INSTRUMENTATION & PROCESS CONTROL Question Papers (Supple, 2006)

SET :1

1. (a) Define time constant of a system. Write the expression for the time constant in terms of the process parameters of a liquid level system.
(b) A tank operating at 3 metre head and 0.022 cubic metre/min outflow through a valve has a cross section area 0.9 square metre. Calculate the time constant.
(c) If this system known to have time constant response requires 5 minutes to indicate 98% of the response, what can be the time constant? [4+6+6]

2. (a) Say whether heated tank and an immersed thermometer with negligible interaction is interacting or non-interacting. Justify your answer.
(b) Write the differential equations and determine the transfer functions individually for heated tank and thermometer.
(c) Determine the overall transfer function of this combination. How is this transfer function related with the individual transfer function? [3+9+4]

3. (a) Explain with analytic expression, the concept of a single controller mode which is anticipatory in nature. List its characteristics.
(b) Why a pure derivative is not preferred? Draw the derivative controller output for the error given below figure1. (Assume the relevant settings) [8+8]
Figure 1:

4. (a) Explain in detail, the realization of proportional-integral action with the aid of bellows, flapper-nozzle etc.
(b) Draw a three mode electronic controller and derive the expression for the output voltage. [8+8]

5. (a) What is meant by process tuning and list the various methods of tuning of PID parameters.
(b) Discuss process reaction method for control loop tuning. [8+8]

6. (a) Explain the baffle - Nozzle system with the help of its characteristic curves.
(b) Explain the pneumatic booster and what is its need.
(c) Differentiate between direct and reverse action final control operation.[6+6+4]

7. A heating furnace requires a control valve passing 10gpm preheated light fuel oil (SP.gr. = 0.8) at full load and only 2 gpm at the smallest heating load. The source pressure constant at 50psi gage, but there is 10psi drop in the oil pre heater and 20 psi drop at the furnace burner nozzles. Remaining pressure drop occurs only at control valve when it is fully opened.
(a) Find out control valve size required for the above application.
(b) Find out required rangeability of the valve
(c) Find out characteristic coefficient (α). [6+4+6]

8. (a) Explain the objectives of controlling distillation column operation with a neat diagram.
(b) Describe the objective of controlling boiler operation with a neat diagram. [8+8]

SET :2

1. A Cylindrical tank with an area of 20 ft2 and a height of 10 ft has a normal liquid depth of 6ft. The flow to the tank is 10±1 cubic ft/min, and the liquid is discharged through a control valve to a process at atmospheric pressure. ( 1 ft = 0.305 metre) Calculate the time constant if the tank is
(a) Open to the atmosphere
(b) Closed, with a constant pressure of 10 psig above the liquid.
(c) Closed, with a fixed amount of air sealed above the liquid. The initial pressure is 10 psig. [16]

2. Three identical tanks are operated in series in non-interacting fashion. For each tank, R=1 and t = 1. If the deviation in flow rate to the first tank is an impulse function of magnitude 2, determine
(a) An expression for H(S) where H is the deviation in level in the third tank.
(b) Obtain the expression for H(t).
(c) Sketch the response H(t). [7+6+3]

3. (a) Explain with analytic expression, the concept of a single controller mode which is anticipatory in nature. List its characteristics.
(b) Why a pure derivative is not preferred? Draw the derivative controller output for the error given below figure1. (Assume the relevant settings) [8+8]
Figure 1:

4. (a) Explain in detail, the realization of proportional-integral action with the aid of bellows, flapper-nozzle etc.
(b) Draw a three mode electronic controller and derive the expression for the output voltage. [8+8]

5. (a) Explain the following terms as applicable to system evaluation with necessary graphs.
i. Stability
ii. measure of quality .
(b) Discuss the quarter - amplitude criterion to evaluate the response. [8+8]

6. (a) Explain the baffle - Nozzle system with the help of its characteristic curves.
(b) Explain the pneumatic booster and what is its need.
(c) Differentiate between direct and reverse action final control operation.[6+6+4]

7. Write steps followed in choosing a valve for better control of flow and should be cost effective. [16]

8. Design a feed forward controller for a stirred heater with respect to steady state error & dynamic forward controller and give the conclusions of the design. [16]

SET :3

1. A thermometer having first order dynamics with a time constant of 1 min is placed in a temperature bath at 800C. After the thermometer reaches a steady state, it is suddenly placed in a bath at 900C at t = 0 and left there for 1 min, after which it is immediately returned to the bath at 800C.
(a) Derive and write the expression for the response of the thermometer.
(b) Draw a sketch showing the variation of thermometer reading with time.
(c) Calculate the thermometer reading at t = 0.5 min and at t = 2.0 min. [16]

2. (a) Give one example for Interacting first order elements in series.
(b) Write the differential equation for this combination and determine the transfer function.
(c) Comment on the transfer function. [3+10+3]

3. (a) what is meant by differential gap and how it is related to the performance of the final control element?
(b) Define proportional band. Explain the relation between proportional gain, proportional band and offset error.
(c) With a neat sketch explain the integral controller mode action. Summarize the characteristics. [5+5+6]

4. (a) With a neat circuit diagram, explain the realization of an electronic two position controller with adjustable neutral zone.
(b) Design an electronic proportional controllers for (0-12v) error input, 10% proportional band and 50% zero error controller output. [8+8]

5. (a) What is meant by process tuning and list the various methods of tuning of PID parameters.
(b) Discuss process reaction method for control loop tuning. [8+8]

6. (a) Explain the baffle - Nozzle system with the help of its characteristic curves.
(b) Explain the pneumatic booster and what is its need.
(c) Differentiate between direct and reverse action final control operation.[6+6+4]

7. Write about the rotating shaft valves? [16]

8. (a) Explain the closed loop characterization of cascade control system.
(b) Explain the primary and secondary loop gain adjustment in a cascade control
system. [8+8]

SET :4

1. (a) Write differential equation for the following single capacitance process as shown in the figure1
Figure 1:
(b) The above single capacitance level process has a normal operating head of 1.2 metre and a normal value of outflow of 3375 cubic centimetre per seconds. The cross section area of the vessel is 0.54 square metre. If the resistance to the flow is parabolic, determine the time constant of the system.
(c) Show that the time constant of the above process is proportional to the time required to change the fluid in the vessel. [3+7+6]

2. (a) Is the Thermometer Bulb and well arrangement a non-interacting system? Justify your answer.
(b) Write the differential equations and determine the transfer function for Thermometer bulb and well arrangement. [6+10]

3. (a) Explain with analytic expression, the concept of a single controller mode which is anticipatory in nature. List its characteristics.
(b) Why a pure derivative is not preferred? Draw the derivative controller output for the error given below figure2. (Assume the relevant settings) [8+8]

4. (a) Explain the method of realizing an electronic PI controller employing delayed positive feedback. Derive the expression for proportional gain and integral time.
(b) Explain with a neat sketch, the working principle of a moving vane type two position controller. [8+8]

5. (a) Explain the following terms as applicable to system evaluation with necessary graphs.


Figure 2:
i. Stability
ii. measure of quality .
(b) Discuss the quarter - amplitude criterion to evaluate the response. [8+8]

6. (a) Explain the baffle - Nozzle system with the help of its characteristic curves.
(b) Explain the pneumatic booster and what is its need.
(c) Differentiate between direct and reverse action final control operation.[6+6+4]

7. (a) Give the schematic of single seated and double seated valves.
(b) What are the advantages and disadvantages of single seated and double seated valves. [8+8]

8. Discuss the cascade control with neat block diagrams
(a) Heat exchangers
(b) Distillation columns
(c) Furnaces. [6+6+4]