### Process Instrumentation and Control - Semester Exam Question

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**6HD Process Instrumentation and Control - April'2000**
Part A (20 x 2 = 40 Marks)

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

- Explain with neat sketches the measurement of temperature using thermocouples and resistance thermometers
Or
- Discuss with neat sketches the working of the following: (a) mass flow meter (b) hot-wire anemometer
- Develop the transfer function for a first order system by considering the unsteady behavior of an ordinary mercury-in-glass thermometer
Or
- Two non-interacting systems are connected in series. The time constants are: t
_{1} = 0.5, t_{2} = 1.0 and R_{2} = 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.
- (a) Explain why a combination of control modes are used. (4)
(b) Plot the response curves for a linear input in the case of:

(i) Proportional controller. (4)

(ii) Proportional + Rate controller. (4)

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

- (a) Define stability of a control system. How do you determine the stability from the characteristic equation? (6)
(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
- Draw the Bode plot for the system
G(S) = 10e^{-0.5S} / [(S + 1) (S + 2) (S + 3)]

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

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Last Modified on: 04-Feb-2022

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