<br />90%<br />x<br />o<br />80%<br />o<br />x<br />70%<br />Valve<br />Signal<br />o<br />x<br />60%<br />o<br />Valve Signal <br />and Actual Strokes<br />x<br />50%<br />o<br />x<br />o<br />x<br />40%<br />Actual<br />Valve<br />Stroke<br />o<br />x<br />30%<br />o<br />x<br />20%<br />o<br />x<br />10%<br />o<br />x<br />x<br />o<br />0%<br />0<br />3<br />4<br />6<br />1<br />2<br />5<br />7<br />9<br />8<br />10<br />Digital Updates<br />Resolution (Quantization Effect)<br />
  26. 26. Split Range Demo 4<br />Objective– Show effect of standard PID for stiction at split range point<br />Activities:<br />In Lab04 Splitter detail use smart split range array = 0 20 20 100<br />In Lab04 Splitter detail set increased stick-slip zone = 20%<br />In Lab04 Valve1 and Valve2 detail set stiction resolution step = 0.5%<br />In Lab04 Measurements detail set Refresh = 1000 sec and Sensitivity = 1%<br />In Lab04 PID detail enablePIDPlus<br />
  27. 27. Recommendations<br /><ul><li>Use smart split range point
  28. 28. compensates for gross differences in manipulated flows
  29. 29. Use cascade control where splitter output is flow controller setpoint
  30. 30. isolates valve nonlinearity from process PID
  31. 31. Use valve position control to increase sensitivity and rangeability
  32. 32. Use smart proportioned load and setpoint feedforward
  33. 33. Use precise control valves with valve drop > 25% system drop and 2x actuator size
  34. 34. Use PIDPlus (sensitivity set to ignore insignificant measurement & valve changes)
  35. 35. eliminates limit cycles
  36. 36. reduces transitions across split range point
  37. 37. reduces valve position control interactions
  38. 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. 39. reduces reagent use and energy use and avoids vent system overload
  40. 40. Use smart directional velocity limit and dynamic reset limit to slow down valve position control to avoid unnecessary corrections and reduce interaction
  41. 41. Mount jacket temperature sensor sufficiently downstream to reduce steam shock
  42. 42. For opposing manipulated flows, use adaptive tuning and control to compensate for changes in process gain, deadtime, and time constant </li></li></ul><li>Visit http://www.processcontrollab.com/to Create Valuable New Skills<br /><ul><li>Free State of the Art Virtual Plant
  43. 43. Not an emulation but a DCS (SimulatePro)
  44. 44. Independent Interactive Study
  45. 45. Structural Changes “On the Fly”
  46. 46. Advanced PID Options and Tuning Tools
  47. 47. Enough variety of valve, measurement, and process dynamics to study 90% of the process industry’s control applications
  48. 48. Learn in 10 minutes rather than 10 years
  49. 49. Online Performance Metrics
  50. 50. Standard Operator Graphics & Historian
  51. 51. Control Room Type Environment
  52. 52. No Modeling Expertise Needed
  53. 53. No Configuration Expertise Needed
  54. 54. Rapid Risk-Free Plant Experimentation
  55. 55. Deeper Understanding of Concepts
  56. 56. Process Control Improvement Demos
  57. 57. Sample Lessons (Recorded Deminars)</li></ul>A new easy fast free method of access is now available that eliminates <br />IT security issues and remote access response delays<br />
  58. 58. Help Us Improve These Deminars!<br />WouldYouRecommend.Us/105679s21/<br />
  59. 59. Join Us June 8, Wednesday 10:00 am CDT<br />PID Control for Sustainable Manufacturing (How PID features can increase process efficiency and capacity and provide environmental and property protection)<br />Look for a recording of Deminar 12 at: www.ModelingAndControl.com<br />www.EmersonProcessXperts.com<br />
  60. 60. QUESTIONS? <br />Thank you for attending – book drawing!<br />Now Available for purchase at amazon.com and the isa bookstore<br />

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