 Hello, I am Milka Jagle, working as assistant professor in mechanical department, Walsh and Institute of Technology, SolarPort. Today, we are going to learn what are modes of control and what are different types of controllers used in control system. Learning outcome. At the end of this session, students will be able to examine the modes of control in accordance with output of control system. So these are the contents. So let us see what is controller. A controller is a device which when introduced in the feedback or forward path of a system controls the steady state and transient response as per the requirement. It can also be defined as the one which compares the control values with desired values and has a function to correct the deviation produced. Figure 1 shows the closed loop control system of single input and single output control system. It is a feedback control system in which a controller is used. So let us see what is mode of control or what are modes of control. The method used by the controller to correct the error is known as the control mode. There are four types of controller used in the control system such as two position or on off controller, proportional controller, integral controller and derivative controller. So these controllers we are going to study in detail in the further slides. The four most popular control modes are on off controller, proportional, integral and derivative. So before going to the further concept I just want you to pause the video for few seconds and think about the need of controller in the controller system. So just write down what is the need of controller in the control system. So let us see controller is required in a control system because it improves the steady state accuracy, it improves the stability of the system, reduces the offset produced within the system, maximum overshoot of the system can be controlled and reduces the noise signals produced in the system. So these are the factors that states why we need the controller in the control system. So let us see the first type of controller that is on off controller. It has only two states, it has only two states fully on and fully off. An on off controller simply drives the manipulated variable from fully off to fully closed depending on the position of the control variable related to the set point. The example of the on off controller is the home appliance that is thermostat. The heating element is turned on when the temperature is below the desired level and it is offed when the temperature is reached its maximum level. Proportional controller, the name itself indicates the output of the proportional controller is proportional to the error signal that is the output is directly proportional to the error signal. KP is the proportionality constant, it is also known as controller gain, it is recommended that KP should be kept greater than the unity because when the error signal is multiplied it gets amplified and the amplified signal can be detected very easily. This controller is used when deviation is less and deviation should not be sudden. The deviation between the output and the input should be less then this type of controller can be used suitably and the deviations produced should not be sudden, the deviation should be within some interval of times. So figure shows the block diagram for proportional controller. So you see the this error is multiplied by proportionality gain KP and the output is given here that is controlled output, integral controller, integral controller used alone and can greatly improve proportional controller because the integral of the error determines the corrective action. As the time goes on the integral increases such that there will be no offset. Here the figure number 5 shows the integral controller, it is a combination of proportional and integral controller. In the further slides we are going to see the limitations of the individual controllers, what are the limitations of proportional integral and why they are used in combinations such as PI, PED or PID. Integral controller does not exhibit the steady state error but it is relatively slow responding. It is particularly effective for very fast process with high noise level, process dominated by dead time and high order system with all time constant of the same magnitude. So integral controller can be effectively used when there is very fast process and the process dominated by the dead time and high order system with all time constant of same magnitude. Derivative controller, the corrective action depends on the derivative of the error. The derivative controller is effective for the systems having large number of time constants. It results in a more rapid response and less offset that is possible by pure proportional control but one must be most careful while using the derivative action in control of very fast processes or if the measurement is noisy for example flow measurement. So figure number six shows derivative controller. So this is the controller which is having a combination of proportional, integral and derivative. So here shows the derivative action. So let's see the characteristics of each type of controller. Proportional controller will have the effect of reducing the rise time and will reduce but never eliminate the steady state error. Integral controller will have the effect of steady state error but it may make the transient response worse. Derivative controller will have the effect of increasing the stability of the system reducing the overshoot and improving the steady state and transient response. So figure shows the PID controller. So because of all these factors the combination of P, I and D controller is most effective. So let us see the limitations of controllers. Proportional controller system generates offset error. It also increases maximum overshoot of the system. Proportional control system in this the steady state error due to step input reduces to zero and the system response is low. Derivative control provides the step for each value of the error signal. So due to this disadvantages P, I and D controllers are not used individually rather the composite of this controller is used. So figure shows the PID controller as we have discussed the limitations and characteristics of PID. So the most effective and the most control output can be gained by using PID controller. Most of the industrial controllers are PID in nature. The major reasons behind the popularity of PID controller are its simplicity in structure and its applicability to variety of processes. Moreover the controller can be tuned for a process even without detailed mathematical model of the process. But the choice of PID, PID or PID structure depends on the type of the process we intend to control. These are the references. Thank you.