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CBE / MET 433

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 .

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CBE / MET 433

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  1. CBE / MET 433 22 Feb 12 (Transfer functions and Block Diagrams) Professor Douglas Cooper, author Loop Pro-Trainer

  2. What are Valve CharacteristicsInherent Characteristics • The three most common valve characterizations are equal percentage, linear, and quick opening Professor Douglas Cooper, author Loop Pro-Trainer

  3. 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. 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

  4. Feedback Block Diagram Transmitter Transducer Valve Energy Transfer Controller Process

  5. Feedback Block Diagram + + + -

  6. Feedback Block Diagram (simplified) + + + -

  7. Closed Loop Transfer Function (let R(s)=0) + + + -

  8. Closed Loop Transfer Function (let R(s)=0) + + + -

  9. Open Loop vs Closed Loop Transfer Function (R(s)=0) Open Loop: + + + - Closed Loop:

  10. Transfer Functions (Chap 3-5) Define: For heated, stirred tank: + + + + + + - -

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