Split Range Control - Greg McMillan Deminar
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Transcript of Split Range Control - Greg McMillan Deminar
Slide 1
Interactive Opportunity AssessmentInteractive Opportunity Assessment
Demo and Seminar (Deminar) Series for Web Labs –
Split Range Control March 9, 2011
Sponsored by Emerson, Experitec, Monsanto, & MynahCreated by
Greg McMillan and Jack Ahlerswww.processcontrollab.com Website - Charlie Schliesser (csdesignco.com)
[File Name or Event]Emerson Confidential27-Jun-01, Slide 2 Slide 2
Welcome 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/
[File Name or Event]Emerson Confidential27-Jun-01, Slide 3 Slide 3
ISA Automation Week - Oct 17-20ISA Automation Week - Oct 17-20
Call for PapersDeadline is March 28 !
[File Name or Event]Emerson Confidential27-Jun-01, Slide 4 Slide 4
Legends Cutler and Liptak Give KeynotesLegends Cutler and Liptak Give Keynotes
[File Name or Event]Emerson Confidential27-Jun-01, Slide 5 Slide 5
Top Ten Signs of an Excellent Operator Training System (OTS)
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 2011http://www.controlglobal.com/articles/2011/AutomationOperators1102.html
[File Name or Event]Emerson Confidential27-Jun-01, Slide 6 Slide 6
(1) Executives ask operators to autograph screen prints of online process metrics
Top Ten Signs of an Excellent Operator Training System (OTS)
Top Ten Signs of an Excellent Operator Training System (OTS)
[File Name or Event]Emerson Confidential27-Jun-01, Slide 7 Slide 7
New Split Range Lab04New Split Range Lab04
PID Output is split between multiple final control elements, such as dampers, valves, and VFDs
[File Name or Event]Emerson Confidential27-Jun-01, Slide 8 Slide 8
Valve 1
Valve 2
Load to set valves operating point
Zone near seat where stiction is increasedS’v = Sv * (1+ Zone-Stroke)
Splitter DetailSplitter Detail
[File Name or Event]Emerson Confidential27-Jun-01, Slide 9 Slide 9
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 Applications
[File Name or Event]Emerson Confidential27-Jun-01, Slide 10 Slide 10
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
Split Range Problems
[File Name or Event]Emerson Confidential27-Jun-01, Slide 11 Slide 11
The Essential Problem
[File Name or Event]Emerson Confidential27-Jun-01, Slide 12 Slide 12
0
10
20
30
40
50
60
70
80
90
100
0 10 20 30 40 50 60 70 80 90 100
Inherent Characteristic
Installed Characteristic 1
Installed Characteristic 2
Installed Characteristic 3
Installed Characteristic 4
Valve pressure drop ratio (DPR)for installed characteristic:
Characteristic 1: DPR = 0.5 Characteristic 2: DPR = 0.25Characteristic 3: DPR = 0.125Characteristic 4: DPR = 0.0625
Installed Valve Characteristic for Equal Percentage Trim
[File Name or Event]Emerson Confidential27-Jun-01, Slide 13 Slide 13
ovo KSA
]1)/(1[4 coio KKTT
mpvo KKKK
Limit Cycles from Stick-Slip and Backlash
mm S
K%100
cvo KBA /
)]/(21[5 5.0cio KTT
Stiction
Backlash
[File Name or Event]Emerson Confidential27-Jun-01, Slide 14 Slide 14
1. 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
2. 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)
3. Smart proportioned feedforward control to help solutions 1 and 2
4. 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
5. 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
6. Velocity limit and dynamic reset limit to slow down transition into split range
7. Precise valves (sliding stem with diaphragm actuators & digital positioners)
8. Splitter sets flow controllers instead of valves to isolate installed characteristic
9. Split range point chosen to compensate for differences in valve and process gain
10. Adaptive tuning and control to schedule tuning as function of PID output
Split Range Solutions
[File Name or Event]Emerson Confidential27-Jun-01, Slide 15 Slide 15
Smart Split Range Point Smart Split Range Point
Neutralizer
AC 1-1
AT 1-1
PID Controller
Large(Coarse)
Small(Fine)
Splitter
Split RangeBlock
Reagent
For large valve 4x small valve flow:
PID Small LargeOut Valve Valve
0% 0% 0%20% 100% 0%20% 100% 0%100% 100% 100%
Smart in terms of valve gaincompensation but not smartin terms of valve sensitivity !
[File Name or Event]Emerson Confidential27-Jun-01, Slide 16 Slide 16
Smart Split Range Point
222
111 S
KK
KKS
pv
pv
21 100 SGS
)100(2211
111 G
KKKK
KKS
pvpv
pv
[File Name or Event]Emerson Confidential27-Jun-01, Slide 17 Slide 17
PID Valve Sensitivity and Rangeability Solution 1
PID Valve Sensitivity and Rangeability Solution 1
Neutralizer
AC 1-1a
AT 1-1
PID Controlleror PIDPlus withsensitivity limit
Large(Coarse)
Small(Fine)
AC 1-1b
Proportional only Controlleror PIDPlus withsensitivity limit
Reagent
[File Name or Event]Emerson Confidential27-Jun-01, Slide 18 Slide 18
PID Valve Sensitivity and Rangeability Solution 2
PID Valve Sensitivity and Rangeability Solution 2
Neutralizer
AC 1-1
AT 1-1
PID Controlleror PIDPlus withsensitivity limit
Large(Coarse)
Small(Fine)
ZC 1-1
Integral only Controlleror PIDPlus withsensitivity limit
Reagent
[File Name or Event]Emerson Confidential27-Jun-01, Slide 19 Slide 19
NomenclatureAo = 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)
[File Name or Event]Emerson Confidential27-Jun-01, Slide 20 Slide 20
Split Range Demo 1Split 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 Lab04 Splitter detail vary low load between 5% and 15% and check response– In Lab04 Splitter detail vary high load between 35% and 45% and check response
[File Name or Event]Emerson Confidential27-Jun-01, Slide 21 Slide 21
Split Range Demo 2Split Range Demo 2 Objective – Show effect of the smart split range point
Activities:– In Lab04 Splitter detail set smart split range array = 0 20 20 100– In Lab04 Splitter detail vary low load between 5% and 15% and check response– In Lab04 Splitter detail vary high load between 35% and 45% and check response
[File Name or Event]Emerson Confidential27-Jun-01, Slide 22 Slide 22
Split Range Demo 3Split 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 Lab04 Splitter detail set load 25% and check response
[File Name or Event]Emerson Confidential27-Jun-01, Slide 23 Slide 23
o
x
x
o
x
o
o
o
o
o
o
o
o
ox
x
x
x
x
xx
x
ActualValve Stroke
ValveSignal
Val
ve S
ign
alan
d A
ctua
l Str
oke
Digital Updates0 1 2 3 4 5 6 7 8 9 10
0%
90%
80%
70%
60%
50%
40%
30%
20%
10%
100%
Sensitivity (Threshold Effect)
[File Name or Event]Emerson Confidential27-Jun-01, Slide 24 Slide 24
Resolution (Quantization Effect)
Digital Updates
o
o
o
o
o
o
o
o
o
o
x
x
x
x
x
x
x
x
x
x
o
x
ActualValve
Stroke
ValveSignal
0 1 2 3 4 5 6 7 8 9 100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
100%V
alve
Sig
nal
an
d A
ctua
l Str
oke
s
[File Name or Event]Emerson Confidential27-Jun-01, Slide 25 Slide 25
Split Range Demo 4Split 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 enable PIDPlus
[File Name or Event]Emerson Confidential27-Jun-01, Slide 26 Slide 26
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
[File Name or Event]Emerson Confidential27-Jun-01, Slide 27 Slide 27
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A new easy fast free method of access is now available that eliminates IT security issues and remote access response delays
[File Name or Event]Emerson Confidential27-Jun-01, Slide 28 Slide 28
Help Us Improve These Deminars!Help Us Improve These Deminars!
WouldYouRecommend.Us/105679s21/
[File Name or Event]Emerson Confidential27-Jun-01, Slide 29 Slide 29
Join Us June 8, Wednesday 10:00 am CDTJoin 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
[File Name or Event]Emerson Confidential27-Jun-01, Slide 30 Slide 30
QUESTIONS? QUESTIONS?
THANK YOU FOR ATTENDING – BOOK DRAWING!
NOW AVAILABLE FOR
PURCHASE AT AMAZON.COM
AND THE ISA BOOKSTORE
THANK YOU FOR ATTENDING – BOOK DRAWING!
NOW AVAILABLE FOR
PURCHASE AT AMAZON.COM
AND THE ISA BOOKSTORE