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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

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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  • 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
  • 14. Split Range Solutions
    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
    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)
    Smart proportioned feedforward control to help solutions 1 and 2
    Model Predictive Control for rangeability and different costs - see article “Model Predictive Control can Solve Valve Problem” and Application Notes 1 and 2
    • http://www.controlglobal.com/articles/2005/533.html
    • 15. http://www.modelingandcontrol.com/2009/03/application_notes.html
    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
    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
  • 27. Recommendations
    • Use smart split range point
    • 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
    • 42. For opposing manipulated flows, use adaptive tuning and control to compensate for changes in process gain, deadtime, and time constant
  • Visit http://www.processcontrollab.com/to Create Valuable New Skills
    • Free State of the Art Virtual Plant
    • 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

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