6HD Process Instrumentation and Control - April'2000

Part A (20 x 2 = 40 Marks)

1. Define the Laplace transform
2. What is initial value theorem?
3. Define step function and impulse function
4. Give the transfer function for second order system
5. Define the terms: Decay ratio and Rise time
6. Define transportation lag
7. Differentiate between negative feedback and positive feedback
8. What is meant by on-off control?
9. Express the proportional controller
11. Define the stability of a linear system
12. What is meant by controller timing?
13. Define amplitude ration
14. Name any two flow metering of liquids
15. Explain the terms open loop and closed loop systems
16. What is the advantage of using resistance thermometers?
17. What are radiation pyrometers? Where is it used?
18. What are the objectives of automatic process control?
19. Define Nyquist stability criteria
20. Explain the cross over frequency
21. Part B (5 x 12 = 60 Marks)

22. Explain with neat sketches the measurement of temperature using thermocouples and resistance thermometers
23. Or

24. Discuss with neat sketches the working of the following: (a) mass flow meter (b) hot-wire anemometer
25. Develop the transfer function for a first order system by considering the unsteady behavior of an ordinary mercury-in-glass thermometer
26. Or

27. Two non-interacting systems are connected in series. The time constants are: t1 = 0.5, t2 = 1.0 and R2 = 1. Obtain an expression for the response of liquid level in tank 2, if a unit step change is made in the inlet flow to tank 1.
28. (a) Explain why a combination of control modes are used. (4)
29. (b) Plot the response curves for a linear input in the case of:

(i) Proportional controller. (4)

(ii) Proportional + Rate controller. (4)

Or
30. (a) Develop the Block diagram of a simple control system. (6)
31. (b) Indicate the important components of a control system. (6)

32. (a) Define stability of a control system. How do you determine the stability from the characteristic equation? (6)
33. (b) Using Routh test, determine the value of K with the transfer function

C/R = 3K / [(S + 1) (2S + 1) (S + 3)]

to be stable.

Or
34. Draw the Bode plot for the system
35. G(S) = 10e-0.5S / [(S + 1) (S + 2) (S + 3)]

36. Describe with a neat sketch a simple control setup for a distillation column. What are the major difficulties in controlling compositions in a distillation column?
37. Or

38. With the help of neat diagrams, explain the dynamics and control of a shell and tube heat exchanger.