introduction to industrial control systems
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Introduction to Industrial Control Systems. Chapter 1. Objectives. List the classifications of industrial control systems Describe the differences among industrial control systems and provide examples of each type Define common terms associated with industrial control systems. - PowerPoint PPT PresentationTRANSCRIPT
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Introduction toIndustrial Control
Systems
Chapter 1
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Objectives
• List the classifications of industrial control systems
• Describe the differences among industrial control systems and provide examples of each type
• Define common terms associated with industrial control systems
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Objectives (cont’d.)
• Describe the differences between open- and closed-loop systems
• Define common terms associated with open- and closed-loop systems
• List the factors that affect the dynamic response of a closed-loop system
• Describe the operation of feed-forward control
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Objectives (cont’d.)
• List three factors that cause the controlled variable to differ from the setpoint
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Industrial Control Classifications
• Motion control– Automatic control system that controls the
physical motion or position of an object
• Process control– One or more variables are regulated during the
manufacturing of a product– Two categories:
• Batch processing• Continuous process
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Open- and Closed-Loop Systems
• Open loop system– Simple– Must be manually balanced– Examples
• Closed loop system– Self-correcting and self-regulating– Used by most automated processes
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Elements of Open- and Closed-Loop Systems
• Common terms:– Controlled variable– Measured variable– Measurement device– Feedback signal– Setpoint– Error detector
– Error signal– Controller– Actuator– Manipulated variable– Manufacturing
process– Disturbance
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FIGURE 1-5 Closed-loop block diagram that shows elements, input/output signals, and signal direction
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FIGURE 1-6 Open-loop block diagram that shows elements, input/output signals, and signal direction
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Feedback Control
• Error must exist before some corrective action can be made
• Causes of errors:– The setpoint is changed– A disturbance appears– The load demand varies
• Signals may be positive or negative
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Practical Feedback Application
• Heat exchanger
FIGURE 1-8 Closed-loop temperature control system
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Dynamic Response of a Closed-Loop System
• Dynamic response:– Measure of loop’s corrective action
• Factors:– Response time– Time duration– Static inertia of controlled variable
• Leads to pure lag
– Dead time
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Feed-Forward Control
• Prevent errors from occurring
• Minimize not prevent
• Also use feedback control
• Typically used only in critical applications within the plant
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FIGURE 1-9 Feed-forward control of a temperature control system
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FIGURE 1-10 Feed-forward control loop with a feedback control loop