(Transfer functions and Block Diagrams) 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 Equal percentage - flow capacity increases exponentially with valve trim travel. Equal increments of valve travel produce equal percentage changes in the existing Cv. Professor Douglas Cooper, author Loop Pro-Trainer

What are Valve Characteristics Installed 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

Feedback Block Diagram Transmitter Transducer Valve Energy Transfer Controller Process

Feedback Block Diagram + - +

Feedback Block Diagram (simplified) + - + +

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

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

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

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