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Control Loop Foundation Batch and Continuous
Processes
Control Loop Foundation Batch and Continuous
ProcessesTerry Blevins Principal Technologist
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PresentersPresenters
Terry Blevins, Principal Technologist
Mark Nixon, Manager, Future Architecture
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Control Loop Foundation Short CourseControl Loop Foundation Short Course IntroductionBackground – Historic PerspectiveMeasurement – Basic Transmitter Types, LimitationsAnalyzers – Examples of On-line AnalyzersFinal Elements – Valves and Variable Speed DrivesField Wiring and Communications – Traditional, HART, FF , WirelessHARTControl Strategy Documentation – Plot Plan, Flow Sheet, P&ID, Loop DiagramOperator Graphics and Metrics – Considerations in Display DesignProcess Characterization – Identifying process dynamics and gain Control ObjectivesSingle Loop Control – PID basics, selecting PID structure, action
Tuning and Loop Performance – Manual and automated tuning techniques Multi-loop Control – Feedforward, Cascade, Override, Split-rangeModel Predictive Control – Addressing Difficult Dynamics, InteractionsProcess Modeling – Process simulation for Checkout/TrainingApplications – Continuous, Batch, Combustion, Distillation Accessing the book web Site Open Discussions book drawing & Wrap-up
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Control Loop Foundation Short CourseControl Loop Foundation Short Course Short Course will provide a summary of
key points and examples from Control Loop Foundation
All workshops and application examples in the book are based on DeltaV control capability. This book is available at www.isa.org and this week at the ISA booth.
The application section is designed to show how control techniques may be combined to address more complex process requirements
The book web site may be accessed to perform the workshops and to obtain hands-on experience using application example. Copies of the modules and trends may be downloaded from the web site and imported into a DeltaV system.
A new class, Control Loop Foundation - Course 9025, Is available through the education department.
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IntroductionIntroduction
Control Loop Foundation address the concepts and terminology that are needed to work in the field of process control.
The material is presented in a manner that is independent of the control system manufacturer.
Much of the material on the practical aspects of control design and process applications is typically not included in process control classes taught at the university level.
The book is written to act as a guide for engineers who are just starting to work in this field.
Experienced control engineers will benefit from the application examples on process control design and implementation of multi-loop control strategies.
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Background - Different Construction TechniquesBackground - Different Construction Techniques
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Wiring PracticesWiring Practices
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Plant OrganizationPlant Organization
Common terms used to describe plant organization are introduced.
Plant Area – classification by name and area number
Units within a process Area
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Lab, Control Room, Lab and Rack RoomLab, Control Room, Lab and Rack Room
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Existing System – Electronic and Pneumatic Existing System – Electronic and Pneumatic
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Impact of DCS SystemsImpact of DCS Systems
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Integration of External System/InterfaceIntegration of External System/Interface
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Modern DCS ControllerModern DCS Controller
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Impact of Digital Communications Impact of Digital Communications
Ethernet Fieldbus –
Foundation Fieldbus, Profibus
Wireless - WirelessHART
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Wireless ImpactWireless Impact
• Wireless Field Devices• Relatively simple - Obeys
Network Manager• Gateway and Access
Points • Allows control system
access to WirelessHART Network Gateways
• Manages communication bandwidth and routing
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Impact of Standard on ControlImpact of Standard on Control ISA88 – Batch terminology IEC 61131 – Function blocks,
Ladder Logic, Structured Text, Sequential Function Charts.
IEC 61804 – Function blocks for the process industry,
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MeasurementMeasurement
Introduction to devices used for basic measurement– Magnetic flow meter– Vortex flow meter– Differential pressure for flow
measurement– Corilois flow meter– Absolute and gauge pressure– Temperature – RTD,
thermocouple– Level based on
pressure/differential pressure– Level - Radar
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Device CalibrationDevice Calibration
Concept of devices calibration and configuration is introduce.
Role of hand held devices and EDDL is addressed
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AnalyzersAnalyzers
Difference between sampling and situ analyzers is addressed
Impact of sampling system on maintenance and measurement delay is highlighted
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Analyzer ExampleAnalyzer Example
A couple of common situ analyzers are addressed to show features and options– Flue Gas O2 – pH/ORP
Calibration of analyzer and role of sample/hold when used in control is addressed.
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Final Control ElementFinal Control Element
Basic final control elements are addressed:– Sliding stem valve– Rotarty valve– Damper drive– Variable speed drive– Block valve
Advantages and limitations are discussed
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Final Control Element TerminologyFinal Control Element Terminology
Common terms associated with final control elements are defined– Positioner– Actuator– Valve Body
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Installed CharacteristicsInstalled Characteristics
Types of valve characteristics and their impact on installed characteristics is addressed
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Field Wiring and CommunicationsField Wiring and Communications Installation of 2-wire vs 4-wire devices is addressed Common problems are address e.g. need for electric isolation when
utilizing a 4-wire device
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Fieldbus InstallationFieldbus Installation
Special requirements for a fieldbus installation are addressed
Common terminology is defined:– Multi-drop– Power
conditioner– Terminator
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Control System DocumentationControl System Documentation
Documentation that is typically generated for a control system installation are addressed.
The purpose of each document is explained.
Reference provided to ISA-5.4 standard for Instrument Loop Diagrams
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Tag Convention – ISA S5.1Tag Convention – ISA S5.1
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Representation of Signals and InstrumentsRepresentation of Signals and Instruments
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Symbols for Field devices and ElementsSymbols for Field devices and Elements
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Process SymbolsProcess Symbols
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Symbol Example – P&ID DrawingSymbol Example – P&ID Drawing
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Symbol Example(Cont.)Symbol Example(Cont.)
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Symbol Example(Cont.)Symbol Example(Cont.)
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Symbol Example(Cont.)Symbol Example(Cont.)
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Display Observing Color Usage
Operator Graphics and MetricsOperator Graphics and Metrics
An operator interface design is addressed by Alarm Standard EEMUA 191
Advocates that alarms should be in alarm color. Pipes, pumps, valves, etc. should not be in alarm colors, or any other bright color.
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Display ToolsDisplay Tools Basic tools for construction
a display are discussed– Dynamos, dynamic elements,
faceplates, links for creating a display hierarchy
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Performance Metrics Performance Metrics
Example used to illustrate how operation metrics may be added to an operator display
Benefits of integrating this type of information into the operator interface
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·A plant may be thought of as being made up of a series of processes.
·A good understanding of these processes is required to design a control system for the plant.
Process CharacterizationProcess Characterization
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Process DefinitionProcess Definition
Process – Specific equipment configuration (in a manufacturing plant)
which acts upon inputs to produce outputs.
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Process TerminologyProcess Terminology
Controlled output (controlled parameter) – Process output that is to be maintained at a desired value by adjustment of process input(s).
Setpoint – Value at which the controlled parameter is to be maintained by the control system.
Manipulated input (manipulated parameter) – Process input that is adjusted to maintain the controlled parameter at the setpoint.
Disturbance input – Process input, other than the manipulated input, which affects the controlled parameter.
Constraint output (constraint parameter) – Process output that must be maintained within an operating range.
Constraint limit – Value that a constraint parameter must not exceed for proper operation of the process.
Other input – Process input that has no impact on controlled or constraint outputs.
Other output – Process output other than controlled or constraint outputs.
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Example – Application of TerminologyExample – Application of Terminology
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Impact of Disturbance InputImpact of Disturbance Input
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Example – Lime Mud Filter ProcessExample – Lime Mud Filter Process
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Example – Lime Mud Filter ( Cont.)Example – Lime Mud Filter ( Cont.)
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Pure Gain ProcessPure Gain Process
When the process output tracks the process input except for a change in signal amplitude, the process is known as a pure gain.
The change in signal amplitude is determined by the process gain.
For a step change in process input, the process gain is defined as the change in the process output divided by the change in process input
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Example – Pure Gain ProcessExample – Pure Gain Process
An example of a pure gain process is the jack shaft used in some boiler combustion control systems.
Gain is determine by the length of the lever arms attached to the jack shaft.
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Pure Delay ProcessPure Delay Process
When the process output tracks the process input except for a delay in the output signal, the process is know as a pure delay process.
For a step change in the process input, process deadtime is defined as the time from the input changing until the first affect of the change is seen in the process output.
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Examples – Pure Delay ProcessExamples – Pure Delay Process
Example of pure delay processes are a conveyor belt and a pipeline.
Delay is the result of transport time and will vary with the speed of the belt or the flow rate through the pipe.
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First Order ProcessFirst Order Process When process
output immediately begin to respond to a step change in a process input and the rate of change is proportional to its current value and the final value the output will achieve, the process is know as a first order process.
The dynamic response is fully captured by identifying the process gain and the process time constant.
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Example – First Order ProcessExample – First Order Process
An example of a pure lag process is a tank with outlet flow determined by tank level and the outlet flow restriction caused by the orifice.
The level will settle at a value which results in an outlet flow that matches the inlet flow.
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First Order Plus Deadtime ProcessFirst Order Plus Deadtime Process
Most process in industry may be approximated as first order plus deadtime processes.
A first order plus deadtime process exhibits the combined characteristics of the lag and delay process.
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Example – Steam HeaterExample – Steam Heater
•An example of a first order plus deadtime process is a steam heater.
•The process lag is caused by the heating process
•The process deadtime is caused by transport delay
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Higher Ordered SystemsHigher Ordered Systems
•The dynamic response of a process is the results of many components working together e.g. I/P, Valve actuator, heat or fluid/gas transport, etc.•The net process response of these higher order systems can be approximated as first order plus deadtime.
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Combined Impact of Process DynamicsCombined Impact of Process Dynamics
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Integrating ProcessIntegrating Process• When a process output
changes without bound when the process input is changed by a step, the process is know as a non-self- regulating or integrating process.
• The rate of change (slope) of the process output is proportional to the change in the process input and is known as the integrating gain.
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Example – Integrating ProcessExample – Integrating Process
An example of a non-self-regulating process is tank level where outlet flow is established by a gear pump.
If the inlet flow does not match the outlet flow, then level will continue to change until the tank overflows or runs dry.
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Inverse Response ProcessInverse Response Process
For a few processes, the initial change in the process output to a step change in a process input will be in the opposite direction of the final output change.
Processes exhibiting this characteristic are said to have an inverse response.
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Example – Inverse Response ProcessExample – Inverse Response Process
The level of a vertical thermosiphon reboiler in a distillation column may exhibit an inverse response to a rapid increase in heat input.
The size or direction of the change in heat input may determine if an inverse response is obtained.
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Process LinearityProcess Linearity
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Example – Non-linear ProcessExample – Non-linear Process Most processes may be
approximated as linear over a small operating range. However, over a wide range of operation, processes may exhibit some non-linearity.
A common cause of non-linearity is a change in process gain – reflecting the installed characteristics of the final control element i.e. valve acting with the other equipment making up the process, as illustrated in this example.
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Workshop – Use of Process SimulationWorkshop – Use of Process Simulation
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Workshop - Process CharacterizationWorkshop - Process Characterization
Three example processes are include in workshop– First order plus
deadtime– Integrating– Inverse response
Web site is accessed to perform step test. Only a web browser is needed – no software to install.
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Control ObjectiveControl Objective
For the case, production is greatest when the band of variation is reduced to zero and the process parameter is maintained at the value corresponding to maximum production
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Impact of Operating Target Impact of Operating Target
To benefit from improvement in control, the loop must operate at the target that provides maximum production.
The plant design conditions may be used as a guide in establishing setpoints for best operation
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Operating at a LimitOperating at a Limit
For this case, maximum production is obtained by maintaining the process parameter at a limit determined by some plant limitation.
How close to the limit you can operate is determined by the quality of the control
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Impact of Reduced VariabilityImpact of Reduced Variability
Production improvement is obtained by operating closer to product specification or operating limit.
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Example - Ammonia Plant Example - Ammonia Plant
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Example - Ammonia Plant (Cont.) Example - Ammonia Plant (Cont.)
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Example - Ammonia Plant (Cont.) Example - Ammonia Plant (Cont.)
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Other Control ObjectivesOther Control Objectives
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Balancing Control Complexity and BenefitsBalancing Control Complexity and Benefits Various techniques may be
used to improve the control of a process
As the complexity of the control system increases, so does cost for operator training and maintenance
The complexity (cost) of the control system should be balanced with the benefits provided
The benefits of control improvement may be influenced by market conditions i.e. value of product, cost of feedstock, energy cost
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Single Loop ControlSingle Loop Control
In some cases manual control may be appropriate
Manual Loader Block may be used to implement manual control
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Manual Control ImplementationManual Control Implementation
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Processing of Analog Input SignalProcessing of Analog Input Signal
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Impact of AliasingImpact of Aliasing
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Setup of Anti-aliasing FilterSetup of Anti-aliasing Filter
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Processing by Analog Input BlockProcessing by Analog Input Block
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Filtering Provided by Analog Input BlockFiltering Provided by Analog Input Block
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Manual Loader BlockManual Loader Block
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Analog Output BlockAnalog Output Block
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Analog Output Block - Rate LimitingAnalog Output Block - Rate Limiting
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Analog Output Block – Increase to Close OptionAnalog Output Block – Increase to Close Option
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Feedback ControlFeedback Control
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Proportional Only ControlProportional Only Control
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Proportional Plus Integral (PI) ControlProportional Plus Integral (PI) Control
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Proportional, Integral, Derivative (PID) ControlProportional, Integral, Derivative (PID) Control
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PID Structure SelectionPID Structure Selection
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PID Direct/Reverse SelectionPID Direct/Reverse Selection
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PID Function BlockPID Function Block
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PID Form – Standard and SeriesPID Form – Standard and Series
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Setting PID Form and StructureSetting PID Form and Structure
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Block Mode – Selection of Source of SP and OUTBlock Mode – Selection of Source of SP and OUT
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Target Modes of BlockTarget Modes of Block
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Other Actual Modes of BlockOther Actual Modes of Block
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Duty Cycle ControlDuty Cycle Control
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Duty Cycle Control (Cont.)Duty Cycle Control (Cont.)
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Increase-Decrease Control – Motor Driven ActuatorIncrease-Decrease Control – Motor Driven Actuator
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Workshop – Feedback ControlWorkshop – Feedback Control
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Tuning and Loop Performance – Default Setting Tuning and Loop Performance – Default Setting
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Manual Tuning Technique Manual Tuning Technique
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Tools to Automate TuningTools to Automate Tuning
Example base on DeltaV Insight On-demand Tuning
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Impact of Sticky Valve Impact of Sticky Valve
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Use of Signal Characterizer to Compensate for Non-linearityUse of Signal Characterizer to Compensate for Non-linearity
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Characterizer SetupCharacterizer Setup
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Multi-loop Control - Feedforward ControlMulti-loop Control - Feedforward Control
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Feedforward Control ImplementationFeedforward Control Implementation
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Commissioning Dynamic CompensationCommissioning Dynamic Compensation
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Workshop – Feedforward ControlWorkshop – Feedforward Control
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Cascade ControlCascade Control
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Example – Boiler Steam TemperatureExample – Boiler Steam Temperature
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Cascade Control ImplementationCascade Control Implementation
Selecting FRSI_OPT for dynamic reset in primary loop and CONTROL_OPTS for Use PV for BKCAL_OUT in secondary loop can often improve dynamic response.
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Workshop – Cascade ControlWorkshop – Cascade Control
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Override ControlOverride Control
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Example – Override ControlExample – Override Control
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Override Control ImplementationOverride Control Implementation
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Workshop – Override ControlWorkshop – Override Control
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Control Using Two Manipulated ParametersControl Using Two Manipulated Parameters
Three methods Addressed: Split Range
Control Valve Position
Control Ratio Control
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Split Range Control ImplementationSplit Range Control Implementation
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Split Range SetupSplit Range Setup
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BA
Example – Split Range ControlExample – Split Range Control
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Workshop – Split Range ControlWorkshop – Split Range Control
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Valve Position ControlValve Position Control
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Valve Position Control ImplementationValve Position Control Implementation
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Example – Valve Position ControlExample – Valve Position Control
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Workshop – Valve Position ControlWorkshop – Valve Position Control
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Ratio ControlRatio Control
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Ratio Control ImplementationRatio Control Implementation
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Example – Ratio ControlExample – Ratio Control
In this example the ratio setpoint is adjusted using feedback control based on a downstream analysis of the blended material
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Workshop – Ratio ControlWorkshop – Ratio Control
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Process Simulation for Ratio WorkshopProcess Simulation for Ratio Workshop
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Model Predictive Control (MPC)Model Predictive Control (MPC)
Operating Within Process Constraint
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MPC May be Layered on Existing ControlMPC May be Layered on Existing Control
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Workshop – Model Predict ControlWorkshop – Model Predict Control
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Process ModelingProcess Modeling
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Simulation DiagramSimulation Diagram
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Simulation ModuleSimulation Module
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Example – Process Simulation CompositeExample – Process Simulation Composite
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Workshop – Process ModelingWorkshop – Process Modeling
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Application – Boiler Drum LevelApplication – Boiler Drum Level
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Batch ReactorBatch Reactor
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Batch Reactor- ProcessingBatch Reactor- Processing
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Batch Reactor - ControlBatch Reactor - Control
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Continuous ReactorContinuous Reactor
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Continuous Reactor - ControlContinuous Reactor - Control
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Single Fuel Power BoilerSingle Fuel Power Boiler
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Power Boiler Combustion ControlPower Boiler Combustion Control
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Distillation ColumnDistillation Column
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Distillation Column ControlDistillation Column Control
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Ammonia Plant H/N Ratio ControlAmmonia Plant H/N Ratio Control
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Ammonia Plant H/N Ratio Control (Cont.)Ammonia Plant H/N Ratio Control (Cont.)
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Control Loop Foundation Web SiteControl Loop Foundation Web Site
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Exercise and Process InformationExercise and Process Information
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Workspace –Dynamic Simulation/ControlWorkspace –Dynamic Simulation/Control
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Chart and Solution SelectionsChart and Solution Selections
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SummarySummary
Feedback on the book can be provide through the Control Loop Foundation website
Questions? Drawing for books
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How to Get More InformationHow to Get More Information Emerson Education Class
– Control Loop Foundation, Course 9025 CEUs: 3.2– This course is for engineers, managers, technicians, and others that are new to
process control or need a refresher course. This course includes the practical aspects of control design and process applications that course developers personally learned through years of hands on experience while designing and commissioning process control applications. Overview
– This 4-1/2 day course covers the concepts and terminology that are needed to understand and work with control systems. Upon completion of this course the student will be able to effectively work with and commission single and multi-loop control strategies. Interactive workshops allow the student to apply what they learn in the class. Prerequisites
– Windows experience. Control Loop Foundation - ISA Book
– May be purchase through the ISA web site - http://www.isa.org/ Book Web Site
– Explore book workshops - http://www.controlloopfoundation.com/