Most important points in Mechatronics subject

 Most important points for end sem exam Mechatronics subject 

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PLC System and Components

All PLCs have similar basic elements. These elements work together to bring information into the PLC from the field, assess that information, and send information back out to various field. Without any of those major elements, the PLC can fail to operate properly. The basic elements embrace a power supply, central processing unit (CPU or processor), co-processor modules, input and output modules (1/0), and a computer peripheral

Q)Discuss the selection criteria for PLC. 1. System (Task) Requirements2. Application Requirements.3. Input/Output Capacity.4. Type of Inputs/Outputs5. Size of Memory is Required6. CPU processing speed7. Electrical Requirements8. Speed of Operation.9. Communication Requirements.10.Software Interface.11 Operator Interface.12. Physical Environments.

Signals, and hence remain unaffected to the external noise sources.

Disadvantages of Closed loop control system ConstructionThey are relatively more complicated in construction and hence it adds up to the cost making it costlier than open loop system Oscillatory response Since it consists of feedback loop, it may produce oscillatory response of the system and it also reduces the overall gain of the system.Stability It is less stable than open loop system but this disadvantage can be striked off because we can create the sensitivity of the system very small so as to make the system as stable as poss

Open loop control system

If mechatronics control system not having automatic correction of the deviation in its output,It is called an open loop control system.So that in this system, sensing of the actual output and comparing of this output with the desired input does not take place.The open loop control system is not in a position to give the desired output and it cannot take into account the disturbances. The changes in output are possible to correct only through changing the input manuallyInput is equal to in box Open loop control system is equal OutputOpen loop control systems are simple in construction, stable and less costly. But these systems areImprecise and changeable.Any non-feedback control system can be considered as a feedback control system if it is under the of control system.Open loop control systems have less costly parts as compared to close loop system and simple in design. – Let us consider a example of home temperature control system. This system controls the temperature in a room, keeping it constant.An open loop system usually has a timer which instructs the system to switch on the heater for some time and then switch it off.Accuracy cannot be achieved as the system based on switch on/off based. It can be controller as per the set value of timer.Advantages

Simplicity and stability: They are very to layout and hence open loop systems are inexpensive and stable due to their simplicity.Construction: Since open loop system are having a simple layout so they are easier to construct.

Disadvantages

Accuracy and Reliability: These systems do not have a feedback mechanism, therefore they are very inaccurate in terms of result output and hence they are unreliable too.Disturbances: Due to the absence of a feedback mechanism, they are unable to remove the disturbances occurring from external sources.

 

 

 

 

Closed loop control system

In this type of system the output affects the input quantity in such a way as to keep the desired output value.An open loop control system can be convert into closed loop control system by include a feedback system.This feedback system automatically corrects the changes in output due to outside disturbances. Hence closed loop control system is an automatic control system.In a closed loop control system, the controlled output of the system is measured and compared with the desired input so can be found error from signal.An air conditioner uses a thermostat to sense the temperature and control the process of its electrical parts to keep the room temperature at a preset constant. When the load changes, the error signals generated by the system will adjust the output. However, closed loop control systems are usually more complex and thus more costly to diagram of the control system of an air conditioner. One benefit of using the closed loop control system is that it is capable to regulate its output automatically by feeding the output signal back to the input.

 

Advantage

AccuracyThey are more correct than open loop.system because of their complex construction.They are equally accurate and are not disturbed in the presence of non-linearity.Noise reductionSince they are consisted with a feedback mechanism, so they removes the errors between input and output

 

 

 

 

Q)Explain Timers

These are special operands of a PLC, which represent a time delay relay in a relay logic system.The time functions are a mounted part of the central process unit.The number of these varies from manufacturer to manufacturer and from product to product.It is possible to attain time delays within the range of few milliseconds to few hours.

On delay timer.When the input signal becomes on, the output signal becomes on with certain delay. But once the input signal becomes off, the output signal also becomes off at a similar instant.If the input becomes on and off with the time which less than the delay time, there is no change within the output and remains in the ‘off condition even the input is turned on and off i.e., output is not observed till the input pulse width is larger than the delay time.

●Offdelay timer.When the input signal becomes on, the output signal becomes on at identical time. But once the input signal becomes off, the output signal becomes ‘off with certain delay.If the input becomes on and off with the time which less than the delay time, there is no change within the output and remains within the ‘on’ condition even the input is turned on and off i.e., the delay in the output isn’t observed till the input pulse width is larger than the delay time.

Q. Using a suitable example discuss the working of the latching in a PLC.In PLC always situations where it is necessary to hold an output energized, even when the input is OFF.Let take example of motor where is started by pressing push button switch.Though the switch contacts do not remain closed, the motor is required to continue running until a stop push button switch is pressed.The latch circuit is used to carry out such on Operation.Latch maintain energized until another input is received.In above circuit PB1 ON then motor M ON when PB2 OFF.Same M output taken as input to start motor M. If PB1 is OFF then also motor M ON.

 

Q)Give suitable examples and discuss the importance of Counter.-A counter is a easy device supposed to do one simple thing-count. Using them, however, can typically be a challenge because each manufacturer (for whatever reason) looks to use them a completely different approach. Rest assured that the following Information can allow you to simply and easily program anybody's counters.-There are up-counters (they only count up 1, 2, 3...). These are known as CTU,(count up) CNT,C, or CTR. There are down counters (they only count down 9, 8, 7...). These are usually known CTD (count down)-when they are a separate instruction. There are additionally up-down counters (they count up and/or down 1, 2, 3, 4, 3, 2, 3, 4, 5,...) These are usually called UDC(up-down counter) once they are separate instructions.-Where the pulses that we need to count are returning from. Typically this is from one of the inputs.(a sensor connected to input 0000 for example).-How several pulses we want to count before we react. Let's count 5 widgets before we box them, for example.-When we can reset the counter therefore it will count again. After we count five widgets lets reset the counter.-When the program is running on the plc the program typically displays the current or "accumulated" value for us therefore we will see the current count value.

 

 

 

 

 

 

 

 

 

Q)In a certain bank each of three bank officers has a unique key to vault. The bank rules require that two out of the three officers be present when the value is opened.Draw the ladder diagram for a relay logic circuit that will uniatch the door and turn on the light when two of the three keys are inserted.Consider A, B and C are three back officers unique key R,, R, and R, three relay connected to vault door.Ladder diagram for given conditions is

-Hence if any two keys connected to door then door will open.

Q)Witte ladder logic, for a simple traffic light controller for the following sequence of operations as

Step 1: Tum Green ON for 35 seconds. 2: Tum Yellow ON for 5 seconds.Step 3: Tum Red ON for 40 seconds.Step 4: Repeat the sequence i.e. Step 1 Step 2 Step 3.

 

 

 

 

 

 

 

3.3 Identification of Key Elements of Mechatronics Systems and Represent into Block Diagram

1. Elements of mechatronics system

2. Electro-mechanical elements

3. Electrical/electronic

4. Control system elements

 

1. Elements of Mechatronics System

Mechanical elements in mechatronics system are structure, mechanism, thermo-fluid, and hydraulic aspects of a mechatronics system.The mechanical elements are alsoincluding static/dynamic characteristics of a system.The mechanical elements of mechatronics systems need mechanical power to generate motion, force, heat, etc2. Electro-Mechanical elementsElectromechanical elements are actuators.Actuators like DC servomotor, stepper motor, relay, solenoid; light emitting diode (LED), speaker, shape memory alloy, electromagnet, and pump are used to implement decision taken by controller.3. Electrical/Electroni cElectrical elements are resistor, capacitor, inductor, transformer, circuits and analog signals.Electronic elements are analog/digital electronics, transistors, thyristors, opto-isolators, operational amplifiers, power conditioning, electronics, and signalThe electrical/electronic elements are used to interface electro-mechanical sensors and actuators to the control interface hardware elements.

4. Control System elements Control system hardware parts are analog-to-digital converter (ADC), digital-to-analog converter (DAC), digital input/output (1/0), counters, timers, microprocessor, microcontroller, data acquisition system (DAC) and digital signal processing (DSP) board.The mechatronics control system allows communication of sensor to the controller and communication of control signal from the controller to the actuator.The control computing control algorithm, which uses sensor signals and compute control actions to apply with the help of actuator.

 

 

Q)Using a suitable example discuss the working of the following in a PLC: (1) Latch (1) Counter.

P₁→ Start button

T₁→ Green light

T₂→ yellow light

T3→ Red light

 

Q)Draw a ladder diagram for the following sequence.

(i) Two Push Buttons PB1 and PB2 are used to operate red and green light.(ii) When PB1 is pushed alone, GREEN lamp should be OFF and Switch ON RED lamp. (iii) If PB2 is pushed alone, no lamp should ON

Soln.:

PB1 Push button 1 .CR1→ Relay 1 PB₂→Push button 2.G→ Green lamp R→ Red lamp-Condition 1If PB, ON and PB, OFF then (CR, ON) Condition 2IFCR, ON then R (Red lamp) and G (Green lamp) ON Condition 3If PB, ON then CR, ON and Both Red lamp (R) and Green lamp (G) OFF.

 

 

 

Q. Define “Transfer Function” and discuss its importance in the context of control of a mechatronic system.

The transfer function of a control system is defined as, “The ratio of the Laplace transform of the output variable to Laplace transform of the input variable assuming all initial conditions to be zero. A control system consists of an output and an input signal. The output and input are related with each other through transfer function.Transfer function is represented by a blocks, transfer function equation and arrows collectively it known as block diagram of a mechatronics control system.Mechatronics control system consist of a reference input as excitation which operates through a transfer operation termed as transfer function and produces an effect resulting in controlled output or response..The relationship between the output and input is related to each other through a transfer function.

Input Transfer function Output

 In Transfer function Laplace Transform generally input is represented by R(s) and output is represented by C(s) , then the transfer function is

G(s)=C(s)/R(s)=R(s).G(s) = C(s)

Transfer function of the system multiplied by inputfunction gives the output function of the system.It is not necessary that output and input of a control system are of same category. For example, in feedback control system the input is electrical signal taken from sensors and the output is actuators mechanical signal.But for analysis of a system all kinds of signals should be represented in a same form. This is possible by transforming all signals into their Laplace form.The transfer function of a system is represented by Laplace form taking ratio of output Laplace transfer function to input Laplace transfer function. So block diagram of a control system is represented as R(s) C(s)Where R(s)= Lr(t) and C(s) = LC(t) and G(s)=LC(t)/Lr(t)Where, Lr(t) and Lc(t) are time domain function of input and output signal respectively.

 

 

 

 

Q)Give four normally open switches (P1, P2, S1 and S2). with DC motor(M), write PLC program to satisfy the following objectives: (1) When P1(Push Button) is pushed the cycle shall start. The cycle remain continue until P2 (stop Button) is pushed.(ii) When S1 is pushed and $2 is not pushed then motor is ON clockwise direction(iii) When S2 is pushed & S1 is not pushed then, motor is on in counter clockwise direction(iv) When P2 pushed program stops.

Soln. :PB1→ Push button 1;   S₁PB2→ Push button 2;  s2 Push button Note: To change the direction of rotation of motor, we can change current direction.●diagram P₁→Start buttonT1→ Green lightT₂→ yellow lightT3→ Red light

Q. What are zeros and poles

To define poles and zeros consider transfer function consist of two polynomial.

H(s) = (N(s))/(D(s))

N(s) and D(s) are polynomial

Zeros: The roots of N(s) i.e. numerators of the transfer function obtained by setting N(s) = 0 and solving for S.

Poles: the roots of D(s) i.e. denominators of the transfer function obtained by setting D(s) = 0 and solving for.

Q)Give four normally open switches (P1, P2, S1 and S2). with DC motor(M), write PLC program to satisfy the following objectives: (1) When P1(Push Button) is pushed the cycle shall start. The cycle remain continue until P2 (stop Button) is pushed.(ii) When S1 is pushed and $2 is not pushed then motor is ON clockwise direction(iii) When S2 is pushed & S1 is not pushed then, motor is on in counter clockwise direction(iv) When P2 pushed program stops.

Soln. :

PB1→ Push button 1;  S₁PB2→ Push button 2;  s2 Push button Note: To change the direction of rotation of motor, we can change current direction.●diagram P₁→Start buttonT1→ Green lightT₂→ yellow lightT3→ Red light

 

 

 

 

 

 

 

 

 

 

 

 

 

Q. Draw a suitable block diagram and discuss the application of Anti-lock braking in four wheel automobiles.

Distance maintains between two vehicles systemMeasure distance and velocity to autonomously maintain desired distance between vehicles.

This technology provides the capability to control the distance between the vehicle and an obstacle (or another vehicle) by integration the detector with the controller and ABS systems.

The driver is ready to set the speed and also the desired distance between the cars ahead of him.

The ABS system and also the cruise control system are coupled along to securely accomplish this outstanding capability.

One logical extension of the obstacle avoidance capability is slow speed semi-autonomous driving wherever the vehicle maintains a constant distance from the vehicle ahead in traffic congestion conditions.

Anti-lock braking system (ABS) is a system used in vehicle to avoid skid. ABS comes into action when sudden brake apply on system.

When sudden brake applied on the wheels then possibility of Wheel lock. Due to the ‘wheel lock’ driver losses control over vehicle.\

The ABS prevents the wheels from locking, thus preventing uncontrolled skidding of the vehicle and reducing the distance traveled without falling.

Anti-lock braking system is a safety system in cars and other automobiles that prevents their wheels from locking and helps drivers maintain steering control. Also known as an anti-skid braking system, it sometimes enables the wheels of the vehicle to maintain tractive contact on the ground so it does not go into uncontrollable skids.

ABS generally offers improved vehicle control and helps to reduce the gap between dry and slippery surfaces.

Computer numerical control (CNC) machines CNC machine is that the best and basic example of application of Mechatronics in manufacturing automation. efficient operation of standard machine tools like Lathes, milling machines, drilling machine relies on operator ability and training-+.Also lots of time is consumed in workpart setting, tool setting and controlling the process parameters viz. feed, speed, depth of cut. so typical machining is slow and costly to fulfill the challenges of often changing product/part shape and size.+Computer numerical control (CNC) machines are currently wide utilized in little to massive scale industries. CNC machine tools are integral a part of computer aided manufacturing (CAM) or computer Integrated manufacturing (CIM) system. CNC means that operative a machine tool by a series of coded directions consisting of numbers, letters of the alphabets, and symbols that the machine control unit (MCU) will understand.+These directions are converted into electrical pulses of current that the machine's motors and controls follow to hold out machining operations on a workpiece. Numbers, letters, and symbols are the coded instructions that refer to specific distances, positions, functions or motions that the machine tool will understand.CNC automatically guides the axial movements of machine tools with the help of computers. The auxiliary operations like coolant on-off, tool change, door open close are automated with the assistance of micro-controllers. modern machine tools are currently equipped with friction-less drives like re- circulating ball screw drives, Linear motors etc.

CNC Components

Machine tool

Actuators (motors)

Drive circuits to operate the actuators

Sensors to provide feedback signals

Conditioning circuits for the sensor signals

Controller (PC-based and microcontroller-based)

Mechanical body and parts.

 

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Q. Draw a block diagram for any household appliance consisting of various elements which build the system. Explain the function of each block therein.

 In a domestic washing machine a number of operations need to be carried out in the correct sequence. These could involve the pre-wash cycle, once the closes within the drum are given a wash in cold water, followed by a main wash cycle when they are washed in hot water, than a rinse cycle once the closes are rinsed with cold water variety of times, followed by spinning to remove water from the clothes.Each of those operations involves variety of steps.In former times the program was accomplished by a system by suggests that of a group of cam operated switches.In modern washing machines the controller could be a microprocessor and also the program isn’t equipped by the mechanicalFor the pre-wash cycle an electrically operated valve is opened and cold water going into the drum for a period of your time determined by the software system of the microchip. Depending on the load of the washing good a selected level of water within the drum are reached and also the water valve are closed A sensor used to provides a signal once the water level has reached the predetermined level and provides an output from the microchip that is employed to switch off the current to the valve. The microchip switches on the drum motor to rotate the drum. The drum is rotating for a time determined by the microchip. After this time the microchip switches on the pump to empty the water from the drum.The rinse a part of the operation is currently switched as a sequence of signals to open valves which permit cold water going into the machine, switch it off, operate the motor to rotate the drum, operate the pump to empty the water from the drum and repeat the sequence variety of times.1 The final a part of the operation is once the microchip switches on simply the motor a higher speed than for the rinses to spin the clothes.

Industrial Conveyor System

Conveyor systems help to transport content with minimal effort. There are different types of conveyor systems that have a frame, which supports rollers, wheels or belts, on which materials can be transported from one place to another. They can be powered by motor, gravity, or manually. Different products require amaterial handling system for the transportation of different goods that can be transported.The conveyor belt system is often operated by a PLC control system in the industry. The PLC can be used as an operating system in industrial conveyor belt. Different types of PLCs are available in the market today which facilitates easy implementation of conveyor control system.The PLC program contains rules tha” help to create a logic relationship between the input and output of the controller. Basically they use logic operands: and, or. If-then rules are used. The PLC reads all field input devices through the input interface. The application executes a user’s program stored in memory, then turns the field output device on or off, or any control required for the processing application, depending on any control program the user has programmed. PLC program solves rules (sequential execution). The PLC operates in a synchronous way so that the information within the scan cycle does not change.

 

 

 

 

 

 

 

Q. Draw suitable sketch to depict the unit step response of a second order system when :System poles are negative and real.System poles are complex conjugate pair with negative real partSystem poles are a imaginary pair with no real part.System poles are positive and real.

 

 

 

 

 

 

Q)SCADA (Supervisory Control and Data Acquisition)

SCADA is a word form for supervisory control and data Acquisition. SCADA systems are used to monitor and control a plant or equipment in industries like telecommunications, water and waste control, energy, oil and gas refinement and transportation.These systems cover the transfer of data between a SCADA central host computer and a number of remote terminal Units (RTUS) and/or Programmable Logic Controllers (PLCs), and also the central host and also the operator terminals.These systems are often comparatively easy, like one that monitors environmental conditions of a small office building, or very complicated, like a system that monitors all the activity in a nuclear energy plant or the activity of a municipal water system.SCADA Systems consist ofOne or more field data interface devices, usually RTUS, or PLCs, which interface to field sensing devices and local control Switchboxes and valve actuators.A communications system employed to transmit information between field data interface devices and control units and the computers in the SCADA central host. The system can be radio, telephone, cable, satellite, etc, Or whatever combination of these.A central host computer server servers or (sometimes called a SCADA Center, master station, or Master Terminal Unit (MTU).A collection of standard and/or custom software [sometimes called Human Machine Interface (HMI) software systems used to provide the SCADA central host and operator terminal application, confirm the communications system, and monitor and control remotely located field data interface devices.

 

 

 

 

 

Q)A solenoid valve is used to control both the extension as well as the retraction stroke of a double-acting cylinder. Draw a ladder diagram to execute the following operation:

Solenoid valve is used in double acting cylinder so

 

 

 

 

 

 

 

 

 

 

 

 

3.11 Routh Hurwitz Criterion

To understand Routh Hurwitz criterion consider a close loop system transfer function.

Where a's and b's are real constant and m <= n . Routh Hurwitz criterion find the number of closed loop poles in the right half s plane.Routh simplified the process by introducing a tabulated method in place of Hurwitz determinants.

1) Rise time (T_{r})The time required for the signal go from 0.1 of the final value to 0.9 of the final value.

2) Peak time (T_{p})

The time required to reach maximum peak

3) Percentage overshoot

1 The percentage amount that the signal overshoot the steady state.

Consider unit step response is y(t). Maxiinum value of unit step response y max steady state value of unit step response is y s5 Maximum overshoot given by unit step response is y max -y ss So in percentage form maximum overshoot is

%overshoot = ovcrshoot /y ss *100%.    = y max -y ss/ y ss *100%

Majority time maximum overshoot occur at first overshoot and in some cases it occurs at later overshoot.A negative undershoot may occur when transfer function has an odd number of zeros in right half S-plane.

4) Settling time (T,)

The time required for the transients damped oscillation to reach and stay within ± 2% of the steady state value.

5) Delay Time (Td)

The delay time T_{d} is the time needed for the response to reach half of its final value the very first time.

6) Steady state errors

It is a difference between output obtained and set pint of system. Steady state error occurs in control system due to the discrepancy between the output and the reference input at steady state

 

Q)Discuss, in detail, the advantages and disadvantages of adding derivative term to the proportional term.

Soln :The capability to forest the future behavior of error don't have I controller.Therefore, it gives response to the set point change. D-controller overcomes this problem oy predicting future behavior of the error.Its output controlled by rate of change of error with respect to time, multiplied by derivative constant.It gives the quick start for the output so that it increasing system response.In Fig reaction of D controller is extra, compared to Pl controller and as well settling time of output is decreased.It increases the faithfulness of system by compensating phase lag caused by I-controller. Increasing the derivative gain and speed of response So that by combining these three controllers, we get the desired response for the system.Derivation controller action responds to the rate at which the error is changing that is the derivative of the error. P(t) = Kd  dep/dt In derivative control mode, if error is zero, mode provide no output. If the error is constant in time then it provides no output. If the error is changing w.r.t time, the mode contributes an output of K, percent for every 1%. per second rate of change of error sign of output depends on error negative or positive. If error positive output also positive.The major advantage of a derivative controller is that it improves the transient response of the system.Disadvantages 1) It never improves the steady-state error. 2) It produces saturation effects and also amplifies the noise signals produced in the system.

 

 

Gain and Phase Margins

Gain and phase margins are common terms to describe how stable a system is.Gain and phase margins are used more because they are simple than because they are ideal measurement of stability.Gain and phase margins are measured from the open loop frequency response of the system.Gain and phase margins can not be acquired directly from a closed loop frequency response.

Gain  Margins

Definition: Gain margin is defined as the amount of change in open-loop gain needed to make a closed-loop system unstable. The gain margin is the difference between 0 dB and the gain at the phase cross-over frequency that gives a phase of -180°.  closed-loop system is stableTo measure the gain margin of a system, find the point that the open loop phase response crosses 180 degree. –At the same frequency as this point, find the open loop amplitude response.The distance below 0dB that the open loop amplitude response reads at this frequency is the gain margin.

 Phase Margins

Definition: Phase margin is defined as the amount of change in open-loop phase needed to make a closed-loop system unstable. The phase margin is the difference in phase between -180 and the phase at the gain cross-over frequency that gives a gain of 0 dB. If the phase 4GHja) at the frequency of GH(j*omegaw) |=1 is greater than -180 meaning a positive phase margin, the closed-loop system is stable. To measure the phase margin of a system find the point that the open loop amplitude crosses 0dB. At the same frequency as this point, find the open loop phase responses. The distance above – 180 degrees that the open loop phase response read at this frequency is the phase margin. In the following example gain margin is 32.5 dB. The phase margin is 33 degrees. (180 degrees) 147 degrees = 33 degrees

 

 

 

 

 

Q. Explain the term Natural Frequency

W{n} = square root (k/m)

Is called natural frequency because it is the frequency at which the undamped system would naturally oscillate. If spring stretched and mass released then it allow to move mass without external force. If we provide damping to the system b ne0 the resulting transient homogeneous solution is

X_{n}(t) = (A + Bt) * e ^ (-w) * n ^ t

Here system have exponentially decaying motions. The behavior of system is critically damped because it have verge of damped oscillatory motions.

Q. Explain the term Damping Factors.

b_{c} = 2sqrt(km) = 2m*omega_{n}

In the case of critical damping, the oscillator returns to the equilibrium position as quickly as possible, without oscillating, and passes it once at most

Definition: Critical damping is defined as the threshold between overdamping and  underdamping, b_{c}

 

4.5.3 Damping Ratio (£)

Xi=£

£= b/b_{c} = b/(2sqrt(km))

 

A critically damped system has a damping ratio of 1Natural frequency @, and Damping ratio () gives root of equation.

S_{i} = - xi * omega_{n} + omega_{n} * sqrt(xi ^ 2 – 1)

If b ne0

S_{2} = - xi * omega_{n} – omega_{n} * sqrt(xi ^ 2 – 1) then transient homogeneous solution is

And xi < 1

X(t)=e^ - xi omega n^ t [A * cos(omega_{n} * sqrt(1 – xi ^ 2 * t)) + B * sin(omega_{n} * sqrt(1 – xi ^ 2 * t))]

Omega_{d} = omega_{n} * sqrt(1 – £ ^ 2) is called damped natural frequency.

 Q)Explain manual tuning of PID control.

Soln :Obtain an open-loop response and determine what needs to be improved .Add a proportional control to improve the rise time.Add a derivative control to improve the overshoot.Add an integral control to eliminate the steady-state error.Adjust each of P. I & D unti! you obtain a desired overall response referring to the table shown previously to find out which controller controls what characteristics.It is not necessary to implement all three controllers (P. 1 & D) into a single system. For example, if a Pl controller gives a good enough response, then you don't need to add D contro the system. Simple is better.

Q)Parallel PID Controller.

-In general, this type of PID is preferred over series one because in Parallel PID, output of one controller does not affect the output of other. This allows freedom Independently. to control parameters.A typical structure of a PID control system is shown.The error signal e(t) is used to generate the proportional, integral, and derivative actions, with the resulting signals weighted and summed to form the control signal u(t) applied to the plant model.where u(e) is the input signal to the multivariable processes, the error signal e(t) is defined as e(t) = r(t) - y(t), and r(t) is the reference input signal.A standard PID controller structure is also known as the "three-term" controller. This principle mode ofaction of the PID controller can be explained by the parallel connection of the P, 1 and D elements shown in Fig.Block diagram of the PID controller.Where Kp is the proportional gain, T, is the integral time constant, T, is the derivative time constant.The "three term functionalities are highlighted below. The terms K,.T, and T, definitions are: The proportional term: providing an overall control action proportional to the error signal through the all pass gain factor.The integral term: reducing steady state errors through low frequency compensation by an integrator.The derivative term: improving transient response through high frequency compensation by a differentiator.

 

 

 Q)Proportional Integral Derivative (PID) Control system. Derive the equation for the control signal, u, for the Proportional Integral Derivative (PID) controller. Discuss, in detail, the advantages and disadvantages of adding derivative term to the proportional term.

Soln : The proportional integral derivative controller produces an output, which is the combination of the outputs of proportional, integral and derivative controllers.Therefore, the transfer function of the proportional Integral derivative controller.The proportional, integral derivative controller is used to improve the stability of the control System and to decrease steady state error.PID eliminate offset from proportional mode.It also provides fastest response.Controller variable increases quickly and return suddenly to original value with less oscillation.

Advantages

 1) Process independent: The best controller where the specifics of the process can not be modeled Leads to a "reasonable" solution when tuned for most situations.

2) Inexpensive: Most of the modern controllers are PID.3)Can be tuned without a great amount of experience required.

Disadvantages

 1)Not optimal for the problems

 2)Can be unstable uniess tuned properly 3) Not dependent on the processpoint.

 4)Hunting (oscillation about an operating 5) Derivative noise amplification

Q)Proportional Derivative (PD) Control

Q) Derive the equation for the control signal, u, for the Proportional plus Derivative (PD) controller in parallel form. Discuss, in detail, the advantages and disadvantages of adding a Derivative term to the Proportional term.

 

Q)Explain Derivation control with neat diagram and equation. Why derivative controller can not be used alone ?

Soln: The proportional derivative controller produces an output, which is the combination of the outputs of proportional and derivative controllers.The proportional derivative controller is used to improve the stability of control system without affecting the steady state error.Derivative control is combined with proportional mode to reduce oscillations.Derivative control is anticipate the linear change in error by extra summing output to the proportional action.

Advantages 1)Easy to stabilize

2) Faster response than just P controller

Disadvantage 1)Can amplify high frequency noise.