Process Instrumentation and Control - Questions

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1. Sketch the transient response characteristics of
1. a bare thermocouple
2. a shielded thermocouple.
Draw electrical analogies for these two devices.
2. Discuss the manometer dynamics with respect to the damping coefficient. On what physical parameters of the manometer does this coefficient depend?
3. Draw the block diagram of a control system illustrating a cascade control loop. Explain its purpose.
4. Discuss on the criteria for specifying the control and controller settings.
5. Draw the instrumentation flow diagram for a shell and tube heat exchanger. State the importance of such diagrams.
6. With a neat sketch, explain the working of a proportional plus derivative mode of control. Why the derivative controller cannot be used independently.
7. Show by plot the transient output response of a derivative controller when it has been disturbed by
1. Linear input
2. Sinusoidal input
3. Step input
8. Write short notes on the dynamic behavior and dynamic characteristics of an instrument.
9. Explain the terms 'amplitude ratio', 'proportional band', 'transducer', 'distance velocity lag' and 'offset'.
10. Describe how proportional plus integral action can be generated in a pneumatic controller. State under what circumstances it is an advantage to use this combination. Under what conditions would you prefer to replace the integral by derivative action?
11. State and explain Ziegler-Nichols rules for controller settings.
12. Name and define all the basic elements of a control system and show in a block diagram their positions in the closed-loop which forms the system. Indicate where and how time lags can arise in the system and explain how they add to the difficulty of control.
13. Give one example each of a system with zero order and first order dynamics. Derive the transfer function of a first order system.
14. Discuss the merits and demerits in using hydraulic, pneumatic and electric control system in process control.
15. Explain, what is meant by the terms 'capacity lag', 'transfer lag', 'transportation lag' and 'dead time'.
16. Explain with the help of a control circuit, how temperature of water in a shell and tube heat exchanger, heated by hot oil (shell side) can be controlled.
17. Explain how an on-off controller having no differential gap, is used to control liquid level in a tank and indicate the draw backs.
18. Discuss the factors that are to be considered in choosing a feed back or feed forward controller in process control.
19. Explain with the help of a neat sketch, the working of a pneumatic proportional plus integral (PI) controller to control temperature in a process.
20. Write the expression for proportional (P), proportional plus integral (PI), proportional plus derivative (PD) and proportional plus integral plus derivative (PID) control actions and explain the terms used therein.
21. Derive an expression for the step response in inlet flow rate to two non-inter acting tanks in series with equal time constant.
22. Consider a chemical reactor in which a reaction takes place. Make a dynamic analysis of the system. Setup the block diagram.

Last Modified on: 04-Feb-2022

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