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Technical Round Materials-Instrumentation and Control Engineering-Free Download

Technical Round Materials-Instrumentation and Control Engineering-Free Download

? Question 1. What Is Instrumentation?

Answer :

The technology which is used to measured and control the process system of plant is called instrumentation. It is branch of engineering.

? Question 2. What Is Reynolds Number?

Answer :

We know with help of reynolds number what type of flow in fluid.

? Question 3. Why Do We Use 4-20ma Signal Instead Of 0-10 Ma?

Answer :

To elevate zero so that we can come to know whether it is dead zero or from signal.

? Question 4. What Is The Difference Between Dry Leg And Wet Leg?

Answer :

Dry leg means in lab. And wet leg means in feild

? Question 5. How Can We Calibrate A Positioner?

Answer :

A positioner is a device put into a valve to ensure that it is at a correct position of opening as per the control signal. An I/P converter only sends the opening/closing request to valve but can not confirm its position.

Positioner senses the valve opening through a position feedback link connected to valve stem which is its input signal. I/P converter output is its setpoint input. The difference between these two is the error signal based on which the positioner positions the valve to correct position to reduce error to zero. Hence positioner is nothing but a pneumatic feedback controller.

Controlled external supply air to positioner provides power to positioner to position a valve. Also positioner is used in a valve when valve operating signal range is different from I/P converter output range.

? Question 6. Explain What Is The Working Principle Of The Magnetic Meter?

Answer :

An electric potential is developed when a conductor is moved across the magnetic field. In most electrical machinery the conductor is a wire. The principle is equally applicable to a moving, electrically conductive liquid. The primary device of commercial magnetic meters consist of straight cylindrical electrically insulated tube with a pair of electrodes nearly flush with the tube walls and located at opposite end of a tube diameter. This device is limited to electrically conducting liquids. The magnetic meter is particularly suited to measurement of slurries and dirty fluids.

? Question 7. Tell Me The Mechanism Behind The Turbine Meter?

Answer :

Turbine meters consist of straight flow tube within which a turbine or fan is free to rotate about it s axis which is fixed along g the centre line of the tube. Mostly, a magnetic pick up system senses the rotation of the rotor through the tube walls. The turbine meter is a flow rate device, since the rotor speed is directly proportional to the flow rate. The output is usually in the form of electric pulses from the magnetic pick up with a frequency proportional to the flow rate.

? Question 8. How To Choose Differential Range?

Answer :

The most common range for differential range for liquid measurement is 0-100. This range is high enough to minimize the errors caused by unequal heads in the seal chambers. It is also dependent on the differences in the temperature of the load lines. The 100 range permits an increased in capacity up to 400. While decrease down up to 20 by merely changing the range tubes or range adjustments.

? Question 9. What Is The Working Of Rota Meter?

Answer :

Variable area meters are special form of head meters. Where in the area of flow restrictor is varied. So as to hold the differential pressure constant. The rota meter consists of a vertical tapered tube through which the metered fluid flows in upward direction. As the flow varies the ‘float' rises or falls to vary the area of the passages that the differential across it balances the gravitational force on the ‘float'. The differential pressure is maintained constant. The position of the ‘float' is the measure of the rate of flow.

? Question 10. Explain What Are De-saturators?

Answer :

When, in some processes, e.g. batch processes, long transient responses are expected during which a sustained deviation is present the controller integral action continuously drives the output to a minimum or maximum value. This phenomenon is called ‘integral saturation of the control unit'. When this condition is met, then this unit is de-saturated.

? Question 11. Do You Know How Is Automatic Reference Junction Compensation Carried Out In Temperature Recorders?

Answer :

In automatic reference junction compensation, variable nickel resistor is used. As the temperature changes, so does its resistance. This reference junction compensator is located, so that it will be at the temperature of the reference junction. The reference junction is at the poset where the dissimilar wire of the thermocouple is rejoined. This joint is invariably at the terminal strip of the instrument.

? Question 12. What Is Solenoid Valve? Where It Is Used?

Answer :

A solenoid is electrically operated valve. It consists of solenoid coil in which magnetic plunger moves. This plunger is connected to the plug and tends to open or close the valve.

There are two types of solenoid valves:

1. Normally Open
2. Normally closed

Use: It is used for safety purpose in different electric work

? Question 13. What Is Ratio Control System?

Answer :

A ratio control system is characterized by the fact that variations in the secondary variable don't reflect back on the primary variable. A ratio control system is the system where secondary flow is hold in some proportion to a primary uncontrollable flow.

If we assume that the output of a primary transmitter is A. and the output of the secondary transmitter is B, and that the multiplication factor of the ratio relay is K, then for equilibrium conditions which means set valve is equal to measured valve.

we find the following relation:

KA-B=0 or B/A = K where ‘K' is the ratio setting off the relay.

? Question 14. How To Test A Transistor With A Multimeter?

Answer :

1. Emitter +ve of meter and base -ve output =Low resistance

2. Emitter -ve of meter and base +ve output =High resistance

3. Collector +ve and base -ve output =Low

4. Collector -ve and base +ve output =Low

Emitter: Collector = High resistance

PNP: Opposite Results

? Question 15. What Is Motion Balance Principle?

Answer :

A controller which generates an output signal by motion of its parts. The increase in the baffle is to move towards the nozzle. The nozzle back pressure will increase. This increase in the back pressure acting on the balancing bellows, will expand the bellows. The nozzle is moved upward due to this. The nozzle will move until motion almost equals the input baffle motion.

? Question 16. What Is Force Balance Principle? State Some Of Its' Advantages?

Answer :

Force balance principle: A controller which generates an output signal by opposing torque. The input force is applied on the input bellows which moves the beam. This crackles nozzle back pressure. The nozzle back pressure is sensed by the balancing bellows which brings the beam to balance. The baffle movement is very less about 0.002 for full scale output.

Advantages:

a. Moving parts are fewer.

b. Baffle movement is negligible

c. Frictional losses are less

? Question 17. What Is Zener Diode? What Is Voltage Regulator?

Answer :

The breakdown region of a p-n diode can be made very sharp and almost vertical diodes with almost vertical breakdown region are known a s zener diodes. A zener diode operating in the breakdown region is equivalent to a battery. Because of this current through zener diode can change but the voltage remains constant. It is this constant voltage that has made the zener diode an important device in voltage regulation.

Voltage regulator: The output remains constant despite changes in the input voltage due to zener effect.

? Question 18. What Is Intrinsically Safe System?

Answer :

Intrinsic safety is a technique for designing electrical equipment for safe use in locations made hazardous by the presence of flammable gas or vapours in the air.

Intrinsically safe circuit is one in which any spark or thermal effect produce either normally or under specified fault conditions is incapable of causing ignition of a specified gas or vapour in air mixture at the most ignited concentration.

? Question 19. What Is Furnace Draft Control?

Answer :

Balanced draft boilers are generally used negative furnace pressure. When both forced draft and induced draft are used together, at some point in the system the pressure will be same as that of atmosphere. Therefore the furnace pressure must be negative to prevent hot gas leakage.

Excessive vacuum in the furnace however produces heat losses through air infiltration. The most desirable condition is that the one have a very slight negative pressure of the top of furnace.

? Question 20. What Are Different Types Of Control Valves?

Answer :

The commonly used control valves can be defined as follows:

a. Depending on Action:

Depending on action there are two types of control valves 1. Air to close 2. Air to close

b. Depending on body:

Depending on body there are 4 types of control valves

1. Globe valves single or double seated

2. Angle valves

3. Butterfly valves

4. Three way valves

? Question 21. Name Different Types Of Bourdon Tubes?

Answer :

Types of bourdon tubes:

1. C type
2. Spiral
3. Helix

? Question 22. What Are Primary Elements Of Measuring Pressure? Which Type Of Pressure Can Be Measured By These Elements?

Answer :

Primary elements of measuring pressure are:

a. Bourdon Tube
b. Diaphragm
c. Capsule
d. Bellows
e. Pressure springs

These elements are known as elastic deformation pressure elements.

? Question 23. What Is The Use Of Valve Positioner?

Answer :

Valve positioner can be used for following reasons:

a. Quick action
b. Valve hysterisis
c. Viscous liquids
d. Split range.
e. Line pressure changes on valve
f. Bench set not standard
g. Reverse valve operations

? Question 24. What Is The Use Of Double Seated Valve?

Answer :

In double seated valves the upward and downward forces on the plug due to reduction of fluid pressure are nearly equalized. It is generally used on bigger size valves and high pressure systems. Actuator forces required are less.

? Question 25. What Is The Use Of Single Seated Valve?

Answer :

The single seated valve is used on smaller sizes where an absolute shut off is required. The use of single seated valve is limited by pressure drop across the valve in the closed or almost closed position.

? Question 26. Name Different Parts Of A Pressure Gauge? Explain The Use Of Hair Spring In The Pressure Gauge?

Answer :

Pressure gauge includes following components:

a. ‘C' type bourdon tube.
b. Connecting link
c. Sector gear
d. Pinion Gear
e. Hair spring
f. Pointer
g. Dial

Use of hair spring: Hair spring is responsible for controlling torque. It is also used to eliminate any play into linkages.

? Question 27. Tell Me How Is Flow Measured In Square Root?

Answer :

Flow varies directly as the square root of pressure. Thus, F=K of square root of applied pressure. Since this flow varies as the square root of differential pressure.

The pressure pen does not directly indicate flow. Thus flow can be determined by taking the square root of the pen. Assume the pen reads 50% of the chart. So, flow can be calculated using the pen measure in the chart.

? Question 28. Explain How Can A D.p. Transmitter Be Calibrated?

Answer :

D.P. transmitter can be calibrated using following steps:

1. Adjust zero of Xmtrs.

2. Perform static pressure test: Give equal pressure on both sides of transmitter. Zero should not shift either side. If the zero shifts then carry out static alignment.

3. Perform vacuum test: Apply equal vacuum to both the sides. Zero should not shift.

4. Calibration procedure: Give 20 psi air supply to the transmitter and vent L.P. side to atmosphere. Connect output of the instrument to the standard test gauge. Adjust zero. Apply required pressure to the high pressure side and adjust the span. Adjust zero gain if necessary.

? Question 29. What Is Bernoulli's Theorem. State Its Application?

Answer :

Bernoulli's theorem states that the ‘total energy of a liquid flowing from one point to another remains constant'. It is applicable for non-compressible liquids. For different types of liquid flow Bernoulli's equation changes. There is direct proportion between speed of fluid and its dynamic pressure and its kinetic energy.

It can be used in various real life situations like measuring pressure on aircraft wing and calibrating the airspeed indicator. It can also be used to low pressure in the venturi tubes present in carburetor.

? Question 30. Explain Why Is The Orifice Tab Provided?

Answer :

Following reasons justify for providing orifice tab:

1. Indication of orifice plate in a line
2. The orifice diameter is marked on it.
3. The material of the orifice plate.
4. The tag number of the orifice plate.
5. To mark the inlet of an orifice.

? Question 31. Do You Know How Do You Identify An Orifice In The Pipeline?

Answer :

An orifice tab is welded on the orifice plate which extends out of the line giving an indication of the orifice plate.

? Question 32. Explain What Are Different Types Of Orifice Plates? State Their Uses?

Answer :

Different orifice plates are:

1. Concentric

2. Segmental

3. Eccentric

Concentric: These plates are used for ideal liquid as well as gases and steam service. Concentric holes are present in these plates, thats why it is known as concentric orifice.

Segmental: This plate has hole in the form of segment of the circle. This plate is used for colloidal and sherry flow measurement.

Eccentric: This plate has the eccentric holes. This plate is used in viscous and sherry flow measurement.

? Question 33. Why Thermo Wells Are Used? What Materials Are Used In Thermo Wells?

Answer :

In numerous applications, it is neither desirable nor practical to expose a temperature sensor directly to a material. Wells are therefore used to protect against damage corresion, arosion, aborsion and high pressure processes. A thermo well is also useful in protecting a sensor from physical damage during handling and normal operations.

Materials used in thermo wells: Stainless steel, Inconel, Monel, Alloy Steel, Hastelloy

? Question 34. Can You Explain The Burnout Feature?

Answer :

Burnout provides the warnsug feature of driving indicator at the end of scale, if the input circuit is open. A burnout resistor is provided which develops a voltage drop between the measuring circuit and amplifier. The polarity of the signal determines the direction of the servo drive upon an open circuit in the input.

Upscale burnout: R value 10 M
Downscale burnout: R value 22 M

? Question 35. What Is Constant Voltage Unit?

Answer :

The constant voltage circuit consists of a rectifier, CR and a filter capacitor. It is followed by two stages of zener regulation. Abridge configuration is provided to lamp line voltage zener regulation. Regulation 1 and regulation 2 provides relatively provide constant current. Resistors form a bridge that may remoment line voltage effects.

? Question 36. Tell Me The Working Of An Enraf Level Gauge?

Answer :

Enraf level gauge is based on the ser powered null balance technique. A displacer serves as continuous level sensing element. A two phase ser motor controlled by a capacitive balance system winds unwinds the the measuring wire until the tension in the weight springs is in balance with the weight of the displaced part immersed in the liquid. The sensing system in balance measures the two capacitance formed by the moving central sensing rod provided by the two capacitor plates and the si plates.

? Question 37. Do You Know The Working Of An Electronic Level Troll?

Answer :

The variation in level of buoyancy resulting from a change in liquid level varies the net weight of the displacer increasing or decreasing the load on the torque arm. This change is directly proportional to change in level and specific gravity of the liquid. The resulting torque tube movement varies the angular motion of the rotor in RVDT providing a rotor change proportional to the rotor displacement, which is converted and amplified to a D.C. current.

? Question 38. Explain How D.p. Transmitter Can Be Applied To Open Tank?

Answer :

In open tank the lower pressure side is vented to the atmosphere. All pressure is applied to the high pressure side. This vessel pressure is measured through high pressure side.

? Question 39. Do You Know How D.p. Transmitter Can Be Applied To Close Tank?

Answer :

In closed tank, bottom of the tank is connected to the high pressure side of the transmitter. Top of tank is connected to the lower pressure side of the transmitter. In this way vessel pressure can be measured.

? Question 40. What Is The Function Of 3-way Manifold Valve?

Answer :

excessive pressure to your differential pressure transmitter, you could damage your instrument. This is known as over-ranging the transmitter.

A three-way manifold valve is a device that prevents the instrument from being over-ranged. It also allows the isolation of the transmitter from the process loop (an option which could be used generaly for maintenance or re-calibration or fitting new equipment).

? Question 41. Why We Giving Input To Electronic Amplifier In Inverting Pin? What Is The Reason Behind That?

Answer :

if we need a phase shift than we give input n inverting pin or when we need to boost signal at higher level, i.e; using cascade stages of amplification(even) than we also use inverting pin.

? Question 42. What Is Instrumentation Instrumentation Engineering?

Answer :

Instrumentation engineering is the engineering specialization focused on the principle and operation of measuring instruments which are used in design and configuration of automated systems in electrical, pneumatic domains etc.

They typically work for industries with automated processes, such as chemical or manufacturing plants, with the goal of improving system productivity, reliability, safety, optimization and stability.

? Question 43. What Is Instrumentation Control?

Answer :

In addition to measuring field parameters, instrumentation is also responsible for providing the ability to modify some field parameters.

Some examples include:

Device Field Parameter(s) Valve Flow, Pressure Relay Voltage, Current Solenoid Physical Location, Level Circuit breaker Voltage, Current.

? Question 44. What Is Instrumentation Measurement?

Answer :

Instrumentation can be used to measure certain field parameters (physical values):

These measured values include:

* pressure, either differential or static
* flow
* temperature - Temperature_measurement
* level - Level Measurement
* density
* viscosity
* radiation
* current
* voltage
* inductance
* capacitance
* frequency
* resistivity
* conductivity
* chemical composition
* chemical properties
* various physical properties

? Question 45. Can We Use A Control Valve Without Positioner?

Answer :

Control valve can not be without positioner. The purpose of the positioner is to control the control valve stroke so as to keep the valve in desired position. The positioner receives signal from the controller, and send the boosted signal to the actuator to reach the desired position as and when the valve reaches the desired position the positioner cuts the boosted signal to the actuator and keeps the position.

? Question 46. Why 4-20 Ma Signal Is Preferred Over A 0-10v Signal?

Answer :

Generally in a transistor some amount of voltage is required for turning it on. This voltage is the cut in voltage. Up to this voltage the exists a nonlinearity in its characteristics. Beyond this cut in voltage the char. of transistor is linear. This nonlinear region lays between 0-4ma, beyond 4ma it linear. This is why 4-20 ma range is used.

? Question 47. What Is Remote Mount With Mta Option? (in Case Of Dual Sensor Vortex Flowmeter, Rosemount Has Written In Its Catalog Drawings)?

Answer :

Remote mount with MTA means MTA connector for mounting remote connection.

MTA is the Connector used for connection. Generally we called it MTA Connector.

There are many types of MTA connector such as MTA 100connectors, Mta 156 connectors etc.

? Question 48. How To Write The Program For Single Push Button By Using Ladder Diagram?

Answer :

1. Create a Push button
2. Connect a Counter series to PB
3. Create a compare button
4. Initialize 1 at one end
5. Counter output in another
6. Connect the Coil which has to be energized
7. Initialize 2 at one end
8. Counter output in another
9. Connect the Coil which has to be reenergized.

s

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 to change the variable under and make it conform with 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?

The output will move from one steady state to another for the sustained change in input. This means that for change in some input variable the output variable will rise until it reaches a steady state (inflow = outflow). It is the tendency of the process to adopt a specific value of controlled variable for nominal load with no control operations.

Why do we need mathematical modeling of process?

The physical equipment of the chemical process we want to control have not been constructed. Consequently we cannot experiment to determine how the process reacts to various inputs and therefore we cannot design the appropr iate control system. If the process equipment needs to be available for experimentation the procedure is costly. Therefore we need a simple description of how the process reacts 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 is increased by a step the total volume of the boiling water and consequently the liquid level will decreased for a short period and then it will start increasing.

9. Define interacting system and give an example.

Load changes in first process affects the second process and vise versa when both are connected in series nature is called interacting system. Eg. Two level tanks are connected in series.

10. A tank operating at 10ft head, 51pm outflow through a valve and has a cross section area of 10 sq f calculate the time constant.

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

11. What is meant by non-self regulation?

A system that grows without limit for a sustained change in input (constant outflow or outflow independent of inflow condition).

12. Write any two characteristics of first order process modeling

The smaller the value of time constant the steeper the initial response of the system. A first order lag proce ss is self regulating the ultimate value of the response equal to Kp (steady state gain of the process) for a unit step change in the input.

13. Distinguish between continuous process and batch process.

A process in which the materials or work flows more or less continuously through a plant apparatus while being treated is termed as continuous process. The problem 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 physical location 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 controlled variable 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 regulates the flow of energy or materials to the process. It directly determines the value of manipulated variable.

16. Define Process control

It is the scheme that describes how much the manipulated variable should change inorder to bring the controlled variable back to the setpoint.

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 the performance of the process.

– Controlled variable indirectly indicates Eg. Annealing

18. What is Servo operation and Regulatory operation.

If the purpose of the control system is to make the process follow the changes in setpoint as quick as possible, then it is servo operation.

19. What is mathematical modeling.

Set of equations that characterize the process is termed as Mathematical Modelling.

20. Define an non-interacting system.

The dynamic behaviour one tank is affected by the other, but the reverse is not true, then it is non-interacting system. Here the liquid heads are independent of each other.

21. Define an interacting system.

The dynamic behavior one tank is affected by the other, but the reverse is also true, then it is non-interacting system. Here the liquid heads are dependent of each other.

22. 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.

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

Define appropriate performance criterion (ISE, IAE, ITATE). Compute the value of the performance criterion using a P, PI, or PID controller with the best setting for the adjusted parameters Kp, Ti, Td. Select controller which give the best value for the performance criterion.

24. Define proportional control mode

A controller mode in which the controller output is directly proportional to the error signal P=Kpep+p0 P-controller output Kp= Propotional gain, ep=error in percent of variable range, P0-Bias.

25. Define proportional band.

Proportional band is def ined as the change in input of proportional controller mode required to produce a full-scale change in output

26. Write the relation ship between proportional band and proportional gain

The reciprocal of gain expressed as a percentage is called proportional band. Kp=100/PB

27. Define offset.

It is the steady state deviation (error) resulting from a change in value of load variable.

28. Define error (deviation)?

It is the difference at any instant between the value of controlled variable and the set point. E=S.P-P.V

29. Sketch Pneumatic P+I controller

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

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

Electronic signals operate over great distance without time lags. Electronic signals can be made compatible with digital controllers. Electronic devices can be designed to be essentially maintenance free. Intrinsic safety techniques eliminate electrical hazards. Less expensive to install. More energy efficient. Due to the above said properties electronic controllers are preferred to pneumatic controller.

31. Explain the function of controller.

The element in process control loop that evaluates error of the controlled variable and initiates corrective action by a signal to the controlling variable.

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

The present output depends on the time history of errors and such history is not known, the actual value of controller output floats at an undetermined value. If the deviation persists controller saturates at either 100% or 0% and remain there until an error drives it towards opposite extreme.

33. Sketch the input – output characteristic of single – speed floating controller.

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

34. Why derivative mode of control is not recommended for a noisy process?

The series capacitor in the derivative controller will amplify the noise in the error signal.

35. Define integral (reset) windup?

The over charging in the presence of a continuous error of the integral capacitor which must discharge through a long time constant discharge path and which prevents a quick return to the desired control point.

36. What are the two modes of controller.

Discontinuous and continuous mode are the two modes of controller.

37. Define Discontinuous mode of controller

If for only two values of error, control action is taken, it is Discontinuous mode of controller.

38. Define Continuous mode of controller

If for every value of error, control action is taken, it is Discontinuous mode of controller.

39. Give an example for Discontinuous and Continuous mode of controller.

Discontinuous-ON-OFF controller.

40. Define cycling.

Oscillations of error about zero is called cycling.

42. Define controller turning.

Deciding what values to be used for the adjusted parameters of the controller is called controller turning.

43. What is reaction curve.

In process controller, the reaction curve is obtained by applying a step change (either in load or in set point) and plotting the response of the controlled variable with respect to time.

44. What performance criterion should be used for the selection and turning of controller?

Keep the maximum error as small as possible. Minimize the integral of the errors until the process has settled set Point.

45. Define ultimate gain

The maximum gain of the proportional controller at which the sustained oscillations occur is called ultimate gain (Ku).

46. What is ITAE and when to go for it?

ITAE means Integral Time Absolute Error. To suppress the errors that persist for long time, the ITAE criterion will tune the controllers better because the presence of large t amplifies the effect of even small errors in the value if integral.

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

Process Parameters (K,ô), Controller parameters (Kp,Ti, Td),performance creation (ISE, IAE, IATE)

48. 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 we use controller turning.

Typically, a control designer synthesizes a feedback system with gain margin larger than 1800.

49. Why is it necessary to choose controller settings that satisfy both gain margin and phase margin?

The gain margin and Phase margin are the safety factors which is used for the design of a feedback system. Beyond the phase margin and gain margin the system goes to unstable position.

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

It is the procedure in which adjusting the proportional gain of controller upto ¼ th decay ratio waveform is obtained.

51. Name the time integral performance criteria measures.

Integral Square Error (ISE), Integral of absolute value of error (IAE), Integral of time weighted absolute error.

52. Define Integral Square Errors (ISE)

If we want to suppress large errors, ISE is better than IAE Because errors are squared and contribute more to the value of integral.

53. Define Integral Absolute Errors (IAE)

If we want to suppers small errors, IAE is better than ISE Because when we square small numbers, they even become smaller.

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

To suppress errors that persist for long times, ITAE criterion will tune the controllers better because the presence of large t amplifies the effect of even small errors in value of integral.

55. Define One-quarter decay ratio

It is reasonable trade off between fast rise time and reasonable setting time.

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

Proportional Control is the satisfactory control for liquid level process.

57. Give the satisfactory control for gas pressure process.

Proportional Control is the satisfactory control for liquid level process.

58. Give the satisfactory control for vapour pressure process.

PI Control is the satisfactory control for vapour pressure process having fast response.

59. Give the satisfactory control for temperature process.

PID Control is the satisfactory control for temperature process.

60. Give the satisfactory control for composition process.

PID Control is the satisfactory control for composition process.

61. Define ratio control

Ratio control is a special type of feed forward control where two disturbances are measured and held in a ratio to each other.

62. Define cascade control

Cascade control is defined as a control system composed of two loops where the set point of one loop (the inner loop) is the output of the control ler of the other loop (the outer loop)

63. When cascade control will give improved performance than conventional feedback control?

In some process the secondary variables in it introduce disturbance throughout the system is measured and controlled by a separate loop.

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

In heat exchangers, the control objective is to keep the exit temperature of stream. But the flow rate of the stream creates the low disturbance throughout of its a function. The secondary loop is used to compensate the flow rate of the stream.

65. What is meant by auctioneering control?

Such control configurations select among several measurements the one with the highest value and feed it to the controller. Thus it is a selective controller which possesses several measured outputs and only one manipulated input.

66.Give any two types of selective control system.

Override control for the protection of process equipment, auctioneering control.

67. What is limit switch?

In some cases it is necessary to change from the normal control action and attempt to prevent a process variable from exceeding an allowable upper or lower limit. This can be achieved b y the use of special t ype switches called limit switches.

68. Mention the types of limit switches.

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

69. What is HSS?

High Select Switch (HSS) is a limit switch which is used whenever a variable should not exceed an upper limit.

70. What is LSS?

Low Select Switch (LSS) is a limit switch which is used whenever a variable should not exceed an lower limit.

71. What is override control?

During the operation of the plant, it is possible that some of the process variables exceed the limit. In such cases it is necessary to change from the normal control action and attempt to prevent a process variable from exceeding an allowable an allowable upper or lower limit. This can be achieved by the use of special type switches called limit switches called limit switches (HSS and LSS). This type of protective control is called override control.

72. What is split-range control?

To control A single process output can be controlled by co-coordinating the actions of several manipulated variables all of which have same ef f ect on controlled output. Such systems are called split-range control systems.

73. Differentiate split-range control and selective control.

Split-range control system involves one measurement and more than one manipulated variables but sele ctive control system involves one manipulated variables and several controlled outputs.

74. Why are fuel and air sent at a specified ratio into a combustion chamber?

To obtain the most efficient combustion.

75. What are decouplers?

The special element introduced in a system with two strongly interacting loops to cancel the interaction effect between the two loops and thus render two non-interacting control loops is called decoupler.

76. 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.

77. What are the advantages of feed forward controller

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

78. What are the disadvantages of feed forward controller

Requires identification of all possible disturbances and their direct impact. Cannot cope with unmeasured disturbances.

79.What are the advantages of feedback controller.

It does not require identification and measurement of disturbance.

80. What are the disadvantages of feed forward controller

It is unsatisfactory for slow processes with significant dead time.

81. What is flashing in control valve?

When a liquids enters a valve and the static pressure at the vena contracta less than the fluid vapour pressure and the valve outlet pressure is also less the fluid vapour pressure the condition called flashing exists.

82. When do you use a valve positioner?

If the diaphragm actuator does not supply sufficient force to position the valve accurately and overcome any opposition that flowing conditions create a positioner may be required.

83. Give two examples for electric actuator

Motor, Solenoids.

84. What is the need of I/P converter in a control system?

In some process loop the controller is electronic and the fin al control element is electronic one. To interconnect these two we need a device that should linearly converts electric current in to gas pressure (4-20mA-315 psi). such device is called I/P converter.

85. Why installed characteristics of a control valve is different from inherent characteristics?

Inherent characteristics is which the valve exhibits in the laborator y condition where the pressure drop is held constant. Installed or resultant characteristics is the relationship between flow and stroke when the valve is subjected to pressure conditions of the process.

86. Explain the function of pneumatic transmission lines.

Used to transmit the input signals into standard instrumentation pneumatic output signals (3 to 15 psi or 20 to 100 KPa).

87.What is the purpose of final control element.

Components of a control system (such as valve) is used to directly regulates the flow of energy or materials to the process. It directly determines the value of manipulated variable.

88.What is meant by cavitations in control valve?

When a liquid enters a valve and the static pressure at the vena contracta drops to less than the fluid vapor pressure and the recovering to above fluid vapour pressure, this pressure recovery causes an implosion or collapse of the vapour bubbles formed at the vena contracta. This condition is called cavitation.

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

For equal incre ment of stem travel at constant pressure drop an equal percentage change in existing flow occurs.

90.What are the characteristics of control valve?

Inherent characteristics, Installed characteristics.

91. Differentiate inherent characteristics and installed characteristics.

Inherent characteristics is which the valve exhibits in the laborator y condition where the pressure drop is held constant. Installed or resultant characteristics is the relationship between flow and stroke when the valve is subjected to pressure conditions of the process.

92. What is “quick opening” control valve.

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

93. What is “Linear” control valve.

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

94. Define Control Valve sizing.

Q=Cv.sqrt(P/Sg) Q-Flow rate

Cv-Valve coefficient

P-pressure difference across valve. Sg-Specific gravity of liquid.

95. Name any one final control element.

Control Valve.

96. 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.

97. Name one application of electrical actuator

Solenoid coil used to change gears.

98. Name the two types of plugs.

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

99. Define Rangeability

It is the ratio of maximum controllable flow to minimum controllable flow.

100. What is rotating shaft type control valves.

1. Rotating-plug valves

2. Butterfly valves

3. Louvers.

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