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Unformatted text preview: 1 28150. Introduction to process control 5. Second and higher order systems Krist V. Gernaey 28 September 2009 28150 Learning objectives • At the end of this lesson you should be able to: – Explain the response of basic process transfer functions (firstorder, secondorder, integrating process) to standard inputs – Plot and interpret poles and zeros of a transfer function 28 September 2009 28150 Outline • Response of firstorder processes (repetition) • Integrating processes • Response of secondorder processes • Poles and zeros • Processes with time delays • Approximation of higherorder transfer functions 28 September 2009 28150 Outline • Response of firstorder processes (repetition) • Integrating processes • Response of secondorder processes • Poles and zeros • Processes with time delays • Approximation of higherorder transfer functions 28 September 2009 28150 Firstorder process: step response • General transfer function: • Input: • Time domain response: Time M ( ) ( ) 1 + ⋅ = s K s U s Y τ ( ) s M s U S = ( ) ( ) 1 + ⋅ ⋅ ⋅ = s s M K s Y τ () ( ) τ / 1 t e M K t y ⋅ ⋅ = 28 September 2009 28150 Firstorder process: step response 2 28 September 2009 28150 Firstorder process: ramp response • Input: • Time domain response: – For t >> τ : ( ) 2 s a s U R = Time Slope = a ( ) ( ) 2 3 2 1 2 1 1 s s s s s a K s Y α α τ α τ + + + ⋅ = + ⋅ ⋅ ⋅ = ( ) 2 2 1 s a K s a K s a K s Y ⋅ + ⋅ ⋅ + ⋅ ⋅ ⋅ = τ τ τ ( ) ( ) t a K e a K t y t ⋅ ⋅ + ⋅ ⋅ = 1 / τ τ ( ) ( ) τ ⋅ ⋅ = t a K t y 28 September 2009 28150 Firstorder process: ramp response 28 September 2009 28150 First order process: sinusoidal response • Input: • Time domain response: – With: ( ) t A t U ω sin sin ⋅ = Time A P ( ) ( ) ( ) 2 2 1 ω τ ω + ⋅ + ⋅ ⋅ ⋅ = s s A K s Y ( ) + + + ⋅ ⋅ + ⋅ ⋅ ⋅ + ⋅ = 2 2 2 2 2 2 2 1 1 ω ω ω τ ω τ τ ω τ ω s s s s A K s Y ( ) ( ) t t e A K t y t ω ω τ ω τ ω τ ω τ sin cos 1 / 2 2 + ⋅ ⋅ ⋅ ⋅ ⋅ + ⋅ = ( ) ( ) φ ω τ ω τ ω τ ω τ + + ⋅ + ⋅ + ⋅ ⋅ ⋅ = t A K e A K t y t sin 1 1 2 2 / 2 2 ( ) τ ω φ ⋅ = 1 tan 28 September 2009 28150 First order process: sinusoidal response 28 September 2009 28150 Outline • Response of firstorder processes (repetition) • Integrating processes • Response of secondorder processes • Poles and zeros • Processes with time delays • Approximation of higherorder transfer functions 28 September 2009 28150 Integrating processes: example • Assume a tank with a pump connected to the outflow line: • Steadystate at t = 0 • Switching to deviation variables: • Laplace transform: ( ) ( ) t q t q dt dh A i = q i q Pump h h h q q i = = ( ) ( ) ( ) t q t q dt t h d A i ′ ′ = ′ ( ) ( ) ( ) s Q s Q s H A s i ′ ′ = ′ ⋅ ⋅ 3 28 September 2009 28150 Integrating processes: example • After rearranging: • The two TFs in the system are...
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This note was uploaded on 11/20/2009 for the course CHME DTUabroad taught by Professor Rafiqulgani during the Fall '09 term at Rensselaer Polytechnic Institute.
 Fall '09
 RafiqulGani

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