Anna University Model Question Paper BE VI sem E&I PROCESS CONTROL




Common for B.E. E&IE / I&CE



Time: 3hrs                                                                                                                  Max. Marks: 100

Answer all Questions

PART – A (10 x 2 = 20 Marks)


  1. List any four objectives of process control.
  2. Distinguish between continuous process and batch process.
  3. Sketch the input – output characteristic of a single – speed floating controller.
  4. Why derivative mode of control is not recommended for a noisy process?
  5. Why is it necessary to choose controller settings that satisfy both gain margin and phase margin?
  6. What is tuning a controller based on quarter – decay ratio?
  7. Why are fuel and air sent at a specified ratio into a combustion chamber?
  8. When is inferential control used?
  9. What is meant by cavitation in a control valve?
  10. What is “equal percentage” in the equal percentage valve?


PART – B (5 x 16 = 80 Marks)

11.a)i)  A process has two time-constants of 10 sec and 25 sec and a steady – state gain of 1.3. Find the gain of the proportional controller required to give a damping ratio of 0.5 in the closed loop response.                                                                                                                                   (8)


       ii)  For the system shown in Fig. 1., find the offset that results due to unit step change in U when the process transfer function is

                          1)     1/1+12s,   2)  1/s(1+12s)                                                                             (8)



3 / 1 + 10s

2 / 1+5s








                                   +                                                                                          +                     C





                                                                         Fig .1



12.a)    A water heating system is shown in Fig .2                                                                (16)

F1 , T1



F2 , T2











                                                                         Fig. 2

                        The following data apply under steady state :

                        In flow rate of water (F1)                                = 0.5 litre/sec

                        Temperature of inflowing water (T1)                   = 25o C

                        Temperature of outflowing water (T2)                = 40o C

                        Hold up volume of water (V)                                     = 5 litres

                        Specific heat of water = 4.18J/gmoC; Density of water = 1gm/cm3

      i)    Determine heat power input Q under the steady state condition.

     ii)    Develop equation to describe the change in T2 due to simultaneous changes in T1 and Q and represent the process by means of a block diagram with transfer function written inside each block. Assume F1 = F2.



12.b)i)  Define self-regulation. Give an example of a self-regulated process.                                    (4)


       ii)  Obtain for the level process shown in Fig.3 the transfer function relating h2 and other parameters. The area of cross section of tank I is A1 and that of tank II is A2.            (12)







Tank I

Tank II








13.a)i)  What are the situations under which an ON/OFF controller would provide satisfactory  response?                                                                                                                                 (4)


       ii)  A 5m diameter cylindrical tank is emptied by a constant outflow of 1.0m3/min. A two-position controller is used to open and close a fill valve with an open flow of 2.0m3/min. For level control the neutral zone is 1.0m [or hysteresis ±0.5m] and the set point is 12.0m. Sketch the level versus time and calculate the cycling period.                                                           (12)




13.b)i)  Explain the working of a pneumatic P+I controller.                                                               (8)


        ii) A PI controller is reverse acting with PB = 20% and repeats per minute = 12 and derivative time 0.2 minutes. Determine the time at which the controller output reaches zero percent if the input error ep to the controller varies ep = 0.9t%, t ≥ 0


            The controller output at t = 0 was72%.                                                                       (8)


14.a)i)  Explain feed forward control with an example from distillation column.                              (8)


       ii)  Describe split range control. Under what circumstances is it recommended?                        (8)


Table of Contents



14.b)i)  Explain cascade control with a block diagram and example.                                                 (8)


ii)  Discuss the problems to be encountered while designing a controller for a multivariable control system.                                                                                                                          (8)


15.a)i)  Explain with a sketch the working of a pneumatic actuator with positioner.                         (8)


ii)  Discuss the factors to be considered before the selection of control valve for a given application.                                                                                                                              (8)



15.b)i)  Write down the flow equation of an equal percentage valve and sketch its inherent valve characteristic.                                                                                                                            (4)


ii)  Explain how you will practically determine the installed valve characteristic of a control valve in an installation and also the reasons for determining the installed characteristic.   (6)

iii)  An equal percentage valve has a rangeability of 32. If the maximum flow rate is 100m3/hour, find the flow at 2/3 open setting.                                                                                             (6)



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