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CBE / MET 433. 22 Feb 12 (Transfer functions and Block Diagrams). Professor Douglas Cooper, author Loop Pro-Trainer. What are Valve Characteristics Inherent Characteristics. The three most common valve characterizations are equal percentage, linear, and quick opening . - PowerPoint PPT Presentation
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CBE / MET 43322 Feb 12
(Transfer functions and Block Diagrams)
Professor Douglas Cooper, author Loop Pro-Trainer
What are Valve CharacteristicsInherent Characteristics
• The three most common valve characterizations are equal percentage, linear, and quick opening
2Professor Douglas Cooper, author Loop Pro-Trainer
What are Valve CharacteristicsInstalled Characteristics
• In many process applications the pressure drop across a valve varies with the flow. In these instances an equal percentage valve will act to linearize the process.
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Equal percentage valves are the most commonly used control valves. • How do you know what inherent valve characteristic to choose to get a
linear installed characteristic?– The correct selection of valve characteristic to linearize the process
gain will ease the tuning process and make for a robust system.– Most times this selection is through experience, guesswork or the
valve manufacturer’s recommendation.Professor Douglas Cooper, author Loop Pro-Trainer
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Feedback Block DiagramTransmitter
Transducer
Valve
Energy Transfer Controller
Process
5
Feedback Block Diagram
11s
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Feedback Block Diagram (simplified)
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7
Closed Loop Transfer Function (let R(s)=0)
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8
Closed Loop Transfer Function (let R(s)=0)
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time (t)
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11
Transfer Functions (Chap 3-5)
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