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

ANNA UNIVERSITY :: CHENNAI – 600 025

MODEL QUESTION PAPER

VI – SEMESTER

IL334 – PROCESS CONTROL

Time: 3hrs                                                                                                                  Max. Marks: 100

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)

 4
 Process
 3 / 1 + 10s
 2 / 1+5s
 U

 R

+

+                                                                                          +                     C

–

Fig .1

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

 F1 , T1 Water
 T2
 F2 , T2
 V
 Q

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.

### OR

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)

 T
 R1
 q1
 q2
 T
 R2
 Tank I
 Tank II
 h1
 h2

Fig.3

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)

#### OR

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)

## OR

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)

## OR

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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