pid control of slow valves and secondary loops greg mcmillan deminar series

Interactive Opportunity Interactive Opportunity AssessmentAssessmentInteractive Opportunity Interactive Opportunity AssessmentAssessment

Demo and Seminar (Deminar) Series for Web Labs –

PID Control of Slow Valves and Secondary Loops

May 12, 2010Sponsored by Emerson, Experitec, and Mynah

Created byGreg McMillan and Jack Ahlers

[File Name or Event]Emerson Confidential27-Jun-01, Slide 2 Slide 2

WelcomeWelcome WelcomeWelcome 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, and was honored by InTech Magazine in 2003 as one of the most influential innovators in automation. 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/


The Latest on Unleashing PID Power The Latest on Unleashing PID Power for Batch Processesfor Batch Processes

The Latest on Unleashing PID Power The Latest on Unleashing PID Power for Batch Processesfor Batch Processes

Chapter 3 Features:Chapter 3 Features:PID Types and StructuresPID Types and Structures

Positive Feedback Integral ModePositive Feedback Integral ModeDynamic Reset LimitingDynamic Reset Limiting

Cascade LoopsCascade LoopsFull Throttle StartupFull Throttle Startup

Appendix C Features:Appendix C Features:Unification of Tuning MethodsUnification of Tuning Methods


Question?Question?Question?Question?

Why does a loop with a large upset oscillate but is fine for small upset Why does a loop with a large control valve oscillate Why does a loop with a detuned secondary PID oscillate Why does a loop with a slow secondary process measurement (e.g.

fouled sensor or large signal filter) oscillate


Question?Question?Question?Question?

Why does a loop with a large upset oscillate but is fine for small upset Why does a loop with a large control valve oscillate Why does a loop with a detuned secondary PID oscillate Why does a loop with a slow secondary process measurement (e.g.

fouled sensor or large signal filter) oscillate

Answer : Controller output is changing faster Answer : Controller output is changing faster than the valve or secondary loop can respondthan the valve or secondary loop can respond


Top Ten Things You Don’t Want to Hear in a Top Ten Things You Don’t Want to Hear in a Project Definition MeetingProject Definition Meeting


(10) I don’t want any smart instrumentation talking back to me (9) Let’s study each loop to see if the valve really needs a positioner (8) Lets slap an actuator on our piping valves and use them for control

valves (7) We just need to make sure the control valve spec requires the

tightest shutoff (6) What is the big deal about process control, we just have to set the

flow per the PFD (5) Cascade control seems awfully complex (4) The operators can tune the loops (3) Let’s do the project for half the money in half the time (2) Let’s go with packaged equipment and let the equipment supplier

select and design the automation system

And the Number 1 Thing You Don’t Want to Hear :




(1) Let’s go out for bids and have purchasing pick the best deal


Loop Lab02 Demo 1Loop Lab02 Demo 1Loop Lab02 Demo 1Loop Lab02 Demo 1 Objective – Show access to cascade loop lab setup and

how to make load upsets to see response for fast valve Activities:

– Show access to Cascade Loop Lab02 user interface

– Show access to PID faceplate and detail

– Show access to “Process History View” trend chart

– Click on secondary PID faceplate and put secondary PID in AUTO mode

– Make load change to show secondary response by putting secondary PID momentarily in manual and changing its output (e.g. 50% to 60%)

– Click on any block in block diagram to access Detail for parameters that will be changed in these demos via tabs for PID, process, and valve

– Put secondary PID in CAS mode and click on primary PID faceplate

– Make load change to show cascade response by putting primary PID momentarily in manual and changing its PID output (e.g. 50% to 60%)

Note: AC1-1 is primary PID and AC1-2 is secondary PID


Volume Booster with Integral BypassVolume Booster with Integral Bypass(Furnace Pressure and Surge Control(Furnace Pressure and Surge ControlVolume Booster with Integral BypassVolume Booster with Integral Bypass(Furnace Pressure and Surge Control(Furnace Pressure and Surge Control

Signal from Positioner

Air Supply fromFilter-Regulator

Air Loadingto Actuator

Adjustable BypassNeedle Valve


Booster and Positioner SetupBooster and Positioner Setup(Furnace Pressure and Surge Control)(Furnace Pressure and Surge Control)

Booster and Positioner SetupBooster and Positioner Setup(Furnace Pressure and Surge Control)(Furnace Pressure and Surge Control)

Port A

Port B

Supply

ZZ

ZZ

ZZ

Z

Control Signal

Digital Valve Controller

Must be functionally tested

before commissioning!

1:1

Bypass

VolumeBooster

Open bypass justenough to ensurea non-oscillatory

fast response

Air Supply

High CapacityFilter Regulator

Increase air line size

Increase connection size

Terminal Box


Loop Lab02 Demo 2Loop Lab02 Demo 2Loop Lab02 Demo 2Loop Lab02 Demo 2 Objective – Show response of secondary PID to slow

valve for small and large upsets Activities:

– First look at Demo 1 for fast valve and fast secondary loop

– Click on any block in block diagram – Click on Control Valve tab

– Change Slew Inc and Slew Dec of valve from 100%/sec to 1%/sec

– Click on secondary PID faceplate and put secondary PID in AUTO mode

– Make small load change to show response by putting secondary PID momentarily in manual and changing its PID output (e.g. 50% to 52%)

– Make large load change to show response by putting secondary PID momentarily in manual and changing its PID output (e.g. 50% to 70%)


Ramping Response of Actuator for a Ramping Response of Actuator for a Large Step or a Large ActuatorLarge Step or a Large Actuator

Ramping Response of Actuator for a Ramping Response of Actuator for a Large Step or a Large ActuatorLarge Step or a Large Actuator

0

5

10

15

20

25

30

35

40

45

50

0 1 2 3 4 5 6 7 8 9 10

Time (sec)

Str

oke

(%)

Multiply time by 10 for large actuator without volume booster


Exponential Response of Actuator for Exponential Response of Actuator for a Small Step or a Small Actuatora Small Step or a Small Actuator

Exponential Response of Actuator for Exponential Response of Actuator for a Small Step or a Small Actuatora Small Step or a Small Actuator

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0 1 2 3 4 5 6 7 8 9 10

Str

oke

(%)

Time (sec)


Loop Lab02 Demo 3Loop Lab02 Demo 3Loop Lab02 Demo 3Loop Lab02 Demo 3 Objective – Show response of secondary PID with

Dynamic Reset Limit to slow valve Activities:

– First look at Demo 2 for slow valve

– Click on any block in block diagram – Click on PID tab

– Enable Dynamic Reset Limit for secondary PID

– Make large load change to show response by putting secondary PID momentarily in manual and changing its PID output (e.g. 50% to 70%)


Positive Feedback Implementation of Positive Feedback Implementation of Integral Mode with Dynamic Reset LimitIntegral Mode with Dynamic Reset Limit

Positive Feedback Implementation of Positive Feedback Implementation of Integral Mode with Dynamic Reset LimitIntegral Mode with Dynamic Reset Limit

SP

proportional

derivative

Gain

Rate

CO

filter

filter

CV filterFilter Time Rate Time

filter

Filter Time = Reset Time

ER is external reset(e.g. secondary PV)Dynamic Reset Limit

ER

PositiveFeedback


Loop Lab02 Demo 4Loop Lab02 Demo 4Loop Lab02 Demo 4Loop Lab02 Demo 4 Objective – Show response of self-regulating primary

PID to slow secondary loop for small and large upsets Activities:

– First look at Demo 3 with dynamic reset limit for slow valve

– Click on any block in block diagram – Click on Control Valve tab

– Change valve Slew Inc and Slew Dec from 1%/sec to 100%/sec

– Click on PID tab and disable Dynamic Reset Limit for secondary PID

– Click on Process tab and increase secondary Lag 2 Inc and Lag 2 Dec from 2 to 10 sec

– On secondary PID detail, increase reset time from 2 to 10 sec

– Put secondary PID is in CAS mode

– Click on primary PID faceplate and detail

– Make small load change to show response by putting primary PID momentarily in manual and changing its PID output (e.g. 50% to 52%)

– Make large load change to show response by putting primary PID momentarily in manual and changing its PID output (e.g. 50% to 70%)


Cascade Control Benefit Cascade Control Benefit (self-regulating process) (self-regulating process) Cascade Control Benefit Cascade Control Benefit (self-regulating process) (self-regulating process)

io

io

io

iinner loop process time constant

oouter loop process time constant

iinner loop process deadtime

oouter loop process deadtime


Loop Lab02 Demo 5Loop Lab02 Demo 5Loop Lab02 Demo 5Loop Lab02 Demo 5 Objective – Show response of self-regulating primary

PID with Dynamic Reset Limit to slow secondary loop Activities:

– First look at Demo 4 for slow secondary PID


– Enable Dynamic Reset Limit for primary PID



Cascade Control Benefit Cascade Control Benefit (integrating process) (integrating process)

Cascade Control Benefit Cascade Control Benefit (integrating process) (integrating process)

io

io

io

iinner loop process time constant

oouter loop process time constant

iinner loop process deadtime

oouter loop process deadtime


Loop Lab02 Demo 6Loop Lab02 Demo 6Loop Lab02 Demo 6Loop Lab02 Demo 6 Objective – Show response of integrating primary PID

to fast secondary loop for small and large upsets Activities:

– First look at Demo 5 with dynamic reset limit for slow secondary PID

– Click on PID tab and disable Dynamic Reset Limit for primary PID

– Click on Process tab and decrease secondary Lag 2 Inc and Lag 2 Dec from 10 to 2 sec

– On secondary PID detail, decrease reset time from 10 to 2 sec

– On Primary PID detail, increase reset time from 10 to 50 sec

– Click on Process tab, increase primary Lag 2 Inc and Lag 2 Dec from 10 to 50 sec, and then change process type to integrating

– On Primary PID detail, increase gain from 1.0 to 5.0 and add 2 sec rate




Effect of Slow Secondary Loop Effect of Slow Secondary Loop (cascade control integrating process)(cascade control integrating process) Effect of Slow Secondary Loop Effect of Slow Secondary Loop

(cascade control integrating process)(cascade control integrating process)

Secondary loop slowed down by a factor of 5

Secondary SP

Secondary CO

Primary PV

Secondary SP

Primary PV

Secondary CO



to slow secondary loop for small and large upsets Activities:

– First look at Demo 6 of integrating process for fast secondary PID

– Click on Process tab and increase secondary Lag 2 Inc and Lag 2 Dec from 2 to 10 sec

– On secondary PID detail, increase reset time from 2 to 10 sec




Top Ten Things Missing in University Top Ten Things Missing in University Courses on Process ControlCourses on Process Control


(10) Control valves with backlash, stick-slip, and slewing rates (9) Measurements with slow sensors or damping settings (8) Volumes with mixing lags dependent upon agitation and geometry (7) Volumes with transportation delays dependent on flow rate (6) Control action (direct and reverse) and valve action (inc-open and

inc-close) (5) Control algorithms for anti-reset windup and dynamic reset limit (4) PID structures and options (3) Industry standards for function blocks and communication (2) Control and InTech magazines

And the Number 1 Thing Missing in University Courses:




(1) ISA books



with Dynamic Reset Limit to slow secondary loop Activities:

– First look at Demo 7 of integrating process for slow secondary PID


– Enable Dynamic Reset Limit for primary PID



SolutionsSolutionsSolutionsSolutions

Select secondary loops that are 4x faster than primary loop Use boosters on valve positioner output(s) for large valves Tune secondary controllers for a fast response Minimize secondary measurement filter and damping settings and

keep secondary sensors clean (e.g. electrodes and thermowells) Use Dynamic Reset Limit in secondary PID for slow valve Use Dynamic Reset Limit in primary PID for slow secondary PID


Summary of DemosSummary of DemosSummary of DemosSummary of Demos

Demo SecPID

Mode

SecondaryDynamic

Reset

PrimaryDynamic

Reset

ValveSlewRate

SecondaryProcess

Response

PrimaryProcess

Type

1 CAS Disabled Disabled Fast Fast Self-Reg

2 AUTO Disabled Disabled Slow Fast Self-Reg

3 AUTO Enabled Disabled Slow Fast Self-Reg

4 CAS Disabled Disabled Fast Slow Self-Reg

5 CAS Disabled Disabled Fast Slow Self-Reg

6 CAS Disabled Disabled Fast Fast Integ

7 CAS Disabled Disabled Fast Slow Integ

8 CAS Disabled Enabled Fast Slow Integ


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Look for a recording of Today’s Deminar Look for a recording of Today’s Deminar later this week at:later this week at:www.ModelingAndControl.com

www.EmersonProcessXperts.com


QUESTIONS? QUESTIONS? QUESTIONS? QUESTIONS?

pid control of slow valves and secondary loops greg mcmillan deminar series

Education

process control

large control valve

cascade control

control valves

control valve spec

secondary response

fast secondary loop

ph control