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Posted Date: 01 Sep 2008 Posted By: gopal Member Level: Diamond
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2005 Jawaharlal Nehru Technological University Chemical engineering III B.Tech II Semester Supplementary Examinations, November/December 2005 PROCESS DYNAMICS AND CONTROL Question paper
Code No: RR320803 Set No. 3
III B.Tech II Semester Supplementary Examinations,
November/December 2005
PROCESS DYNAMICS AND CONTROL
(Chemical Engineering)
Time: 3 hours Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks
? ? ? ? ?
1. (a) How do you represent a physical system by first and second order ordinary
differential equations ? ExpreaCode No: RR320803 Set No. 4
III B.Tech II Semester Supplementary Examinations,
November/December 2005
PROCESS DYNAMICS AND CONTROL
(Chemical Engineering)
Time: 3 hours Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks
? ? ? ? ?
1. (a) An isothermal CSTR irreversible reaction is described by
dCA
dt
+ 1
t
+ kCA =
1
t
CAo
where k and t are constants. CA is the concentration of the component in the
reactor and CAo is the concentration of the entering component to the reactor.
Write the transfer function model for the system. What are the process time
constant and process steady state gain of the model.
(b) A temperature sensing device can be modelled as a first order system with a
time constant of 6 sec. A step change is introduced in the input temperature
of 1500 C to 250 C. Find the temperature after 10 sec. [8+8]
2. (a) Show the block diagram representation of several non interacting first order
systems in series. How do you express the overall transfer function from indi-
vidual transfer functions of several first order systems in series?
(b) A step change of magnitude 3 is introduced into the transfer function
Y (s) X (s)=10
[2s2 + 0.3s + 0.5]
Determine the overshoot and frequency of oscillation [8+8]
3. Discuss the working principle & mechanism of pneumatic PID controller with the
help of a neat schematic diagram [16]
4. (a) Develop the block diagram of a generalized feed back control system with one
disturbance, incorporating in each block the appropriate transfer function and
on each stream the appropriate variable. [8]
(b) Develop the closed loop responses for set point and load changes. [4+4]
5. (a) Given the characteristic equation s4 + 3s3 + 5s2 + 4s + 2 = 0 , determine
the stability by Routh criterion.
(b) What is the order of the closed loop dynamic response for second order process
with PI control? Can PI control destabilize such a process. [8+8]
6. Discuss the rules for plotting root - locus diagrams in detail.
considering unit step input for the system.
(b) A primary transducer is subjected to a sudden change. The time constant of
the transducer is 2 seconds. How long will it take for the transducer to show
half the temperature difference? [10+6]
7. The open loop transfer function of a control system is given below:
GH(s) =
KC(2s + 1)e-0.25
s2(0.5s + 1)
Draw the open loop Bode plot for the system and determine the value of KC for a
phase margin of 300. [16]
8. Write in detail on valve sizing and selection.
2. Consider a second order system with the following transfer function. G(s) = 1
s2+s+1 .
Introduce a step change of magnitude 5 into the system and find
(a) percent over shoot
(b) decay ratio
(c) maximum value of Y(t)
(d) rise time
(e) ultimate value of Y(t)
(f) period of oscillation. [3+3+3+3+2+2]
3. A first order process is controlled by a PD controller. The control valve is assumed
to be a first order. Assuming the measuring element is having negligible time
constant. Develop a block diagram for the feedback control system and obtain an
overall transfer function. [16]
4. (a) Develop the block diagram of a generalized feed back control system with one
disturbance, incorporating in each block the appropriate transfer function and
on each stream the appropriate variable. [8]
(b) Develop the closed loop responses for set point and load changes. [4+4]
5. (a) Discuss the theorems of the Routh test
(b) For characteristic equation s4 + 6s3 + 11s2 + 36s + 120 = 0, determine the
stability using Routh Criterion. [8+8]
6. Sketch the root locus for the following equation.
1 +K(s + 1)(2s + 1)= 0
on your sketch you should locate quantitative all poles, zeros, and asymptotes. In
addition show the parameter that is being varied along the locus and direct in
which the loci travel as this parameter is increased
7. (a) State and explain Bode stability criterion. [8]
(b) Sketch Bode plots for the following components of a control system
i. 1/(S+1)
ii. 10/(S+1)
iii. e-S
[2+3+3]
8. (a) Explain ratio control in detail with a neat schematic diagram.
(b) Quote some commonly encountered examples from chemical industry where
ratio control can be used.
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