INSTRUMENTATION & PROCESS CONTROL Question Papers (Supple, 2005)

SET :1

1. (a) Show that the mercury thermometer which is suddenly immersed in hot waterwith some temperature will follow first order dynamics.
(b) A thermometer having time constant of 1 min is initially at 50C. It is immersedin a bath maintained at 1000 C at t =0;i. Determine the temperature reading at t = 1.2 min.ii. If at t = 1.5 min, the thermometer is removed from the bath and put ina bath at 750C, determine the maximum temperature indicated by thethermometer.iii. What will be the indicated temperature at t = 20 min? [6+10]

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 forThermometer 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 outputfor the error given below figure1. (Assume the relevant settings) [8+8]Figure 1:

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

5. (a) Explain the following terms as applicable to system evaluation with necessarygraphs.
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) Distinguish different types of butterfly valves.
(b) Mention which are the rotating shaft valves. [12+4]

8. Explain feed forward control for the following
(a) Heat exchangers
(b) Drum boiler
(c) Distillation column. [5+5+6]

SET :2

1. In the following figure1, P1,P2 and P3 refer to changes in the pressures upstream,in the tank and downstream respectively and the flows into and out of the tank areinfluenced by the tank pressure.Figure 1:
(a) Write the differential equation for the above system and get the transfer func-tion.
(b) What is the order of the above system? How will the order change if there areseveral inlets and outlets? [10+6]

2. Three identical tanks are operated in series in non-interacting fashion. For eachtank, R=1 and t = 1. If the deviation in flow rate to the first tank is an impulsefunction 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) Describe the output of a three mode controller for an assumed error variation.Discuss its features.
(b) Specification of a PI controller are Kp=7, Ki= 2 sec−1 and PI (0) (controlleroutput at t=0)=24%. Plot the controller output as the function of time forthe given error as shown in figure2. [8+8]

4. (a) With a neat circuit diagram, explain the realization of an electronic two posi-tion 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]Figure 2:

5. (a) Plot the transient response of a process with time constants of 50sec and20sec and a time delay of 10sec. Use the reaction curve method to obtain therecommended settings for a three - mode controller.
(b) What is the phase margin for the recommended controller gain? [10+6]

6. (a) What is the principle of a solenoid and explain how it can be used to changethe gears of a two-position transmission. (Let an SCR is used to activate thesolenoid coil).
(b) A stepping motor has 130 steps per revolution. Find the digital input ratethat producer 10.5 revolutions per second. [10+6]

7. Write short notes on.
(a) Sliding stem Valves
(b) Rotating shaft Valves. [8+8]

8. (a) Explain clearly the split range control of the pressure in the steam header?
(b) Determine the properties of the inner loop in a cascade control system andwrite the principle advantages of cascade control system? [8+8]

SET :3

1. (a) A flow head equation has the equation q = hn. Calculate the resistance.
(b) A liquid storage device is spherical in shape. Calculate the capacitance as afunction of head.
(c) If the outflow at a vessel is proportional to the square root of head, what shapevessel results ini. a steady change in headii. a rate of change of head proportional to head? [4+4+8]

2. (a) Define self regulation ?
(b) Explain how self and non self regulated systems operate for step input withexamples. [5+11]

3. (a) Explain with neat sketches, the characteristics of two position and three position controller modes.
(b) What is cycling? Suggest a suitable modification to overcome cycling.[6+10]

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

5. (a) Explain the following terms as applicable to system evaluation with necessarygraphs.i. Stabilityii. 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) Briefly explain valve sizing
(b) A fully open valve passes 200gpm of water at a pressure differential of 10.0psicalculate valve sizing. [8+8]

8. Explain the economic considerations of feed forward controller? [16]

SET :4

1. In the following liquid level system as shown in figure1, the pump removes waterat a constant rate of 10 m3/min and this rate is independent of head. The crosssectional area of the tank is 1 m2 and the resistance is 0.5 m/m3/min. Derive thetransfer function H(S)/Q(S) when
(a) The tank level operates about the steady state value of hs= 1 m.
(b) The tank level operates about the steady state value of hs = 3 m. [8+8]Figure 1:

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 forThermometer bulb and well arrangement. [6+10]

3. (a) what is meant by differential gap and how it is related to the performance ofthe 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. Summarizethe characteristics. [5+5+6]

4.(a) What are the advantages of the force type pneumatic controllers? Describewith neat diagrams, the working of a force type pneumatic proportional con-troller.
(b) Explain the working principle of a hydraulic proportional controller. Howproportional gain can be adjusted in this controller? [8+8]

5. (a) What is a optimum - tuning control? What are its different approaches?(b) How are the interactions in control being channelized to optimize the controlaction in a boiler? [8+8]

6. (a) Give the principle of the control valve and give its O/P equation.
(b) A pressure difference of 1.5 psi occurs across a constriction in a 4 cm diameterpipe. The constriction constant is 0.008 w3/s/(kPa)1/2. Findi. the flow rate in m3/sec.ii. flow velocity in m/sec. [8+8]

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

8. Draw the feed forward and feed back control systems that regulate the flow throughthe pipe? Discuss about both the control systems and give reasons to select any ofthe two systems in maintaining the desired flow? [16]