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Split Range Control - Greg McMillan Deminar
 

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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    Split Range Control - Greg McMillan Deminar Split Range Control - Greg McMillan Deminar Presentation Transcript

    • 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)
    • 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/
    • ISA Automation Week - Oct 17-20
      Call for Papers
      Deadline is
      March 28 !
    • Legends Cutler and Liptak Give Keynotes
    •  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
    •  Top Ten Signs of an Excellent Operator Training System (OTS)
      (1) Executives ask operators to autograph screen prints of online process metrics
    • PID Output is split between multiple final control
      elements, such as dampers, valves, and VFDs
      New Split Range Lab04
    • 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)
    • 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
    • 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
    • The Essential Problem
      Nearly all split range loops oscillate
      across the split range point
      wearing out valves,
      wasting resources,
      and increasing
      process variability
    • 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
    • Limit Cycles from
      Stick-Slip and Backlash
      Stiction
      Backlash
    • 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
      • 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
    • 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
    • Smart Split Range Point
    • 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
    • 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
    • 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)
    • 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
    • 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
    • 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
    • 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)
    • 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)
    • 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
    • Recommendations
      • Use smart split range point
      • compensates for gross differences in manipulated flows
      • Use cascade control where splitter output is flow controller setpoint
      • isolates valve nonlinearity from process PID
      • Use valve position control to increase sensitivity and rangeability
      • Use smart proportioned load and setpoint feedforward
      • Use precise control valves with valve drop > 25% system drop and 2x actuator size
      • Use PIDPlus (sensitivity set to ignore insignificant measurement & valve changes)
      • eliminates limit cycles
      • reduces transitions across split range point
      • reduces valve position control interactions
      • Use smart directional velocity limit and dynamic reset limit to slow down transition into split range point to avoid unnecessary excursions to opposing flow
      • reduces reagent use and energy use and avoids vent system overload
      • Use smart directional velocity limit and dynamic reset limit to slow down valve position control to avoid unnecessary corrections and reduce interaction
      • Mount jacket temperature sensor sufficiently downstream to reduce steam shock
      • 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
      • Not an emulation but a DCS (SimulatePro)
      • Independent Interactive Study
      • Structural Changes “On the Fly”
      • Advanced PID Options and Tuning Tools
      • Enough variety of valve, measurement, and process dynamics to study 90% of the process industry’s control applications
      • Learn in 10 minutes rather than 10 years
      • Online Performance Metrics
      • Standard Operator Graphics & Historian
      • Control Room Type Environment
      • No Modeling Expertise Needed
      • No Configuration Expertise Needed
      • Rapid Risk-Free Plant Experimentation
      • Deeper Understanding of Concepts
      • Process Control Improvement Demos
      • 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
    • Help Us Improve These Deminars!
      WouldYouRecommend.Us/105679s21/
    • 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
    • QUESTIONS?
      Thank you for attending – book drawing!
      Now Available for purchase at amazon.com and the isa bookstore