PROCESS CONTROL

QUESTION BANK

UNIT – I

PART A

1. List any four objectives of process control.

Suppressing the influence of external disturbances, Optimizing the

Performance, increasing the productivity, Cost effective.

2. Define process

Any system comprised of dynamic variables usually involved in

Manufacturing and production operations. It is defines as a series of

operations

During which some materials are placed in more useful state.

3. What is manipulated variable?

It is a variable which is altered by the automatic control equipment

so as toChange the variable under and make it conform to the desired

value.

4. Define Controlled variable

It is the quantity of control system which is directly measured and

Controlled.

5. What do you mean by self regulation?(M/J06,A/M08)

The output will move from one steady state to another for the

sustainedchange in input. This means that for change in some input

variable the outputvariable will rise until it reaches a steady state (inflow

= outflow). It is thetendency of the process to adopt a specific value of

controlled variable for nominalload with no control operations.

6. Why do we need mathematical modeling of process?(M/J07)

The physical equipment of the chemical process we want to control

hasnot been constructed. Consequently we cannot experiment to

determine how theprocess reacts to various inputs and therefore we

cannot design the appropriatecontrol system. If the process equipment

needs to be available for experimentationthe procedure is costly.

Therefore we need a simple description of how the processreacts to

various inputs, and this is what the mathematical models can provide to

The control designer.

7. Name different test inputs.

Step, Ramp, Impulse, Sinusoidal, Pulse inputs

8. Name a process giving inverse response.

Drum boiler system, in which the flow rate of the cold feed water

isincreased by a step the total volume of the boiling water and

consequently theliquid level, will decrease for a short period and then it

will start increasing.

9. Define interacting system and give an example.

Load changes in first process affect the second process and vice

versawhen both are connected in series nature is called interacting

system. Eg. Twolevel tanks are connected in series.

10. A tank operating at 10ft head, 51pm outflow through a valve and has

a crosssection area of 10 sq ft. calculate the time constant.

T=R/A, R=H/Q=10/(5X5.885X10-4)a

11. What is meant by non-self regulation?

A system that grows without limit for a sustained change in input

(constantoutflow or outflow independent of inflow condition).

12. Write any two characteristics of first order process modeling.(M/J09)

The smaller the value of time constant the steeper the initial

response of thesystem. A first order lag process is self regulating the

ultimate value of theresponse equal to Kp (steady state gain of the

process) for a unit step change in theinput.

13. Distinguish between continuous process and batch

process.(A/M08,N/D13,)

A process in which the materials or work flows more or less

continuouslythrough a plant apparatus while being treated is termed as

continuous process. Theproblem of continuous process is due to load

changes. (e.g.) storage vessel control.A process in which the materials or

work are stationary at one physicallocation while being treated is termed

as batch process. (e.g.) furnace.

14. Explain the function of controller.

The element in a process control loop that evaluated error of the

controlledvariable and initiates corrective action by a signal to the

controlling variable.

15. What is the purpose of final control element?

Components of a control system (such as valve) is used to directly

regulatesthe flow of energy or materials to the process. It directly

determines the value ofmanipulated variable.

16. Define Process control.

It is the scheme that describes how much the manipulated variable

shouldchange in order to bring the controlled variable back to the set

point.

17. List the two types of process control.

Direct process control – Controlled variable directly indicates the

Performance of the process

Eg. Water heater system

Indirect Process control – Controlled variable indirectly indicatesthe

performance of the process.

Eg. Annealing

18. What is Servo operation and Regulatory operation.(M/J 06,N/D06)

If the purpose of the control system is to make the process follow

thechanges in set point as quick as possible, then it is servo operation.

19. What is mathematical modeling?

Set of equations that characterize the process is termed as

MathematicalModeling.

20. Define an non-interacting system.(A/M05)

The dynamic behavior one tank is affected by the other, but the

reverse isnot true, then it is non-interacting system. Here the liquid heads

are independent ofeach other.

21. Define an interacting system.(A/M05)

The dynamic behavior one tank is affected by the other, but the

reverse isalso true, then it is non-interacting system. Here the liquid

heads are dependent ofeach other.

22. List 2 adv of automatic pc.(M/J 06)

23. Whatis meant by dead time and time delay.(A/M 08)

24. Define the time constant of the process (M/J09)

25. Causes of the dead time (M/J07)

26. Need of the process control(M/J07)

PART-B

1. Describe a simple thermal system in which incoming liquid is heated by the heater in the tank and going out with higher temperature. Develop first order transfer function of the thermal process( NOV/DEC 2012) .

2. Develop a mathematical model for the system shown in fig below. What are the states for his system? All the flowrates are volumetric and the cross sectional areas of the tanks are A1, A2 and A3 (ft2), respectively. The flow rate F5 is constant and does not depend on h3, while all other effluent rates are proportional to corresponding hydrostatic liquid pressures the cause the flow. (NOV/DEC 2012) .

3. Consider the system shown in fig. Develop a mathematical model for the system. Assume that the effluent stream from a tank is proportional to the hydrostatic liquid pressure that causes the flow of liquid. Cross-sectional area of tank 1 is A1 (ft2) and of tank 2 is A2

(ft2). The flow rates F1, F2, F3are in ft2/min. take necessary assumptions. (MAY/JUNE 2012)

4. (a) Derive a mathematical model of a first order thermal process.(b) What is the inverse response? Explain the inverse response noticed in the level control of feed water in the boiler.( MAY/JUNE 2012).

5. (a) what is the need for developing the mathematical model of a process, in process control.

(b) For the level process shown in the fig 1 , derive the transfer function H2(S)/Q(S).

h1 =2.5m, h2= 2 m , q= 40 lit/min, C1= 1.5 m2, C2 = 1.2 m2.(NOV/DEC 2010).

6. (a) differentiate servo and regulatory operation with the help of suitable example.

(b) Explain with suitable examples, the difference between the interacting and non- interacting processes.(NOV/DEC 2010).

7. (a) bring out the difference between the continues and batch process with the help of neat diagrams.

(b) List the merits and demerits of the continues and batch process (APR/MAY 2010).

8. (a) derive the mathematical model of a thermal process from fundamentals.

(b) Explain with suitable examples, the difference between the interacting and non- interacting processes.( APR/MAY 2010).

9. (a) define cavitations and flashing.

(b) Describe the working principle of valve positioned.

(c) Compare the operation of control valve with or without positioned(MAY/JUNE 2006).

10. (a) what are the dynamic components of the loop that may exhibit significant time delays In their response?

(b) How are the effects of dead time compensated? What are the important features of dead time compensators? (MAY/JUNE 2009).

11. (a) what is the inverse response? Explain its behaviour with dynamic system.

(b) What is the need for mathematical modeling for process control? Explain the mathematical model for the first order thermal process(MAY/JUNE 2009).

12. (a) with an example , explain self regulation of a process.

(b) Obtain the transfer function h1(S)/q1(S) foe the following liquid process.(APR/MAY 2006)

13(a) obtain mathematical model tubular heat exchanger.( MAY/JUNE 2007)

14 (a) develop the mathematical model for the system (MAY/JUNE

2007)

(b)

15.(a) determine the transfer function H3(S)/Q(S) for the liquid level tank. The flow rate from tank 3 is maintained constant at b by means of a pump.

(b) describe a method to compensate for the inverse response. (APR/MAY 2008)

16. (a) distinguish between servo and regulator operation.

(b) explain the self regulation process with an example(NOV/DEC 2013)

17. derive the mathematical model for the given process (NOV/DEC 2013)

UNIT 2

PART A

1. Mention two drawbacks of derivative action.

(i) The output of controller is zero at constant error condition.

(ii) It will amplify the noise present in the error signal.

2. What are the steps involved to design a best controller?

Define appropriate performance criterion (ISE, IAE, ITATE).

Compute thevalue of the performance criterion using a P, PI, or PID

controller with the bestsetting for the adjusted parameters Kp, Ti, Td.

Select controller which give thebest value for the performance criterion.

3. Define proportional control mode

A controller mode in which the controller output is directly

proportional tothe error signal P=Kpep+p0 P-controller output Kp=

Propotional gain, ep=error inpercent of variable range, P0-Bias.

4. Define proportional band.(M/J07)

Proportional band is defined as the change in input of proportional

controller mode required to produce a full-scale change in output

5. Write the relation ship between proportional band and proportional

gain.

The reciprocal of gain expressed as a percentage is called

proportionalband. Kp=100/PB

6. Define offset.

It is the steady state deviation (error) resulting from a change in

value ofload variable.

7. Sketch Pneumatic P+I controller.

Refer Curtis Johnson, Page No.418, and Fig. 10.17.

8. Why is the electronic controller preferred to pneumatic controller?

Electronic signals operate over great distance without time lags.

Electronicsignals can be made compatible with digital controllers.

Electronic devices can bedesigned to be essentially maintenance free.

Intrinsic safety techniques eliminateelectrical hazards. Less expensive to

install. More energy efficient. Due to theabove said properties electronic

controllers are preferred to pneumatic controller.

9. Explain the function of controller.

The element in process control loop that evaluates error of the

controlledvariable and initiates corrective action by a signal to the

controlling variable.

10. Write any two limitations of single speed floating control.

The present output depends on the time history of errors and such

history isnot known, the actual value of controller output floats at an

undetermined value. Ifthe deviation persists controller saturates at either

100% or 0% and remain thereuntil an error drives it towards opposite

extreme.

11. Sketch the input – output characteristic of single – speed floating

controller.

Refer Curtis Johnson, Page No. 368, and Fig.9.7.

12. Why derivative mode of control is not recommended for a noisy

process?

The series capacitor in the derivative controller will amplify the noise in

theerror signal.

13. Define integral (reset) windup?

The over charging in the presence of a continuous error of the

integralcapacitor which must discharge through a long time constant

discharge path andwhich prevents a quick return to the desired control

point.

14. What are the two modes of controller.

Discontinuous and continuous mode are the two modes of

controller.

15. Define Discontinuous mode of controller.

If for only two values of error, control action is taken, it is

Discontinuousmode of controller.

16. Define Continuous mode of controller.

If for every value of error, control action is taken, it is

Discontinuous modeof controller.

17. Give an example for Discontinuous and Continuous mode of

controller.

Discontinuous-ON-OFF controller.

Continuous – Proportional Controller

18. Define cycling.

Oscillations of error about zero is called cycling

19.How to choose the valve speed in the floating control (M/J06)

20. Define error (deviation)?

It is the difference at any instant between the value of controlled

variableand the set point. E=S.P-P.V

21. Design Electronic P controller with PB =50%(M/J06)

22. Limitation of ON/OFF controller(N/D06)

23. How the offset can be minimized in P controller(N/D06)

24. What are known as control action (A/M 08)

25. Explain briefly on derivative control mode (A/M08)

26. Define differential gap(M/ J07)

27. What is meant by controller tuning (M/J09)

28. Define reverse action (M/J09)

29. Define the decay ratio of the under damped(A/M05)

30. Write the transfer function of the PI controller (A/M05)

31. Why differential control cant be used alone (A/M08)

32. DefineITAE (A/M 08)

PART B

1. With neat schematic diagram explain the single speed floating control.(nov13)

2. With neat sketch explain the of P+I pneumatic controller.(nov13)

3. Explainwith neat diagram the working of electronic PID controller.(nov13)

4. Describethe characteristics of P, PI, PIDcontroller.(nov12)

5. Drawand explain the electronic circuit for realizing the P, PI, PID, PD controller.(nov12)

6. Whenan on-off controller is recommended? How its performance affected by process dead time.(may12)

7. Consider a household heating system with on-off controller. There is a dead band of 2 C that is temperature must drop to 1 F below the set point before the heater kicks on and got to 1 F above the set point before the kicks off. The heater has periodic behavior with periods where the heater is on followed by its off. Discuss the effect of dead band on this periodic

behavior. Sketch the expected heater on-off and temperature profile as dead band is changed.(may12)

8. A pi controller has 20% and integral time of 10sec.for a constant error of 5%.determine the controller output after 10sec.the controller offset is 25%.(may12)

9. Howare p&I actions realized in pneumatic controller how are these actions varied in magnitude. Obtain the transfer function of such a controller.(may12)

10. Comparethe features of ON & OFF,P,I,D control modes and draw their characteristics.(nov10)

11. List 1 disadvantage of all the above four control modes.(nov10)

12. Explain the procedure for tuning pi controller using zielger Nicholas method.(nov10)

13. Designan electronic pid controller to meet the following process range 4 to 20 mA.kc=2.5%/%,ki=5%/% min,kd=2%/%min.controller output 4 to 20 mA.(nov10)

14. What is cycling in the process output in which control mode it occurs.(may10)

15. A second order process with the transfer function of g(s)=5/(10s+1)(3s+1) is controlled by a proportional controller. Find the value of kp required offset due to unit step change in set point is 5% of steady state value of controlled variable.(may10)

16. Aproportional controller in a flow loop of chart scale of 20 to 170 lpm.if the controller output is 14 mA at 100 lpm.find the proportional band.(may10)

17. Explain the damped oscillation of tuning a controller.(may 10)

18. Explainthe effect of differential gap of on-off controller on the response of same.(may06)

19. Varioussteps involved in process reaction curve method of tuning off controllers.(may09)

20. Explainthe various time integral performance criteria with closed loop response.(may09)

21. Explain the concept behind quarter amplitude and minimum area method in judging the control system.(may09)

22. Explain the various steps involved in tuning of controllers by closed loop method.(may09)

23. Why derivative control is not recommended alone for any process.(may06)

24. Design electronic with pid controller following specifications: proportional band 25% derivative gain kd20,integral gain ki 2.5.(may06)

25. Explain briefly about various control action of pneumatic and electronic controllers.(nov04)

26. Compute the response of pd controller to ramp change in the error. Sketch the contributions of proportional and derivative action separately. Discuss the nature of derivative control term.(nov04)

U NIT 3

PART A

1. Write Ziegler- Nicolas turning formulae.

For proportional controller: Kp = 0.5 Ku.

For Proportional – integral controller: Kp = 0.45 Ku, Ti = Pu/1.2.

For Proportional – integral – derivative controller:

Kp = 0.6 Ku, Ti = Pu/2, Td = Pu/8.

2. Define controller turning.(M/J09)

Deciding what values to be used for the adjusted parameters of the

controller is called controller turning.

3. What is reaction curve.

In process controller, the reaction curve is obtained by applying a

stepchange (either in load or in set point) and plotting the response of the

controlledvariable with respect to time.

4. What performance criterion should be used for the selection and

turning ofcontroller?

Keep the maximum error as small as possible.Achieve short

settling time.Minimize the integral of the errors until the process has

settled set Point.

5. Define ultimate gain.

The maximum gain of the proportional controller at which the

sustainedoscillations occur is called ultimate gain (Ku).

6. What is ITAE and when to go for it?(A/M08)

ITAE means Integral Time Absolute Error. To suppress the errors

thatpersist for long time, the ITAE critertion will tune the controllers

better becausethe presence of large t amplifies the effect of even small

errors in the value ifintegral.

7. What are the parameters required to design a best controller?

Process Parameters (K,), Controller parameters (Kp,Ti,

Td),performancecreation (ISE, IAE, IATE)

8. Write any tow practical significance of the gain margin.

It constitutes a measure of how far the system is the brink of

instability.Higher the gain margin (above the value of one), the higher

the safety factor weuse controller turning.Typically, a control designer

synthesizes a feedback system with gainmargin larger than 1800.

9. Why is it necessary to choose controller settings that satisfy both gain

marginand phase margin?

The gain margin and Phase margin are the safety factors which is

used forthe design of a feedback system. Beyond the phase margin and

gain margin thesystem goes to unstable position.

10. What is turning a controller based on quarter – decay ratio?

It is the procedure in which adjusting the proportional gain of

controllerupto ¼ th decay ratio waveform is obtained.

11. Name the time integral performance criteria measures.

Integral Square Error (ISE), Integral of absolute value of error

(IAE),Integral of time weighted absolute error.

12. Define Integral Square Errors (ISE)

If we want to suppress large errors, ISE is better than IAE Because

errorsare squared and contribute more to the value of integral.

13. Define Integral Absolute Errors (IAE)

If we want to suppers small errors, IAE is better than ISE Because

when wesquare small numbers, they even become smaller.

14. Define Integral of Time weighted Absolute Error (ITAE)

To suppress errors that persist for long times, ITAE criterion will

tune thecontrollers better because the presence of large t amplifies the

effect of even smallerrors in value of integral.

15. Define One-quarter decay ratio (M/J06).

It is reasonable tradeoff between fast rise time and reasonable

setting time.

16. Give the satisfactory control for gas liquid level process.

Proportional Control is the satisfactory control for liquid level

process.

17. Give the satisfactory control for gas pressure process.

Proportional Control is the satisfactory control for liquid level

process.

18. Give the satisfactory control for vapour pressure process.

PI Control is the satisfactory control for vapour pressure process

havingfast response.

19. Give the satisfactory control for temperature process.

PID Control is the satisfactory control for temperature process.

20. Give the satisfactory control for composition process.

PID Control is the satisfactory control for composition process.

21. How to obtain reaction curve from control room.(M/J06)

22What is meant by performance inertia (N/D06)

23. Why the derivative can’t be used alone(N/D06)

24. Evaluation criteria (A/M08)

25. Tuning, Performanceindices (A/M08 ,N/D13)

26. Averagingcontrol (M/J07)

27. Adaptivecontrol (M/J09)

28. Split range control (M/J07)

29. Major component of processcontrol (A/M05)

30. Define phase cross over freq in the bode stability criterian (A/M05)

31.Advantage offeed forward control(A/M08)

PART B

1. Whatare the principles that arise during the design of feedback controller. Discuss them on the basis of physical example.(nov04)

2. What are the relative advantages and disadvantages of three time integral criteria ise,iae&itae.how would you select the appropriate for the particular application.(nov04)

3. Using the nyquistcriterian show that feedback system with first and second order open loop response are always stable.(nov04)

4. Describethe Ziegler-nicholas tuning methodology. This procedure is often called continuous cycling tuning method. Why?(nov04)

5. Explain one time response method of tuning controller method.(may06)

6. Noteon ¼ decay ratio.(may06)

7. Why both gain and phase margin should be considered for tuning of a controller.(may06)

8. What is cascade control? Explain need for cascade control with an example.(may09)

9. Discuss the selection of controllers.(may09)

10. Whatis the need for inferential control. Explain the method finding the estimate for a process needs interferential control.(may09)

11. Whatis the necessary condition to achieve a perfect interferential control? Mention some industrial process with need interferential control.(may09)

12. Whendo you prefer cascade control mode.(may10)

13. Explain the design of cascade scheme for a system of our choice from the fundamental.(may10)

14. What are the precaution taken to tuning of cascade control loop.(may10)

15. Explainthe block diagram of cascade control and adaptive control.(dec10)

16. List the advantages and disadvantages of feed forward controlscheme.(dec10)

17. With the block diagram explain the operation of split range control scheme.(dec10)

18.What is itae criterian from iae.(may12)

19. Explainthe feed forward control with an example. compare this with feedback control. Alsobring out this merits and demerits.(may12)

20. Discuss the procedure for setting controller parameters using frequency response method.(nov12)

21. Explain the method of process reaction curve and damped oscillations for tuning the controllers.(nov12)

22. Explainhow to find the controller settings using process reaction curve.(nov13)

23. Determinethe optimum controller settings for the transfer function 1/(s+1)3 using ziegler-nicholas tuning method.

Unit 4

PART A

1. Define ratio control. With example(M/J07)

Ratio control is a special type of feed forward control where two

disturbances are measured and held in a ratio to each other.

2. Define cascade control.

Cascade control is defined as a control system composed of two

loopswhere the set point of one loop (the inner loop) is the output of the

controller ofthe other loop (the outer loop)

3. When cascade control will give improved performance than

conventionalfeedback control?

In some process the secondary variables in it introduce disturbance

throughout the system is measured and controlled by a separate loop.

4. Explain the purpose of cascade control for heat exchangers?

In heat exchangers, the control objective is to keep the exit

temperature ofstream. But the flow rate of the stream creates the low

disturbance throughout ofit’s a function. The secondary loop is used to

compensate the flow rate of thestream.

5. What is meant by auctioneering control?

Such control configurations select among several measurements

the onewith the highest value and feed it to the controller. Thus it is a

selective controllerwhich possesses several measured outputs and only

one manipulated input.

6. Give any two types of selective control system.

Override control for the protection of process equipment,

auctioneeringcontrol.

7. What is limit switch?

In some cases it is necessary to change from the normal control

action andattempt to prevent a process variable from exceeding an

allowable upper or lowerlimit. This can be achieved by the use of special

type switches called limitswitches.

8. Mention the types of limit switches.

High Select Switch (HSS), Low Select Switch (LSS).

9. What is HSS?

High Select Switch (HSS) is a limit switch which is used whenever

avariable should not exceed an upper limit.

10. What is LSS?

Low Select Switch (LSS) is a limit switch which is used whenever

avariable should not exceed an lower limit.

11. What is override control?

During the operation of the plant, it is possible that some of the

processvariables exceed the limit. In such cases it is necessary to change

from the normalcontrol action and attempt to prevent a process variable

from exceeding anallowable an allowable upper or lower limit. This can

be achieved by the use ofspecial type switches called limit switches

called limit switches (HSS and LSS).This type of protective control is

called override control.

12. What is split-range control?

To control A single process output can be controlled by co-

coordinating theactions of several manipulated variables all of which

have same effect on controlled output. Such systems are called split-

range control systems.

13. Differentiate split-range control and selective control.

Split-range control system involves one measurement and more

than onemanipulated variables but selective control system involves one

manipulatedvariables and several controlled outputs.

14. Why are fuel and air sent at a specified ratio into a combustion

chamber?

To obtain the most efficient combustion.

15. What are decouplers?

The special element introduced in a system with two strongly

interactingloops to cancel the interaction effect between the two loops

and thus render two non-interacting control loops is called decoupler.

16. When is inferential control used?

It is used in some cases where the output of the process and the

influence of the disturbance cannot be measured.

17. What are the advantages of feed forwardcontroller?

Acts before the disturbance is felt by the process. It is good for

slow systems.

18. What are the disadvantages of feed forward controller.

Requires identification of all possible disturbances and their direct

impact.Cannot cope with unmeasured disturbances.

19. What are the advantages of feedback controller.(N/D06,13.)

It does not require identification and measurement of disturbance.

20. What are the disadvantages of feed forwardcontroller?

It is unsatisfactory for slow processes with significant dead time.

21. What is meant by inferential control (M/J06,N/D13)

22. Decoupler (M/J05)

23. Block diagram for feedbackcontrol (A/M08)

24. Cv factor of control valve (M/J07)

25. Under what condition would an equal % valve be used instead of a

linear valve (M/J07)

26. Valve flow coefficient referred in control valve sizing (M/J09)

27. An equal % valve has a max flow of 50m3/s and a min of 2m3/s. if

the full travel is 3cm, find the flow at a1cm opening (M/J09)

28. Block diagram of a control loop for the measurement of process

reactioncurve (A/M05)

29. Function of a control valve (A/M05)

30. How are the control valve classified (A/M08)

31. Purpose of the valve position (A/M08) refer unit 5

PART B

1. Discuss the relational of a cascade control system and demonstrate why it provides better response then simple feedback.(nov 04)

2. What are the main advantages and disadvantage of cascade control .for what kind of process can you employ cascade control.(nov 04)

3. What is meant by selective control system? How many different types of selective control system are available .discuss their characteristics.(nov 04)

4. What is split range control? Describe a situation when you could use split range control.(nov 04)

5. Explain feed forward control with an example from distillation column.(apr 06)

6. List the benefits we can except when compared with feedback controller.(apr 06)

7. What is ratio control?(apr 06)

8. With an example, explain the control of valve positioned. (apr 06)

9. With a neat diagram explain the principle of an I/P converter.(may 09)

10. Explain the principle of direct and reverse acting pneumatic actuators with a neat sketch.(may 09)

11. Supposea force of 400N must be applied to open a valve. Find the diaphragm area if a control gauge pressure of 70 Kpa must provide this force.(may 09)

12. Justify the cascade control can give better performance then feedback controller(may 06).

13. Describe an application which needs cascade control.(may 06).

14. Explain the difficulties involved in controlling multivariable system with example from distillation column.(may 06)

15. Explain the working principle of pneumatic actuated control valve with positioned, with the help of neat diagram.(may 10)

16. Match the following plugs and their corresponding floe characteristics curves of pneumatic valve.(may 10)

17. Write short notes on the following. (may 10 &dec 10)

a.) valve sizing

b.) cavitations and flashing

c.)I/P converter.

18. Explain in detail the working of O/P converter .(dec 10)

19. Draw a neat sketch of pneumatic actuated control valve with positioned and explain its working.(dec 10)

20. Explain the feed forward control with an example .compare feed forward controller with fed back controller. Also bring out its merits and demerits.(may 12)

21. A cascade control system is shown in fig. Calculate the maximum gain and critical frequency of the primary controller? Eliminating the inner loop compare these valves the single loop system. Use bode plot technique.(may 12).

22. Explain the concept of ratio control with an example.(nov 12)

23. What is meant for split range control? Explain with an example.(nov 12)

24. Explain the application of feed forward control and cascade control in distillation column.(nov 12)

Unit-5

PART A

1. What is flashing in control valve? (N/D06)

When a liquid enters a valve and the static pressure at the vena

contractaless than the fluid vapour pressure and the valve outlet pressure

is also less thefluid vapour pressure the condition called flashing exists.

2. When do you use a valve positioned? (A/M08.N/D13)

If the diaphragm actuator does not supply sufficient force to

position thevalve accurately and overcome any opposition that flowing

conditions create apositioned may be required.

3. Give two examples for electric actuators.

Motor, Solenoids.

4. What is the need of I/P converter in a control system?(N/D06)

In some process loop the controller is electronic and the final

controlelement is electronic one. To interconnect these two we need a

device that shouldlinearly converts electric current in to gas pressure (4-

20mA-315 psi). Such deviceis called I/P converter.

5. Why an installed characteristic of a control valve is different from

inherentCharacteristics?

An inherent characteristic is which the valve exhibits in the

laboratorycondition where the pressure drop is held constant. An

installed or resultant characteristic is the relationship between flow and

stroke when the valve issubjected to pressure conditions of the process.

6. Explain the function of pneumatic transmission lines.

Used to transmit the input signals into standard instrumentation

pneumaticOutput signals (3 to 15 psi or 20 to 100 KPa).

7. What is the purpose of final control element?

A component of a control system (such as valve) is used to directly

regulatesthe flow of energy or materials to the process. It directly

determines the value ofmanipulated variable.

8. What is meant by cavitations in control valve?(N/D06,A/M08,N/D13)

When a liquid enters a valve and the static pressure at the vena

contractadrops to less than the fluid vapor pressure and the recovering to

above fluid vapourPressure, this pressure recovery causes an implosion

or collapse of the vapourBubbles formed at the vena contracta. This

condition is called cavitations.

9. What is “equal percentage” in the equal percentage valve?

For equal increment of stem travel at constant pressure drop an

equal percentage change in existing flow occurs.

10. What are the characteristics of control valve?

Inherent characteristics, Installed characteristics.

11. Differentiate inherent characteristics and installed characteristics.

(A/M08)

` Inherent characteristics is which the valve exhibits in the

laboratory

Condition where the pressure drop is held constant. Installed or resultant

Characteristics are the relationship between flow and stroke when the

valve is subjected to pressure conditions of the process.

12. What is “quack opening” control valve.

For smaller movement of the stem, there is maximum flow rate.

13. What is “Linear” control valve?

If stem position varies linearly with flow rate, then it is linear.

14. Define Control Valve sizing.

Q=Cv.sqrt(UP/Sg)

Q-Flow rate

Cv-Valve coefficient

UP-pressure difference across valve.

Sg-Specific gravity of liquid.

15. Name any one final control element.

Control Valve.

16. What is the function of control valve in a flow control system?

The function of control valve in flow control system is to regulate

the flow.

17. Name one application of electrical actuators.

Solenoid coil used to change gears.

18. Name the two types of plugs.

Single-seated and double-seated plug type control valves.

19. Define Range ability.

It is the ratio of maximum controllable flow to minimum

controllable flow.

20. What is rotating shaft type control valves?

1. Rotating-plug valves

2. Butterfly valves

3. Louvers.

21. Degree of freedom (M/J09)

22. Evaporationprocess (M/J09)

23. Types of drying process (A/M08)

24. Refluxratio (A/M08)

25. Any 2 factor involved in selection of control valve (A/M05)

26. Flow coefficient of control valve (A/M05)

27. Types of combustion control scheme (M/J08)

28. Why an equal % valve called so (M/J06)

29. Whether the control valve should be over sized or under sized

why(M/J06)

PART B

1. With neat circuit diagram, explain the I/P converter.(nov 13)

2. With necessary diagram, explain the characteristics of control valves.(nov 13) 3. Explain the procedure for control valve sizing for a flow control system.(nov 13)

4. Explain the principles of working and construction of I/P converter.(nov 12)

5. Describe the construction and working of the solenoid.(nov 12)

6. Explain the characteristics of the control valve.(nov12)

7. Describe the steps to be followed for the control valve sizing.(nov 12)

8. What different at different types of valves are commercially used?(may 12)

9. What are the factors that should be known for selecting a control valve.(may 12)

10. Write the flow equation of a equal percentage valve and sketch its inherent valve characteristics (may 12)

11. When are single seated and double seated valves are used? List and compare their advantages and disadvantages?(may 12)

12. A double seated valve is used in a system for a liquid flowing at a maximum rate of 10 gpm. Its specific gravity being 0.9and viscosity 36000 cp. The drop the valve 1 psi. Obtain the valve size.(may 12)

13. Write short notes on the operation of the following processes with neat block diagram.(nov 10)

a.) drying process

b.) heat exchange

14. With the help of the neat diagram, explain any 4 control schemes used in distillation column control. (nov 10)

15. Explain in detail the various control schemes used for binary distillation column(may 10)

16. With the help of the neat diagram describe the operation of

A. Heat exchanger

B.drying process

17. What is the distillation process? Are the manipulated variables and controlled variables and load variables in a distillation process?(may 13)

18. Explain the following terms associated with distillation column.

Bubble point, dew point, rectifying section and stripping section. (may 09)

19. What are the degree of freedom of a binary distillation process.(may 09)

20. Explain the principle of drying process usingany one type of dryers. (may 09)

21. Explain various control schemes involved in the heat exchange process.(may 09)

22. What are the degree of the freedom of a heat exchanger.(may 09)

23. List the benefits of a valve positioned. (apr 06)

24. Explain three different characteristics of control valve. (apr 06)

25 .What are the effects of over sizing or under sizing the valve. (apr 06)

26. Explain cavitations and flashing effect. (apr 06)

27. Explain briefly about the construction and operating principle of different types of pneumatic valves and their floe capacity characteristics. (nov 04)

28. Discuss about the important factors before selecting air - to - pneumatic control valve. (nov 04)

29. Write short notes on (nov 04)

a.) control valve sizing.

B.)Cavitations and flashing.