Does Your DCS Deliver? A Tutorial on Measuring …Standards Certification Education & Training...
Transcript of Does Your DCS Deliver? A Tutorial on Measuring …Standards Certification Education & Training...
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Standards
Certification
Education & Training
Publishing
Conferences & Exhibits
Does Your DCS Deliver?
A Tutorial on Measuring
Control Performance
George Buckbee, P.E.
ExperTune, Inc.
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Presenter
• George Buckbee is V.P. of Product Development at
ExperTune. George holds a B.S. in Chemical
Engineering from Washington University in St. Louis, and
an M.S. in Chemical Engineering from the University of
California at Santa Barbara. His 25 years of industry
experience have been focused in the field of process
control. George is the author of several books, and
dozens of articles. In 2011, George was selected as an
ISA Fellow.
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Abstract
Does Your DCS Deliver?
• Industry guru Peter Drucker once said “You can’t control what you don’t measure, and you can’t
manage what you don’t control.” A Distributed Control System (DCS) is an investment that needs
to be managed, controlled, and measured.
• A Distributed Control System (DCS), along with instrumentation and control valves may cost tens
of millions of dollars. Management rightly wants to know about the control system performance,
and especially the return on the investment. Yet many plants do not measure any aspects of
control performance.
• That trend is changing, however, with modern tools and techniques that can be used to document
the specifics of control system performance. This tutorial explains methods to measure and
monitor control performance, and provides useful tips for improving plant results such as quality,
safety, energy costs, and production.
• This presentation will start with the basics of simple statistical performance measurement, then
progress through more sophisticated techniques, including evaluation of controller dynamic
performance and oscillations. The presentation will cover selecting performance metrics that are
measurable, meaningful, and actionable. Finally, the audience will learn how to combine simple
performance measures into powerful diagnostics for instrumentation, valves, and controllers.
• While sophisticated analysis is presented, this presentation does not require an extensive
mathematical background. Operations management, process and control engineers, and
instrument technicians will all benefit from this discussion.
• When controller performance is measured, many process and control improvements become
instantly obvious. Attendees at this presentation will return to their plants armed with techniques
for measuring, controlling, and improving the performance of their control systems.
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Agenda
Motivations
What is Control System Performance?
Measuring Control System Performance
Diagnostics and Corrective Actions
Conclusions, Q&A
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Motivations:
The Purpose of Control Systems
• What is the Purpose of a Control System?
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Reduce Effect of Disturbances
Ensure Stability
Optimize the Process
Ref #1
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Motivations
• Isn’t it good enough?
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7#
Motivations:
Typical Control System Performance
Typical Statistics
• 10% - 90% Control Loops in Manual
• 30% Control Valves with Problems
• 30% Loops-Tuning is completely wrong
• 40% Loops Oscillating
• Improper PID Loop Configuration
– 30% DCS Systems
– 95% PID on PLC’s
• 85% Sub-Optimal Tuning
• 75% Control Loops increase variability
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Agenda
Motivations
What is Control System Performance?
Measuring Control System Performance
Diagnostics and Corrective Actions
Conclusions, Q&A
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The Purpose of Control:
Reducing the Effect of Disturbances
• Variation in Raw
Material
• Weather
• Operations
• Batch Operations
• Process Conditions
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The Purpose of Control:
Ensure Stability
• Thermal Processes
• Tank Overflows
• Pressure
• Chemical Reactions
• pH
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The Purpose of Control:
Optimize the Process
• Drive Toward
Optimum
• Hold at Best Setpoint
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Agenda
Motivations
What is Control System Performance?
Measuring Control System Performance
Diagnostics and Corrective Actions
Conclusions, Q&A
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Measuring Control Performance
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How do you know if your control system is
living up to it’s purpose?
“You can’t manage what
you can’t control, and you
can’t control what you don’t
measure.”
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Measuring Control Performance
• Criteria for Good Real-Time Performance Measures:
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• Affects the Bottom Line
• Easily UnderstoodMeaningful
• Can be Measured
• In Real Time, 24 x 7Measurable
• Direct Actions
• Immediate ResultsActionable
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15#
Guidance for Tracking & Managing
Control System Performance Data
• Match Business Objectives with Metrics
• Cover Each Unit Fully
– Most Upsets Come from Unexpected Places
• Integrate the Information Into Business Processes
• Follow-Up
• Document the Benefits
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Guidance for
Capturing Control System Performance Data
• Capture Data in Real-Time
• Metrics Should be:
– Measurable
– Meaningful
– Actionable
• Diagnostics Built on These Metrics
– Instrument & Valve Failures
– Loss of Control
– Cause of Oscillation
• Historize, Track, Drill Down, etc.
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Finding Root Cause
• Process vs. Instrument vs. Valve vs. Control
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Measure Decide Action
Jin Real Time
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Agenda
Motivations
What is Control System Performance?
Measuring Control System Performance
Diagnostics and Corrective Actions
Conclusions, Q&A
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Equipment Diagnostics :
Instrumentation
• Dead Instrument
PV Max = PV Min
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Equipment Diagnostics:
Instrumentation
• Spiking
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Equipment Diagnostics:
Oversized Valves
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Process & Control Oscillations
• Oscillation Period
– Fourier Transform
• Oscillation Shape
• Focus on Root
Cause
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What is “Good” Tuning?
• Flat Line?
• Fast SP Change?
• No Overshoot?
• Quarter Amplitude Damping?
• Fast disturbance rejection?
• Don’t move valve too much?
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Automated Tuning Methods
• Look for Bumps 24 x 7
• Automatically Model & Tune
• Compare to Existing Tuning
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Hours
Minutes
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Making the Fix!
• Fix the Right Thing
• Follow-Up
• Document the Results
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Difficult Problems – Interactions
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27#
Motivations:
Why Does it Matter?
• These Metrics:
– Significant Oscillations
– Variability
– Service Factor
– Opportunity Gap
– Controllability
– Valve Travel
– J
• Directly Impact:
– Energy Cost
– Quality
– Safety/Environmental
– Cost
– Waste, Recycle
– Maintenance Costs
– J
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Case Study:
The Challenge
• Distillation Column Swings
• Issues with newly-installed MPC controls when running
at different feed rates rather than design rates
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Oscillations When MPC Is Active
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Impact of Column Swings
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Process Interaction Analysis
(example shown without proprietary data)
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Tuning of Pressure Controller
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Case Study Results:
Stability, MPC, Steam
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Agenda
Motivations
What is Control System Performance?
Measuring Control System Performance
Diagnostics and Corrective Actions
Conclusions, Q&A
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Conclusions:
Possible Improvements
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Infrastructure Ensure
Performance
Optimize
Data Historian
OPC Server
Control Performance
Monitoring
Alarm
Management
Process
Modeling
APC /
MPC
KPIs
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Conclusions
1. Process Control Systems are not deliveringtheir
full benefit. There is significant business
opportunity in:a. Technical Measures
b. Proven Business Benefit
2. Continuous Improvement Requires:
a. Monitor 24x7
b. Diagnose
c. Prioritize
d. Resolve
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37Thank You!
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References
1. Stephanopoulos, George. Chemical Process Control,
Prentice-Hall, New Jersey, 1984
2. Buckbee, George, and Gordon, Lew. “True Control
System Objectives”, InTech. Sept 2009
3. Buckbee, George. Finding the Source of Cycling In
Process Plants. White Paper, 2010.
4. Buckbee, George. Finding the Root Cause of Process
Upsets. White Paper, 2010
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